Gpr109a Limits Microbiota-Induced IL-23 Production To Constrain ILC3-Mediated Colonic Inflammation.

A set of coordinated interactions between gut microbiota and the immune cells surveilling the intestine play a key role in shaping local immune responses and intestinal health. Gpr109a is a G protein-coupled receptor expressed at a very high level on innate immune cells and previously shown to play a key role in the induction of colonic regulatory T cells. In this study, we show that Gpr109a-/-Rag1-/- mice exhibit spontaneous rectal prolapse and colonic inflammation, characterized by the presence of an elevated number of IL-17-producing Rorγt+ innate lymphoid cells (ILCs; ILC3). Genetic deletion of Rorγt alleviated the spontaneous colonic inflammation in Gpr109a-/-Rag1-/- mice. Gpr109a-deficient colonic dendritic cells produce higher amounts of IL-23 and thereby promote ILC3. Moreover, the depletion of gut microbiota by antibiotics treatment decreased IL-23 production, ILC3, and colonic inflammation in Gpr109a-/-Rag1-/- mice. The ceca of Gpr109a-/-Rag1-/- mice showed significantly increased colonization by members of Bacteroidaceae, Porphyromonadaceae, Prevotellaceae, Streptococcaceae, Christensenellaceae, and Mogibacteriaceae, as well as IBD-associated microbiota such as Enterobacteriaceae and Mycoplasmataceae, compared with Rag1-/- mice, housed in a facility positive for Helicobacter and murine norovirus. Niacin, a Gpr109a agonist, suppressed both IL-23 production by colonic DCs and ILC3 number in a Gpr109a-dependent manner. Collectively, our data present a model suggesting that targeting Gpr109a will be potentially beneficial in the suppression of IL-23-mediated immunopathologies.

Role of G-Protein Coupled Receptors in Chemotaxis of Innate Lymphoid Cells.

Innate lymphoid cells (ILCs) are a recently identified family of immune cells mostly present at barrier surfaces. They play an important role in the induction, regulation, and resolution of inflammatory responses. Environmental signals play an important role in development and function of ILCs. G-protein coupled receptors (GPCRs) sense and mediate cellular responses to the environmental signals. ILCs express several G-protein coupled receptors, which play a critical role in migration of these cells to appropriate sites. Here, we describe a method to test the migration of ILCs toward 7α,25-hydroxycholesterol, which is mediated by cell surface-expressed GPR183. A similar strategy can be employed to test the role of other GPCRs in mediating the migration of ILCs toward other chemotactic ligands.

Ufbp1 promotes plasma cell development and ER expansion by modulating distinct branches of UPR.

The IRE1α/XBP1 branch of unfolded protein response (UPR) pathway has a critical function in endoplasmic reticulum (ER) expansion in plasma cells via unknown mechanisms; interestingly, another UPR branch, PERK, is suppressed during plasma cell development. Here we show that Ufbp1, a target and cofactor of the ufmylation pathway, promotes plasma cell development by suppressing the activation of PERK. By contrast, the IRE1α/XBP1 axis upregulates the expression of Ufbp1 and ufmylation pathway genes in plasma cells, while Ufbp1 deficiency impairs ER expansion in plasma cells and retards immunoglobulin production. Structure and function analysis suggests that lysine 267 of Ufbp1, the main lysine in Ufbp1 that undergoes ufmylation, is dispensable for the development of plasmablasts, but is required for immunoglobulin production and stimulation of ER expansion in IRE1α-deficient plasmablasts. Thus, Ufbp1 distinctly regulates different branches of UPR pathway to promote plasma cell development and function.

Carbidopa, a drug in use for management of Parkinson disease inhibits T cell activation and autoimmunity.

Carbidopa is a drug that blocks conversion of levodopa to dopamine outside of central nervous system (CNS) and thus inhibits unwanted side effects of levodopa on organs located outside of CNS during management of Parkinson's Disease (PD). PD is associated with increased expression of inflammatory genes in peripheral and central nervous system (CNS), infiltration of immune cells into brain, and increased numbers of activated/memory T cells. Animal models of PD have shown a critical role of T cells in inducing pathology in CNS. However, the effect of carbidopa on T cell responses in vivo is unknown. In this report, we show that carbidopa strongly inhibited T cell activation in vitro and in vivo. Accordingly, carbidopa mitigated myelin oligodendrocyte glycoprotein peptide fragment 35-55 (MOG-35-55) induced experimental autoimmune encephalitis (EAE) and collagen induced arthritis in animal models. The data presented here suggest that in addition to blocking peripheral conversion of levodopa, carbidopa may inhibit T cell responses in PD individuals and implicate a potential therapeutic use of carbidopa in suppression of T cell mediated pathologies.