The Genetic Basis of Immunoglobulin-Class Switching

In the immune response to a foreign protein, the first antibodies to appear are of the IgM class (or isotype). As the response proceeds, other isotypes (IgG, IgA, and IgE) emerge as the result of immunoglobulin-class switching. The isotype switch has considerable clinical importance because each of the four major isotypes has specialized biologic properties. IgG, for example, is the principal class of antibody in interstitial fluids, whereas IgA is the protective antibody of mucosal surfaces. Isotype switching requires collaboration between antibody-synthesizing B cells and helper CD4+ T cells. In this collaboration, the B cell uses IgM molecules on its . . .