TIM-3 is a molecule selectively expressed on a subset of murine IFN-c-secreting T helper 1 (Th1) cells but not Th2 cells, and regulates Th1 immunity and tolerance in vivo. At this time little is known about the role of TIM-3 on human T cells. To determine if TIM-3 similarly identifies and regulates Th1 cells in humans, we generated a panel of mAb specific for human TIM-3. We report that TIM-3 is expressed by a subset of activated CD4 1 cells, and that anti-CD3/anti-CD28 stimulation increases both the level of expression as well as the number of TIM-3 1 T cells. We also find that TIM-3 is expressed at high levels on in vitro polarized Th1 cells, and is expressed at lower levels on Th17 cells. In addition, human CD4 1 T cells secreted elevated levels of IFN-c, IL-17, IL-2, and IL-6, but not IL-10, IL-4, or TNF-a, when stimulated with anti-CD3/anti-CD28 in the presence of TIM-3-specific, putative antagonistic antibodies. This was not mediated by differences in proliferation or cell death, but rather by induction of cytokines at the transcriptional level. These results suggest that TIM-3 is a negative regulator of human T cells and regulates Th1 and Th17 cytokine secretion.

T cell immunoglobulin- and mucin domain–containing molecule (TIM)3 is a T helper cell (Th)1–associated cell surface molecule that regulates Th1 responses and promotes tolerance in mice, but its expression and function in human T cells is unknown. We generated 104 T cell clones from the cerebrospinal fluid (CSF) of six patients with multiple sclerosis (MS) (n = 72) and four control subjects (n = 32) and assessed their cytokine profiles and expression levels of TIM3 and related molecules. MS CSF clones secreted higher amounts of interferon (IFN)-γ than did those from control subjects, but paradoxically expressed lower levels of TIM3 and T-bet. Interleukin 12–mediated polarization of CSF clones induced substantially higher amounts of IFN-γ secretion but lower levels of TIM3 in MS clones relative to control clones, demonstrating that TIM3 expression is dysregulated in MS CSF clones. Reduced levels of TIM3 on MS CSF clones correlated with resistance to tolerance induced by costimulatory blockade. Finally, reduction of TIM3 on ex vivo CD4+ T cells using small interfering (si)RNA enhanced proliferation and IFN-γ secretion, directly demonstrating that TIM3 expression on human T cells regulates proliferation and IFN-γ secretion. Failure to up-regulate T cell expression of TIM3 in inflammatory sites may represent a novel, intrinsic defect that contributes to the pathogenesis of MS and other human autoimmune diseases.

We previously demonstrated that type 1 astrocytes exhibited homotypic cell contact-dependent inhibition of proliferation with increased expression of cyclin-dependent kinase inhibitor p27(Kip1). Here, we investigated the functional role of p27 in contact-dependent inhibition of astrocytes and reactive gliosis in vitro and in vivo. An increase in the number of proliferating cells was detected in high-density cultures of astrocytes derived from mice carrying a targeted deletion in the p27 gene compared to astrocytes from wild-type mice. Overexpression of p27 by adenovirus vectors inhibited astrocyte proliferation, which was accompanied by downregulation of cyclin A. In a gliosis model in vitro, a transient decrease in the p27 level and an increase in the proliferation rate were observed. Astrocyte proliferation following cortical injury lasted longer in p27-deficient mice than in wild-type mice. Forced expression of p27 in both in vitro and in vivo models of gliosis effectively suppressed astrocyte proliferation. In summary, we demonstrated that p27 contributed to the cell contact-dependent inhibition of astrocyte proliferation and to the cessation of proliferation in reactive astrocytosis. p27 may be used to modulate reactive astrocytosis.