The negative systemic effect of BCGcw inoculated intraperitoneally - II. in vitro demonstration of the presence of suppressor cells in BCGcw-immunized rats

In vitro investigations were undertaken to determine the Con-A and mixed lymphocyte (MLR) blastogenic responses of spleen cells obtained from ACI rats inoculated intraperitoneally (IP) with BCG cell walls (BCGcw). Spleen cells from rats bearing the intramuscular (IM) Morris hepatoma 3924a and rats in which IP BCGcw immunization had caused an enhancement of tumor growth were also examined. Several time points were examined to determine the kinetics of the response. BCGcw-immunized animals showed a dose-related depression in Con-A blastogenesis, which was maximal 7-14 days after immunization. Removal of plastic-adherent cells resulted in near-complete restoration of normal Con-A responsiveness. The Con-A response of normal spleen cells could be depressed by the addition of an adherent population of spleen cells obtained from animals 7-14 days after IP immunization with 900 μg BCGcw. Animals which were immunized with 900 μg BCGcw showed a severe depression in MLR reactivity (<10% of normal) throughout the experiment. Approximately 50% of the normal MLR response was restored by removal of plastic-adherent cells. Studies with animals inoculated with tumor only showed a depression of Con-A and MLR blastogenesis 28 days after tumor inoculation. BCGcw-preimmunized tumor-bearing animals showed a profound decrease in Con-A and MLR reactivity at all time points examined. A correlation is made relating the presence of BCGcw-induced suppressor cells with the observed in vivo enhancement of tumor growth by BCGcw immunization.