Secretory immunoglobulin A (SIgA)

Secretory immunoglobulin A (SIgA) is the predominant antibody class found in mucosal secretions, including saliva, tears, colostrum, and gastrointestinal fluids, where it serves as the primary immunological barrier against pathogens (StatPearls: Immunoglobulin A). Structurally, it consists of two IgA monomers joined by a J-chain and associated with a secretory component, a polypeptide that facilitates its transport across epithelial cells and protects it from proteolytic cleavage (UniProt: P01876). The primary function of SIgA is immune exclusion, a process by which it binds to viruses, bacteria, and toxins to prevent their adherence to and penetration of the mucosal epithelium (PubMed: 31603455). Beyond defense, SIgA is essential for maintaining the homeostasis of the gut microbiota and modulating local inflammatory responses to prevent overreaction to commensal organisms. In therapeutic contexts, SIgA is a major target for mucosal vaccines, such as oral rotavirus and nasal influenza vaccines, which aim to elicit local protective immunity at the site of entry. Furthermore, SIgA is being investigated as a passive immunotherapy for treating enteric infections and managing inflammatory bowel diseases, although its delivery remains a challenge due to the harsh environment of the digestive tract.

Other names

sIgASecretory IgADimeric IgA with secretory componentMucosal IgA

Neutralization of toxins and pathogens; Prevention of epithelial attachment (immune exclusion); Agglutination of microorganisms; Interaction with the polymeric immunoglobulin receptor (pIgR) for transcytosis.