Mechanisms of benzo(a)pyrene-induced modulation of antigen presentation

Benzo(a)pyrene (BaP) has been shown previously to affect humoral immunity in part through alterations in the normal functioning of macrophages. In this study we investigated several specific events affected by BaP. Concanavalin A-elicited macrophages from BaP-exposed animals had a decreased capacity to present keyhole limpet hemocyanin (KLH) to nylon wool nonadherent, KLH-primed lymph node T cells. BaP treatment 7 days before and after administration of KLH resulted in a decrease in the responsiveness of KLH primed T cells to antigen. BaP administration beginning 3 days before (day -3), concurrently with (day 0) or 7 days after (day +7) KLH antigen treatment had no effect on the ability of KLH primed T cells to respond to KLH presented by untreated macrophages. The decreased capacity of BaP-exposed macrophages to present KLH is due in part to a decrease in the amount of KLH taken up by these cells. There was no alteration in the amount of soluble interleukin-1 released by BaP exposed cells nor was there a change in the expression of membrane associated interleukin-1. BaP treatment resulted in a dose-dependent increase in the percentage of Ia⁺ macrophages. These results demonstrate that BaP affects antigen presentation through alteration in macrophage function.