Inhibition of murine splenic B lymphocyte activation following oral exposure to 7,12-dimethylbenz(a)anthracene (DMBA)

Previous results from this laboratory have demonstrated that oral exposure of B6C3F1 mice to DMBA inhibited mitogen-stimulated lymphocyte activation in cells recovered from several lymphoid organs. These studies showed that both LPS and PHA-stimulated lymphocyte proliferation and PHA-induced Ca+2 mobilization were significantly inhibited by DMBA exposure, supporting the hypothesis that DMBA inhibits early events associated with lymphocyte activation. The purpose of the current studies was to test this hypothesis directly for B cell activation. B6C3F1 mice were treated with 0, 1.0, or 10 mg/kg/day doses of DMBA for 14 days (total cumulative doses of 0, 14, or 140 mg/kg). B lymphocyte populations were then selected on the flow cytometer by direct positive staining of spleen cells with phycoerythrin-labeled anti-Ly5 (B lymphocyte marker) antibodies. Ca+2 mobilization studies were performed using affinity-purified goat anti-mouse IgD antibodies as the stimulant and Indo-1 as the intracellular Ca+2 indicator. Cell proliferation studies were also performed using 3H-thymidine and insoluble anti-IgD antibodies. Anti-IgD stimulated Ca+2 mobilization was significantly reduced at the 140 mg/kg dose of DMBA. A statistically significant decrease in anti-IgD stimulated B lymphocyte proliferation at the 14 mg/kg and 140 mg/kg doses of DMBA was found. These results suggest that B lymphocytes may be important targets for DMBA-mediated immunosuppression