In vivo and in vitro immunosuppressive effects of benzo[k]fluoranthene in female Balb/c mice.

Although polycyclic aromatic hydrocarbons (PAHs) have been known to suppress immune responses, few studies have addressed the immunotoxicity of benzo[k]fluoranthene (B[k]F). In this study, we investigated the immunosuppression by B[k]F, both in vivo and in vitro, in female BALB/c mice. To assess the effects of B[k]F on humoral immunity as splenic antibody response to sheep red blood cells (SRBCs), B[k]F was given a single dose or once daily for 7 consecutive days po with 30, 60, and 120 micromol/kg. B[k]F reduced the number of antibody-forming cells (AFCs) in a dose-dependent manner. Subacute treatment with B[k]F caused weight increases in liver and decreases in spleen and thymus. The number of AFCs was dramatically decreased by B[k]F in a dose-dependent manner. In a subsequent study, mice were subacutely exposed to the same doses of B[k]F without an immunization with SRBCs, followed by splenic and thymic lymphocyte phenotypings using a flow cytometry and ex vivo mitogen-stimulated proliferation. B[k]F-exposed mice exhibited reduced splenic and thymic cellularity, decreased numbers of total T cells, CD4(+) cells, and CD8(+) cells in spleen, and immature CD4(+)CD8(+) cells, CD4(+)CD8(-) cells, and CD8(+)CD4(-) cells in thymus. The number of CD4(+) IL-2(+) cells was reduced by about 11%, 31%, and 53% following exposure of mice to 30, 60, and 120 micromol/kg of B[k]F, respectively. In the ex vivo lymphocyte proliferation assay, B[k]F inhibited splenocyte proliferation by LPS and Con A. In the in vitro mitogen-stimulated proliferation by untreated splenic suspensions, B[k]F only suppressed splenocyte proliferation to LPS. These results suggested that B[k]F-induced immunosuppression might be mediated, at least in part, through the IL-2 production, and caused by mechanisms associated with metabolic processes.