Highlights d Inflammatory cues and the microbiota modulate Gpr35 expression across species d LPA modulates GPR35-dependent functions in zebrafish and mouse macrophages d GPR35-expressing macrophages have a protective role during intestinal inflammation d GPR35 controls intestinal inflammation by inducing TNF and corticosterone

As it has been established that demethylation of lysine 27 of histone H3 by the lysine-specific demethylase JMJD3 increases immune responses and thus elicits inflammation, we hypothesize that inhibition of JMJD3 may attenuate autoimmune disorders. We found that in vivo administration of GSK-J4, a selective inhibitor of JMJD3 and UTX, ameliorates the severity of experimental autoimmune encephalomyelitis (EAE). In vitro experiments revealed that the anti-inflammatory effect of GSK-J4 was exerted through an effect on dendritic cells (DCs), promoting a tolerogenic profile characterized by reduced expression of costimulatory molecules CD80/CD86, an increased expression of tolerogenic molecules CD103 and TGF-β1, and reduced secretion of proinflammatory cytokines IL-6, IFN-γ, and TNF. Adoptive transfer of GSK-J4-treated DCs into EAE mice reduced the clinical manifestation of the disease and decreased the extent of inflammatory CD4+ T cells infiltrating the central nervous system. Notably, Treg generation, stability, and suppressive activity were all exacerbated by GSK-J4-treated DCs without affecting Th1 and Th17 cell production. Our data show that GSK-J4-mediated modulation of inflammation is achieved by a direct effect on DCs and that systemic treatment with GSK-J4 or adoptive transfer of GSK-J4-treated DCs ex vivo may be promising approaches for the treatment of inflammatory and autoimmune disorders.

Dendritic cells (DCs) promote T-cell mediated tolerance to self-antigens and induce inflammation to innocuous-antigens. This dual potential makes DCs fundamental players in inflammatory disorders. Evidence from inflammatory colitis mouse models and inflammatory bowel diseases (IBD) patients indicated that gut inflammation in IBD is driven mainly by T-helper-1 (Th1) and Th17 cells, suggesting an essential role for DCs in the development of IBD. Here we show that GSK-J4, a selective inhibitor of the histone demethylase JMJD3/UTX, attenuated inflammatory colitis by reducing the inflammatory potential and increasing the tolerogenic features of DCs. Mechanistic analyses revealed that GSK-J4 increased activating epigenetic signals while reducing repressive marks in the promoter of retinaldehyde dehydrogenase isoforms 1 and 3 in DCs, enhancing the production of retinoic acid. This, in turn, has an impact on regulatory T cells (Treg) increasing their lineage stability and gut tropism as well as potentiating their suppressive activity. Our results open new avenues for the treatment of IBD patients.

Regulatory T cells are a specific subset of lymphocytes that suppress immune responses and play a crucial role in the maintenance of self-tolerance. They can be generated in the thymus as well as in the periphery through differentiation of naïve CD4+ T cells. The forkhead box P3 transcription factor (Foxp3) is a crucial molecule regulating the generation and function of Tregs. Here we show that the foxp3 gene promoter becomes hyperacetylated in in vitro differentiated Tregs compared to naïve CD4+ T cells. We also show that the histone deacetylase inhibitor TSA stimulated the in vitro differentiation of naïve CD4+ T cells into Tregs and that this induction was accompanied by a global increase in histone H3 acetylation. Importantly, we also demonstrated that Tregs generated in the presence of TSA have phenotypical and functional differences from the Tregs generated in the absence of TSA. Thus, TSA-generated Tregs showed increased suppressive activities, which could potentially be explained by a mechanism involving the ectonucleotidases CD39 and CD73. Our data show that TSA could potentially be used to enhance the differentiation and suppressive function of CD4+Foxp3+ Treg cells.

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..

