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MCAT Content / Immune System / Antigen Antibody Recognition

Antigen-antibody recognition

Topic: Immune System

Specific antibodies are formed that can recognize and bind the antibody to result in adaptive immunity against an antigen.



The antigen is processed by the APC and bound to MHC class II receptors and MHC class I receptors on the cell membrane of the APC. The antigen is presented to immature helper T cells and cytotoxic T cells through binding the MHC II (helper T) or MHC I (cytotoxic T) to T-cell receptors. These T lymphocytes mature and proliferate. Helper T cells activate B cells, which proliferate and produce antibodies specific to the antigen. In contrast, cytotoxic T cells destroy pathogens that bear the antigen that was presented to them by the APCs. Memory B and T cells are formed after the infection ends.

Practice Questions

Khan Academy

MCAT Official Prep (AAMC)

Online Flashcards Biology Question 19

Biology Question Pack, Vol 2. Passage 9 Question 57

Biology Question Pack, Vol 2. Passage 12 Question 79

Biology Question Pack, Vol 2. Passage 17 Question 108

Sample Test B/B Section Passage 2 Question 8

Key Points




• Specific antibodies are then produced to fight against the antigens.

Key Terms

Antigen: a substance that induces an immune response, usually a molecule found on a pathogen such as a toxin or a molecule expressed by the pathogen or pathogen-infected cells.

Antigen-presenting cell: a cell that presents captured antigens to immature T-cells. Dendritic cells and macrophages are the best examples, but several other cells can present antigens as well.

Memory T cells: a type of T cell that rapidly differentiates into helper and cytotoxic T cells if its associated antigen is detected.

MHC I: molecules are expressed on all nucleated cells and are essential for the presentation of normal “self” antigens. Cells that become infected by intracellular pathogens can present foreign antigens on MHC I as well, marking the infected cell for destruction.

MHC II: molecules are expressed only on the surface of antigen-presenting cells (macrophages, dendritic cells, and B cells). Antigen presentation with MHC II is essential for the activation of T cells

Antibody: protein produced in the blood to fight against an antigen

Adaptive immunity: a specific type of immunity developed over time

Pathogen: any organism or substance, especially a microorganism, capable of causing diseases, such as bacteria, viruses, protozoa, or fungi

Cytotoxic T cell: a T lymphocyte that kills cells that are damaged

Phagocytosis: the process by which certain living cells called phagocytes ingest or engulf other cells or particles

B cell: a lymphocyte, developed in the bursa of birds and the bone marrow of other animals, that produces antibodies and is responsible for the immune system

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