Microbial metabolites such as short chain fatty acids (SCFAs) are highly produced in the intestine and potentially regulate the immune system. We studied the function of SCFAs in regulation of T cell differentiation into effector and regulatory T cells. We report that SCFAs can directly promote T cell differentiation into T cells producing IL-17, IFN-γ, and/or IL-10 depending on cytokine milieu. This effect of SCFAs on T cells is independent of GPR41- or GPR43 but dependent on direct histone deacetylase (HDAC) inhibitor activity. Inhibition of HDACs in T cells by SCFAs increased the acetylation of p70 S6 kinase and phosphorylation rS6, regulating the mTOR pathway required for generation of Th17, Th1, and IL-10+ T cells. Acetate (C2) administration enhanced the induction of Th1 and Th17 cells during C. rodentium infection but decreased anti-CD3-induced inflammation in an IL-10-dependent manner. Our results indicate that SCFAs promote T cell differentiation into both effector and regulatory T cells to promote either immunity or immune tolerance depending on immunological milieu.

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In this study, we report a novel biological function of vitamin A metabolites in conversion of naive FoxP3− CD4+ T cells into a unique FoxP3+ regulatory T cell subset (termed “retinoid-induced FoxP3+ T cells”) in both human and mouse T cells. We found that the major vitamin A metabolite all-trans-retinoic acid induces histone acetylation at the FoxP3 gene promoter and expression of the FoxP3 protein in CD4+ T cells. The induction of retinoid-induced FoxP3+ T cells is mediated by the nuclear retinoic acid receptor α and involves T cell activation driven by mucosal dendritic cells and costimulation through CD28. Retinoic acid can promote TGF-β1-dependent generation of FoxP3+ regulatory T cells but decrease the TGF-β1- and IL-6-dependent generation of inflammatory Th17 cells in mouse T cells. Retinoid-induced FoxP3+ T cells can efficiently suppress target cells and, thus, have a regulatory function typical for FoxP3+ T cells. A unique cellular feature of these regulatory T cells is their high expression of gut-homing receptors that are important for migration to the mucosal tissues particularly the small intestine. Taken together, these results identify retinoids as positive regulatory factors for generation of gut-homing FoxP3+ T cells.

Batf belongs to the activator protein 1 superfamily of basic leucine zipper transcription factors that includes Fos, Jun, and Atf proteins. Batf is expressed in mouse T and B lymphocytes, although the importance of Batf to the function of these lineages has not been fully investigated. We generated mice (BatfΔZ/ΔZ) in which Batf protein is not produced. BatfΔZ/ΔZ mice contain normal numbers of B cells but show reduced numbers of peripheral CD4+ T cells. Analysis of CD4+ T helper (Th) cell subsets in BatfΔZ/ΔZ mice demonstrated that Batf is required for the development of functional Th type 17 (Th17), Th2, and follicular Th (Tfh) cells. In response to antigen immunization, germinal centers were absent in BatfΔZ/ΔZ mice and the maturation of Ig-secreting B cells was impaired. Although adoptive transfer experiments confirmed that this B cell phenotype can be driven by defects in the BatfΔZ/ΔZ CD4+ T cell compartment, stimulation of BatfΔZ/ΔZ B cells in vitro, or by a T cell–independent antigen in vivo, resulted in proliferation but not class-switch recombination. We conclude that loss of Batf disrupts multiple components of the lymphocyte communication network that are required for a robust immune response.