Cytotoxic Assays and Other Immunologic Studies of Leukemias Induced by Friend Virus

Summary

Sensitivity to Friend virus infection varied between complete susceptibility in DBA/2 and (C3H × DBA/2)F₁ hybrid mice to relative resistance in other DBA/2 F₁ hybrids. Sera from DBA/2 hybrid mice, resistant to Friend leukemic spleen homogenate or spleen cells were cytotoxic against Friend virus-induced leukemic cells. Cytotoxic antibodies were found in the presence and absence of H-2 antibodies. Sensitivity of spleen cells to cytotoxic action increased 15 to 20 days after infection. The cytotoxic activity of serum antibodies appeared specific for Friend virus-induced leukemias, as no effect could be detected on two other virus-induced tumors, leukemias of varying origin, or normal spleen or lymph-node cells. Sera known to be cytotoxically active on Gross lymphoma cells had no effect on Friend leukemic cells. The cytotoxic titer was markedly reduced when sera were absorbed with Friend leukemic cells in vivo and in vitro. Both absorptions and cytotoxic tests were performed on several independently induced Friend leukemias, which thus seemed to cross-react. Admixture of cytotoxic serum with leukemic spleen homogenate either inhibited tumor growth or significantly increased the time until macroscopically detectable Friend leukemia developed.