Differential Induction of Antimicrobial REGIII by the Intestinal Microbiota and Bifidobacterium breve NCC2950

The intestinal microbiota is a key determinant of gut homeostasis, which is achieved, in part, through regulation of antimicrobial peptide secretion. The aim of this study was to determine the efficiency by which members of the intestinal microbiota induce the antimicrobial peptide REGIII and to elucidate the underlying pathways. We showed that germfree mice have low levels of REGIII-gamma in their ileum and colon compared to mice with different intestinal microbiota backgrounds. Colonization with a microbiota of low diversity (altered Schaedler flora) did not induce the expression of REGIII-gamma as effectively as a complex community (specific pathogen free). Monocolonization with the probiotic Bifidobacterium breve, but not with the nonprobiotic commensal Escherichia coli JM83, upregulated REGIII-gamma expression. Induction of REGIII-gamma by B. breve was abrogated in mice lacking MyD88 and Ticam1 signaling. Both live and heat-inactivated B. breve but not spent culture medium from B. breve induced the expression of REGIII-gamma, the human ortholog and homolog of REGIII-gamma, in human colonic epithelial cells (Caco-2). Taken together, the results suggest that REGIII-gamma expression in the intestine correlates with the richness of microbiota composition. Also, specific bacteria such as Bifidobacterium breve NCC2950 effectively induce REGIII production in the intestine via the MyD88-Ticam1 pathway. Treatment with this probiotic may enhance the mucosal barrier and protect the host from infection and inflammation.