The biological features of CD8~+CD28~- T suppressor cells in spontaneous tolerance of rats liver transplantation

ObjectiveTo explore the biological features of spleen CD8 +CD28 - T cells from spontaneous tolerance models of rats with orthotopic liver transplantation. MethodsThe proportion of spleen CD8 +CD28 - T cells from spontaneous tolerance model and acute rejection model was determined by flow cytometry. The suppressor activities of spleen CD8 +CD28 - T cells were tested by mixed lymphocyte reaction in vitro and infusion in vivo. The cytokines mRNA was detected by RT-PCR and apoptosis was estimated by annexin Ⅴ-FITC. ResultsThe percentage of spleen CD8 +CD28 - T cells in spontaneous tolerance models was increased to 31.5%±2.6%,which was higher than that in normal controls(5.4%±1.5%) and that in acute rejection model(6.0%± 1.3%). Spleen CD8 +CD28 - T cells isolated from spontaneous tolerance models inhibited the proliferation of mixed lymphocyte reaction and the inhibition was reversed by exogenous IL-2 40U/ml. They strongly expressed IFN-γ mRNA,and prolonged median survival time (15±1.8 days vs 10±0.8 days,P0.05) of skin allograft by infusion. No increased apoptosis was induced by CD8 +CD28 - T cells. The same function was not found in spleen CD8 +CD28 - T cells isolated from acute rejection model. The combination of IL-2 and mitogen proliferated CD8 +CD28 - T cells effectively. ConclusionSpleen CD8 +CD28 - T cells isolated from spontaneous tolerance model is a unique kind of suppressor T cells. The mechanism probably involves IFN-γ and anergy of alloreactive T cells.