Human spumavirus replication in human cells.

It was previously reported that the replication of the human syncytium-forming virus (HSFV), a spumavirus, occurred only in fibroblast-like cell lines (human fetal diploid lung #645 [HFDL]) but not in epithelial-like lines (recovered amnion) [RA]. Factors that may be involved in such a phenomenon were the subject of this investigation. While both permissive (HFDL) and nonpermissive (RA) cell lines supported the replication of several representative animal viruses and adsorbed HSFV equally well, immunofluorescent staining of HSFV antigens revealed markedly fewer fluorescing cells in nonpermissive cultures. Infectious center assays of infected nonpermissive cells indicated the formation of significantly fewer infectious centers. The rate of DNA synthesis was markedly greater in the permissive cell lines. In addition, in the permissive cell line, the amount of proviral DNA revealed by the Hirt procedure and isopycnic banding in CsCl was significantly increased and was infectious as determined by the calcium phosphate-DMSO transfection assay. These results indicate that resistance of HSFV infection in nonpermissive cell cultures is probably an intracellular event.