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Surgery_Schwartz. effects of TNF.Although the circulating half-life of soluble TNF is brief, it acts upon almost every differentiated cell type, eliciting a wide range of important cellular responses. Moreover, it is one of the first cytokines to be released following trauma. In particular, TNF elicits many metabolic and immunomodulatory activities. It stimulates muscle breakdown and cachexia through increased catabolism, insulin resistance, and redistribution of amino acids to hepatic circulation as fuel substrates. TNF also mediates coagulation activation, cell migration, and macrophage phago-cytosis and enhances the expression of adhesion molecules, prostaglandin E2, platelet-activating factor, glucocorticoids, and eicosanoids. TNF-α increases endothelial cell permeability and activates macrophages, NK cells and lymphocytes to induce the secretion of various cytokines. While TNF is clearly play-ing a role in injury-induced inflammation, reports are conflict-ing whether postinjury TNF concentrations


Surgery_Schwartz

Surgery_Schwartz. cells and lymphocytes to induce the secretion of various cytokines. While TNF is clearly play-ing a role in injury-induced inflammation, reports are conflict-ing whether postinjury TNF concentrations correlated with the development of multiple organ dysfunction syndrome.132Interleukin-1 Family. The IL-1 family of proteins contains 11 members. The best-studied of these are IL-1α and IL-1β and IL-1 receptor antagonist (IL-1Ra), but member cytokines also include IL-18, IL-33, IL-36, IL-3,7 and IL-38. IL-1α and IL-1β, which are encoded by two distinct IL-1 genes, share similar bio-logic functions despite limited sequence homology. They uti-lize the same cell surface receptor, termed IL-1 receptor type 1 (IL-1RI), which is present on nearly all cells. Once bound to its receptor, IL-1 initiates signaling events that result in the synthe-sis and release of a variety of inflammatory mediators. Members of the IL-1 family are expressed as proforms (pIL-1) that are matured through enzymatic


Surgery_Schwartz

Surgery_Schwartz. signaling events that result in the synthe-sis and release of a variety of inflammatory mediators. Members of the IL-1 family are expressed as proforms (pIL-1) that are matured through enzymatic cleavage. The IL-1α precursor is constitutively expressed and stored in a variety of healthy cells, including epithelium and endothelium, and its expression can be increased in response to proinflammatory or stress-associated stimuli.133Both the precursor and mature forms of IL-α have nearly identical biologic activities as measured by their ability to trig-ger IL-6 and TNF release. With appropriate signals, IL-1α can move both to the cell membrane, where it can act on adjacent cells bearing the IL-1R and to the nucleus where it can stim-ulate gene transcription. Pro-IL-1α can also be released pas-sively from damaged injured cells in its active form. In this way, IL-1α is believed to function as a DAMP, which promotes the synthesis of inflammatory mediators, such as chemokines and eicosanoids.


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Surgery_Schwartz. from damaged injured cells in its active form. In this way, IL-1α is believed to function as a DAMP, which promotes the synthesis of inflammatory mediators, such as chemokines and eicosanoids. These mediators attract neutrophils to the injured site, facilitate their exit from the vasculature, and promote their activation. Once they have reached their target, neutrophil lifes-pan is extended by the presence of IL-1α.8,134IL-1β is a multifunctional proinflammatory cytokine whose expression and synthesis is tightly regulated and con-fined to activated cells, such as monocytes, tissue macrophages, and dendritic cells.134 In contrast to IL-1α, IL-1β is synthesized as an inactive precursor, pro-IL-1β, which is processed by the inflammasome in response to various stimuli, including cyto-kines and foreign pathogens, via pattern recognition receptors such as TLR4 as well as ROS. Mature IL-1β is then released from the cell via an unconventional secretory pathway.135 IL-1β has a spectrum of


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Surgery_Schwartz. and foreign pathogens, via pattern recognition receptors such as TLR4 as well as ROS. Mature IL-1β is then released from the cell via an unconventional secretory pathway.135 IL-1β has a spectrum of proinflammatory effects that are largely simi-lar to those induced by TNF, and injection of IL-1β alone is sufficient to induce an acute inflammatory response. High doses of either IL-1β or TNF are associated with profound hemody-namic compromise. Interestingly, low doses of both IL-1β and TNF administered together elicit hemodynamic events similar to those elicited by high doses of either mediator, which sug-gests a synergistic effect.There are two primary receptor types for IL-1: IL-1R1 and IL-1R2. IL-1R1 is widely expressed and mediates inflammatory signaling on ligand binding. IL-1R2 is proteolytically cleaved from the membrane surface to soluble form on activation and thus serves as another mechanism for competition and regula-tion of IL-1 activity. IL-1α or IL-1β bind first to the


Surgery_Schwartz

Surgery_Schwartz. proteolytically cleaved from the membrane surface to soluble form on activation and thus serves as another mechanism for competition and regula-tion of IL-1 activity. IL-1α or IL-1β bind first to the IL-1R1, which is considered the ligand-binding chain. This is followed by recruitment of a transmembrane co-receptor, termed the 5Brunicardi_Ch02_p0027-p0082.indd 4201/03/19 6:49 PM 43SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2Table 2-5Cytokines and their sourcesCYTOKINESOURCECOMMENTTNFMacrophages/monocytesKupffer cellsNeutrophilsNK cellsAstrocytesEndothelial cellsT lymphocytesAdrenal cortical cellsAdipocytesKeratinocytesOsteoblastsMast cellsDendritic cellsAmong earliest responders after injury; half-life <20 min; activates TNF receptors 1 and 2; induces significant shock and catabolismIL-1Macrophages/monocytesB and T lymphocytesNK cellsEndothelial cellsEpithelial cellsKeratinocytesFibroblastsOsteoblastsDendritic cellsAstrocytesAdrenal cortical


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Surgery_Schwartz. significant shock and catabolismIL-1Macrophages/monocytesB and T lymphocytesNK cellsEndothelial cellsEpithelial cellsKeratinocytesFibroblastsOsteoblastsDendritic cellsAstrocytesAdrenal cortical cellsMegakaryocytesPlateletsNeutrophilsNeuronal cellsTwo forms (IL-1 α and IL-1 β); similar physiologic effects as TNF; induces fevers through prostaglandin activity in anterior hypothalamus; promotes β-endorphin release from pituitary; half-life <6 minIL-2T lymphocytesPromotes lymphocyte proliferation, immunoglobulin production, gut barrier integrity; half-life <10 min; attenuated production after major blood loss leads to immunocompromise; regulates lymphocyte apoptosisIL-3T lymphocytesMacrophagesEosinophilsMast cellsIL-4T lymphocytesMast cellsBasophilsMacrophagesB lymphocytesEosinophilsStromal cellsInduces B-lymphocyte production of IgG4 and IgE, mediators of allergic and anthelmintic response; downregulates TNF, IL-1, IL-6, IL-8IL-5T lymphocytesEosinophilsMast cellsBasophilsPromotes


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Surgery_Schwartz. cellsInduces B-lymphocyte production of IgG4 and IgE, mediators of allergic and anthelmintic response; downregulates TNF, IL-1, IL-6, IL-8IL-5T lymphocytesEosinophilsMast cellsBasophilsPromotes eosinophil proliferation and airway inflammationIL-6MacrophagesB lymphocytesNeutrophilsBasophilsMast cellsFibroblastsEndothelial cellsElicited by virtually all immunogenic cells; long half-life; circulating levels proportional to injury severity; prolongs activated neutrophil survival(Continued)Brunicardi_Ch02_p0027-p0082.indd 4301/03/19 6:49 PM 44BASIC CONSIDERATIONSPART ITable 2-5Cytokines and their sourcesCYTOKINESOURCECOMMENTAstrocytesSynovial cellsAdipocytesOsteoblastsMegakaryocytesChromaffin cellsKeratinocytesIL-8Macrophages/monocytesT lymphocytesBasophilsMast cellsEpithelial cellsPlateletsChemoattractant for neutrophils, basophils, eosinophils, lymphocytesIL-10T lymphocytesB lymphocytesMacrophagesBasophilsMast cellsKeratinocytesProminent anti-inflammatory cytokine; reduces mortality


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Surgery_Schwartz. for neutrophils, basophils, eosinophils, lymphocytesIL-10T lymphocytesB lymphocytesMacrophagesBasophilsMast cellsKeratinocytesProminent anti-inflammatory cytokine; reduces mortality in animal sepsis and ARDS modelsIL-12Macrophages/monocytesNeutrophilsKeratinocytesDendritic cellsB lymphocytesPromotes Th1 differentiation; synergistic activity with IL-2IL-13T lymphocytesPromotes B-lymphocyte function; structurally similar to IL-4; inhibits nitric oxide and endothelial activationIL-15Macrophages/monocytesEpithelial cellsAnti-inflammatory effect; promotes lymphocyte activation; promotes neutrophil phagocytosis in fungal infectionsIL-18MacrophagesKupffer cellsKeratinocytesAdrenal cortical cellsOsteoblastsSimilar to IL-12 in function; levels elevated in sepsis, particularly gram-positive infections; high levels found in cardiac deathsIFN-γT lymphocytesNK cellsMacrophagesMediates IL-12 and IL-18 function; half-life of days; found in wounds 5–7 d after injury; promotes ARDSGM-CSFT


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Surgery_Schwartz. infections; high levels found in cardiac deathsIFN-γT lymphocytesNK cellsMacrophagesMediates IL-12 and IL-18 function; half-life of days; found in wounds 5–7 d after injury; promotes ARDSGM-CSFT lymphocytesFibroblastsEndothelial cellsStromal cellsPromotes wound healing and inflammation through activation of leukocytesIL-21T lymphocytesPreferentially secreted by Th2 cells; structurally similar to IL-2 and IL-15; activates NK cells, B and T lymphocytes; influences adaptive immunityHMGB1Monocytes/lymphocytesHigh mobility group box chromosomal protein; DNA transcription factor; late (downstream) mediator of inflammation (ARDS, gut barrier disruption); induces “sickness behavior”ARDS = acute respiratory distress syndrome; GM-CSF = granulocyte-macrophage colony-stimulating factor; IFN = interferon; Ig = immunoglobulin; IL = interleukin; NK = natural killer; Th1 = helper T cell subtype 1; Th2 = helper T cell subtype 2; TNF = tumor necrosis factor.(Continued)accessory protein (IL-1RAcP). A


Surgery_Schwartz

Surgery_Schwartz. Ig = immunoglobulin; IL = interleukin; NK = natural killer; Th1 = helper T cell subtype 1; Th2 = helper T cell subtype 2; TNF = tumor necrosis factor.(Continued)accessory protein (IL-1RAcP). A complex is formed of IL-1RI plus IL-1 plus the coreceptor. The signal is initiated with recruit-ment of the adaptor protein MyD88 to the Toll-IL-1 receptor (TIR) domains of the receptor complex and signal transduction via intermediates, which are homologous to the signal cascade initiated by TLRs. These events culminate in the activation of NF-kB and its nuclear translocation.136Recent animal studies have implicated postinjury IL-1β in the exacerbation of traumatic brain injury.137 In a mouse model of polytrauma, which included both cortical brain injury and tibial fracture, mice that received both injuries demonstrated increased neuroinflammation, brain damage, and behavioral deficits compared to mice given an isolated-TBI. These changes correlated with increased IL-1β levels in the brain.


