IgA2

Immunoglobulin A2 (IgA2) is one of two human IgA subclasses, the other being IgA1. IgA2 is produced by plasma cells in mucosal tissues and is relatively enriched in secretions, especially in the colon, while IgA1 is more abundant in serum.

Structurally, IgA2 is an IgA heavy-chain isotype with a shorter hinge region than IgA1. This shorter hinge confers increased resistance to proteolysis by bacterial proteases, a feature that supports function in the gut. In secretions, IgA2 is typically found as secretory IgA (SIgA), a dimer formed by two IgA monomers joined by a J chain and associated with the secretory (SC) component derived from the polymeric Ig receptor during transepithelial transport.

Functionally, IgA2 participates in immune exclusion and neutralization of pathogens at mucosal surfaces and can engage Fc alpha receptors (CD89/FcαRI) on neutrophils and other myeloid cells to mediate phagocytosis. Compared with IgA1, IgA2 generally has reduced susceptibility to proteases and provides defense particularly at bacteria-rich mucosal sites. IgA does not strongly activate the classical complement pathway.

Genetically, IgA2 is encoded by the IGHA2 gene on chromosome 14 and has two functional human allotypes. Its distribution varies by tissue; it is especially enriched in distal intestinal secretions. Clinically, selective IgA2 deficiency is rare and discussed within the broader context of selective IgA deficiency.