To determine the effect of benzo[a]pyrene (B[a]P) on the developing immune system of immature rats, newborn animals received different concentrations (0.1, 1.0 and 10.0 mg/kg/day) of B[a]P in the first 14 days after birth. These rats were euthanised on day 23 of the experiment and it was found that the decreasing numbers of erythrocytes were in direct correlation to the dose of B[a]P. In subject animals, the overall counts of T cells in the spleen and the mitogenic activity increased. A

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... in the production of both IFN-γ and IL-4 (measured at the mRNA level) as well as the decreasing IFN-γ /IL-4 ratio in rat splenocytes were dependent on the dose of B[a]P. From this we may deduce that exposure to B[a]P in immature animals may modulate the immune response to infection and/or vaccination.