Immunosuppression by leukemia viruses. Effect of Friend leukemia virus on humoral immune competence of leukemia-resistant C57BL/6 mice.

Infection of genetically resistant C57BL/6 mice with Friend leukemia virus resulted in a marked but transient immunodepression of the humoral immune response to sheep erythrocytes. The primary immune response to sheep erythrocytes was depressed in mice infected 1 or 3 days before challenge immunization, but no suppression was observed when the interval was greater. The suppression coincided with the time of transient viremia in the mice. The secondary immune response to sheep erythrocytes was inhibited when virus was injected within a few days before booster immunization. Induction of immunologic "memory" to sheep erythrocytes was also blocked in C57BL/6 mice given virus before priming with the SRBC. The immunosuppressive activity appeared due to a marked but transient effect of the virus on antibody precursor cells, as ascertained by cell transfer experiments. These observations are pertinent to the general question to the cellular site of action of immunosuppressive tumor viruses and the relationship between immunosuppression and the neoplastic properties of the RNA viruses.