Fig. 3.

Schematic representation of the protective mechanism of IgA, secretory IgA (sIgA), or secretory component (SC) in the intestinal mucosa. 1: plasma cells in the lamina propria (LP) produce polymeric IgA, which is transported across epithelial cells (a process known as transcytosis) to the lumen by the polymeric Ig receptor (pIgR), where it may interact with antigens of bacteria, viruses, toxins, etc. to exclude them from contact with the epithelium. 2: in the LP, polymeric IgA (pIgA) can bind to immune complexes, including those comprising infectious agents, leading to their removal by removed by transcytosis. 3: pIgR-mediated trafficking of pIgA through epithelial cells can interfere with intracellular viral assembly in the Golgi apparatus. 4: free SC in the lumen has been shown to neutralize pathogen-derived toxins and adehsins. 5: sIgA facilitates uptake of pathogens into IgA-inducing Peyer’s patches and isolated lymphoid compartments and presentation to dendritic cells the subepithelial dome region. Recognition of sIgA by dendritic cells is reported to inhibit IL-12 cytokine secretion, leading to induction of helper T cell 2 (Th2) or regulatory T cell (Treg) responses.