Lymphocyte-induced macrophage cytotoxicity. Production of specific macrophage arming factor by sensitized Lyt 1+2+ T-lymphocytes.

T cells obtained from C57BL (H-2b) mice, that were immunized against allogeneic SL2 (H-2d) tumor cells, were able to produce a factor with the capacity to render macrophages cytotoxic. The factor producing T cells were of the Lyt 1+2+ phenotype. The factor was only produced by the T cells after triggering in vitro by SL2 cells or other cells with H-2d antigens. The macrophages armed with the factor only killed tumor cells with H-2d antigens. The factor was absorbed from the supernatant by macrophages and by cells bearing H-2d antigens but not by other cells. This showed that the factor has an affinity for macrophages and the specific sensitizing alloantigen. Therefore, the specificity of the lymphocytes is the same as the specificity of the factor and the factor-armed macrophages. The factor produced by the Lyt 1+2+ T cells is therefore the specific macrophage arming factor.