INDUCTION OF PREB CELL APOPTOSIS BY 7,12-DIMETHYLBENZ[A]ANTHRACENE INLONG-TERM PRIMARY MURINE BONE-MARROW CULTURES

Numerous studies demonstrate that polycyclic aromatic hydrocarbons (PA H) suppress immunity by modifying the function of both B and T cells. Relatively few studies have assessed the effects of these common envir onmental chemicals on immature lymphocytes. In the present study, long -term primary bone marrow cultures were employed to investigate the ef fects of a prototypic PAH and aryl hydrocarbon receptor (AhR) agonist, 7, 12-dimethylbenz[a]anthracene (DMBA), on immature B lymphocytes. In this system, immature preB cells are maintained in a supportive micro environment provided by bone marrow stromal cells. Results presented h ere demonstrate that (1) exposure of primary bone marrow cultures to D MBA results in preB cell death ty apoptosis; (2) notably low doses of DMBA (greater than or equal to 10(-8) M) induce preB cell apoptosis; ( 3) in long-term cultures, bone marrow stromal cells, but not preB cell s, express AhR mRNA and protein as determined by in situ hybridization , RT-PCR, and immunoblotting; (4) freshly isolated unfractionated bone marrow cells, but not purified bone marrow B cells, express AhR prote in as assessed by immunohistochemistry; (5) alpha-naphthoflavone, a co mpetitive AhR inhibitor and cytochrome P450 antagonist, completely blo cks DMBA-induced preB cell apoptosis in primary bone marrow cultures; and (6) DMBA or benzo[a]pyrene injection in vivo results in bone marro w cell apoptosis consistent with the death of hematopoietic cells clus tered around stromal elements. The results implicate programmed cell d eath as a mechanism underlying DMBA-mediated immunosuppression and sug gest that preB cell death is influenced by local interactions with AhR (+) bone marrow stromal cells. (C) 1997 Academic Press.