Abstract
Host-range variants of mouse mammary tumour viruses (MMTVs) have previously been shown to productively infect cells of several species in vitro (Howard & Schlom, 1978). We report here that cell lines have been identified which exhibit differential restriction for replication of different MMTV variants. In addition, a cell line has been identified that changes as a function of passage in culture from being permissive to being restrictive to infection with MMTVs. MMTVs propagated in both murine and non-murine cells retained their antigenic reactivities in a group-specific radioimmunoassay for MMTVs and demonstrated no evidence for the presence of type-C viruses as determined by a variety of techniques. These studies thus establish in vitro cell substrate tropisms that can be used to differentiate between MMTVs.