Thy 1+ donor cells that promote allograft tolerance in sublethally irradiated MHC-disparate hosts.

We have previously demonstrated that depletion of Thy 1+ cells impairs the capacity of C57BL/6J, H-2b bone marrow cells, BMC, and BALB/cxC57BL/6J F1 BMC and spleen cells (SC) to establish mixed lymphoid chimerism and tolerance for donor-specific skin grafts in sublethally irradiated (240 cGy x3) BALB/c, H-2d hosts. In the present studies incubation with anti Ly2.2 + C markedly reduced the capacity of BALB/cxC57BL/6J, F1 SC to induce tolerance and chimerism (P less than .001). Incubation with anti-L3T4 + C had an inhibitory effect of borderline significance (P less than .04). Incubation with L-leucyl-L-leucine methyl ester (which removes NK cells, Tc, and precursor Tc) had no effect on the capacity of either C57BL/6J BMC or BALB/cxC57BL/6J F1 BMC or SC to establish chimerism and induce skin graft tolerance. These results suggest that tolerance-promoting Thy 1+ cells are not cytotoxic T cells. Both Ly2+ noncytotoxic CD8+ and L3T4+ noncytotoxic CD4+ cells may be involved. Alternatively the requisite Thy 1+ cells may be immature T cells that express both Ly2 and L3T4.