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Surgery_Schwartz. injuries demonstrated increased neuroinflammation, brain damage, and behavioral deficits compared to mice given an isolated-TBI. These changes correlated with increased IL-1β levels in the brain. Treatment Brunicardi_Ch02_p0027-p0082.indd 4401/03/19 6:49 PM 45SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2with IL-1R antagonist post injury reduced volume loss in the injured cortex as well as markers of axonal injury, resulting in improved outcome in these animals.IL-18 is also a member of the IL-1 superfamily of cytokines.138 First noted as an IFN-γ-inducing factor produced by LPS-stim-ulated macrophages, IL-18 expression is found both in immune cells and nonimmune cells at low to intermediate levels. How-ever, activated macrophages and Kupffer cells produce large amounts of mature IL-18. Similar to IL-1β, IL-18 is synthe-sized and stored as an inactive precursor form (pro-IL-18), and activation requires activation of the inflammasome resulting the processing of


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Surgery_Schwartz. of mature IL-18. Similar to IL-1β, IL-18 is synthe-sized and stored as an inactive precursor form (pro-IL-18), and activation requires activation of the inflammasome resulting the processing of pro-IL-18 by caspase-1.139 It then exits the cell through a nontraditional secretory pathway. The IL-18 receptor (IL-18R) is composed of two subunits, IL-18Rα and IL-18Rβ, and is a member of the IL-1R superfamily that is structurally similar in their cytoplasmic domains to the TLR. One unique biological property of IL-18 is the potential, in conjunction with IL-12, to promote the Th1 response.IL-18 induces IFNγ production by CD4+ T cells. IFNγ, in turn, activates macrophages to produce inflammatory cytokines. Independent of its ability to induce interferon, IL-18 can act similarly to other proinflammatory cytokines by acting directly to increase in cell adhesion molecule expression, nitric oxide synthesis, and chemokine production by macrophages.140In a cohort of critically ill patients with


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Surgery_Schwartz. cytokines by acting directly to increase in cell adhesion molecule expression, nitric oxide synthesis, and chemokine production by macrophages.140In a cohort of critically ill patients with acute lung injury and ARDS, inflammasome-related mRNA transcripts (CASP1, IL1B, and IL18) were increased in peripheral blood. Moreover, plasma IL-18 were also elevated and served as a marker of mor-tality risk.141 Recent studies suggest that IL-18 therapy may hold promise as effective therapy in promoting immune recovery after severe surgical stress.142IL-33, a second important IL-1 family member, is mainly expressed in surface epithelium and endothelium, where it is normally bound via an N-terminal chromatin-binding motif.143 Nuclear localization is important for its function and perhaps its regulation. Expression in mice of an IL-33 that lacks the nuclear localization sequence, results lethal inflammation, suggesting that nuclear localization acts to prevent unregulated extracel-lular release.144


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Surgery_Schwartz. Expression in mice of an IL-33 that lacks the nuclear localization sequence, results lethal inflammation, suggesting that nuclear localization acts to prevent unregulated extracel-lular release.144 Similar to HMGB1 and other IL-1 family mem-bers, IL-33 lacks a signal sequence for active secretion so that its release is injury-dependent. Once released from damaged cells, full length IL-33 is biologically active, but it can be further pro-cessed by inflammatory proteases to a mature form that exhibits tento thirtyfold higher activity. Il-33 can binds to a member of the IL-1R family, ST2, leading to activation of NF-kB-mediated transcriptional events. ST2+ cells include macrophages, mast cells, Th2 cells, and tissue regulatory T cells (Tregs) which are important controllers of immune homeostasis.Interleukin-2 Family. Interleukin-2 (IL-2) is a multifunc-tional cytokine produced primarily by CD4+ T cells after antigen activation, which plays pivotal roles in the immune response. Other


Surgery_Schwartz

Surgery_Schwartz. Family. Interleukin-2 (IL-2) is a multifunc-tional cytokine produced primarily by CD4+ T cells after antigen activation, which plays pivotal roles in the immune response. Other cellular sources for IL-2 include CD8+ and NK T cells, mast cells, and activated dendritic cells. Discovered as a T cell growth factor, IL-2 also promotes CD8+ T cell and natural killer cell cytolytic activity and modulates T cell differentiation pro-grams in response to antigen. Thus, IL-2 promotes naive CD4+ T cell differentiation into T helper 1 (Th1) and T helper 2 (Th2) cells while inhibiting T helper 17 (Th17) and T follicular helper (Tfh) cell differentiation. Moreover, IL-2 is essential for the development and maintenance of T regulatory (Treg) cells and for activation-induced cell death, thereby mediating tolerance and limiting inappropriate immune reactions. The upregulation of IL-2 requires calcium as well as protein kinase C signaling, which leads to the activation of transcription factors such as


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Surgery_Schwartz. tolerance and limiting inappropriate immune reactions. The upregulation of IL-2 requires calcium as well as protein kinase C signaling, which leads to the activation of transcription factors such as nuclear factor of activated T cells (NFAT) and NF-κB. MicroRNAs also play a role in the regulation of IL-2 expression.145IL-2 binds to IL-2 receptors (IL-2R), which are expressed on leukocytes. IL-2Rs are formed from various combinations of three receptor subunits: IL-2Rα, IL-2Rβ, and IL-2Rγ. These subunits form in low, medium, and high affinity forms of the receptor depending on the subunit combination. IL-2Rγ has been renamed the common cytokine receptor γ chain (γc), which is now known to be shared by IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. Constitutive IL-2 receptor expression is low and is inducible by T cell receptor ligation and cytokine stimulation. Importantly, the transcription of each receptor subunit is indi-vidually regulated via a complex process to effect tight control of


Surgery_Schwartz

Surgery_Schwartz. is inducible by T cell receptor ligation and cytokine stimulation. Importantly, the transcription of each receptor subunit is indi-vidually regulated via a complex process to effect tight control of surface expression. Once the receptor is ligated, the major IL-2 signaling pathways that are engaged include Janus Kinase (JAK)-signal transducer and activator of transcription (STAT), Shc-Ras-MAPK, and phosphoinositol-3-kinase (PI3-K)-AKT. Partly due to its short half-life of <10 minutes, IL-2 is not read-ily detectable after acute injury. IL-2 receptor blockade induces immunosuppressive effects and can be pharmacologically used for organ transplantation. Attenuated IL-2 expression observed during major injury or blood transfusion may contribute to the relatively immunosuppressed state of the surgical patient.146Interleukin-6 Family. Following burn or traumatic injury, damage-associated molecular patterns (DAMPs) from dam-aged or dying cells stimulate TLRs to produce IL-6, a


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Surgery_Schwartz. state of the surgical patient.146Interleukin-6 Family. Following burn or traumatic injury, damage-associated molecular patterns (DAMPs) from dam-aged or dying cells stimulate TLRs to produce IL-6, a proin-flammatory cytokine that plays a central role in host defense. IL-6 levels in the circulation are detectable by 60 minutes post injury, peak between 4 and 6 hours, and can persist for as long as 10 days. Further, plasma levels of IL-6 are proportional to the degree of injury. In the liver, IL-6 strongly induces a broad spec-trum of acute-phase proteins such as C-reactive protein (CRP) and fibrinogen, among others, while it reduces expression of albumin, cytochrome P 450, and transferrin. In lymphocytes, IL-6 induces B cell maturation into immunoglobulin-producing cells and regulates Th17/Treg balance. IL-6 modulates T cell behavior by inducing the development of Th17 cells and inhib-iting Treg cell differentiation in conjunction with transforming growth factor-β. IL-6 also promotes


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Surgery_Schwartz. balance. IL-6 modulates T cell behavior by inducing the development of Th17 cells and inhib-iting Treg cell differentiation in conjunction with transforming growth factor-β. IL-6 also promotes angiogenesis and increased vascular permeability, which are associated with local inflam-matory responses. To date, ten IL-6 family cytokines have been identified, including IL-6, oncostatin M, neuropoietin, IL-11, IL-27, and IL-31.147The interleukin-6 receptor (IL-6R, gp80) is expressed on hepatocytes, monocytes, B cells, and neutrophils in humans. However, many other cells respond to IL-6 through a process known as trans-signaling.148 In this case, soluble IL-6Rs (sIL-6R) exist in the serum and bind to IL-6, forming an IL-6/sIL-6R complex. The soluble receptor is produced by proteo-lytic cleavage from the surface of neutrophils in a process that is stimulated by C-reactive protein, complement factors, and leu-kotrienes. The IL6/sIL6R complex can then bind to the gp130 receptor, which is


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Surgery_Schwartz. from the surface of neutrophils in a process that is stimulated by C-reactive protein, complement factors, and leu-kotrienes. The IL6/sIL6R complex can then bind to the gp130 receptor, which is expressed ubiquitously on cells. Upon IL-6 stimulation, gp130 transduces two major signaling pathways: the JAK-STAT3 pathway and the SHP2-Gab-Ras-Erk-MAPK pathway, which is regulated by cytoplasmic suppressor of cytokine signaling (SOCS3). These signaling events can lead to increased expression of adhesion molecules as well as proinflammatory chemokines and cytokines. High plasma IL-6 levels have been associated with mortality during Brunicardi_Ch02_p0027-p0082.indd 4501/03/19 6:49 PM 46BASIC CONSIDERATIONSPART Iintra-abdominal sepsis.149 Moreover, prolonged (more than 3 days) elevation of IL-6 concentrations has been reported to correlate with the occurrence of complications and mortality following severe traumatic injury. More recently, a meta-analy-sis analyzed the predictive value of


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Surgery_Schwartz. concentrations has been reported to correlate with the occurrence of complications and mortality following severe traumatic injury. More recently, a meta-analy-sis analyzed the predictive value of IL-6 for the development of complications and mortality after trauma and found that the con-centration of IL-6 in the first 24 hours after trauma was predic-tive for the development of multiple organ failure and death.150Interleukin-10 Family. We have talked almost exclusively about the factors that initiate the proinflammatory response fol-lowing cellular stress or injury. The reestablishment of immune homeostasis following these events requires the resolution of inflammation and the initiation of tissue repair processes. Interleukin-10 (IL-10) plays a central role in this anti-inflammatory response by regulating the duration and magnitude of inflamma-tion in the host.151The IL-10 family currently has six members, includ-ing IL-10, IL-19, IL-20, IL-22, IL-24, and IL-26. IL-10 is produced


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Surgery_Schwartz. by regulating the duration and magnitude of inflamma-tion in the host.151The IL-10 family currently has six members, includ-ing IL-10, IL-19, IL-20, IL-22, IL-24, and IL-26. IL-10 is produced by a variety of immune cells of both myeloid and lymphoid origin. Its synthesis is up-regulated during times of stress and systemic inflammation; however, each cell type that produces IL-10 does so in response to different stimuli, allow-ing for tight control of its expression. IL-10 exerts effects by binding to the IL-10 receptor (IL-10R), which is a tetramer formed from two distinct subunits, IL-10R1 and IL-10R2. Specifically, IL-10 binds first to the IL10R1 subunit, which then recruits IL-10R2, allowing the receptor complex to form. While IL-10R2 is widely expressed, IL-10R1 expression is confined to leukocytes so that the effects of IL-10 are confined to the immune system. Once receptor ligation occurs, signaling proceeds by the activation of JAK1 and STAT3. In particular, STAT3 in


