T-helper-17 (Th17) cells have critical roles in mucosal defense and in autoimmune disease pathogenesis 1-3. They are most abundant in the small intestine lamina propria (SILP), where their presence requires colonization of mice with microbiota 4-7. Segmented Filamentous Bacteria (SFB) are sufficient to induce Th17 cells and to promote Th17-dependent autoimmune disease in animal models 8-14. However, the specificity of Th17 cells, the mechanism of their induction by distinct bacteria, and the means by which they foster tissue-specific inflammation remain unknown. Here we show that the T cell receptor (TCR) repertoire of intestinal Th17 cells in SFB-colonized mice has minimal overlap with that of other intestinal CD4+ T cells and that most Th17 cells, but not other T cells, recognize antigens encoded by SFB. T cells with antigen receptors specific for SFB-encoded peptides differentiated into RORγt-expressing Th17 cells, even if SFB-colonized mice also harbored a strong Th1 cell inducer, Listeria monocytogenes, in their intestine. The match of T cell effector function with antigen specificity is thus determined by the type of bacteria that produce the antigen. These findings have significant implications for understanding how commensal microbiota contribute to organ-specific autoimmunity and for developing novel mucosal vaccines.

Sphingosine 1-phosphate (S1P) in blood and lymph controls T cell traffic and proliferation through type 1 S1P receptor (S1P1) signals, but suppression of IFN-γ generation has been the only consistently observed effect on T cell cytokines. The fact that S1P enhances the development of Th17 cells from Ag-challenged transgenic S1P1-overexpressing CD4 T cells suggested that the S1P-S1P1 axis may promote the expansion of Th17 cells in wild-type mice. In a model of Th17 cell development from CD4 T cells stimulated by anti-CD3 plus anti-CD28 Abs and a mixture of TGF-β1, IL-1, and IL-6, S1P enhanced their number and IL-17-generating activity the same as IL-23. As for IL-23 enhancement of Th17 cell development, that by S1P was prevented by IL-4 plus IFN-γ and by IL-27. The prevention of S1P augmentation of Th17 cell development by the S1P receptor agonist and down-regulator FTY720 implies that FTY720 immunosuppression is attributable partially to inhibition of Th17-mediated inflammation.

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S-1-P) are both low molecular weight lysophospholipid (LPL) ligands that are recognized by the Edg family of G protein-coupled receptors. In endothelial cells, these two ligands activate Edg receptors, resulting in cell proliferation and cell migration. The intercellular adhesion molecule-1 (ICAM-1, CD54) is one of many cell adhesion molecules belonging to the immunoglobulin superfamily. This study showed that LPA and S-1-P enhance ICAM-1 expression at both the mRNA and protein levels in human umbilical cord vein endothelial cells (HUVECs). This enhanced ICAM-1 expression in HUVECs was first observed at 2 h postligand treatment. Maximal expression appeared at 8 h postligand treatment, as detected by flow cytometry and Western blotting. Furthermore, the effects of S-1-P on ICAM-1 expression were shown to be concentration dependent. Prior treatment of HUVECs with pertussis toxin, a specific inhibitor of G(i), ammonium pyrrolidinedithiocarbamate and BAY 11-7082, inhibitors of the nuclear factor (NF)-kappaB pathway, or Clostridium difficile toxin B, an inhibitor of Rac, prevented the enhanced effect of LPL-induced ICAM-1 expression. However, pretreatment of HUVECs with exoC3, an inhibitor of Rho, had no effect on S-1-P-enhanced ICAM-1 expression. In a static cell-cell adhesion assay system, pretreatment of LPL enhanced the adhesion between HUVECs and U-937 cells, a human mononucleated cell line. The enhanced adhesion effect could be prevented by preincubation with a functional blocking antibody against human ICAM-1. These results suggest that LPLs released by activated platelets might enhance interactions of leukocytes with the endothelium through a G(i)-, NF-kappaB-, and possibly Rac-dependent mechanism, thus facilitating wound healing and inflammation processes.

