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Antigen can originate either from within the body ("self-protein" or "self antigens") or from the external environment ("non-self"). [2] The immune system identifies and attacks "non-self" external antigens. Antibodies usually do not react with self-antigens due to negative selection of T cells in the thymus and B cells in the bone marrow. [5]
Antigen presentation stimulates immature T cells to become either mature "cytotoxic" CD8+ cells or mature "helper" CD4+ cells. An antigen-presenting cell (APC) or accessory cell is a cell that displays an antigen bound by major histocompatibility complex (MHC) proteins on its surface; this process is known as antigen presentation.
In contrast, the B cell antigen-specific receptor is an antibody molecule on the B cell surface and recognizes native (unprocessed) antigen without any need for antigen processing. Such antigens may be large molecules found on the surfaces of pathogens, but can also be small haptens (such as penicillin) attached to carrier molecule. [60]
Antigen presentation is a vital immune process that is essential for T cell immune response triggering. Because T cells recognize only fragmented antigens displayed on cell surfaces, antigen processing must occur before the antigen fragment can be recognized by a T-cell receptor.
The antibodies created against these environmental antigens in the first years of life can cross react with ABO-incompatible red blood cells when it comes in contact with during blood transfusion later in life. Anti-A and anti-B antibodies are usually IgM type. O-type individuals can produce IgG-type ABO antibodies.
A neoantigenic determinant is an epitope on a neoantigen, which is a newly formed antigen that has not been previously recognized by the immune system. [29] Neoantigens are often associated with tumor antigens and are found in oncogenic cells. [30]
Class switching is mediated by the enzyme AID (activation-induced cytidine deaminase) and occurs after the B cell binds an antigen through its B cell receptor. Class-switching usually requires interaction with a T helper cell. [3] [4] In humans, there are five heavy chain isotypes α,δ,γ,ε,μ, corresponding to five antibody isotypes:
The S antigen is relatively common (~55% of the population) and the s antigen is very common (~89% of the population). Anti-S and anti-s can cause hemolytic transfusion reactions and hemolytic disease of the newborn.The U antigen is a high incidence antigen, occurring in more than 99.9% of the population. The U was originally short for ...