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Surgery_Schwartz. confined to leukocytes so that the effects of IL-10 are confined to the immune system. Once receptor ligation occurs, signaling proceeds by the activation of JAK1 and STAT3. In particular, STAT3 in conjunction with IL-10 is absolutely required for the transcription of genes responsible for the anti-inflammatory response (AIR). IL-10 inhibits the secretion of proinflamma-tory cytokines, including TNF and IL-1, partly through the downregulation of NF-κB and thereby functions as a nega-tive feedback regulator of the inflammatory cascade.151 In macrophages, IL-10 suppresses the transcription of 20% of all LPS-induced genes. Further, experimental models of inflam-mation have shown that neutralization of IL-10 increases TNF production and mortality, whereas restitution of circulating IL-10 reduces TNF levels and subsequent deleterious effects. Increased plasma levels of IL-10 also have been associated with mortality and disease severity after traumatic injury.Interleukin-12


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Surgery_Schwartz. IL-10 reduces TNF levels and subsequent deleterious effects. Increased plasma levels of IL-10 also have been associated with mortality and disease severity after traumatic injury.Interleukin-12 Family. Interleukin-12 (IL-12) is unique among the cytokines in being the only heterodimeric cytokine. This family, which includes IL-12, IL-23, IL-27, and IL-35, consists of an α-chain that is structurally similar to the IL-6 cytokine and a β-chain that is similar to the class I receptor for cytokines. The individual IL-12 family members are formed from various combinations of the α and β subunits. Despite the sharing of individual subunits, and the similarities of their receptors, the IL-12 cytokines have different biological func-tions. IL-12 and IL-23 are considered proinflammatory, stimu-latory cytokines with key roles in the development of Th1 and Th17 subsets of helper T cells. In contrast, both IL-27 and IL-35 appear to have immunoregulatory functions that are associated with cytokine


Surgery_Schwartz

Surgery_Schwartz. cytokines with key roles in the development of Th1 and Th17 subsets of helper T cells. In contrast, both IL-27 and IL-35 appear to have immunoregulatory functions that are associated with cytokine inhibition in specific Treg cell populations, par-ticularly the Th17 cells.152 The effects of these cytokines require specific receptor chains that are also shared among the cyto-kines. The complexity of signaling is evidenced by the fact that these receptor chains can function both as dimers and as mono-mers. Ligation of the IL-12 receptors initiate signaling events via the JAK-STAT pathway.IL-12 synthesis and release is increased during endotox-emia and sepsis.153 Together with IL-18, it stimulates lympho-cytes to increase secretion of IFN-γ. IL-12 also stimulates NK cell cytotoxicity and helper T cell differentiation in this setting. IL-12 release is inhibited by IL-10, and its deficiency inhibits phagocytosis in neutrophils. In experimental models of inflam-matory stress, IL-12


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Surgery_Schwartz. and helper T cell differentiation in this setting. IL-12 release is inhibited by IL-10, and its deficiency inhibits phagocytosis in neutrophils. In experimental models of inflam-matory stress, IL-12 neutralization conferred a mortality benefit in mice during endotoxemia.IL-23, an important IL-12 family member, is a heterodi-meric cytokine comprised of a unique p19 subunit linked to a p40 subunit that is common with IL-12. IL-23 appears to be an important survival signal for a specific subset of T helper (Th) cells, Th-17 cells, where it provides a secondary stimu-lus for Th-17 differentiation.152 The Th-17 population of cells has recently been demonstrated to expand following traumatic injury and may mark an early phenotypic shift in cell population that has prognostic significance.154,155Interleukin-17 Family. IL-17A (also called IL-17) is the major effector cytokine predominantly produced by a subset of helper T cells, the T helper (Th)-17 cells.156 It is the founding member of the


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Surgery_Schwartz. Family. IL-17A (also called IL-17) is the major effector cytokine predominantly produced by a subset of helper T cells, the T helper (Th)-17 cells.156 It is the founding member of the IL-17 family of cytokines, which includes IL-17A through F. The original described activity for IL-17A was to promote the differentiation of bone marrow progenitor cells along the granulopoietic lineage. Subsequent studies have confirmed that IL-17A is required for increasing circulating neutrophil numbers following stress. In the setting of infection, it is now known that IL-17 acts in conjunction with IL-23 to upregulate granulocyte-colony stimulating factor to promote granulopoi-esis. IL-17A has also been shown to regulate the production of specific chemokines in both gut and lung epithelial cells and thus can modulate both the emigration of neutrophils into these tissues and their activation at the site. IL-17 also induces the expression of matrix metalloproteinases, which can make the extracellular


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Surgery_Schwartz. can modulate both the emigration of neutrophils into these tissues and their activation at the site. IL-17 also induces the expression of matrix metalloproteinases, which can make the extracellular matrix more accessible for immune cell recruitment.156IL-17 has the ability to induce the expression of impor-tant proinflammatory cytokines, including IL-1β, IL-6, and TNF from macrophages and other cells, and in this way, cre-ates a self-sustaining loop that enhances its own production and strengthens its overall effects.157 Recent data supports a pivotal role for IL-17 in the posttrauma immune response and has iden-tified associations between increased IL-17 expression associ-ated with Th17immune response outcomes following blunt trauma.154Interferons. Interferons were first recognized as soluble mediators that inhibited viral replication through the activa-tion of specific antiviral genes in infected cells. Interferons are categorized into three types based on receptor specificity and


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Surgery_Schwartz. mediators that inhibited viral replication through the activa-tion of specific antiviral genes in infected cells. Interferons are categorized into three types based on receptor specificity and sequence homology. The two major types, type I and type II are discussed in the following section.Type I interferon family is composed of twenty distinct proteins. These include IFN-α, IFN-β, and IFN-ω, which are structurally related and bind to a common receptor.158 They are likely produced by most cell types and tissues after the detec-tion of PAMPs/ DAMPs by cytosolic or membrane receptors, including TLR in macrophages and dendritic cells. Type 1 IFNs bind to a heterodimeric transmembrane receptor interferon (α and β) receptor 1, resulting in STAT activation and nuclear trans-location. In the nucleus, dimeric STATs recruit an additional Brunicardi_Ch02_p0027-p0082.indd 4601/03/19 6:49 PM 47SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2transcriptional factor to form a complex


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Surgery_Schwartz. dimeric STATs recruit an additional Brunicardi_Ch02_p0027-p0082.indd 4601/03/19 6:49 PM 47SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2transcriptional factor to form a complex capable of binding to interferon-stimulated response elements, inducing hundreds of IFN-stimulated genes.Type I interferons influence adaptive immune responses by inducing the maturation of dendritic cells and by stimulat-ing class I MHC expression. IFN-α and IFN-β also enhance immune responses by increasing the cytotoxicity of natural killer cells both in culture and in vivo. Further, they have been implicated in the enhancement of chemokine synthesis, particu-larly those that recruit myeloid cells and lymphoid cells. Thus, IFN/STAT signaling has important effects on the mobilization, tissue recruitment, and activation of immune cells that compose the inflammatory infiltrate. In contrast, type I IFNs appear to inhibit inflammasome activity, possibly via IL-10.159The single type II interferon,


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Surgery_Schwartz. and activation of immune cells that compose the inflammatory infiltrate. In contrast, type I IFNs appear to inhibit inflammasome activity, possibly via IL-10.159The single type II interferon, IFN-γ is secreted by various T cells, NK cells, and antigen-presenting cells in response to bacterial antigens and cytokines. It functions as a key regula-tor of macrophage activation toward the “M1” proinflammatory phenotype.160 In response to IFN-γ, macrophages produce high levels of proinflammatory cytokines such as Il-1β, IL-12, IL-23, and TNF-α as well as reactive nitrogen and oxygen species. As a consequence, macrophages demonstrate enhanced phagocyto-sis and killing. In addition, IFN-γ signaling generates additional cytokines and inflammatory factors to sustain inflammation and help to maintain Th1 responses.IFN-γ regulation of macrophage activity may contribute to acute lung injury after major surgery or trauma. A dimin-ished IFN-γ level, as seen in knockout mice, is associated with


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Surgery_Schwartz. Th1 responses.IFN-γ regulation of macrophage activity may contribute to acute lung injury after major surgery or trauma. A dimin-ished IFN-γ level, as seen in knockout mice, is associated with increased susceptibility to both viral and bacterial pathogens. In addition, IFN-γ promotes differentiation of T cells to the helper T cell subtype 1 and also enhances B-cell isotype switching to immunoglobulin G.158Receptors of all IFN subtypes belong to the class II of cytokine receptors and utilize JAK-STAT signaling pathway for nuclear signaling, although different STAT activation (e.g., STAT1 and STAT2) is favored by individual receptors.Granulocyte-Macrophage Colony-Stimulating Fac-tor/Interleukin-3/Interleukin-5 Family. Granulocytemacrophage colony-stimulating factor (GM-CSF), IL-3, and IL-5 compose a small family of cytokines that regulates the growth and activation of immune cells. They are largely the products of activated T cells, which when released, stimulate the behavior of myeloid


Surgery_Schwartz

Surgery_Schwartz. a small family of cytokines that regulates the growth and activation of immune cells. They are largely the products of activated T cells, which when released, stimulate the behavior of myeloid cells by inducing cytokine expression and antigen presentation. In this way, GM-CSF, IL-3, and IL-5 are able to link the innate and acquired immune responses. With the exception of eosinophils, GM-CSF/IL-3/IL-5 are not essential for constitutive hematopoietic cell function. Rather, they play an important role when the host is stressed by serving to increase the numbers of activated and sensitized cells required to bol-ster host defense.161 Currently, GM-CSF is in clinical trials for administration to children with an injury severity score >10 fol-lowing blunt or penetrating trauma. The goal of the study is to provide evidence of the effectiveness of GM-CSF as an agent that can ameliorate posttraumatic immune suppression.Receptors for the GM–CSF/IL-3/IL-5 family of cytokines are expressed at very


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Surgery_Schwartz. is to provide evidence of the effectiveness of GM-CSF as an agent that can ameliorate posttraumatic immune suppression.Receptors for the GM–CSF/IL-3/IL-5 family of cytokines are expressed at very low level on hematopoietic cells. Similar to the other cytokine receptors discussed, they are heterodimers composed of a cytokine-specific α subunit and a common β sub-unit (βc), which is shared by all three receptors and is required for high affinity signal transduction. The binding of cytokine to its receptor activates JAK2-STAT, MAPK, and PI3-K—mediated signaling events to regulate a variety of important cell behaviors, including effector function in mature cells.EicosanoidsOmega-6 Polyunsaturated Fat Metabolites: Arachidonic Acid. Eicosanoids are derived primarily by oxidation of the membrane phospholipid, arachidonic acid (AA), which is relatively abundant in the membrane lipids of inflammatory cells. The major precursor of arachidonic acid is the omega-6 (n-6) polyunsaturated fatty acid


