From the Guidelines
Secretory IgA (sIgA) plays a crucial role in protecting mucosal surfaces from pathogens, and its deficiency can lead to increased susceptibility to mucosal infections, allergies, and autoimmune disorders. The production of sIgA is influenced by factors such as breastfeeding and exposure to environmental antigens, which stimulate the infant's own sIgA production 1. sIgA is primarily produced by plasma cells in mucosal-associated lymphoid tissue and is transported across epithelial cells into secretions such as tears, saliva, breast milk, and intestinal fluids. Its main functions include neutralizing pathogens and toxins before they can attach to mucosal surfaces, preventing bacterial adherence to epithelial cells, and maintaining homeostasis with commensal bacteria.
Key Functions of Secretory IgA
- Neutralizing pathogens and toxins before they can attach to mucosal surfaces
- Preventing bacterial adherence to epithelial cells
- Maintaining homeostasis with commensal bacteria
- Protecting the gastrointestinal and respiratory tracts from infection
Diagnosis and Management of Secretory IgA Deficiency
The diagnosis of secretory IgA deficiency (SIGAD) is based on low or absent levels of IgA in serum, with normal levels of IgG and IgM 1. Patients with SIGAD should be monitored over time for the occurrence of complications, such as respiratory and gastrointestinal tract infections, atopy, autoimmune diseases, celiac disease, and malignancy. The management of SIGAD involves aggressive, prolonged, or prophylactic antibiotics as necessary, and monitoring of lung, liver, gastrointestinal, and kidney function and vigilance for symptoms and signs of autoimmune disease.
Importance of Secretory IgA in Mucosal Immunity
sIgA is the predominant antibody found in mucosal secretions and serves as the body's first line of immunological defense against pathogens at mucosal surfaces 1. The development of sIgA begins in infancy and is influenced by factors such as breastfeeding, which provides passive immunity through maternal sIgA, and exposure to environmental antigens, which stimulates the infant's own sIgA production. Deficiencies in sIgA can lead to increased susceptibility to mucosal infections, allergies, and autoimmune disorders.
From the Research
Secretory IgA Functions
- Secretory IgA (SIgA) plays a crucial role in protecting and regulating mucosal surfaces, including intestinal, respiratory, and urogenital epithelia 2
- SIgA is involved in immune exclusion, a process that limits the access of microorganisms and mucosal antigens to mucosal barriers 2
- SIgA helps control the symbiotic relationship between commensals and the host, and prevents opportunistic pathogens from entering and disseminating in the systemic compartment 2
Secretory IgA Mechanisms
- Clearance by peristalsis is one of the mechanisms by which SIgA fulfills its function at mucosal surfaces 2
- SIgA is involved in sampling of antigen-SIgA complexes by microfold (M) cells, and intimate contact with Peyer's patch dendritic cells (DC) 2
- SIgA down-regulates inflammatory processes, and modulates epithelial and DC responsiveness 2
Secretory IgA in Mucosal Vaccines
- Secretory IgA (S-IgA) antibodies are the major contributor to pathogen-specific immune responses in mucosal tissues 3
- S-IgA has unique structural and functional features that underpin the mechanism of action of mucosal vaccines 3
- Characterization of S-IgA induced by mucosal vaccines is important for their successful use in a clinical setting 3
Secretory IgA in Immunotherapy
- SIgA antibodies have potential in immunotherapy against infectious pathogens, including the mucosal delivery of bioactive antibodies 4
- SIgA combines multiple facets, including intracellular and serosal neutralization of antigens, activation of non-inflammatory pathways, and homeostatic control of the endogenous microbiota 4