Effect of tumor cells on the generation of cytotoxic T lymphocytes in vitro. I. Accessory cell functions of mouse tumor cells in the generation of cytotoxic T lymphocytes in vitro: replacement of adherent phagocytic cells by tumor cells or 2-mercaptoethanol.

In agreement with previous reports, the primary in vitro response to alloantigens has been shown to be dependent on the presence of macrophages (Mphs). Splenocytes extensively depleted of adherent phagocytic cells did not generate cytotoxic T lymphocytes, and this activity could be completely restored by small numbers of adherent peritoneal cells (accessory cells). Either P388D1 (Mph-like tumor), P388 ("null" tumor) or P815 (mastocytoma) tumor cells, or 2-mercaptoethanol, could completely replace the accessory function normally mediated by accessory cells. These tumor cells did not non-specifically "enhance" the cytotoxic activity generated with normal nondepleted spleen cells. The restored cultures maintained killing specificity to H-2 targets which was mediated by effector T cells as shown by sensitivity to anti-theta and complement. Therefore, Mphs seem not to be the sole cells capable of mediating an accessory function in a primary response to alloantigens in vitro.