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Surgery_Schwartz. phospholipid, arachidonic acid (AA), which is relatively abundant in the membrane lipids of inflammatory cells. The major precursor of arachidonic acid is the omega-6 (n-6) polyunsaturated fatty acid (PUFA) linolenic acid, a major source of which is soybean oil. Not surprising, an excess of linolenic acid is thought to promote inflammation via increased availability of AA, and in turn, eicosanoids.Eicosanoids generated from AA include prostaglandins, thromboxanes, and leukotrienes. When a cell senses the proper stimulus, AA is released from phospholipids or diacylglycerols by the enzymatic activation of phospholipase A2 (Fig. 2-6A). Prostanoids, which include all of the prostaglandins (PG) and the thromboxanes, result from the sequential action of the cyclooxy-genase (COX) enzyme and terminal synthetases on arachidonic acid. In contrast, arachidonic acid may be oxidized along the lipoxygenase pathway via the central enzyme 5-lipoxygenase, to produce several classes of leukotrienes and


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Surgery_Schwartz. synthetases on arachidonic acid. In contrast, arachidonic acid may be oxidized along the lipoxygenase pathway via the central enzyme 5-lipoxygenase, to produce several classes of leukotrienes and lipoxins, which have anti-inflammatory functions. In general, the effects of eico-sanoids are mediated via specific receptors, which are members of a superfamily of G protein-coupled receptors.Eicosanoids are not stored within cells but are instead generated rapidly in response to many proinflammatory stimuli, including hypoxic injury, direct tissue injury, endotoxin (lipo-polysaccharide), norepinephrine, vasopressin, angiotensin II, bradykinin, serotonin, acetylcholine, cytokines, and histamine. They have a broad range of physiologic roles, including neuro-transmission, and vasomotor regulation. Eicosanoids are also involved in immune cell regulation (Table 2-6), by modulating the intensity and duration of inflammatory responses.Glucocorticoids, NSAIDs, and leukotriene inhibitors can


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Surgery_Schwartz. Eicosanoids are also involved in immune cell regulation (Table 2-6), by modulating the intensity and duration of inflammatory responses.Glucocorticoids, NSAIDs, and leukotriene inhibitors can successfully block the end products of eicosanoid pathways to modulated inflammation.The production of eicosanoids is celland stimulus-specific. Therefore, the signaling events that are initiated will depend on the concentrations and types of eicosanoids gener-ated, as well as the unique complement of receptors expressed by their target cells. For example, prostaglandin E2 (PGE2) suppresses the effector function of macrophages (i.e., phago-cytosis and intracellular pathogen killing) via a mechanism that is dependent on increased cAMP levels. PGE2 also modulates chemokine production and enhances local accumulation of reg-ulatory T cells and myeloid-derived suppressor cells. Prostacy-clin (PGI2) has an inhibitory effect on Th1 and Th2-mediated immune responses, while enhancing Th17 differentiation


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Surgery_Schwartz. accumulation of reg-ulatory T cells and myeloid-derived suppressor cells. Prostacy-clin (PGI2) has an inhibitory effect on Th1 and Th2-mediated immune responses, while enhancing Th17 differentiation and cytokine production. Leukotrienes are potent mediators of capil-lary leakage as well as leukocyte adherence, neutrophil activa-tion, bronchoconstriction, and vasoconstriction. Leukotriene B4 is synthesized from arachidonic acid in response to acute Ca2+ signaling induced by inflammatory mediators.162 High affinity leukotriene receptors (BLT1) are expressed primarily in leu-kocytes, including granulocytes, eosinophils, macrophages, and differentiated T cells, whereas the low affinity receptor is expressed in many cell types. Leukotrienes, most notably leu-kotriene B4 (LTB4), has been implicated in the development of both acute lung injury and acute kidney injury following hemor-rhagic shock in animal models.163,164Brunicardi_Ch02_p0027-p0082.indd 4701/03/19 6:49 PM 48BASIC


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Surgery_Schwartz. implicated in the development of both acute lung injury and acute kidney injury following hemor-rhagic shock in animal models.163,164Brunicardi_Ch02_p0027-p0082.indd 4701/03/19 6:49 PM 48BASIC CONSIDERATIONSPART IPhospholipidPhospholipase A2CorticosteroidsCyclooxygenaseLipoxygenaseProstaglandinsPGD2PGE2PGF2˜PGI2ThromboxaneTXA2Hydroxyeicosatetraenoic acid(HETE)LeukotrienesLTA4LTB4LTC4LTD4LTE4Hydroperoxyeicosatetraenoic acid(HPETE)Cyclic endoperoxides(PGG2,PGH2)Arachidonic acidAFree eicosapentaenoic acidCyclooxygenaseLipoxygenase3-seriesprostaglandins5-seriesleukotrienesPGG3LTA5LTC5LTB5PGH35-HPEPEAnti-inflammatory andinflammation resolvingE-seriesresolvinsBFigure 2-6. Schematic diagram of (A) arachidonic acid and (B) eicosapentaenoic acid metabolism. LT = leukotriene; PG = prostaglandin; TXA2 = thromboxane A2; HPEPE = hydroperoxyeicosapentaenoic acid.Omega-3 Polyunsaturated Fat Metabolites: All-cis-5, 8, 11, 14, 17-Eicosapentaenoic Acid. The second major family of PUFAs is the


Surgery_Schwartz

Surgery_Schwartz. TXA2 = thromboxane A2; HPEPE = hydroperoxyeicosapentaenoic acid.Omega-3 Polyunsaturated Fat Metabolites: All-cis-5, 8, 11, 14, 17-Eicosapentaenoic Acid. The second major family of PUFAs is the omega-3 fatty acid, α-linolenic acid, which is found primarily in cold water fish. α-Linolenic acid is the metabolic precursor of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Omega-3 PUFAs are also sub-strates for the cyclooxygenase and lipoxygenase enzymes that produce eicosanoids, but the mediators produced have a differ-ent structure from the AA-derived mediators, and this influences their actions (Fig. 2-6B). For example, omega-3 fatty acids are reported to have specific anti-inflammatory effects, including inhibition of NF-κB activity, TNF release from hepatic Kupffer cells, and leukocyte adhesion and migration. Key derivatives of omega-3 PUFAs have also been identified and synthesized. These include resolvins, protectins, and maresins. In a vari-ety of model systems,


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Surgery_Schwartz. and leukocyte adhesion and migration. Key derivatives of omega-3 PUFAs have also been identified and synthesized. These include resolvins, protectins, and maresins. In a vari-ety of model systems, resolvins have been shown to attenuate the inflammatory phenotypes of a number of immune cells by decreasing neutrophil recruitment, reducing synthesis of pro-inflammatory cytokines and regulating transcription factor activation.165,166The ratio of dietary omega-6 to omega-3 PUFA is reflected in the membrane composition of various cells, including cells of the immune system, which has potential implications for the inflammatory response. For example, a diet that is rich in omega-6 PUFA will result in cells whose membranes are “omega-6 PUFA rich.” When omega-6 PUFAs are the main plasma membrane lipid available for phospho-lipase activity, more proinflammatory PUFAs (i.e., 2-series prostaglandins) are generated. Many lipid preparations are soy-based and thus primarily composed of omega-6 fatty


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Surgery_Schwartz. available for phospho-lipase activity, more proinflammatory PUFAs (i.e., 2-series prostaglandins) are generated. Many lipid preparations are soy-based and thus primarily composed of omega-6 fatty acids. These are thought to be “inflammation-enhancing.” Nutritional supplementation with omega-3 fatty acid has the potential to dampen inflammation by shifting the cell mem-brane composition in factor of omega 3-PUFAs. In a study of surgical patients, preoperative supplementation with omega-3 fatty acid was associated with reduced need for mechanical ventilation, decreased hospital length of stay, and decreased mortality with a good safety profile.167Plasma Contact SystemComplement. Following traumatic injury, there is almost immediate activation of the complement system, which is a major effector mechanism of the innate immune system. The complement system was thought to act initially as the required “first line of defense” for the host against pathogens, by bind-ing and clearing them from


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Surgery_Schwartz. mechanism of the innate immune system. The complement system was thought to act initially as the required “first line of defense” for the host against pathogens, by bind-ing and clearing them from the circulation. Recent data indicate Brunicardi_Ch02_p0027-p0082.indd 4801/03/19 6:49 PM 49SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2depicted as a linear process in which parallel pathways are activated, it actually functions more like a central node that is tightly networked with other systems. Then, depending on the activating signal, several initiation and regulatory events act in concert to heighten immune surveillance.Complement activation proceeds via distinct pathways. Pathway initiation occurs by the binding and activation of a specific recognition unit to its designated ligand. The classical pathway, which is often referred to as “antibody-dependent” is initiated by direct binding of C1q to its common ligands, which include IgM/IgG aggregates. Alternately, C1q


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Surgery_Schwartz. ligand. The classical pathway, which is often referred to as “antibody-dependent” is initiated by direct binding of C1q to its common ligands, which include IgM/IgG aggregates. Alternately, C1q can activate complement by binding to soluble pattern recognition molecules such as pentraxins (e.g., C-reactive protein [CRP]). In a series of subsequent activation and amplification steps, the pathway ulti-mately leads to the generation of C3a and C5a, which are potent anaphylotoxins, in addition to C3b, which acts as an opsonin. An additional product, C5b, initiates the formation of the mem-brane attack complex, which becomes inserted into cell mem-brane to form a lytic pore. The subsequent effect of complement signaling is neutrophil activation leading to ROS production, as well as protease and vasoactive mediator secretion.168 The complement cascade also results in the release of proinflamma-tory cytokines synergistically with TLR-signaling, which con-tributes to systemic inflammation and


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Surgery_Schwartz. vasoactive mediator secretion.168 The complement cascade also results in the release of proinflamma-tory cytokines synergistically with TLR-signaling, which con-tributes to systemic inflammation and generalized capillary leak following severe injury.An additional means of complement activation via the lectin pathway is initiated by mannose-binding lectins (MBL) or ficolins, which bind specific carbohydrate structures. This pathway has been speculated to be a major mechanism for complement activation post injury by interactions with matrix fragments and mitochondrial DAMPs. In addition, both low pH and serine proteases of the coagulation cascade may contribute to complement activation. As a consequence, high levels of acti-vated complement components may help to continue to drive systemic inflammation post injury.169Kallikrein-Kinin System. The kallikrein-kinin system, also referred to as the “contact” system, is a group of proteins that contribute to both coagulation and inflammation.


