They also produce several cytokines in response to stimulation signals CH5424802 chemical structure from pathogen-associated molecular patterns or whole bacteria. Hence, DCs contribute to immunological homeostasis by promoting inflammatory responses to pathogens, inducing tolerance to self antigen, and suppressing excessive immune responses.1,2 Dendritic cells play a critical role in the maintenance of immunological homeostasis and DC dysregulation can lead to autoimmune diseases and chronic inflammatory disorders. Abnormally excessive immune responses to commensal bacteria, food antigens and self antigens have been reported in the pathogenesis
of these diseases. Therefore, conditioning DCs to display desirable EMD 1214063 price properties, such as inducing an immunosuppressive DC phenotype, might represent a novel therapeutic strategy for these diseases. Recent studies have indicated that signalling through nuclear receptors, such as the retinoic acid receptor, the farnesoid X receptor (FXR) and the peroxisome proliferator-activated receptor-α, plays an important role in modulating the transcription of cytokine genes in innate immune cells.3 Interleukin-1 (IL-12) produced by DCs has been implicated in promoting a type 1 helper T cell immune response
and contributing to the pathogenesis of several chronic inflammatory disorders.4–6 We previously demonstrated that Am80, a retinoic acid receptor agonist, promotes
DC differentiation towards an IL-12 hypo-producing phenotype and that this molecule potentially represents a novel therapeutic molecule for inflammatory bowel disease.7 The identification of similar molecules that induce an IL-12 hypo-producing DC phenotype might allow the development of novel therapeutic molecules for chronic inflammatory disorders. We hypothesized that bile acids (BAs), which are ligands for FXR and TGR5, might regulate DC differentiation and so we examined whether a BA can induce an IL-12 hypo-producing DC phenotype. Bile acids are a family DNA Synthesis inhibitor of steroid molecules generated in the liver by cholesterol oxidation. They accumulate in the blood, intestine and liver via enterohepatic circulation. In addition to their role in nutrient absorption, BAs are signalling molecules that can regulate immune cell responses via FXR and TGR5.8 FXR is a member of the nuclear receptor superfamily of ligand-activated transcription factors8–12 and is primarily expressed in enterohepatic tissues. FXR is known to regulate genes involved in BA synthesis, detoxification and excretion, and an increase in intracellular BA concentrations promotes transcriptional activation of FXR.13–15 In addition, it has been reported that the FXR signalling pathway influences immunological responses such as cytokine production by immune cells.