NEUTRALIZATION KINETICS OF FRIEND AND RAUSCHER LEUKEMIA VIRUSES STUDIED WITH SPLEEN FOCUS ASSAY METHOD

The rates of neutralization of Friend and Rauscher viruses in vitro by specific antisera were measured with the spleen focus assay method in order to obtain quantitative information on the antigenic relationship between these viruses. Sera were obtained from C3H mice pretreated with formalinized cell suspensions from leukemias induced in the same strain by Friend, Rauscher, Moloney, Gross and Graffi viruses; the Friend and Rauscher virus preparations used were harvested from the plasma of infected C3H mice, and the titrations of residual virus were also carried out in mice of the C3H strain. Both Friend and Rauscher viruses were neutralized by sera from mice pretreated with Friend, Rauscher and Moloney leukemias, but no neutralizing activity was detected in sera from mice pretreated with either Gross or Graffi leukemias. Friend and Rauscher viruses behaved identically to one another with regard to the kinetics of their neutralization, whether antisera prepared against Friend or Rauscher or Moloney leukemias were used, and despite marked differences in the potency and quality of these antisera. The data are considered to provide strong evidence that the antigenic sites on Friend and Rauscher viruses which participate in these neutralization reactions are identical.