The gut homing receptor integrin α4β7 is essential for the migration of pro-inflammatory T cells into the gut mucosa. Since intestinal neoplasia has been associated with chronic inflammation, we investigated whether interfering with gut-homing affects intestinal tumorigenesis. Using chemically induced and spontaneous intestinal tumor models we showed that lack of β7 integrin significantly impairs tumor growth without affecting tumor frequencies, with a mild translatable effect on overall survival. This correlates with human data showing lower MAdCAM-1 expression and disease-free survival in colorectal cancer patients. Thus, paradoxically in contrast to extra-intestinal tumors, blocking migration of immune cells into the gut might have a positive therapeutic effect on intestinal neoplasia.

During recent years, numerous studies have shown that epigenetics, heritable changes that do not involve alterations in the DNA sequence, play an important role in the development, function, and regulation of the immune system as well as in the onset and progress of autoimmune diseases. For that reason, in the following chapter, we will review some of the most important concepts about epigenetics and how they modulate the development and function of immune cells, specifically macrophages, dendritic cells, and T cells. Moreover, we will review the role of epigenetics on autoimmune diseases, as well as the use of pharmacological modulation of the epigenetic machinery, as an innovative way to approach a potential new treatment or improve the current treatments of autoimmune diseases.

22The gastrointestinal microenvironment, dominated by dietary compounds and the commensal bacteria, 23 is a major driver of intestinal CD4 + T helper (Th) cell differentiation. Dietary compounds can be sensed 24 by nuclear receptors (NRs) that consequently exerts pleiotropic effects including immune modulation. 25However, how NRs regulate distinct intestinal Th subsets remain poorly understood. Here, we found 26 that under homeostatic condition Liver X receptor (LXR), a sensor of cholesterol metabolites, controls 27RORγt + Treg and Th17 cells in the intestine draining mesenteric lymph node (MLN). Mechanistically, 28 while lack of LXR signaling in CD11c + myeloid cells led to an increase in RORγt + Treg, modulation 29 of MLN Th17 was independent of LXR signaling in either immune or epithelial cells. Of note, LXRα 30 modulated only the Th17 cells, but not RORγt + Treg in the MLN and horizontal transfer of microbiota 31 between LXRα −/− and WT mice was sufficient to partially increase the MLN Th17 in WT mice. While 32LXRα deficiency increased the abundance of Ruminococcaceae and Lachnospiraceae bacterial 33 families compared to the WT littermates, microbiota ablation including ablation of SFB was not 34 sufficient to dampen LXRα-mediated expansion of MLN Th17. Altogether, our results suggest that 35 LXR modulates RORγt + Treg and Th17 cells in the MLN through distinct mechanisms.The intestinal barrier is continuously exposed to the changing external environment. To face this 56 challenge, our immune system has evolved to rapidly adapt to environmental changes by mounting 57 tolerogenic and effector responses on demand. A dynamic equilibrium between these two arms of the 58 immune system is required to maintain homeostasis, and failure of mounting an appropriate regulatory 59 response may lead to uncontrolled inflammatory reactions and chronic immune disorders. 60Owing to their ability to react in an antigen-specific manner CD4 + T helper (Th) cells are central 61 players in ensuring a protective response while limiting collateral damage. Mounting a functional Th 62 cell response in the intestine relies on the anatomical distribution of T cells in immunological inductive 63 and effector sites, where the former is constituted by intestine-draining lymphoid structures such as 64 MLN and the latter being the intraepithelial and lamina propria compartments 1 . The inductive sites 65 represent the arena where naïve CD4 + T cells encounter their cognate antigens for the first time and 66 functionally commit to specific effector subsets. Under steady state, retinoic acid-related orphan 67 receptor gt (RORgt) + Th cells (Th17) and Foxp3 expressing regulatory T cells (Treg) are the most 68 represented Th subsets in the MLN. Despite a certain degree of lineage and functional flexibility, Th17 69 and Treg cells play complementary roles in maintaining intestinal homeostasis. Although the 70 expression of RORgt and Foxp3 was originally thought to be mutually exclusive, a distinct new 71 population of RORgt + Foxp3 + regulatory T ...