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 naive DA rats were examined. Proliferation of CD4(+) T cells from both naive and tolerant hosts was similar to both PVG and Lewis stimulator cells. In mixed lymphocyte culture to PVG, proliferation of naive CD4(+)CD25(-) T cells was greater than naive 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 naive CD4(+)CD25(+) T cells proliferate to both PVG and Lewis but not to self-DA. CD4(+)CD25(+) T cells from tolerant, but not naive hosts, expressed receptors for interferon (IFN)-gamma 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 naive 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-gamma or IL-5. The proliferation to third-party and self of each cell population from tolerant and naive hosts was similar and not affected by IFN-gamma or IL-5. Our findings suggest CD4(+)CD25(+) T cells that mediate transplant tolerance depend on IFN-gamma or IL-5 from alloactivated Th1 and Th2 cells.