Secretory IgA possesses intrinsic modulatory properties stimulating mucosal and systemic immune responses

Secretory IgA (SIgA) is essential in protecting mucosal surfaces by ensuring immune exclusion. In addition, SIgA binds selectively to M cells in Peyer's patches (PP), resulting in transport across the epithelium and targeting of dendritic cells (DC) in the dome region. The immunological consequences of such an interaction are unknown. In this study, we find that oral delivery of SIgA comprising human secretory component and mouse IgA induces human secretory component-specific Ab and cellular responses in mucosal and peripheral tissues in mice. This takes place in the absence of coaddition of cholera toxin, identifying so far unraveled properties in SIgA. Specific immune responses are accompanied by sustained IL-10 and TGF-beta expression in draining mesenteric lymph nodes and spleen. SIgA also triggers migration of DC to the T cell-rich regions of PP, and regulates expression of CD80 and CD86 on DC in PP, mesenteric lymph nodes, and spleen. These results provide evidence that mucosal SIgA re-entering the body exerts a function of Ag delivery that contributes to effector and/or regulatory pathways characteristic of the intestinal mucosal compartment.