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.

Dendritic cells (DCs) together with regulatory T cells (Tregs) are essential mediators of immune homeostasis. Disruption of function or frequency of either cell type can lead to fatal autoimmunity. We previously described that mice constitutively lacking DCs (ΔDC) develop autoimmunity characterized by reduced body weight, autoantibodies, and pronounced intestinal inflammation. In this study, we show that lack of DCs leads to an altered gene expression profile in peripheral but not thymic Tregs with increased expression of inhibitory receptors. The suppressive function of Tregs from DDC mice was impaired in T cell cocultures. In a model of transfer colitis, Tregs from ΔDC mice were only functional in the presence of DCs in recipient mice. Lack of MHC class II on DCs also resulted in upregulation of inhibitory receptors on Tregs, reduced body weight, and elevated serum IgA levels. Further analysis of the IgA response revealed an expansion of IgA + germinal center B cells and plasma cells in mesenteric lymph nodes and more IgA-coated commensal bacteria in feces of ΔDC mice. Thus, we show a critical role for DCs to establish intestinal homeostasis by regulating Treg function for prevention of spontaneous inflammation.

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 ...

The influence of corticosteroids on the fibrinolytic activity in different tissues of the eye was investigated. Rats were treated with corticosteroids, and the fibrinplate method of Todd 1962) was used to estimate the fibrinolytic activity. After 14 days treatment with corticosteroids the fibrinolytic activity decreased. In the control eyes no fibrinolytic activity was left after 6 h of autolysis. The eyes treated with corticosteroids, however, still had fibrinolytic activity.