ABSTRACT
T cell Ig mucin 3 (Tim-3) has been found to play an important role in Th1-mediated auto- and alloimmune responses, but the function of soluble form of Tim-3 (sTim-3) remains to be elucidated. In this study, we report the inhibitory effect of sTim-3 on T cell-mediated immune response. In this study, sTim-3 mRNA was found, among different tissues and organs, only in splenic cells, and the activation of splenocytes resulted in up-regulated production of both sTim-3 mRNA and protein. We constructed a eukaryotic expression plasmid, psTim-3, which expresses functional murine sTim-3. In C57BL/6 mice inoculated with B16F1 melanoma cells, the growth of tumor was facilitated by the expression of this plasmid in vivo. Furthermore, sTim-3 inhibited the responses of T cells to Ag-specific stimulation or anti-CD3 mAb plus anti-CD28 mAb costimulation and the production of cytokines IL-2 and IFN-gamma in vitro. In tumor rejection model, sTim-3 significantly impaired T cell antitumor immunity, evidenced by decreased antitumor CTL activity and reduced amount of tumor-infiltrating lymphocytes in tumor. Real-time PCR analysis of gene expression in tumor microenvironment revealed the decreased expression of Th1 cytokine genes and the unchanged profile of the genes related to T regulatory cell function, suggesting that the inhibitory effect of sTim-3 on the generation of Ag-specific T cells in vivo is dominated by T effector cells rather than T regulatory cells. Our studies thus define sTim-3 as an immunoregulatory molecule that may be involved in the negative regulation of T cell-mediated immune response.
Subject(s)
Down-Regulation/immunology , Receptors, Virus/physiology , T-Lymphocytes/immunology , Animals , CHO Cells , Cell Line , Cell Line, Tumor , Cell Proliferation , Cricetinae , Cricetulus , Female , Hepatitis A Virus Cellular Receptor 2 , Ligands , Melanoma, Experimental/immunology , Melanoma, Experimental/metabolism , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Organ Specificity/immunology , Protein Binding/immunology , RNA, Messenger/metabolism , Receptors, Virus/biosynthesis , Receptors, Virus/genetics , Receptors, Virus/metabolism , Solubility , T-Lymphocytes/metabolismABSTRACT
AIM: To explore the role of T cell immunoglobulin- and mucin- domain containing molecule-3 (Tim-3) in the induction of tumor immune tolerance by investigating the expression of two types of Tim-3 at the early stage of tumorigenesis and the temporal-spatial relationship between the expression of Tim-3 and other immuno-inhibitory genes in tumor. METHODS: By using semi-quantitative RT-PCR method, we investigated the expression of Tim-3, forkhead box P3 (Foxp3), cytotoxic T lymphocyte antigen 4 (CTLA-4), glucocorticoid-induced tumor necrosis factor receptor family-related receptor (GITR), TGF-beta, IL-10 and IFN-gamma at different time in tumor of tumor-bearing mice. Meanwhile, the growth of tumor was determined. RESULTS: At the early stage of tumorigenesis, sTim-3 was expressed before flTim-3 in tumor. When flTim-3 was expressed, the expression of sTim-3 was down-regulated. The expression of Foxp3, and GITR was simultaneous with that of flTim-3 and was up-regulated gradually with tumor growth. The expression of CTLA-4 was earlier than that of flTim-3 and also up-regulated gradually. The expression of flTim-3 and Foxp3 was also consistent with each other in tissue distribution. The growth of tumor was postively correlated with the expression of flTim-3, Foxp3, and CTLA-4 and negatively with the expression of sTim-3. CONCLUSION: Along with the growth of tumor, immune tolerance was gradually established in tumor. flTim-3 but not sTim-3 may induce tumor immunological tolerance.
