NLRP6 deficiency expands a novel CD103(+) B cell population that confers immune tolerance in NOD mice

INTRODUCTION: Gut microbiota have been linked to modulating susceptibility to Type 1 diabetes; however, there are many ways in which the microbiota interact with host cells, including through microbial ligand binding to intracellular inflammasomes (large multi-subunit proteins) to initiate immune responses. NLRP6, a microbe-recognizing inflammasome protein, is highly expressed by intestinal epithelial cells and can alter susceptibility to cancer, obesity and Crohn’s disease; however, the role of NLRP6 in modulating susceptibility to autoimmune diabetes, was previously unknown. METHODS: We generated NLRP6-deficient Non-obese diabetic (NOD) mice to study the effect of NLRP6-deficiency on the immune cells and susceptibility to Type 1 diabetes development. RESULTS: NLRP6-deficient mice exhibited an expansion of CD103(+) B cells and were protected from type 1 diabetes. Moreover, NLRP6-deficient CD103(+) B cells express regulatory markers, secreted higher concentrations of IL-10 and TGFb1 cytokines and suppressed diabetogenic T cell proliferation, compared to NLRP6-sufficient CD103(+) B cells. Microarray analysis of NLRP6-sufficient and -deficient CD103(+) B cells identified 79 significantly different genes including genes regulated by lipopolysaccharide (LPS), tretinoin, IL-10 and TGFb, which was confirmed in vitro following LPS stimulation. Furthermore, microbiota from NLRP6-deficient mice induced CD103(+) B cells in colonized NLRP6-sufficient germ-free mice; however, the long-term maintenance of the CD103(+) B cells required the absence of NLRP6 in the hosts, or continued exposure to microbiota from NLRP6-deficient mice. DISCUSSION: Together, our data indicate that NLRP6 deficiency promotes expansion and maintenance of a novel TGF -dependent CD103(+) Breg population. Thus, targeting NLRP6 therapeutically may prove clinically useful.