Requirement for a serum component in cytotoxin ('lymphotoxin')-mediated target cell lysis

Serum was found to play an essential role in cytotoxin-mediated target cell lysis. The degree of cytotoxic activity on target L cells was directly related to the concentration of sera in the media incubating the L cells. Furthermore, when ether-ethanol-extracted sera were used in the incubation media, almost no cytotoxic activity was found, indicating that a lipid component of sera, removed by the extraction procedure, might be involved in the action of cytotoxin. The effects of increased sera concentrations and extracted sera occur primarily in the initial 24-hr incubation of L cells (prior to the addition of cytotoxin) rather than when cytotoxin is added, indicating that serum acts by influencing target cell susceptibility to cytotoxin rather than on cytotoxin itself.