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Surgery_Schwartz. post injury.169Kallikrein-Kinin System. The kallikrein-kinin system, also referred to as the “contact” system, is a group of proteins that contribute to both coagulation and inflammation. Prekalli-krein circulates in the plasma bound to high molecular weight kininogen (HK). A variety of stimuli lead to the binding of prekallikrein-HK complex to Hageman factor (factor XII) to initiate the intrinsic clotting cascade. This results in formation of the serine protease kallikrein, which is both proinflamma-tory and procoagulant. HK is cleaved by kallikrein to form bradykinin (BK).The kinins (e.g., BK) mediate several physiologic pro-cesses, including vasodilation, increased capillary perme-ability, tissue edema, and neutrophil chemotaxis.170 They also increase renal vasodilation and consequently reduce renal per-fusion pressure. Kinin receptors are members of the rhodopsin family of G-protein-coupled receptors and are located on vas-cular endothelium and smooth muscle cells. Kinin receptors


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Surgery_Schwartz. reduce renal per-fusion pressure. Kinin receptors are members of the rhodopsin family of G-protein-coupled receptors and are located on vas-cular endothelium and smooth muscle cells. Kinin receptors are rapidly upregulated following TLR4 and cytokine signal-ing and appear to have important effects on both immune cell behavior and on immune mediators.171 For example, activation of the kinin receptor, B1, results in increased neutrophil che-motaxis, while increased B2 receptor expression causes activa-tion of arachidonic-prostaglandin pathways. Bradykinin and kallikrein levels are increased following hemorrhagic shock and tissue injury. The degree of elevation in the levels of these mediators has been associated with the magnitude of injury and mortality.Table 2-6Systemic stimulatory and inhibitory actions of eicosanoidsORGAN/FUNCTIONSTIMULATORINHIBITORPancreas Glucose-stimulated insulin secretion Glucagon secretion12-HPETEPGD2, PGE2PGE2Liver Glucagon-stimulated glucose


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Surgery_Schwartz. and inhibitory actions of eicosanoidsORGAN/FUNCTIONSTIMULATORINHIBITORPancreas Glucose-stimulated insulin secretion Glucagon secretion12-HPETEPGD2, PGE2PGE2Liver Glucagon-stimulated glucose production PGE2Fat Hormone-stimulated lipolysis PGE2Bone ResorptionPGE2, PGE-m, 6-K-PGE1, PGF1α, PGI2 Pituitary Prolactin Luteinizing hormone Thyroid-stimulating hormone Growth hormonePGE1PGE1, PGE2, 5-HETEPGA1, PGB1, PGE1, PGE1PGE1 Parathyroid Parathyroid hormonePGE2PGF2Lung BronchoconstrictionPGF2α TXA2, LTC4, LTD4, LTE4PGE2Kidney Stimulation of renin secretionPGE2, PGI2 Gastrointestinal system Cytoprotective effectPGE2 Immune response Suppression of lymphocyte activityPGE2 Hematologic system Platelet aggregationTXA2PGI25-HETE = 5-hydroxyeicosatetraenoic acid; 12-HPETE = 12-hydroxyperoxyeicosatetraenoic acid; 6-K-PGE1 = 6-keto-prostaglandin E1; LT = leukotriene; PG = prostaglandin; PGE-m = 13,14-dihydro-15-keto-PGE2 (major urine metabolite of PGE2); TXA2 = thromboxane A2.that


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Surgery_Schwartz. acid; 6-K-PGE1 = 6-keto-prostaglandin E1; LT = leukotriene; PG = prostaglandin; PGE-m = 13,14-dihydro-15-keto-PGE2 (major urine metabolite of PGE2); TXA2 = thromboxane A2.that complement is also participates in the elimination of immune complexes as well as damaged and dead cells. In addi-tion, complement is recognized as contributing to mobiliza-tion of hematopoietic stem/progenitor cells (HSPC) and lipid metabolism.168 Although complement activation is typically Brunicardi_Ch02_p0027-p0082.indd 4901/03/19 6:49 PM 50BASIC CONSIDERATIONSPART ISerotoninSerotonin is a monoamine neurotransmitter (5-hydroxytrypta-mine; 5-HT) derived from tryptophan. Serotonin is synthesized by neurons in the CNS as well as by intestinal enterochromaf-fin cells, which are the major source of plasma 5-HT. Once in the plasma, 5-HT is taken up rapidly into platelets via the serotonin transporter (SERT), where it is either stored in the dense granules in millimolar concentrations or targeted for


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Surgery_Schwartz. 5-HT. Once in the plasma, 5-HT is taken up rapidly into platelets via the serotonin transporter (SERT), where it is either stored in the dense granules in millimolar concentrations or targeted for deg-radation. It is interesting that the surface expression of SERT on platelets is sensitive to plasma 5-HT levels, which in turn modulates platelet 5-HT content. Receptors for serotonin are widely distributed in the periphery and are found in the GI tract, cardiovascular system, and some immune cells.172 Serotonin is a potent vasoconstrictor and also modulates cardiac inotropy and chronotropy through nonadrenergic cyclic adenosine mono-phosphate (cAMP) pathways. Serotonin is released at sites of injury, primarily by platelets. Recent work has demonstrated an important role for platelet 5-HT in the local inflammatory response to injury. Using mice that lack the nonneuronal iso-form of tryptophan hydroxylase (Tph1), the rate-limiting step for 5-HT synthesis in the periphery, investigators


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Surgery_Schwartz. in the local inflammatory response to injury. Using mice that lack the nonneuronal iso-form of tryptophan hydroxylase (Tph1), the rate-limiting step for 5-HT synthesis in the periphery, investigators demonstrated fewer neutrophils rolling on mesenteric venules.173 Tph1-/mice, in response to an inflammatory stimulus, also showed decreased neutrophil extravasation. Together, these data indicate an impor-tant role for nonneuronal 5-HT in neutrophil recruitment to sites of inflammation and injury.HistamineHistamine is a short-acting endogenous amine that is widely distributed throughout the body. It is synthesized by histidine decarboxylase (HDC), which decarboxylates the amino acid his-tidine. Histamine is either rapidly released or stored in neurons, skin, gastric mucosa, mast cells, basophils, and platelets and plasma levels are increased with hemorrhagic shock, trauma, thermal injury, and sepsis.174 Not surprisingly, circulating cyto-kines can increase immune cell expression of HDC to


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Surgery_Schwartz. and platelets and plasma levels are increased with hemorrhagic shock, trauma, thermal injury, and sepsis.174 Not surprisingly, circulating cyto-kines can increase immune cell expression of HDC to further contribute to histamine synthesis. There are four histamine receptor (HR) subtypes with varying physiologic roles, but they are all members of the rhodopsin family of G-protein coupled receptors. H1R binding mediates vasodilation, bronchocon-striction, intestinal motility, and myocardial contractility. H1R knockout mice demonstrate significant immunologic defects, including impaired B and T cell responses.H2R binding is best described for its stimulation of gastric parietal cell acid secretion. However, H2R can also modulate a range of immune system activities, such as mast cell degranula-tion, antibody synthesis, Th1 cytokine production, and T-cell proliferation. H3R was initially classified as a presynaptic auto-receptor in the peripheral and central nervous system (CNS). However,


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Surgery_Schwartz. antibody synthesis, Th1 cytokine production, and T-cell proliferation. H3R was initially classified as a presynaptic auto-receptor in the peripheral and central nervous system (CNS). However, data using H3R knockout mice demonstrates that it also participates in inflammation in the CNS. H3R knockout mice display increased severity of neuroinflammatory diseases, which correlates with dysregulation of blood-brain barrier per-meability and increased expression of macrophage inflammatory protein 2, IFN-inducible protein 10, and CXCR3 by peripheral T cells. H4R is expressed primarily in bone marrow, but it has also been detected in leukocytes, including neutrophils, eosino-phils, mast cells, dendritic cells, T cells, and basophils. H4R is emerging as an important modulator of chemoattraction and cytokine production in these cells. Thus, it is clear that cells of both the innate and adaptive immune response can be regulated by histamine, which is up-regulated following injury.175CELLULAR


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Surgery_Schwartz. and cytokine production in these cells. Thus, it is clear that cells of both the innate and adaptive immune response can be regulated by histamine, which is up-regulated following injury.175CELLULAR RESPONSE TO INJURYCytokine Receptor Families and Their Signaling PathwaysCytokines act on their target cells by binding to specific membrane receptors. These receptor families have been organized by struc-tural motifs and include type 1 cytokine receptors, type II cytokine receptors, chemokine receptors, tumor necrosis factor receptors (TNFR), and transforming growth factor receptors (TGFR). In addition, there are cytokine receptors that belong to the immuno-globulin receptor superfamilies. Several of these receptors have characteristic signaling pathways that are associated with them. These will be briefly reviewed in the following section.JAK-STAT SignalingA major subgroup of cytokines, comprising roughly 60 factors, bind to receptors termed type I/II cytokine receptors. Cytokines that


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Surgery_Schwartz. will be briefly reviewed in the following section.JAK-STAT SignalingA major subgroup of cytokines, comprising roughly 60 factors, bind to receptors termed type I/II cytokine receptors. Cytokines that bind these receptors include type I IFNs, IFN-γ, many inter-leukins (e.g., IL-6, IL-10, IL-12, and IL-13), and hematopoietic growth factors. These cytokines play essential rolls in the initia-tion, maintenance, and modulation of innate and adaptive immu-nity for host defense. All type I/II cytokine receptors selectively associate with the Janus kinases (JAK1, JAK2, JAK3, TYK2), which represent a family of tyrosine kinases that mediate the signal transduction for these receptors. As such, the JAK-STAT signaling pathway is considered a central communication hub for the immune system.176JAKs are constitutively bound to the cytokine receptors, and on ligand binding and receptor dimerization, activated JAKs phosphorylate the receptor to recruit signal transducer and acti-vator of transcription


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Surgery_Schwartz. constitutively bound to the cytokine receptors, and on ligand binding and receptor dimerization, activated JAKs phosphorylate the receptor to recruit signal transducer and acti-vator of transcription (STAT) molecules (Fig. 2-7). Activated STAT proteins further dimerize and translocate into the nucleus where they modulate the transcription of target genes. Rather than being a strictly linear pathway, it is likely that individual cytokines activate more than one JAK-STAT combination. The molecular implications for this in terms of cytokine signaling are still being unraveled, but the development of JAK-specific inhibitors (jakinibs) is moving the field forward quickly.177 Inter-estingly, STAT-DNA binding can be observed within minutes of cytokine binding. STATs have also been shown to modulate gene transcription via epigenetic mechanisms. Thus, JAKs and STATs are central players in the regulation of key immune cell function, by providing a signaling platform for proinflamma-tory


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Surgery_Schwartz. modulate gene transcription via epigenetic mechanisms. Thus, JAKs and STATs are central players in the regulation of key immune cell function, by providing a signaling platform for proinflamma-tory cytokines (IL-6 via JAK1 and STAT3); anti-inflammatory cytokines (IL-10 via STAT3) and integrating signals required for helper and regulatory T cell development and differentiation. The JAK/STAT pathway is inhibited by the action of phospha-tase, the export of STATs from the nucleus, as well the interac-tion of antagonistic proteins.178 JAK/STAT signaling has also been implicated in the secondary muscle wasting that occurs with chronic, persistent inflammation.179Suppressors of Cytokine SignalingSuppressor of cytokine signaling (SOCS) molecules are a fam-ily of proteins that function as a negative feedback loop for types I and II cytokine receptors by terminating JAK/STAT signaling. There are currently eight family members (SOCS1-7 and CIS [cytokine-inducible SH2-containing protein]) that


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Surgery_Schwartz. feedback loop for types I and II cytokine receptors by terminating JAK/STAT signaling. There are currently eight family members (SOCS1-7 and CIS [cytokine-inducible SH2-containing protein]) that are associated with cytokine receptor signaling. Pattern recognition receptors, including both TLR and C-type lectin receptors, also activate SOCS.180 Interestingly, induction of SOCS proteins is also achieved through activators of JAK/STAT signaling, creating an inhibitory feedback loop through which cytokines Brunicardi_Ch02_p0027-p0082.indd 5001/03/19 6:49 PM 51SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2JAKJAKPPJAKJAKPSTATSTATPPPSTATPSTATSTATSTATSOCSPSTATNuclear translocationNucleusReceptordimerizationFigure 2-7. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway also requires dimer-ization of monomeric units. STAT molecules possess “docking” sites that allow for STAT dimerization. The STAT complexes translocate into the nucleus


