Accessory cell function of a lined macrophage in the induction of suppressor T cells in vitro.

Antigen-specific Ts against DTH to BCG were induced in vitro by culturing the splenic T cells of C3H/He mice together with the lined macrophage, SL-1, pulsed with PPD. The suppressor activity was determined by the suppression of DTH in CY-treated syngeneic recipients which had received the cultured cells before BCG sensitization. SL-1 cells express I-A and I-J antigens on the surface, while SL-4 cells, which originated in the same mouse strain as SL-1, do not express any Ia antigens. When I-A antigens on SL-1 were blocked by anti-I-A antibody without complement before PPD-pulsing, the induction of Ts was rather enhanced. When I-J antigens on SL-1 were blocked by anti-I-J alloantiserum, no Ts were induced. Instead, these I-J-blocked and PPD-pulsed SL-1 cells induced effector cells of DTH in vitro. Ia-negative lined macrophage SL-4 cells did not show any activity either in suppressor or in effector cell induction. From these results, we propose a model for the immune modulation led by APC.