Murine T-cell-mediated cytotoxicity against syngeneic and allogeneic cell lines induced by fetal calf serum

Mouse spleen cells from normal animals developed easily measurable cytotoxicity against various cell lines when cultured in vitro without deliberate sensitization. Cytotoxicity, measured by a 3-hr ⁵¹Cr-release assay, was maximum on Days 3 and 4 of culture and was dependent on the presence of fetal calf serum. Neither cell recovery nor blastogenesis, however, invariably correlated with the amount of cytotoxicity generated. Nylon wool adsorption of effector cells cultured 3 days had only a marginal effect on cytotoxicity, whereas cytolysis was markedly reduced (but not totally eliminated) by treatment with anti-T-cell serum and complement. When target cells were in relative excess to effector cells, ⁵¹Cr release was proportional to effector cell number and proceeded for at least 22 hr. The cytotoxicity was not tumor or H-2 specific, and targets without known C-type viral antigens (gp71) were killed as readily as those with easily measurable viral antigens. Nontumorigenic fibroblasts were lysed, but concanavalin A-induced blast cells were not. Cytotoxicity was not augmented in cultures of spleen cells from mice injected with fetal calf serum or with tumor fragments exposed to fetal calf serum. Mercaptoethanol was not necessary for the generation of cytotoxic activity, but T cells and Sephadex G-10 or nylon wool-adherent cells were necessary and the function of the adherent cell could not be replaced by mercaptoethanol. Removal of plastic adherent cells had no effect. Fetal calf serum retained its activity when heated for 45 min at 56 °C or when dialyzed. Dilution and reconcentration by Amicon filtration revealed that the mass of the active material was between 30,000 and 100,000 daltons.The early appearance, transient nature, and nonspecificity of this cytotoxicity distinguish it from antigen-specific reactions. The effector's stability at 37 °C and its relatively easily detectable T-cell markers distinguish it from natural killer and cytotoxic cells. This activity is like lectin-induced cytotoxicity but differs because allogeneic blast cells are not lysed. The observed cytotoxic activity may be of in vivo relevance (vis-à-vis natural killer cells) or, more likely, an in vitro expression of a stage of cell differentiation that T cells may normally pass through during their response to antigen.