Carcinogen-treated skin allografts rejected by T lymphocytes specific for class I but not class II MHC antigens

Treatment of skin with the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA), which reduces the density of epidermal class II MHC-expressing Langerhans cells (LC), enhances its survival when transplanted onto histoincompatible hosts. We have examined the ability of T lymphocytes which reject DMBA-treated skin to lyse P388D1 cells expressing either only class I or class I and II antigens. Lymphocytes isolated from solvent-treated grafts showed greater cytotoxicity for the targets expressing both antigens, indicating that some of these lymphocytes were specific for class II MHC antigens. In contrast, lymphocytes isolated from carcinogen-treated grafts lysed both targets similarly and hence did not contain any cells specific for class II MHC antigens. Anti-class I MHC antibody blocked cytotoxicity by both leukocyte populations to similar extents, but anti-class II MHC antibodies preferentially blocked T cells isolated from the solvent-treated grafts. There was no difference in the phenotype of the cytotoxic cells isolated from solvent- and carcinogen-treated grafts. Thus, whereas solvent-treated skin grafts are rejected by T cells specific for class I and II MHC antigens, DMBA-treated skin grafts are only rejected by class I MHC-specific T cells which may account for the enhanced survival of the carcinogen-treated grafts.