Cytokines affecting CD4+ T regulatory cells in transplant tolerance. II. Interferon gamma (IFN-γ) promotes survival of alloantigen-specific CD4+ T regulatory cells

CD4(+) T cells that transfer alloantigen-specific transplant tolerance are short lived in culture unless stimulated with specific-donor alloantigen and lymphocyte derived cytokines. Here, we examined if IFN-gamma maintained survival of tolerance transferring CD4(+) T cells. Alloantigen-specific transplant tolerance was induced in DA rats with heterotopic adult PVG heart allografts by a short course of immunosuppression and these grafts functioned for > 100 days with no further immunosuppression. In previous studies, we found the CD4(+) T cells from tolerant rats that transfer tolerance to an irradiated DA host grafted with a PVG heart, lose their tolerance transferring ability after 3 days of culture, either with or without donor alloantigen, and effect rejection of specific-donor grafts. If cultures with specific donor alloantigen are supplemented by supernatant from ConA activated lymphocytes the tolerance transferring cells survive, suggesting these cells depend on cytokines for their survival. In this study, we found addition of rIFN-gamma to MLC with specific-donor alloantigen maintained the capacity of tolerant CD4(+) T cells to transfer alloantigen-specific tolerance and their ability to suppress PVG allograft rejection mediated by co-administered nave CD4(+) T cells. IFN-gamma suppressed the in vitro proliferation of tolerant CD4(+) T cells. Tolerant CD4(+) CD25(+) T cells did not proliferate in MLC to PVG stimulator cells with no cytokine added, but did when IFN-gamma was present. IFN-gamma did not alter proliferation of tolerant CD4(+) CD25(+) T cells to third-party Lewis. Tolerant CD4(+) CD25(+) T cells' expression of IFN-gamma receptor (IFNGR) was maintained in culture when IFN-gamma was present. This study suggested that IFN-gamma maintained tolerance mediating alloantigen-specific CD4(+) CD25(+) T cells.