Sphingosine 1-phosphate (S1P) in blood and lymph controls lymphoid traffic and tissue migration of T cells through signals from the type 1 S1PR (S1P1), but less is known of effects of the S1P-S1P1 axis on nonmigration functions of T cells. CD4 T cells from a double transgenic (DTG) mouse express OTII TCRs specific for OVA peptide 323–339 (OVA) and a high level of transgenic S1P1, resistant to suppression by T cell activation. OVA-activated DTG CD4 T cells respond as expected to S1P by chemotactic migration and reduction in secretion of IFN-γ. In addition, DTG CD4 T cells stimulated by OVA secrete a mean of 2.5-fold more IL-17 than those from OTII single transgenic mice with concomitantly higher levels of mRNA encoding IL-17 by real-time PCR and of CD4 T cells with intracellular IL-17 detected by ELISPOT assays. OVA challenge of s.c. air pockets elicited influx of more OTII TCR-positive T cells producing a higher level of IL-17 in DTG mice than OTII control mice. Augmentation of the number and activity of Th17 cells by the S1P-S1P1 axis may thus enhance host defense against microbes and in other settings increase host susceptibility to autoimmune diseases.

Sphingosine 1-phosphate (S1P) generated by cells of innate immunity and the type 1 S1P G protein-coupled receptor (S1P 1 ) on mobile T cells constitute a major system for control of lymphoid organ traffic and tissue migration of T cells. Now we show that T cell activation mediated by the T cell antigen receptor translocates plasma membrane S1P 1 to nuclear envelope membranes for association there with G i/o , Erk 1/2, and other proteins that plasma membrane S1P 1 uses to signal T cell proliferation. However, nuclear S1P 1 and plasma membrane S1P 1 transduce opposite effects of S1P on T cell proliferation and relevant signaling as exemplified by respective decreases and increases in T cell nuclear concentrations of both phospho-Erk and active (phosphorylated) c-Jun. T cell antigen receptor-mediated activation of T cells therefore both eliminates migration responses to S1P by down-regulation of plasma membrane S1P 1 and translocates the S1P-S1P 1 axis into the nuclear domain where signals are directed to transcriptional control of immune functions other than migration.Most studies of the intracellular traffic of G protein-coupled receptors (GPCRs) 2 have focused on their response to occupancy by ligand, which initiates rapid movement from the cell surface to intracellular compartments, including vesiculotubular structures of the perinuclear domain, by diverse pathways and then reinsertion into the plasma membrane (1-3). Recent analyses of cellular traffic of the type 1 GPCR for lysophosphatidic acid (LPA 1 ) have shown that ligand elicits signal transduction, cell surface down-regulation, and prolonged localization of LPA 1 in the nuclear domain (4, 5). When localized in the nuclear envelope, LPA 1 signals transcriptional events by mechanisms not used when LPA 1 is in the plasma membrane. In endothelial cells and hepatocytes, the LPA-nuclear LPA 1 axis stimulates prominent transcription of proinflammatory proteins, including type 2 cyclooxygenase (COX-2) and inducible nitric-oxide synthase. However, constituents of the LPA 1 nuclear signaling complex other than G proteins have not been identified, and it is unclear what elements regulate transcription initiated by LPA 1 nuclear signals. Perhaps most importantly, it is not known by what pathways LPA synthesized principally extracellularly reaches nuclear envelope LPA 1 . In contrast, it is well established that the related lysosphingolipid sphingosine 1-phosphate (S1P) is synthesized intracellularly, taken up readily by non-synthesizing cells, and capable of functioning as an intracellular messenger. S1P produced by mast cells and mononuclear phagocytes, but not T cells, is secreted into T cell corridors where it elicits and regulates T cell movements in lymphoid organs and chemotaxis in non-immune tissues as well as some migration-independent T cell immune functions (6, 7). The introduction of S1P into suspensions of T cells preincubated without S1P down-regulates plasma membrane type 1 GPCR for S1P (S1P 1 ) for a few hours, without changes in mRNA encoding S1P ...