Suppressive effects of acetylaminofluorene on immune responses

Abstract

An arylamide carcinogen, 2-Acetylaminofluorene (AAF), inhibited mouse spleen cell blastogenesis in response to the T-cell lectin, concanavalin A (Con A), phorbol 12-myristate 13-acetate (PMA)/Ionomycin activation, and following stimulation by alloantigens as measured by mixed lymphocyte responses (MLR). AAF also markedly suppressed the T-cell dependent antibody forming cell response to sheep red blood cells (sRBC). However, the general metabolic activities such as protein synthesis and glutathione level in spleen cell cultures were not depressed by AAF-exposure. Meanwhile, AAF was most inhibitory on both the sRBC IgM antibody forming cell response and Con A-stimulated proliferation when added during the first 24 hr following initiation of culture. Direct addition of high concentrations of AAF (100 μM) to spleen cell cultures at 48 hr following Con A stimulation produced a very modest inhibition (＜20%) of T-cell proliferation as compared to 90% when added at the time cultures were initiated. Similarly, AAF (75 and 100 μM) produced a greater than 80% inhibition of the in vitro AFC response when spleen cells were sensitized with antigen in presence of AAF. In contrast, no inhibition of the IgM AFC response was produced when AAF (75 μM) was added to spleen cell cultures 48 or 72 hr after antigen sensitization. Con A-triggered cell cycle progression was attenuated at G1 stages by the addition of AAF (50 and 100 μM) with no inhibition of S to G2/M phase transition. These results suggest a mechanism of AAF-mediated immune suppression through a blockade of cell cycle progression from G1 to S phase, although it is not clear how AAF block the cell cycle progression. On the other hand, the addition of exogenous interleukin 2 (IL-2, 100 or 200 units/ml) could not preclude this AAF-induced inhibition of lymphoproliferation. IL-2 activities, which were determined by using CTLL-2 cell line, in Con A-stimulated splenocyte culture supernatants at 48 hr were enhanced by AAF add...