Chapter 19 - Immunoglobulin Transport and Immunoglobulin Receptors

Abstract

The first line of antigen-specific mucosal defense is provided by antibodies that are transported across epithelial cells into external secretions. Secretory immunoglobulin (Ig)A, the most abundant mucosal Ig, is transported by the polymeric immunoglobulin receptor (pIgR). IgG antibodies, which are transported by the neonatal Fc receptor (FcRn), are also abundant in mucosal tissues and secretions, particularly in the female genitourinary tract. Transport of IgA by pIgR occurs predominantly in the basolateral-to-apical direction, thus facilitating movement of newly synthesized IgA from the lamina propria into external secretions. By contrast, transport of IgG by FcRn is bidirectional, i.e., apical-basolateral as well as basolateral-apical. Thus, FcRn can mediate transport of maternal milk-derived IgG from the gut into the circulation of suckling neonates, and also transport of locally synthesized IgG into secretions. Both pIgR and FcRn can transport antibody–antigen immune complexes, with important implications for mucosal homeostasis and prevention of allergic and inflammatory diseases.