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Surgery_Schwartz. (JAK/STAT) signaling pathway also requires dimer-ization of monomeric units. STAT molecules possess “docking” sites that allow for STAT dimerization. The STAT complexes translocate into the nucleus and serve as gene transcription fac-tors. JAK/STAT activation occurs in response to cytokines (e.g., interleukin-6) and cell stressors, and has been found to induce cell proliferation and inflammatory function. Intracellular molecules that inhibit STAT function, known as suppressors of cytokine sig-naling (SOCSs), have been identified. P = phosphate.can effectively self-regulate by extinguishing their own signal. SOCS molecules can positively and negatively influence the activation of macrophages and dendritic cells and are crucial for T-cell development and differentiation.181 All SOCS proteins are able to regulate receptor signaling through the recruitment of proteasomal degradation components to their target proteins, whether the target is a specific receptor or an associated adaptor


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Surgery_Schwartz. are able to regulate receptor signaling through the recruitment of proteasomal degradation components to their target proteins, whether the target is a specific receptor or an associated adaptor molecule. Once associated with the SOCS complex, target pro-teins are readily ubiquinated and targeted for proteasomal deg-radation. SOCS1 and SOCS3 can also exert an inhibitory effect on JAK-STAT signaling via their N-terminal kinase inhibitory region (KIR) domain, which acts as a pseudo-substrate for JAK.SOCS3 has been shown to be a positive regulator of TLR4 responses in macrophages via inhibition of IL-6 receptor-medi-ated STAT3 activation.181,182 A deficiency of SOCS activity may render a cell hypersensitive to certain stimuli, such as inflamma-tory cytokines and growth hormones. Interestingly, in a murine model, SOCS knockout resulted in a lethal phenotype in part because of unregulated interferon signaling.Chemokine Receptors Are Members of the G-ProteinCoupled Receptor Family All


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Surgery_Schwartz. in a murine model, SOCS knockout resulted in a lethal phenotype in part because of unregulated interferon signaling.Chemokine Receptors Are Members of the G-ProteinCoupled Receptor Family All chemokine receptors are mem-bers of the G-protein-coupled seven transmembrane family of receptors (GPCR), which is one of the largest and most diverse of the membrane protein families. GPCRs function by detect-ing a wide spectrum of extracellular signals, including photons, ions, small organic molecules, and entire proteins. After ligand binding, GPCRs undergo conformational changes, causing the recruitment of heterotrimeric G proteins to the cytoplasmic sur-face (Fig. 2-8). Heterotrimeric G proteins are composed of three subunits, Gα, Gβ, and Gγ, each of which have numerous mem-bers, adding to the complexity of the signaling. When signaling, however, G proteins perform functionally as dimers because the signal is communicated either by the Gα subunit or the Gβγ complex. The GPCR family includes


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Surgery_Schwartz. of the signaling. When signaling, however, G proteins perform functionally as dimers because the signal is communicated either by the Gα subunit or the Gβγ complex. The GPCR family includes the receptors for catechol-amines, bradykinins, and leukotrienes, in addition to a variety of other ligands important to the inflammatory response.183 In gen-eral, GPCRs can be classified according to their pharmacological properties into four main families: class A rhodopsin-like, class B secretin-like, class C metabotropic glutamate/pheromone, and frizzled receptors. As noted above, GPCR activation by ligand binding results in an extracellular domain shift, which is then transmitted to cytoplasmic portion of the receptor to facilitate coupling to its principle effector molecules, the heterotrimeric G proteins. Although there are more than 20 known Gα subunits, they have been divided into four families based on sequence similarity, which has served to define both receptor and effec-tor coupling.


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Surgery_Schwartz. G proteins. Although there are more than 20 known Gα subunits, they have been divided into four families based on sequence similarity, which has served to define both receptor and effec-tor coupling. These include Gαs and Gαi, which signal through the activation (Gαs) or inhibition (Gαi) of adenylate cyclase to increase or decrease cyclic adenosine monophosphate (cAMP) levels, respectively. Increased intracellular cAMP can activate gene transcription through the activity of intracellular signal transducers such as protein kinase A. The Ga subunits also include the Gq pathway, which stimulates phospholipase C-β to produce the intracellular messengers inositol triphosphate and diacylglycerol. Inositol triphosphate triggers the release of calcium from intracellular stores, while diacylglycerol recruits protein kinase C to the plasma membrane for activation. Finally, Gα12/13 appears to act through Rho and Ras-mediated signaling.Tumor Necrosis Factor SuperfamilySignaling pathway for tumor


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Surgery_Schwartz. recruits protein kinase C to the plasma membrane for activation. Finally, Gα12/13 appears to act through Rho and Ras-mediated signaling.Tumor Necrosis Factor SuperfamilySignaling pathway for tumor necrosis factor receptor 1 (TNFR-1) (55 kDa) and TNFR-2 (75 kDa) occurs by the recruitment of sev-eral adapter proteins to the intracellular receptor complex. Opti-mal signaling activity requires receptor trimerization. TNFR-1 initially recruits TNFR-associated death domain (TRADD) and induces apoptosis through the actions of proteolytic enzymes known as caspases, a pathway shared by another receptor, CD95 (Fas). CD95 and TNFR-1 possess similar intracellular sequences known as death domains (DDs), and both recruit the same adapter proteins (Fas-associated death domains [FADDs]) before activating caspase 8. TNFR-1 also induces apoptosis by activating caspase 2 through the recruitment of receptor-inter-acting protein (RIP). RIP also has a functional component that can initiate nuclear factor


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Surgery_Schwartz. caspase 8. TNFR-1 also induces apoptosis by activating caspase 2 through the recruitment of receptor-inter-acting protein (RIP). RIP also has a functional component that can initiate nuclear factor kB (NF-kB) and c-Jun activation, both favoring cell survival and proinflammatory functions. TNFR-2 lacks a DD component but recruits adapter proteins known as TNFR-associated factors 1 and 2 (TRAF1, TRAF2) that inter-act with RIP to mediate NF-kB and c-Jun activation. TRAF2 also recruits additional proteins that are antiapoptotic, known as inhibitors of apoptosis proteins (IAPs).Transforming Growth Factor-a Family of ReceptorsTransforming growth factor-β1 (TGF-β1) is a pleiotropic cyto-kine expressed by immune cells that has potent immunoregula-tory activities. Specifically, recent data indicate that TGF-β is Brunicardi_Ch02_p0027-p0082.indd 5101/03/19 6:49 PM 52BASIC CONSIDERATIONSPART Iessential for T cell homeostasis, as mice deficient in TGF-β1 develop a multiorgan autoimmune


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Surgery_Schwartz. that TGF-β is Brunicardi_Ch02_p0027-p0082.indd 5101/03/19 6:49 PM 52BASIC CONSIDERATIONSPART Iessential for T cell homeostasis, as mice deficient in TGF-β1 develop a multiorgan autoimmune inflammatory disease and die a few weeks after birth, an effect that is dependent upon the presence of mature T cells. The receptors for TGF-β ligands are the TGF-β superfamily of receptors, which are type I transmem-brane proteins that contain intrinsic serine/threonine kinase activ-ity. These receptors comprise two subfamilies, the type I and the type II receptors that are distinguished by the presence of a glycine/serine-rich membrane domain found in the type I receptors. Each TGF-β ligand binds a characteristic combination of type I and type II receptors, both of which are required for signaling. Whether the type I or the type II receptor binds first is ligand-dependent, and the second type I or type II receptor is then recruited to form a het-eromeric signaling complex. When TGF-β binds to


Surgery_Schwartz

Surgery_Schwartz. Whether the type I or the type II receptor binds first is ligand-dependent, and the second type I or type II receptor is then recruited to form a het-eromeric signaling complex. When TGF-β binds to the TGF-βR, heterodimerization activates the receptor which then directly recruits and activates a receptor-associated Smad (Smad 2 or 3) through phosphorylation. An additional “common” Smad is then recruited. The activated Smad-complex translocates into the nucleus and, with other nuclear cofactors, regulates the transcrip-tion of target genes. TGF-β can also induce the rapid activation of the Ras-extracellular signal-regulated kinase (ERK) signaling pathway in addition to other MAPK pathways (JNK, p38MAPK). How does TGF-β inhibit immune responses? One of the most important effects is the suppression of interleukin-2 production by T cells. It also inhibits T cell proliferation.184 More recently, it was noted that TGF-β can regulate the maturation of differenti-ated dendritic cells and


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Surgery_Schwartz. suppression of interleukin-2 production by T cells. It also inhibits T cell proliferation.184 More recently, it was noted that TGF-β can regulate the maturation of differenti-ated dendritic cells and dendritic cell-mediated T-cell responses. Importantly, TGF-β can induce “alternative activation” macro-phages, designated M2 macrophages, which express a wide array of anti-inflammatory molecules, including IL-10 and arginase1.TRANSCRIPTIONAL AND TRANSLATIONAL REGULATION OF THE INJURY RESPONSETranscriptional Events Following Blunt TraumaInvestigators have examined the transcriptional response in cir-culating leukocytes in a large series of patients who suffered severe blunt trauma. This work identified an overwhelming 5GRELigandProtein kinase CactivationCA2+ releaseRGESecond messengers(cAMP, IP3)LigandERCell membraneCytoplasmG-protein receptors(vasoactive polypeptides, mitogens, phospholipids, neurotransmitters, prostaglandins)Figure 2-8. G-protein–coupled receptors are transmembrane


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Surgery_Schwartz. IP3)LigandERCell membraneCytoplasmG-protein receptors(vasoactive polypeptides, mitogens, phospholipids, neurotransmitters, prostaglandins)Figure 2-8. G-protein–coupled receptors are transmembrane pro-teins. The G-protein receptors respond to ligands such as adrenaline and serotonin. On ligand binding to the receptor (R), the G protein (G) undergoes a conformational change through guanosine triphosphate–guanosine diphosphate conversion and in turn activates the effector (E) component. The E component subse-quently activates second messengers. The role of inositol triphosphate (IP3) is to induce release of calcium from the endoplasmic reticulum (ER). cAMP = cyclic adenosine triphosphate.shift in the leukocyte transcriptome, with more than 80% of the cellular functions and pathways demonstrating some altera-tion in gene expression. In particular, changes in gene expres-sion for pathways involved in the systemic inflammatory, innate immune, compensatory anti-inflammatory, and adaptive


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Surgery_Schwartz. some altera-tion in gene expression. In particular, changes in gene expres-sion for pathways involved in the systemic inflammatory, innate immune, compensatory anti-inflammatory, and adaptive immune responses were simultaneous and marked. Moreover, they occurred rapidly (within 4–12 hours), and were prolonged for days and weeks. When different injuries (i.e., blunt trauma, burn injury, human model of endotoxemia) were compared, the patterns of gene expression were surprisingly similar, sug-gesting that the stress response to both injury and inflammation is highly conserved and may follow a universal pathway that includes common denominators. Finally, delayed clinical recov-ery and organ injury were not associated with a distinct pattern of transcriptional response elements.3 These data describe a new paradigm based on the observation of a rapid and coordinated transcriptional response to severe traumatic injury that involves both the innate and adaptive immune systems. Further, the


