The fact that IgA comprises the body's major isotype of antibody on a biosynthetic basis is not widely appreciated because IgG, not IgA, is the predominant isotype in serum. Nevertheless, the bulk of the body's Ig-producing cells reside in the various mucosal and exocrine sites, especially along the intestinal tract, and most of them make IgA antibodies against environmental antigens, including the local microbial flora. These antibodies can then function in multiple ways as a first line of immune defense at boundaries with the external environment (1).
It has long been recognized that a major source of the precursors of the IgA plasma cells in the intestine is the organized lymphoid tissue of the Peyer's patches (2). Here B cells in the germinal centers are thought to switch from IgM to IgA under the influence of T cells and cytokines, in...
