Molecular mechanism of 7,12-dimethylbenz[a]anthracene-induced immunosuppression: evidence for action via the interleukin-2 pathway

Previous studies in this laboratory have demonstrated that exposure of mice to the carcinogenic polycyclic aromatic hydrocarbon 7,12-dimethylbenz[a]anthracene results in suppression of both humoral and cell-mediated immunity. This suppression is unaccompanied by any significant alteration in splenic lymphocyte subpopulation composition, suggesting that the immune deficit was due to a modulation of lymphocyte function. Additional studies implicated the T helper lymphocyte as the probable target for 7,12-dimethylbenz[a]anthracene-induced immunosuppression, apparently through an inhibition of interleukin 2 production. The purpose of the present study was to examine the mechanism of 7,12-dimethylbenz[a]anthracene-induced T lymphocyte dysfunction at the molecular level and to determine the consequences of 7,12-dimethylbenz[a]anthracene exposure on the interleukin 2 pathway. In vitro exposure of Con A-activated splenocytes to 7,12-dimethylbenz[a]anthracene resulted in suppression of the mitogenic response, suppressed interleukin 2 production, and reduced the expression of the high affinity receptor for interleukin 2. In contrast, expression of the low affinity interleukin 2 receptor was not affected. In addition, interleukin 2-dependent lymphoblasts and long term cultured splenocytes exhibited a dose-dependent decrease in proliferation following in vitro exposure to 7,12-dimethylbenz[a]anthracene. These results suggest that 7,12-dimethylbenz[a]anthracene-induced immunosuppression may be mediated, at least in part, through the interleukin 2/interleukin 2 receptor pathway.