Arginase 1 (Arg1), which converts l-arginine into ornithine and urea, exerts pleiotropic immunoregulatory effects. However, the function of Arg1 in inflammatory bowel disease (IBD) remains poorly characterized. Here, we found that Arg1 expression correlated with the degree of inflammation in intestinal tissues from IBD patients. In mice, Arg1 was upregulated in an IL-4/ IL-13and intestinal microbiota-dependent manner. Tie2-Cre Arg1 fl/fl mice lacking Arg1 in hematopoietic and endothelial cells recovered faster from colitis than Arg1-expressing (Arg1 fl/fl) littermates. This correlated with decreased vessel density, compositional changes in intestinal microbiota, diminished infiltration by myeloid cells, and an accumulation of intraluminal polyamines that promote epithelial healing. The proresolving effect of Arg1 deletion was reduced by an l-arginine-free diet, but rescued by simultaneous deletion of other l-arginine-metabolizing enzymes, such as Arg2 or Nos2, demonstrating that protection from colitis requires l-arginine. Fecal microbiota transfers from Tie2-Cre Arg1 fl/fl mice into WT recipients ameliorated intestinal inflammation, while transfers from WT littermates into Arg1-deficient mice prevented an advanced recovery from colitis. Thus, an increased availability of l-arginine as well as altered intestinal microbiota and metabolic products accounts for the accelerated resolution from colitis in the absence of Arg1. Consequently, l-arginine metabolism may serve as a target for clinical intervention in IBD patients.

Type 1 diabetes (T1D) is a chronic multi-factorial disorder characterized by the immune-mediated destruction of insulin-producing pancreatic beta cells. Variations at a large number of genes influence susceptibility to spontaneous autoimmune T1D in non-obese diabetic (NOD) mice, one of the most frequently studied animal models for human disease. The genetic analysis of these mice allowed the identification of many insulin-dependent diabetes ( Idd ) loci and candidate genes, one of them being Cd101 . CD101 is a heavily glycosylated transmembrane molecule which exhibits negative-costimulatory functions and promotes regulatory T (Treg) function. It is abundantly expressed on subsets of lymphoid and myeloid cells, particularly within the gastrointestinal tract. We have recently reported that the genotype-dependent expression of CD101 correlates with a decreased susceptibility to T1D in NOD.B6 Idd10 congenic mice compared to parental NOD controls. Here we show that the knockout of CD101 within the introgressed B6-derived Idd10 region increased T1D frequency to that of the NOD strain. This loss of protection from T1D was paralleled by decreased Gr1-expressing myeloid cells and FoxP3 + Tregs and an enhanced accumulation of CD4-positive over CD8-positive T lymphocytes in pancreatic tissues. As compared to CD101 +/+ NOD.B6 Idd10 donors, adoptive T cell transfers from CD101 −/− NOD.B6 Idd10 mice increased T1D frequency in lymphopenic NOD scid and NOD.B6 Idd10 scid recipients. Increased T1D frequency correlated with a more rapid expansion of the transferred CD101 −/− T cells and a lower proportion of recipient Gr1-expressing myeloid cells in the pancreatic lymph nodes. Fewer of the Gr1 + cells in the recipients receiving CD101 −/− T cells expressed CD101 and the cells had lower levels of IL-10 and TGF-β mRNA. Thus, our results connect the Cd101 haplotype-dependent protection from T1D to an anti-diabetogenic function of CD101-expressing Tregs and Gr1-positive myeloid cells and confirm the identity of Cd101 as Idd10 .

TCR ligation is critical for the selection, activation, and integrin expression of T lymphocytes. Here, we explored the role of the TCR adaptor protein slp-76 on iNKT-cell biology. Compared to B6 controls, slp-76 ace/ace mice carrying a missense mutation (Thr428Ile) within the SH2-domain of slp-76 showed an increase in iNKT cells in the thymus and lymph nodes, but a decrease in iNKT cells in spleens and livers, along with reduced ADAP expression and cytokine response. A comparable reduction in iNKT cells was observed in the livers and spleens of ADAP-deficient mice. Like ADAP −/− iNKT cells, slp-76 ace/ace iNKT cells were characterized by enhanced CD11b expression, correlating with an impaired induction of the TCR immediate-early gene Nur77 and a decreased adhesion to ICAM-1. Furthermore, CD11b-intrinsic effects inhibited cytokine release, concanavalin A-mediated inflammation, and iNKT-cell accumulation in the liver. Unlike B6 and ADAP −/− mice, the expression of the transcription factors Id3 and PLZF was reduced, whereas NP-1-expression was enhanced in slp-76 ace/ace mice. Blockade of NP-1 decreased the recovery of iNKT cells from peripheral lymph nodes, identifying NP-1 as an iNKT-cell-specific adhesion factor. Thus, slp-76 contributes to the regulation of the tissue distribution, PLZF, and cytokine expression of iNKT cells via ADAP-dependent and -independent mechanisms.Keywords: ADAP r Cytokine r iNKT cell r Integrin r slp-76Additional supporting information may be found in the online version of this article at the publisher's web-site Eur. J. Immunol. 2016Immunol. . 46: 2121Immunol. -2136 Introduction iNKT cells express a panoply of NK-cell receptors [1] and a canonical TCR through which they recognize (glyco-)lipid antigens [2]. iNKT cells activate similar signaling cascades after TCR ligation like other T lymphocytes [3], but utilize unique transcription factors for their development such as the promyelocytic leukemia zinc finger (PLZF) [4][5][6]. According to two different developmental models PLZF characterizes distinct maturation stages and polarized subsets. The sequential lineage model suggests a gradual decrease of PLZFexpression following selection of iNKT cells which show a Th2-dominated cytokine profile during earlier and a Th1-dominated cytokine profile during later stages of intrathymic maturation [1,7]. The second model describes lineage diversification and simultaneous differentiation into Th1-, Th2-, or Th17-polarized subsets that are defined by the level of PLZF-expression [8]. Although many iNKT cells release both Th1 and Th2 cytokines on a single cell level [9], the production of IL-17 and IFN-γ is mutually exclusive within NK1.1 − cells [10][11][12]. Several transcription factors, such as Egr2, T-bet, ThPOK, Id2, Id3, and the Tec kinases Itk and Rlk have been implicated in the differentiation of iNKT cell subsets [6,8,[13][14][15][16][17] which home to distinct tissues. Specifically, liver and spleen constitute the main source for the Th1-polarized sublineage which is PLZF low . Th2-or ...