Secretory IgA (sIgA) is the predominant immunoglobulin found in mucosal secretions such as saliva, tears, colostrum, nasal mucus, gastrointestinal fluids, and tracheobronchial secretions. It is composed of two IgA monomers linked by a J-chain and an additional secretory component, and it is produced by plasma cells in the lamina propria of mucosal tissues. Importantly, sIgA synthesis occurs independently from serum IgA production—meaning that low serum IgA levels do not necessarily indicate low sIgA levels.
Biologically, sIgA plays a critical protective role at mucosal surfaces by preventing microorganisms from adhering to epithelial cells, activating the alternative complement pathway, and modulating inflammatory responses. In newborns, sIgA transferred through breast milk provides passive immunity and helps guard against gastrointestinal infections, highlighting its importance in early immune defense.
In research and clinical settings, sIgA is a valuable biomarker for studying mucosal immunity, infection susceptibility, immune system maturity, and inflammatory conditions. Clinically, its measurement may assist in evaluating mucosal immune function, monitoring immune deficiencies, assessing stress or inflammation-related changes in immunity, and analyzing protective immunity in infants. In research, sIgA is commonly used to investigate host–pathogen interactions, vaccine responses at mucosal surfaces, and mechanisms of mucosal barrier protection.
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