Evidence for maedi-visna virus in milk epithelial cells of naturally infected ewes

Epithelial cells (MEC) were isolated from milk of four maedi-visna virus (MVV) infected and two uninfected ewes, cultured in vitro, and their epithelial nature was confirmed by immunocytochemistry with cytokeratin monoclonal antibodies. PCR analysis on MEC DNA confirmed the presence of proviral DNA in half cultures from infected animals. Expression of MVV proteins was shown both by immunocytochemistry using anti-p27 mAbs and by western blot with hyperimmune serum. Supernatants of MEC from infected ewes were showed to contain infectious viruses when assayed on the indicator goat synovial membrane cells (GSM). Furthermore, p27 protein was detected in supernatants of infected MEC suggesting active production of viral particles. No cytopathic effect was noted in MEC cultures from all infected animals; however, cocultivation of MEC with GSM promoted CPE development. These results suggested that MEC of ewes naturally infected with MVV may play an important role in sustaining virus transmission through the milk.