The gut microbiota plays a pivotal role in both intestinal homeostasis and disease. This is accomplished partly by tightly regulated interactions between gut symbiotic bacteria and host cells. Our recent studies have shown that under homeostatic conditions more invasive members of the gut microbiota, notably rare Gram-negative Enterobacteriaceae, are able to breach the mucosal epithelial barrier and induce production of IgG antibodies systemically. These homeostatically generated IgG antibodies recognize antigens that are conserved in both commensal and pathogenic bacteria, and confer critical protection against systemic infection by either commensal or pathogenic bacteria. In addition, gut microbiota-induced IgG antibodies were detected in both mouse and human breast milk. We are currently investigating the role of maternal commensal-specific IgG antibodies in neonatal immunity. Our preliminary data suggest that maternal IgG antibodies, delivered via the placenta or breast milk, protect neonatal mice against Citrobacter rodentium enteric infection. Together, our studies demonstrate a novel function for the gut microbiota to maintain host-microbe symbiosis via induction of protective IgG antibodies.
Sponsored by the Host Microbiome Initiative