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Surgery_Schwartz. describe a new paradigm based on the observation of a rapid and coordinated transcriptional response to severe traumatic injury that involves both the innate and adaptive immune systems. Further, the data support the idea that individuals who are destined to die from their injuries are characterized primarily by the degree and dura-tion of their dysregulated inflammatory response rather than a “unique signature” indicative of a “second hit.”Transcriptional Regulation of Gene ExpressionMany genes are regulated at the point of DNA transcription and thus influence whether messenger RNA (mRNA) and its subse-quent product are expressed (Fig. 2-9). Gene expression relies on the coordinated action of transcription factors and coactiva-tors (i.e., regulatory proteins), which are complexes that bind to highly specific DNA sequences upstream of the target gene known as the promoter region. Enhancer sequences of DNA mediate gene expression, whereas repressor sequences are non-coding regions that


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Surgery_Schwartz. to highly specific DNA sequences upstream of the target gene known as the promoter region. Enhancer sequences of DNA mediate gene expression, whereas repressor sequences are non-coding regions that bind proteins to inhibit gene expression. For example, nuclear factor κB (NF-κB), one of the best-described transcription factors, has a central role in regulating the gene products expressed after inflammatory stimuli (Fig. 2-10). The NF-κB family of transcription factors is composed of five mem-bers that share a common domain. They form numerous homo or heterodimers that are normally retained in the cytosol through Brunicardi_Ch02_p0027-p0082.indd 5201/03/19 6:49 PM 53SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2TranscriptionDNAmRNAmRNAProteinInactivemRNAInactiveproteinCytoplasmCell membraneNucleusFigure 2-9. Gene expression and protein synthesis can occur within a 24-hour period. The process can be regulated at various stages: transcription, messenger RNA (mRNA)


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Surgery_Schwartz. membraneNucleusFigure 2-9. Gene expression and protein synthesis can occur within a 24-hour period. The process can be regulated at various stages: transcription, messenger RNA (mRNA) processing, or pro-tein packaging. At each stage, it is possible to inactivate the mRNA or protein, rendering these molecules nonfunctional.Ligand(e.g.: TNF, IL-1)PI-˜B kinaseDegradation of I-˜BUbiquitinizationI-˜Bp65p50I-˜Bp65p50I-˜Bp65p50Pp65p50Nuclear translocationNucleusNF-˜B activationFigure 2-10. Inhibitor of κB (I-κB) binding to the p50-p65 subunits of nuclear factor κB (NF-κB) inactivates the molecule. Ligand binding to the receptor activates a series of downstream signaling molecules, of which I-κB kinase is one. The phosphorylated NF-κB complex further undergoes ubiquitinization and proteosome degradation of I-κB, activating NF-κB, which translocates into the nucleus. Rapid resynthesis of I-κB is one method of inactivating the p50-p65 complex. IL-1 = interleukin-1; P = phosphate; TNF =


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Surgery_Schwartz. degradation of I-κB, activating NF-κB, which translocates into the nucleus. Rapid resynthesis of I-κB is one method of inactivating the p50-p65 complex. IL-1 = interleukin-1; P = phosphate; TNF = tumor necrosis factor.the inhibitory binding of inhibitor of κB (I-κB). In response to an inflammatory stimulus (e.g., TNF, IL-1, or DAMP) a sequence of intracellular mediator phosphorylation reactions leads to the degradation of I-κB and subsequent release of NF-κB to allow nuclear translocation and the initiation of transcription.Epigenetic Regulation of TranscriptionThe DNA access of protein machineries involved in transcription processes is tightly regulated by histones, which are a family of basic proteins that associate with DNA in the nucleus. Histone proteins help to condense the DNA into tightly packed nucleo-somes that limit transcription. Emerging evidence indicates that transcriptional activation of many proinflammatory genes requires nucleosome remodeling, a process that is


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Surgery_Schwartz. into tightly packed nucleo-somes that limit transcription. Emerging evidence indicates that transcriptional activation of many proinflammatory genes requires nucleosome remodeling, a process that is regulated by the histone modifying enzymes.185 There are at least seven identified chromatin modifications, including acetylation, meth-ylation, phosphorylation, ubiquitinylation, sumoylation, ADP ribosylation, deimination, and proline isomerization. Alteration of chromatin packing in this way makes the DNA more or less accessible for transcription. Recently, the development of chro-matin immunoprecipitation (ChIP) coupled to massively parallel DNA sequencing technology (ChIP-Seq) has enabled the map-ping of histone modifications in living cells. In this way, it has allowed the identification of the large number of posttranslational histone modifications that are “written” and “erased” by histone-modifying enzymes. The role of histone modifications in the reg-ulation of gene expression is


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Surgery_Schwartz. of the large number of posttranslational histone modifications that are “written” and “erased” by histone-modifying enzymes. The role of histone modifications in the reg-ulation of gene expression is referred to as “epigenetic” control.The addition of an acetyl group to lysine residues on his-tones is an epigenetic mark associated with gene activation. These acetyl groups are reversibly maintained by histone acet-yltransferases (HATs) and histone deacetylases (HDACs).186 Hemorrhagic shock has been shown to alter the acetylation of histone proteins via an imbalance of HDAC/HAT activity in the heart, lung, and liver in a tissue-specific pattern. In animal mod-els, postshock administration of the HDAC inhibitor valproic acid improved overall survival.187 Valproic acid is currently in Phase 2 clinical trials for the treatment of hemorrhaghic shock.188Translation Regulation of Inflammatory Gene ExpressionOnce mRNA transcripts are generated, they can also be regu-lated by a variety of


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Surgery_Schwartz. 2 clinical trials for the treatment of hemorrhaghic shock.188Translation Regulation of Inflammatory Gene ExpressionOnce mRNA transcripts are generated, they can also be regu-lated by a variety of mechanisms, including (a) splicing, which can cleave mRNA and remove noncoding regions; (b) capping, which modifies the 5’ ends of the mRNA sequence to inhibit breakdown by exonucleases; (c) and the addition of a polyad-enylated tail, which adds a noncoding sequence to the mRNA, to regulated the half-life of the transcript. Recent data has identified microRNAs (miRNAs) as important translational regulators of gene expression via their binding to partially complementary sequences in the 3’-untranslated region (3’-UTR) of target mRNA transcripts.189 Binding of miRNA to the Brunicardi_Ch02_p0027-p0082.indd 5301/03/19 6:49 PM 54BASIC CONSIDERATIONSPART ImRNA usually results in gene silencing. MicroRNAs are endog-enous, single-stranded RNAs of approximately 22 nucleotides in length that are


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Surgery_Schwartz. 5301/03/19 6:49 PM 54BASIC CONSIDERATIONSPART ImRNA usually results in gene silencing. MicroRNAs are endog-enous, single-stranded RNAs of approximately 22 nucleotides in length that are highly conserved in eukaryotes. MicroRNAs are encoded either singly or can be transcribed in a “polycis-tronic” clusters and produced by an elaborate expression and processing mechanism. After a primary miRNA transcript is generated by RNA polymerase II or III, it is processed in the nucleus to produce a short hairpin precursor miRNA transcript. The precursor is then transported into the cytoplasm where the final mature miRNA is generated by a protein termed Dicer. The mature double-stranded miRNA is then incorporated into the RNA-induced silencing complex (RISC) in the cytoplasm. Once programmed with a small RNA, RISC can silence targeted genes by one of several distinct mechanisms, working at (a) the level of protein synthesis through translation inhibition, (b) the transcript level through mRNA


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Surgery_Schwartz. a small RNA, RISC can silence targeted genes by one of several distinct mechanisms, working at (a) the level of protein synthesis through translation inhibition, (b) the transcript level through mRNA degradation, or (c) the level of the genome itself through the formation of heterochromatin or by DNA elimination. MiRNAs are involved in TLR signaling in the innate immune system by targeting multiple molecules in the TLR signaling pathways.190 Traumatic brain injury alters serum miRNA profiles that may be useful both as biomarkers for severe TBI and as therapeutic targets.189CELL-MEDIATED INFLAMMATORY RESPONSENeutrophilsNeutrophils (PMNs) are among the first responders to sites of infection and injury and as such are potent mediators of acute inflammation.191 Mobilization of PMNs from the bone mar-row is facilitated by reduction in bone-marrow expression of stromal cell-derived factor-1 (SDF1, also CXCL12) and subse-quent expression of both SDF1 and its receptor CXCR4 in target


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Surgery_Schwartz. the bone mar-row is facilitated by reduction in bone-marrow expression of stromal cell-derived factor-1 (SDF1, also CXCL12) and subse-quent expression of both SDF1 and its receptor CXCR4 in target tissues.192 This and other chemotactic mediators induce PMN adherence to the vascular endothelium and promote eventual cell migration into the injured tissue. Early signals for PMN recruitment include endogenous “self” molecules released from damaged tissues, like the DAMPs described previously and also include histone proteins as well as adenosine triphos-phate. DAMP molecules can also induce secretion of powerful chemokines such as IL-8 (CXCL8), which can bind to tissue glycosaminoglycans, creating a gradient for PMN migration. PMNs generally have short half-lives (4 to 10 hours). However, inflammatory signals may promote their longevity in target tis-sues, which can contribute to their potential detrimental effects and subsequent bystander injury. In addition, following sterile trauma,


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Surgery_Schwartz. signals may promote their longevity in target tis-sues, which can contribute to their potential detrimental effects and subsequent bystander injury. In addition, following sterile trauma, large numbers of immature PMNs are recruited from the bone marrow into the circulation.193Once primed and activated by inflammatory stimuli, includ-ing TNF, IL-1, and microbial pathogens, PMNs are capable of amplifying the inflammatory response as well as releasing toxic effectors such as ROS and proteolytic enzymes into the extracel-lular space.193 Neutrophils can also dump their granule contents into the extracellular space, and many of these proteins also have important effects on the innate and adaptive immune responses. When highly activated, neutrophils can extrude a meshwork of chromatin fibers, composed of DNA and histones that are deco-rated with granule contents. Termed neutrophils extracellular traps or NETs, they were first described as effective mechanism whereby neutrophils can


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Surgery_Schwartz. composed of DNA and histones that are deco-rated with granule contents. Termed neutrophils extracellular traps or NETs, they were first described as effective mechanism whereby neutrophils can immobilize bacteria to facilitate their killing. In the setting of tissue injury, NETS may allow continued presentation of auto-antigens to the host immune system, which can contribute to further tissue injury.194 NETS may also serve to prime T cells, making their threshold for activation lower.Neutrophils do facilitate the recruitment of monocytes into inflamed tissues. These recruited cells are capable of phagocy-tosing apoptotic neutrophils to contribute to resolution of the inflammatory response and to promote tissue repair.195 How-ever, at least some portion of the neutrophil population from the injury site is capable of reentering the blood stream and return-ing to the bone marrow in a process regulated by chemokine CXC receptor 4.196 Whether reverse migration of neutrophils is beneficial


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Surgery_Schwartz. injury site is capable of reentering the blood stream and return-ing to the bone marrow in a process regulated by chemokine CXC receptor 4.196 Whether reverse migration of neutrophils is beneficial to the host or likely to cause distant organ injury needs further investigation.Monocyte/MacrophagesMonocytes and macrophages are mononuclear phagocytes that play a critical role in inflammation and the injury response.197 Monocytes are leukocytes derived from bone marrow pro-genitors that circulate in the bloodstream and given the right stimuli, exit the vasculature, and differentiate into monocyte-derived macrophages (e.g., alveolar macrophages or Kupffer cells) upon migrating into appropriate tissues. Macrophages represent the large number of phagocytes that are resident in tissues under resting conditions. Distinct from monocytes, they are derived from embryonic precursors and can repopulate their numbers either by self-renewal or from monocytes derived from the bone marrow.198


