Furthermore, IgG1, IgG3, and IgA1 are generally induced by protein antigens (which are likely to be present in the earliest stages of infection) and IgG3/IgG1 are activating antibodies that bind all three Fcγ receptors (FcγR I, II, III) on the surface of effector cells such as natural killer and macrophages (11, 12, 37, 41). This evidence concerns the gene IGHA1 and infection.