Activation in vitro of mouse macrophages by syngeneic, allogeneic, or xenogeneic lymphocyte supernatants

Macrophages from normal C57BL/6 mice, those with a s.c. B16 melanoma, and mice immunized against the tumor were examined for in vitro cytotoxicity to B16 tumor cells. Macrophages were treated by incubation with supernatants from B16 cells grown either in unmixed cultures or in cultures containing syngeneic, normal, or sensitized allogeneic (A mouse), or xenogeneic (rat) lymphocytes. The various treated and untreated macrophages were then cultured for 5 days with viable B16 cells prelabeled with ¹²⁵I 5 iodo 2' deoxyuridine; the cultures were terminated, and the extent of destruction of the B16 target cells was determined from the amounts of radioactivity remaining in adherent tumor cells. Of the untreated macrophages, only those from immunized mice were cytotoxic to the tumor cells; macrophages from normal and tumor bearing mice became cytotoxic by incubation with supernatants from cultures containing lymphocytes from immunized syngeneic mice, sensitized allogeneic mice, or sensitized rats; and macrophages incubated with supernatants from cultures containing normal nonsensitized allogeneic or xenogeneic lymphocytes showed no cytotoxicity. These results suggest that macrophages from tumor bearing animals are potentially cytotoxic to their syngeneic tumors and can be activated by mediators released from sensitized syngeneic, allogeneic, and/or xenogeneic lymphocytes in vitro.