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Immunity (medical)

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This is a background article: See Psychological factors in immunity

Immunity is medical term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of pathogens to stop infection by micro-organisms before they can cause disease. Other components of the immune system adapt themselves to each new disease encountered and are able to generate pathogen-specific immunity

Specific, or adaptive immunity is often sub-divided into two major types depending on how the immunity was introduced. Natural immunity occurs through contact with a disease causing agent, when the contact was not deliberate, whereas artificial immunity develops only through deliberate actions. Both natural and artificial immunity can be further subdivided, depending on the amount of time the protection lasts. Passive immunity is short lived, and usually lasts only a few months, whereas protection via active immunity lasts much longer, and is sometimes life-long. The diagram below summarizes these divisions of immunity.




History of theories of immunityEdit

Cholera art
A representation of the cholera epidemic of the nineteenth century.
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The birth of passive immunotherapy may have begun with Mithridates VI of Pontus, who sought to harden himself against poison, and took daily sub-lethal doses of poison to build tolerance. Mithridates is also said to have fashioned a 'universal antidote' to protect him from all earthly poisons.[2] For nearly 2000 years, poisons were thought to be the proximate cause of disease, and a complicated mixture of ingredients, called Mithridate, was used to cure poisoning during the Renaissance.[2] An updated version of this cure, Theriacum Andromachi, was used well into the 19th century.[5]
Tableau Louis Pasteur
Louis Pasteur in his laboratory, 1885.
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In Europe, the induction of active immunity emerged in an attempt to contain smallpox. Immunization, however, had existed in various forms for at least a thousand years.[3] The earliest use of immunization is unknown, however, around 1000 A.D., the Chinese began practicing a form of immunization by drying and inhaling powders derived from the crusts of smallpox lesions.[3] Around the fifteenth century in India, the Ottoman Empire, and east Africa, the practice of variolation (poking the skin with powdered material derived from smallpox crusts) became quite common.[3] Variolation was introduced to the west in the early 18th century by Lady Mary Wortley Montagu.[3] In 1796, Edward Jenner introduced the far safer method of inoculation with the cowpox virus, a non-fatal virus that also induced immunity to smallpox. The success and general acceptance of Jenner's procedure would later drive the general nature of vaccination developed by Pasteur and others towards the end of the 19th century.[2]

Passive immunityEdit

Main article: Passive immunity


Naturally acquired passive immunityEdit

Maternal passive immunity is a type of naturally acquired passive immunity, and refers to antibody-mediated immunity conveyed to a fetus by its mother during pregnancy. Maternal antibodies (MatAb) are passed through the placenta to the fetus by an FcRn receptor on placental cells. This occurs around the third month of gestation.[8] IgG is the only antibody isotype that can pass through the placenta.[8] Passive immunity is also provided through the transfer of IgA antibodies found in breast milk that are transferred to the gut of the infant, protecting against bacterial infections, until the newborn can synthesize its own antibodies.[7]

Antitoxin diphtheria
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Artificially acquired passive immunityEdit

see also: Temporarily-induced immunity

Artificially acquired passive immunity is a short-term immunization induced by the transfer of antibodies, which can be administered in several forms; as human or animal plasma or serum, as pooled human immunoglobulin for intravenous (IVIG) or intramuscular (IG) use, and in the form of monoclonal antibodies (MAb). Passive transfer is used prophylactically in the case of immunodeficiency diseases, such as hypogammaglobulinemia.[9] It is also used in the treatment of several types of acute infection, and to treat poisoning.[6] Immunity derived from passive immunization lasts for only a short period of time, and there is also a potential risk for hypersensitivity reactions, and serum sickness, especially from gamma globulin of non-human origin.[7]

The artificial induction of passive immunity has been used for over a century to treat infectious disease, and prior to the advent of antibiotics, was often the only specific treatment for certain infections. Immunoglobulin therapy continued to be a first line therapy in the treatment of severe respiratory diseases until the 1930’s, even after sulfonamide antibiotics were introduced.[9]

Passive transfer of cell-mediated immunityEdit


Active ImmunityEdit

Immune response
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When B cells and T cells are activated by a pathogen, memory B-cells and T- cells develop. Throughout the lifetime of an animal these memory cells will “remember” each specific pathogen encountered, and are able to mount a strong response if the pathogen is detected again. This type of immunity is both active and adaptive because the body's immune system prepares itself for future challenges. Active immunity often involves both the cell-mediated and humoral aspects of immunity as well as input from the innate immune system. The innate system is present from birth and protects an individual from pathogens regardless of experiences, whereas adaptive immunity arises only after an infection or immunization and hence is "acquired" during life.

Naturally acquired active immunityEdit

For more details on this topic, see Immune system.

Naturally acquired active immunity occurs when a person is exposed to a live pathogen, and develops a primary immune response, which leads to immunological memory.[6] This type of immunity is “natural” because it is not induced by man. Many disorders of immune system function can affect the formation of active immunity such as immunodeficiency (both acquired and congenital forms) and immunosuppression.

Artificially acquired active immunityEdit

Main article: artificial induction of immunity
Poster for vaccination against smallpox
Poster from 1979, promoting smallpox vaccination.
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In 1807, the Bavarians became the first group to require that their military recruits be vaccinated against smallpox, as the spread of smallpox was linked to combat.[10] Subsequently the practice of vaccination would increase with the spread of war.

There are four types of traditional vaccines:[11]

  • Inactivated vaccines are composed of micro-organisms that have been killed with chemicals and/or heat and are no longer infectious. Examples are vaccines against flu, cholera, bubonic plague, and hepatitis A. Most vaccines of this type are likely to require booster shots.
  • Toxoids are inactivated toxic compounds from micro-organisms in cases where these (rather than the micro-organism itself) cause illness, used prior to an encounter with the toxiod. Examples of toxoid-based vaccines include tetanus and diphtheria.
  • Subunit -vaccines are composed of small fragments of disease causing organisms. A characteristic example is the subunit vaccine against Hepatitis B virus.

Most vaccines are given by hypodermic injection as they are not absorbed reliably through the gut. Live attenuated Polio and some Typhoid and Cholera vaccines are given orally in order to produce immunity based in the bowel.

See alsoEdit

References Edit

  1. 1.0 1.1 Lindquester, Gary J. (2006) Introduction to the History of disease. Disease and Immunity, Rhodes College.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Silverstein, Arthur M. (1989) History of Immunology (Hardcover) Academic Press. Note: The first six pages of this text are available online at: ( easy reader)
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Gherardi E. The Concept of Immunity. History and Applications. Immunology Course Medical School, University of Pavia.
  5. ^ This article incorporates content from the 1728 Cyclopaedia, a publication in the public domain. "Mithridate".
  6. 6.0 6.1 6.2 6.3 6.4 Microbiology and Immunology On-Line Textbook: USC School of Medicine
  7. 7.0 7.1 7.2 Janeway, Charles; Paul Travers, Mark Walport, and Mark Shlomchik (2001). Immunobiology; Fifth Edition, New York and London: Garland Science. ISBN 0-8153-4101-6..
  10. National Institutes of Health "Smallpox - A Great and Terrible Scourge" Variolation
  11. Immunization: You call the shots. The National Immunization Program at the Centers for Disease Control and Prevention

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