Changes in Reactivity In Vitro of CD4(+)CD25(+) and CD4(+)CD25(−) T Cell Subsets in Transplant Tolerance

Transplant tolerance induced in adult animals is mediated by alloantigen-specific CD4(+)CD25(+) T cells, yet in many models, proliferation of CD4(+) T cells from hosts tolerant to specific-alloantigen in vitro is not impaired. To identify changes that may diagnose tolerance, changes in the patterns of proliferation of CD4(+), CD4(+)CD25(+), and CD4(+)CD25(−) T cells from DA rats tolerant to Piebald Virol Glaxo rat strain (PVG) cardiac allografts and from naïve DA rats were examined. Proliferation of CD4(+) T cells from both naïve and tolerant hosts was similar to both PVG and Lewis stimulator cells. In mixed lymphocyte culture to PVG, proliferation of naïve CD4(+)CD25(−) T cells was greater than naïve CD4(+) T cells. In contrast, proliferation of CD4(+)CD25(−) T cells from tolerant hosts to specific-donor PVG was not greater than CD4(+) T cells, whereas their response to Lewis and self-DA was greater than CD4(+) T cells. Paradoxically, CD4(+)CD25(+) T cells from tolerant hosts did not proliferate to PVG, but did to Lewis, whereas naïve CD4(+)CD25(+) T cells proliferate to both PVG and Lewis but not to self-DA. CD4(+)CD25(+) T cells from tolerant, but not naïve hosts, expressed receptors for interferon (IFN)-γ and IL-5 and these cytokines promoted their proliferation to specific-alloantigen PVG but not to Lewis or self-DA. We identified several differences in the patterns of proliferation to specific-donor alloantigen between cells from tolerant and naïve hosts. Most relevant is that CD4(+)CD25(+) T cells from tolerant hosts failed to proliferate or suppress to specific donor in the absence of either IFN-γ or IL-5. The proliferation to third-party and self of each cell population from tolerant and naïve hosts was similar and not affected by IFN-γ or IL-5. Our findings suggest CD4(+)CD25(+) T cells that mediate transplant tolerance depend on IFN−γ or IL-5 from alloactivated Th1 and Th2 cells.