Isolated lymphoid follicles (ILFs) in the small intestine also function in the induction of mucosal immune responses 3.
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SIgA production against specific mucosal antigens is dependent on the sampling by Peyer's patch M cells, processing by underlying antigen-presenting cells such as dendritic cells (DCs), T cell activation, and ultimately B cell class switch recombination in gut-associated lymphoid tissue (GALT), mesenteric lymph nodes, and possibly neighboring lamina propria (MLNs) 1, 2. This review summarizes the intrinsic biological activities now associated with SIgA and their relationships to immunity and intestinal homeostasis.Īs the most abundant class of antibody found in the intestinal lumen of humans and most other mammals, secretory IgA (SIgA) has long been recognized as a first line of defense in protecting the intestinal epithelium from enteric pathogens and toxins. In just the past several years, SIgA has been identified as having the capacity to directly quench bacterial virulence factors, influence the composition of the intestinal microbiota by Fab-dependent and -independent mechanisms, promote the retro-transport of antigens across the intestinal epithelium to dendritic cell (DC) subsets in gut-associated lymphoid tissue, and, finally, to down-regulate pro-inflammatory responses normally associated with the uptake of highly pathogenic bacteria and potentially allergenic antigens. In addition, SIgA functions in mucosal immunity and intestinal homeostasis through mechanisms that have only recently been revealed. Through a process known as immune exclusion, SIgA promotes the clearance of antigens and pathogenic microorganisms from the intestinal lumen by blocking their access to epithelial receptors, entrapping them in mucus, and facilitating their removal by peristaltic and mucociliary activities. Secretory IgA (SIgA) serves as the first line of defense in protecting the intestinal epithelium from enteric toxins and pathogenic microorganisms.
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