Clec12A regulation of the intestinal immune response and microbiota composition

ABSTRACT Inflammatory bowel disease (IBD) affects over 3 million people in the United States alone. IBD is caused by excessive gastrointestinal tract inflammation and depends on the microbiota. The intestinal immune response to the microbiota must be regulated to prevent inflammatory diseases such as IBD. The intestinal immune system can interact with the microbiota via pattern recognition receptors (PRRs), including the inhibitory C-type lectin receptor, Clec12a. Previously, we have determined that Clec12a can bind specific commensals within the intestine. Clec12a has inhibitory capacities, making it a unique PRR for commensal recognition, as it could act as a brake on immune proinflammatory signaling in this microbe and microbial ligand-rich environment. Clec12a is downregulated in individuals predisposed to IBD, suggesting a role for Clec12a in disease development. Interestingly, Clec12a-/- mice have more proinflammatory macrophages and less reparative macrophages, emphasizing that in the absence of Clec12a, there is a dysregulation in the immune response. Further, Clec12a- /- mice exhibit worsened colitis that is microbiota dependent, exemplified by the microbiota being sufficient to drive worsened colitis in WT mice. A major feature of the Clec12a-/- microbiota is a significant expansion of the gram-positive bacteria Faecalibaculum rodentium. These data suggest that Clec12a might dictate microbiota composition by limiting the expansion of harmful bacteria. In fact, Clec12a binds F. rodentium in a species- specific manner. Due to Clec12a having the highest expression on macrophages and monocytes in the gut, we tested whether Clec12a functioned in phagocytosis and observed that Clec12a-/- macrophages phagocytosed F. rodentium at lower levels, and this was also species-specific. Therefore, this proposal aims to identify how Clec12a regulates intestinal inflammation (Aim1) and how Clec12a dictates microbiota composition (Aim2). I will use a novel Clec12a-floxed mouse, allowing for the deletion of Clec12a in a cell-specific manor, while analyzing the effects on inflammation and microbiota composition. This proposal will determine the mechanism by which Clec12a restrains intestinal inflammation and sculpts the microbiota. Our working hypothesis is that Clec12a on transepithelial sampling myeloid cells can control the outgrowth of potentially harmful members of the microbiota through phagocytosis while also constraining harmful inflammatory events. We will test this hypothesis by completing these two aims: AIM 1: Determine how Clec12a regulates intestinal inflammation. AIM 2: Resolve how Clec12a sculpts the intestinal microbiota. This proposal will lay the groundwork for targeting Clec12a, and its inhibitory capacity, to treat IBD. Clec12a is a unique mechanism the immune system employs to sculpt the microbiota without eliciting prototypical inflammation. This mechanism could unveil treatments for other diseases that are influenced by the microbiota.