An in vitro system for studying the initial stages of cottontail rabbit papillomavirus infection

Cottontail rabbit papillomavirus (CRPV) infection of an established cottontail epidermal cell line (Sf1Ep) resulted in the production of CRPV-specific transcripts without concomitant morphological transformation. The most abundant transcripts corresponded in size to those of the E6 and E7 open reading frames (ORFs), which are also among the commonest in domestic and cottontail rabbit papillomas. CRPV RNA production was both time- and dose-dependent, with RNA production diminishing with decreasing viral dose and increasing culture passage. Infected cultures contained episomal CRPV DNA, which did not appreciably change in abundance with time but was significantly reduced with culture passage. All features of in vitro infection, especially RNA production, were inhibited by CRPV-neutralizing, but not HPV-11-neutralizing, monoclonal antibodies. Much of this inhibition could be attributed to a blockage of viral penetration, as indicated by the reduction of CRPV DNA within virus-neutralized cultures. The results indicate that, although CRPV infection of Sf1Ep cells was abortive, it serves as a useful model for analysis of early infection events.