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ZAP-70 is required for the initiation of T cell receptor (TCR) signaling, and Ssu72 is a phosphatase that regulates RNA polymerase II activity in the nucleus. However, the mechanism by which ZAP-70 regulates the fine-tuning of TCR signaling remains elusive. Here, we found that Ssu72 contributed to the fine-tuning of TCR signaling by acting as tyrosine phosphatase for ZAP-70. Affinity purification-mass spectrometry and an in vitro assay demonstrated specific interaction between Ssu72 and ZAP-70 in T cells. Upon TCR stimulation, Ssu72-deficient T cells increased the phosphorylation of ZAP-70 and downstream molecules and exhibited hyperresponsiveness, which was restored by reducing ZAP-70 phosphorylation. In vitro assay demonstrated that recombinant Ssu72 reduced tyrosine phosphorylation of ZAP-70 via phosphatase activity. Cd4 -Cre Ssu72 fl/fl mice showed a defect in the thymic development of invariant natural killer T cells and reductions in CD4 + and CD8 + T cell numbers in the periphery but more CD44 hi CD62L lo memory T cells and fewer CD44 lo CD62L hi naïve T cells, compared with wild-type mice. Furthermore, Cd4 mice developed spontaneous inflammation at 6 mo. In conclusion, Ssu72 phosphatase regulates the fine-tuning of TCR signaling by binding to ZAP-70 and regulating its tyrosine phosphorylation, thereby preventing spontaneous inflammation.Ssu72 fl/fl mice developed spontaneous inflammation at 6 mo. In conclusion, Ssu72 phosphatase regulates the fine-tuning of TCR signaling by binding to ZAP-70 and regulating its tyrosine phosphorylation, thereby preventing spontaneous inflammation., Competing Interests: The authors declare no competing interest.

Invariant NKT (iNKT) cells are a distinct subset of T cells that exert Janus-like functions in vivo by producing IFN-γ and IL-4. Sodium chloride modulates the functions of various immune cells, including conventional CD4 + T cells and macrophages. However, it is not known whether sodium chloride affects iNKT cell function, so we addressed this issue. Sodium chloride inhibited IFN-γ, but not IL-4, production by iNKT cells upon TCR or TCR-independent (IL-12 and IL-18) stimulation in a dose-dependent manner. Consistently, sodium chloride reduced the expression level of tbx21, but not gata-3, in iNKT cells stimulated with TCR engagement or IL-12 + IL-18. Sodium chloride increased phosphorylated p38 expression in iNKT cells and inhibitors of p38, NFAT5, SGK1, and TCF-1 restored IFN-γ production by iNKT cells stimulated with sodium chloride and TCR engagement. Furthermore, adoptive transfer of iNKT cells pretreated with sodium chloride restored antibody-induced joint inflammation to a lesser extent than for untreated iNKT cells in Jα18 knockout mice. These findings suggest that sodium chloride inhibits IFN-γ production by iNKT cells in TCR-dependent and TCR-independent manners, which is dependent on p38, NFAT5, SGK1, and TCF-1. These findings highlight the functional role of sodium chloride in iNKT cell-mediated inflammatory diseases., (©2017 Society for Leukocyte Biology.)