Ultraviolet inactivation of murine leukemia virus and its assay in permissive and non‐permissive cells

Abstract This study confirms the different titration patterns of murine leukemia viruses (MuLV) in permissive and non‐permissive cells reported by Hartley et al. (Lilly and Pincus, in press); the titration kinetics was one‐hit in the permissive host and two‐hit in the restrictive host. The following phenomena were also observed: (1) UV‐inactivation curves were nearly the same, regardless of whether the virus was titrated in permissive or restrictive cells. (2) Infection by MuLV of its restrictive host was enhanced by the UV‐inactivated homologous MuLV. (3) UV‐inactivated NB‐tropic virus propagated in N‐type cells enhanced plaque formation of N‐tropic virus in B‐type cells and not that of B‐tropic virus in N‐type cells. UV‐inactivated NB‐tropic virus propagated in B‐type cells enhanced plaque formation of B‐tropic virus in N‐type cells, but not that of N‐tropic virus in B‐type cells.