Resistance to Friend Leukemia Virus in Mice: Effect of Immunosuppression

Summary Two different types of resistance to Friend leukemia virus were identified by means of immunosuppression by heterologous anti-lymphocyte serum (ALS) in 25 inbred mouse strains and sublines. Sensitivity or resistance to two variants of Friend virus was measured by the capacity of each virus to produce macroscopic foci in the spleens of the infected animals. The first type of resistance (relative resistance) could be overcome by effective immunosuppression with ALS, whereas the second type (absolute resistance) was not affected by ALS treatment. The first type of resistance could also be overcome by increasing the virus input; the second type was not affected by large doses of virus. The variations were not due to the differential effects of ALS as an immunosuppressant in the mouse strains studied, since ALS was always effective in depressing cellular and humoral immunity. In the sensitive strains, ALS treatment facilitated virus replication. This increase in virus replication was also observed after ALS treatment in the relatively resistant strains. Conversely, only negligible virus replication was detected in the absolutely resistant mouse strains, and this was not modified by ALS treatment.