The TIM Family of Cosignaling Receptors: Emerging Targets for the Regulation of Autoimmune Disease and Transplantation Tolerance

Tim-1 blockade with RMT1-10 increases T regulatory cells and prolongs the survival of high-risk corneal allografts in mice

Anti-Tim-1 monoclonal antibody (mAb) RMT1-10 is effective in promoting allograft survival through blocking Tim-1. However, its role in corneal transplantation is unclear. This study aims to evaluate the effect of RMT1-10 on high-risk corneal transplantation. BALB/c mice were transplanted with corneal grafts from C57BL/6 mice and intraperitoneally injected with RMT1-10 or isotype IgG. The transparency of corneal graft was evaluated by slit lamp biomicroscopy. Flow cytometry was used to determine the phenotype of CD4(+) T cells, including CD154, Tim-3, CD25 and Foxp3, and to analyze the proliferation capacity of CD4(+) T cells and the suppressive capacity of T regulatory (Treg) cells. The levels of interferon-gamma (IFN-γ), IL-4 and transforming growth factor-beta1 (TGF-β1) were investigated by intracellular staining and/or ELISA assay. The delayed-type hypersensitivity (DTH) response was evaluated by ear swelling assay. RMT1-10 therapy delayed the onset of rejection and significantly prolonged the survival of corneal allograft. In RMT1-10 treated mice, percentages of CD4(+)CD154(+) cells and CD4(+)Tim-3(+) cells were significantly decreased while the frequency of CD4(+)CD25(+)Foxp3(+) Treg cells was significantly up-regulated, compared with those of isotype IgG treated mice. And, in vitro proliferation of CD4(+) T cells was significantly inhibited by RMT1-10. In addition, percentage of intracellular expression of IFN-γ and IL-4 in CD4(+) T cells isolated from RMT1-10 treated mice was significantly reduced. After co-culturing with RMT1-10 in vitro, CD4(+) T cells produced significantly decreased levels of IFN-γ and IL-4 and significantly increased levels of TGF-β1. Furthermore, RMT1-10 inhibited DTH response of recipient mice and enhanced the suppressive capacity of Treg cells isolated from RMT1-10 treated mice. Our data indicate that Tim-1 blockade with RMT1-10 could suppress immunological rejection and prolong the survival of corneal allograft through regulating T cell responses.

Activation of Peroxisome Proliferator-Activated Receptor γ Prolongs Islet Allograft Survival

Exposing donor mice to carbon monoxide (CO) protects transplanted islet allografts from immune rejection after transplantation (referred as the “donor” effect). In an attempt to understand the mechanisms of the donor effect of CO, we found that donor treatment with CO upregulates expression of peroxisome proliferatoractivated receptor γ (PPARγ), a transcriptional regulator, in isolated islets. In this study, we evaluated whether PPARγ contributes to the survival and function of transplanted islets and whether PPARγ mediates the protective effect of CO in a major mismatch islet allogeneic transplantation model. BALB/c (H-2d) islets in which PPARγ activity was induced by its agonists, 15-deoxy-Δ12–14-prostaglandin J2 (15d-PGJ2) or troglitazone were transplanted into C57BL/6 (H-2b) recipients that had been rendered diabetic by streptozotocin (STZ). Blood glucose levels of recipients were monitored to determine the function of transplanted islets. Our data indicated that PPARγ activation in islets led to a high percentage of BALB/c islets survived long-term in C57BL/6 recipients. Activation of PPARγ in the donor suppresses expressions of proinflammatory cytokines including tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) in transplanted islets. Blocking PPARγ activity by its antagonist, GW9662, abrogated the donor effect of CO in vivo and in vitro. Our data demonstrate that PPARγ plays a critical role in the survival and function of transplanted islets after transplantation in the recipient. The protective effects of CO are at least in part mediated by PPARγ.