The cellular basis of allograft rejection in vivo. III. Restoration of first-set rejection of heart grafts by T helper cells in irradiated rats.

An adoptive transfer model was used to examine the subpopulations of lymphocytes required to effect first-set rejection of directly vascularized heart allografts. PVG heart grafts are not rejected in irradiated DA hosts for at least 50 days. The adoptive transfer of 5 X 10(7) syngeneic lymph node cells (LNC) restores rejection to 14.4 +/- 2.4 days (mean +/- SD). Subpopulations of LNC, were separated by an indirect "panning" technique using the mouse antirat monoclonal antibodies W3/13, MRC OX8, or W3/25 to deplete the unwanted subsets of cells. Each subpopulation was tested, in a number equivalent to the number present in 5 X 10(7) normal LNC, for its ability to cause the rejection of heart grafts. Whole T cells (W3/13+) or helper/inducer T cells (W3/25+) restored graft rejection to 16.4 +/- 3.8 d and 16.0 +/- 2.4 days, respectively. Neither cytotoxic/suppressor T cells (MRC OX8+) nor B cells (Ig+) restored rejection. Indirect immunoperoxidase stains of the grafts showed that although W3/25+ cells predominated in the rejected tissue, MRC OX8+ cells were also present even in grafts from rats restored with inocula that contained less than 1% MRC OX8+ cells. Examination of lymphoid tissues suggested that the MRC OX8+ cells might be of host origin. By the time the grafts were rejected in irradiated hosts, significant thymic regeneration had occurred and there were large numbers of MRC OX8+ cells present in the thymus, as well as some in lymph nodes and spleen.