Requirement of CD4 T cells for skin graft rejection against thymus leukemia (TL) antigen and multiple epitopes on the TL molecule recognized by CD4 T cells

By selective depletion of CD4 and CD8 T cells in vivo using the respective mAbs, we demonstrate that CD4 T cells are necessary for skin graft rejection against thymus leukemia (TL) Ag, The skin expressing T3(b)-TL Ag from transgenic C3H Tg.Con.3-1 mice given chimeric H-2K(b)/T3(b)-TL gene was rejected when grafted onto C3H/He recipient mice. Depletion of CD4, but not of CD8, cells blocked rejection, CD8 CTL were generated in MEM (control)-treated C3H/He recipient mice, while Thy-1(+)CD4(-)CD8(-)CTL were generated in CD8-depleted recipient mice after rejection. However, no CTL were generated in CD4-depleted or both CD4- and CD8-depleted recipient mice. Thus, the generation of both CD8 and Thy-1(+)CD4(-)CD8(-) CTL was dependent on CD4 T cells. Ab blocking indicated that both CD8 and Thy-1(+)CD4(-)CD8(-) CTL were TCR alpha beta and recognized TL Ag. We furthermore demonstrated that CD4 T cells in spleen cells from C3H/He mice that had rejected C3H Tg.Con.3-1 skin showed a weak, but significant, proliferative response to in vitro stimulation with mitomycin C-treated C3H Tg.Con.3-1 spleen cells. Analysis of the reactivity of bulk CD4 T cell lines to 73 synthetic overlapping peptides encompassing the entire T3(b)-TL molecule showed that CD4 T cells recognized multiple epitopes on the T3(b)-TL molecule in an APC-dependent manner.