IgA

IgA is the principal antibody class of mucosal immunity and, taken across all secretions, the most abundantly produced immunoglobulin in the body. Dimeric IgA is assembled with a J chain, transported across epithelia by the polymeric immunoglobulin receptor, and released as secretory IgA carrying the protease-resistant secretory component, which protects it in the luminal environment. Humans produce two subclasses, IgA1 and IgA2, differing in hinge-region glycosylation and tissue distribution. IgA neutralizes viruses and bacteria, coats commensal microbiota without triggering inflammation, and recruits myeloid cells via Fc alpha RI against intracellular pathogens. IgA nephropathy, celiac disease, and selective IgA deficiency are its best-known clinical associations.