Susceptibility to and escape from complement-mediated lysis of guinea-pig hepatoma line-10

Rabbit xenoantisera produced against diethyl-nitrosamine-induced strain-2 guinea-pig hepatoma line-10 cells (L-10) according to various immunization schedules were compared for their cytotoxicity on L-10 cells in the presence of guinea-pig complement. The highest activity was obtained with antisera (Cx-1) produced by repeated intravenous injections of living L-10 cells at high cell dosage, whereas intramuscular injections of living or glutaraldehyde-treated L-10 cells at similar frequency and cell dosage were less effective for the production of cytotoxic antibodies against L-10 cells. Intravenous injections of smaller cell doses were less effective. The cytotoxic antibody in Cx-1 antiserum was shown to be IgG by various methods including gel filtration on Sephadex G-200, ion exchange chromatography and immunoelectrophoresis of purified tumor-specific antibodies. It was concluded that L-10 cells can be lysed by guinea-pig complement and tumor-specific antibodies (IgG). Some antisera contained IgM antibodies which were not cytotoxic. A decrease in susceptibility of L-10 cells to complement-mediated lysis was observed when the cells were maintained in vivo for a long period (more than 20 passage generations). This was due to a lower density of tumor antigens on the cell surface. When tumor cells were treated with a second antibody directed against rabbit IgG or F(ab')2, cytotoxicity of Cx-1 antisera was completely abolished.