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Surgery_Schwartz. resting conditions. Distinct from monocytes, they are derived from embryonic precursors and can repopulate their numbers either by self-renewal or from monocytes derived from the bone marrow.198 Together, monocytes/macrophages are the main effector cells that sense and respond to “danger signals,” primarily through mechanisms that include phagocytosis of cel-lular debris, release of inflammatory mediators, and recruitment of additional immune cells to injury sites. Moreover, these cells fulfill homeostatic roles beyond host defense by performing important functions in the remodeling of tissues, both during development and in the adult animal. SDF1 has also been impli-cated in the recruitment of monocytes to sites of tissue injury.199 Importantly, SDF1 forms a complex with HMGB1, a DAMP molecule, which potently increases its chemotactic function. In conjunction with CXCR4, the SDF1-HMGB1 complex induces early monocyte migration into injured tissues, where they play an important role


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Surgery_Schwartz. molecule, which potently increases its chemotactic function. In conjunction with CXCR4, the SDF1-HMGB1 complex induces early monocyte migration into injured tissues, where they play an important role coordinating between innate and adaptive immunity.In tissues, mononuclear phagocytes are quiescent. How-ever, they respond to external cues (e.g., PAMPs, DAMPs, acti-vated lymphocytes) by changing their phenotype.200 In response to various signals, macrophages may undergo classical M1 acti-vation (stimulated by TLR ligands and IFN-γ) or alternative M2 activation (stimulated by type II cytokines IL-4/IL-13); these states mirror the Th1–Th2 polarization of T cells described in the following section. The M1 phenotype is characterized by the expression of high levels of proinflammatory cytokines, like TNF-α, IL-1 and IL-6, in addition to the synthesis of ROS and RNS. Activated macrophages can also secrete HMGB1 and in this way, can recruit additional macrophages to form a self-activating


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Surgery_Schwartz. like TNF-α, IL-1 and IL-6, in addition to the synthesis of ROS and RNS. Activated macrophages can also secrete HMGB1 and in this way, can recruit additional macrophages to form a self-activating loop.In contrast, M2 macrophages are considered to be involved in the promotion of wound repair and the restoration of immune homeostasis through their expression of arginase-1 and IL-10, in addition to a variety of PRR (e.g., scavenging molecules).201 In truth, this classification system is overly simplistic. In fact, macrophages are highly heterogeneous and possess specialized properties that are precisely adapted to individual tissues. Thus, they are likely to also possess individualized response to local tissue damage.197Brunicardi_Ch02_p0027-p0082.indd 5401/03/19 6:49 PM 55SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2TH1Injury Severity:IL-12, IL-18, IFN-, TNF, IL-1, IL-21, TGF-˜IL-4, IL-5, IL-6, IL-10,


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Surgery_Schwartz. 5401/03/19 6:49 PM 55SYSTEMIC RESPONSE TO INJURY AND METABOLIC SUPPORTCHAPTER 2TH1Injury Severity:IL-12, IL-18, IFN-, TNF, IL-1, IL-21, TGF-˜IL-4, IL-5, IL-6, IL-10, (Glucocorticoids)IL-2IL-3IL-6IL-12IFN-TNF-°GM-CSFTNF-˜IL-3IL-4IL-5IL-6IL-9IL-10IL-13TNF-°GM-CSFCell-mediatedImmunityAntibody-mediatedImmunityless severemore severeTH2Figure 2-11. Specific immunity mediated by helper T lympho-cytes subtype 1 (TH1) and subtype 2 (TH2) after injury. A TH1 response is favored in lesser injuries, with intact cell-mediated and opsonizing antibody immunity against microbial infections. This cell-mediated immunity includes activation of monocytes, B lym-phocytes, and cytotoxic T lymphocytes. A shift toward the TH2 response from naive helper T cells is associated with injuries of greater magnitude and is not as effective against microbial infec-tions. A TH2 response includes the activation of eosinophils, mast cells, and B-lymphocyte immunoglobulin 4 and immunoglobulin E production. (Primary


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Surgery_Schwartz. and is not as effective against microbial infec-tions. A TH2 response includes the activation of eosinophils, mast cells, and B-lymphocyte immunoglobulin 4 and immunoglobulin E production. (Primary stimulants and principal cytokine prod-ucts of such responses are in bold characters.) Interleukin-4 (IL-4) and IL-10 are known inhibitors of the TH1 response. Interferon-γ (IFN-γ) is a known inhibitor of the TH2 response. Although not cytokines, glucocorticoids are potent stimulants of a TH2 response, which may partly contribute to the immunosuppressive effects of cortisol. GM-CSF = granulocyte-macrophage colony-stimulating factor; IL = interleukin; TGF = transforming growth factor; TNF = tumor necrosis factor. (Adapted with permission from Lin E, Calvano SE, Lowry SF. Inflammatory cytokines and cell response in surgery, Surgery 2000 Feb;127(2):117-126.)In a mouse model of hemorrhagic shock/reperfusion, mac-rophages play a key role in the recruitment of hematopoietic stem cells from the


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Surgery_Schwartz. and cell response in surgery, Surgery 2000 Feb;127(2):117-126.)In a mouse model of hemorrhagic shock/reperfusion, mac-rophages play a key role in the recruitment of hematopoietic stem cells from the bone marrow by secreting granulocyte-monocyte stimulating factor (GM-CSF) in response to circu-lating HMGB1.202 In the lung, alveolar macrophages sense DAMPs and extracellular matrix fragments via pattern recog-nition receptors. In response, they upregulate their expression of TLR4, which primes the cell for response against potential infection.203 At the same time, they release proinflammatory cytokines and ROS, which contribute injury to the alveolar epithelial cells. More recently, data indicate that an imbalance of M1/M2 macrophage populations in the lung contribute to acute lung injury following hemorrhagic shock (HS).204 In this study, investigators demonstrated that HS/resuscitation resulted in a significant decrease in M2 phenotype macrophages, with a delayed increase in M1.


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Surgery_Schwartz. following hemorrhagic shock (HS).204 In this study, investigators demonstrated that HS/resuscitation resulted in a significant decrease in M2 phenotype macrophages, with a delayed increase in M1. Augmenting the M2 population prior to injury lessened the degree of lung injury as assessed histologically.Lymphocytes and T-Cell ImmunityThe expression of genes associated with the adaptive immune response is rapidly altered following severe blunt trauma.3 In fact, significant injury is associated with adaptive immune sup-pression that is characterized by altered cell–mediated immu-nity. This correlates with both a decrease in the overall number of lymphocytes as well as the balance between the NK and T cell populations.205CD4+ T cells (helper) play central roles in the function of the immune system through their effects on B cell anti-body production, their enhancement of specific TReg cell func-tions, and their assistance with macrophage activation. CD4+ Th cells are functionally divided


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Surgery_Schwartz. through their effects on B cell anti-body production, their enhancement of specific TReg cell func-tions, and their assistance with macrophage activation. CD4+ Th cells are functionally divided into subsets, which include Th1, Th2, and Th17 cells. Each of these groups produces spe-cific effector cytokines that are under unique transcriptional control. The specific functions of these cells include the rec-ognition and killing of intracellular pathogens (cellular immu-nity, Th1 cells); regulation of antibody production (humoral immunity, TH2 cells); and maintenance of mucosal immu-nity and barrier integrity (Th17 cells). Historically, activi-ties have been characterized as proinflammatory (Th1) and anti-inflammatory (Th2) respectively, as determined by their distinct cytokine signatures (Fig. 2-11). Given the proinflam-matory action of IL-17A produced by Th17 cells, they could also be placed in this category. However, it is clear that the Th17 differentiation is more complex and may


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Surgery_Schwartz. (Fig. 2-11). Given the proinflam-matory action of IL-17A produced by Th17 cells, they could also be placed in this category. However, it is clear that the Th17 differentiation is more complex and may involve the two distinct phenotypes, a pathogenic phenotype characterized by increased IL-17 production and a more regulatory phenotype in which IL-10 expression is increased.206Recent evidence suggests that the population of Th17 cells is altered following severe traumatic injury. Mass cytometry by time-of-flight (CyTOF) was used to collect single cell phenotyp-ing data on circulating peripheral blood mononuclear cells from a cohort of severely injured trauma patients.155 The investigators identified an expansion of Th17 cells at all time points follow-ing injury and was associated with an increase in the cytokine profile associated with a Th17 phenotype. This supports prior work also demonstrating a robust type 17 immune response early (within the first 24 hours) among nonsurvivors,


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Surgery_Schwartz. increase in the cytokine profile associated with a Th17 phenotype. This supports prior work also demonstrating a robust type 17 immune response early (within the first 24 hours) among nonsurvivors, which also identified a Th17 profile more consistent with “pathogenic” Th17 cells.154Successful recovery from injury also depends upon a bal-anced Th1/Th2 response. Following injury, however, there is a reduction in Th1 cell differentiation and cytokine production in favor of an increased population of Th2 lymphocytes and their signaling products. As a consequence, both macrophage activation and proinflammatory cytokine synthesis are inhib-ited. This imbalance, which may be associated with decreased IL-12 production by activated monocytes/macrophages, has been associated with increased risk of infectious complications following surgery and trauma. What are the systemic mecha-nisms responsible for this shift? Several events have been impli-cated, including the direct effect of


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Surgery_Schwartz. risk of infectious complications following surgery and trauma. What are the systemic mecha-nisms responsible for this shift? Several events have been impli-cated, including the direct effect of glucocorticoids on monocyte IL-12 production and T cell IL-12 receptor expression. In addi-tion, sympathoadrenal catecholamine production has also been demonstrated to reduce IL-12 production and proinflammatory cytokine synthesis. Finally, more recent work has implicated circulating immature myeloid cells, termed myeloid-derived suppressor cells, that have immune suppressive activity par-ticularly through their increased expression of arginase.208 These cells have the potential to deplete the microenvironment of argi-nine, leading to further T cell dysfunction.Dendritic CellsRecent studies have focused on the cellular components of the immune system in the context of polytrauma. While the Brunicardi_Ch02_p0027-p0082.indd 5501/03/19 6:49 PM 56BASIC CONSIDERATIONSPART Iactivation of


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Surgery_Schwartz. have focused on the cellular components of the immune system in the context of polytrauma. While the Brunicardi_Ch02_p0027-p0082.indd 5501/03/19 6:49 PM 56BASIC CONSIDERATIONSPART Iactivation of granulocytes and monocyte/macrophages follow-ing trauma has been well described, more recent work has dem-onstrated that dendritic cells (DC) are also activated in response to damage signals, to stimulate both the innate and the adaptive immune responses.Dendritic cells are the most important antigen-presenting cells (APCs) for initiating T-cell responses against protein antigens. Primary “danger signals” that are recognized and activated by DC include debris from damaged or dying cells (e.g., HMGB1, nucleic acids including single nucleotides, and degradation products of the extracellular matrix). DC are fre-quently referred to as “professional APCs” since their principal function is to capture, process, and present both endogenous and exogenous antigens, which, along with their