Early events of importance in determining host cell permissiveness to mouse hepatitis virus infection

Three categories of cell lines are described which differ with respect to their permissiveness to mouse hepatitis virus (MHV), strain A59. Fully permissive L-2 cells gave rise to 100- to 1000-fold higher numbers of infectious centres than did semi-permissive LM, LM-K or C-1300 cells, whereas non-permissive Vero or C-6 cells were refractory to MHV infection. On an infected cell basis, semi-permissive cells (LM, LM-K or C-1300) were as efficient in replicating viral RNA, protein and progeny virions as fully permissive L-2 cells. This result suggested that LM, LM-K and C-1300 cells were deficient in their ability to permit full expression (as compared to L-2 cells) of an early event in MHV infection. Assays of radiolabelled MHV binding to cells of all three categories (L-2, LM, LM-K and C-6) and of infectious MHV binding to L-2 and LM-K cells showed no correlation between virion binding and degree of permissiveness to MHV infection. Internalization of MHV virions into L-2 and LM-K cells, as assayed by proteinase K-resistant infectious centres, showed that, in both cases, maximum virion uptake was complete by approximately 40rain post-inoculation. Direct assays of infectious virion uptake showed similar numbers of internalized viruses (only