Replication kinetics of N- and B-tropic murine leukemia viruses on permissive and nonpermissive cells in vitro

The kinetics of infection by a B-tropic, an N-tropic, and an NB-tropic murine leukemia virus (MuLV) have been studied on the cells of several mouse strains of permissive, restrictive, and F₁ hybrid genotype. The titration curves reveal that host cell restriction is measured by two independent parameters: (1) the slope of the curve ("hitness"); and (2) the level of sensitivity at comparable multiplicities of infection. Once established, infection is propagated from cell to cell at similar rates in both permissive and restrictive cell cultures. Anomalous results were obtained with the cells of strain NZB mice. Rat cells propagated these MuLV with 1-hit kinetics at low levels of sensitivity.