Immune response, class/isotype switching

Class (Isotype) Switching Occurs During Immune Responses... 

Antibodies of the IgG, IgA and IgE classes are made later than IgM during a primary immune response, but account for most of the antibody that is made during a memory response. Although isotype switching and affinity maturation are independent processes, they usually occur simultaneously (Fish et al., 1989), so that the increased affinity of bivalent antibodies of isotypes other than IgM is rapidly enhanced. IgG antibody is the predominant isotype in plasma and lymph, while IgA antibody predominates at mucosal surfaces and in secretions from these surfaces. 

---