Liver X Receptor regulates Th17 and RORγt+ Treg cells by distinct mechanisms

The gastrointestinal microenvironment, dominated by dietary compounds and the commensal bacteria, is a major driver of intestinal CD4+ T helper (Th) cell differentiation. Dietary compounds can be sensed by nuclear receptors (NRs) that consequently exerts pleiotropic effects including immune modulation. However, how NRs regulate distinct intestinal Th subsets remain poorly understood. Here, we found that under homeostatic condition Liver X receptor (LXR), a sensor of cholesterol metabolites, controls RORγt+ Treg and Th17 cells in the intestine draining mesenteric lymph node (MLN). Mechanistically, while lack of LXR signaling in CD11c+ myeloid cells led to an increase in RORγt+ Treg, modulation of MLN Th17 was independent of LXR signaling in either immune or epithelial cells. Of note, LXRα modulated only the Th17 cells, but not RORγt+ Treg in the MLN and horizontal transfer of microbiota between LXRα−/− and WT mice was sufficient to partially increase the MLN Th17 in WT mice. While LXRα deficiency increased the abundance of Ruminococcaceae and Lachnospiraceae bacterial families compared to the WT littermates, microbiota ablation including ablation of SFB was not sufficient to dampen LXRα-mediated expansion of MLN Th17. Altogether, our results suggest that LXR modulates RORγt+ Treg and Th17 cells in the MLN through distinct mechanisms.