Studies on the immunosuppressive effects of 7, 12-Dimethylbenz[a]anthracene

Abstract

Effects of 7,12-Dimethylbenz[a]anthracene (DMBA), which is an environmental pollutant, mutagen and carcinogen, on the immune response were investigated using splenocyte culture alone, exogenous metabolic activation system (S-9 fraction and primary cultured hepatocytes obtained from rat liver) in vitro and female BALB/c mice in vivo. Antibody response of splenocytes to LPS(100 g/ml) in 48 hr continuous exposure with DMBA were suppressed in a dose-dependent manner. Chrysen and 1,2-benz[a]anthracene (1,2-BA), structural analogues of DMBA, were used. They were non-immunosuppressive up to 50 μM. 1,2-BA(50 μM) was not able to block DMPC-induced suppressive of antibody response to LPS. But, α-naphthoflavone (ANF, 5 μM) was able to attenuate slightly DMBA-induced suppression of antibody response to LPS. DMBA did not affect the activation step of, but, early step of differentitation. Splenocytes expressed the metabolic capacity to activate DMBA to immunosuppressive metabolites on TLC chromatogram. To investigate the role of exogenous metabolic activation system, we used rat liver S-9 fraction and primary cultured hepatocytes. Two systems were successfully able to produce DMBA-induced immunosuppression in short-time culture. ANF, an inhibitor of cytochrome P-450, revered completely DMBA-induced immunosuppression in two systems to control level, indicating involvement of DMBA metabolism present in two systems. In addition to ANF, addition of exogenous calf thymus DNA(CTD, 2 mg/ml) to coculture medium of rat primary hepatocyted and murine splenocytes reversed completely DMBA-induced immunosuppression. The binding of [$^3H$]DMBA products to splenocyte DNA increased in time-dependent manner and was reduced by ANF (10 μM) in coculture. These results suggest that DMBA metabolites generated in splenocytes exposed to DMBA for 48 hr and in exogenous metabolic activation systems cultured with splenocytes for short-time (1 or 4 hr) could produce immunosuppression by targeting to sp...