2-ACETYLAMINOFLUORENE INHIBITS THE ACTIVATION OF IMMUNE-RESPONSES BY BLOCKING CELL-CYCLE PROGRESSION AT G(1) PHASE

2-Acetylaminofluorene (AAF) inhibited in a dose dependent manner mouse spleen cell blastogenesis in response to phorbol 12-myristate 13-acet ate (PMA)/Ionomycin (Io) activation, the T-cell lectin, concanavalin A (Con A), and following stimulation by alloantigens as measured by the mixed lymphocyte response (MLR). AAF also markedly suppressed the T-c ell dependent antibody forming cell (AFC) response to sRBC. AAF was mo st inhibitory on both the sRBC IgM AFC response and Con A stimulated p roliferation when added during the first 24 h following initiation of culture. Direct addition of high concentrations of AAF (100 mu M) to s pleen cell cultures at 48 h following Con A stimulation produced a ver y modest inhibition (< 20%) of T-cell proliferation as compared to 90% when added at the time cultures were initiated. Similarly, AAF (75 an d 100 mu M) produced a greater than 80% inhibition of the in vitro AFC response when spleen cells were sensitized with antigen in presence o f AAF. In contrast, no inhibition of the IgM AFC response was produced when AAF (75 mu M) was added to spleen cell cultures 48 or 72 h after antigen sensitization. Con A-triggered cell-cycle progression was att enuated at the G(1) stage by the addition of AAF (50 and 100 mu M) wit h no inhibition of S to G(2)/M phase transition. These results suggest that the mechanism of AAF-mediated immune suppression is through a bl ockade of cell cycle progression from G(1) to S phase.