Library · Cellular process
Antibody class switching
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Antibodies come in five classes, or isotypes: IgG, IgM, IgA, IgD, and IgE. They do not all show up at once. The first antibody the body makes is IgM, and the cell that makes it is the B lymphocyte.
When the antigen, the part of the germ that the body recognizes, binds to the antibody, that cell switches isotype: it starts displaying on its surface the immunoglobulin best suited to getting rid of that particular pathogen. This is called class switching.
What changes with the isotype is the Fc region, the stretch of the antibody that decides what it does once it is bound to its target: calling in the complement system, handing the target over to a macrophage. Think of that region as the handle of a tool: change the handle and you change who can grab it and what it is good for. And be careful not to confuse class switching with something else: sharpening the antibody's aim at the germ falls to two other processes, somatic hypermutation and affinity maturation.
In brief
IgM is the first antibody the body makes; the B cell then switches class.
When antigen binds, the cell displays on its surface the immunoglobulin best suited to that pathogen.
The five classes are IgG, IgM, IgA, IgD, and IgE.
The Fc region defines the isotype and carries out functions such as binding complement and macrophages.
What changes is the part that acts, not the threat that was detected.
Two other processes sharpen the aim: somatic hypermutation and affinity maturation.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Antibody, StatPearlsPublished
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