Prolongation of skin allograft survival in ATS-treated mice by post-transplant injections of species antigenic extracts.

B10.A male mice were grafted with H-2-incompatible murine B10.A(2R) skin allografts and treated with antithymocyte serum on days 2, 4, and 7 after transplantation. Repeated injections of cell-free tissue extracts from livers or spleens of B10.A(2R) mice were given in the standard doses, starting on the day of transplantation or on day 14 or day 28 after transplantation. The standard doses were the equivalents of material extracted from 40 mg or 80 mg of wet weight of liver or spleen tissue. Almost all of the regimens used in which antigen injections were begun on day 14 or day 28 after transplantation were successful and led to a marked prolongation in skin allograft survival. In some experimental groups most of the grafts survived 100 days after grafting and 8--33% grafts showed long-term survival in individual groups. The mechanism of this tolerance is mediated by suppressor cells which were characterized by means of anti-Thy 1.2 antibodies as T lymphocytes. the in vitro experiments have shown that cytotoxic cell precursors may be present in long-term tolerant mice and that they may be reactive to the tolerated antigens after sensitization.