What is Immunoglobulin A, Serum (Total)?
Immunoglobulin A is the second most abundant immunoglobulin in serum (after IgG) and the dominant immunoglobulin at mucosal surfaces — the gastrointestinal, respiratory, and urogenital tracts — where it exists primarily as secretory IgA (sIgA), a dimeric form complexed with a secretory component produced by epithelial cells. Serum IgA is predominantly monomeric, produced by plasma cells in the lamina propria of mucosal tissues and in peripheral lymphoid organs, and represents the systemic pool of IgA rather than the secretory mucosal pool. IgA has a serum half-life of approximately 5–7 days. Two subclasses exist — IgA1 (predominant in serum, approximately 80–85%) and IgA2 (predominant in mucosal secretions) — which can be quantified separately in specialist haematological investigations but are not distinguished by standard total serum IgA quantification. IgA mediates mucosal immune defence primarily through immune exclusion — binding and trapping pathogens and antigens at epithelial surfaces — and through FcαRI-mediated phagocyte activation.