Swine and ruminant pestiviruses require the same cellular factor to enter bovine cells

Pestiviruses initiate infection of susceptible cells by receptor-mediated endocytosis. Cellular plasma membrane or endosomal molecules involved in translocation of these viruses into the cytosol have not been unequivocally identified. We reported previously that a mutant cell line derived from Madin-Darby bovine kidney (MDBK) cells, termed CRIB-1, was resistant to infection with bovine viral diarrhoea virus. CRIB-1 cells were also resistant to infection with classical swine fever virus and border disease virus of sheep, suggesting that entry of these three different pestiviruses into bovine cells requires a common cell membrane function. The resistance is pestivirus-specific: CRIB-1 cells were as susceptible as the parental MDBK cells to 14 other viruses of cattle and swine belonging to unrelated families. The resistance of CRIB-1 cells to pestivirus infection involves a block in virus entry since transfection of virus RNA or virus inoculation in the presence of PEG resulted in productive infection. Furthermore, quantitative analyses of the outcome of PEG-mediated infection of CRIB-1 cells indicated that the intracellular milieu was fully permissive for pestivirus replication. Binding studies revealed that virus attachment to CRIB-1 cells was not completely abrogated. These results indicate that entry of pestiviruses into MDBK cells depends on a common plasma membrane or endosomal function, which is lacking in CRIB-1 cells.