Pure preparations of envelope
glycoproteins E(rns) and E2 of classical swine fever virus (CSFV) synthesized in insect cells were used to study
infection of porcine and bovine cells with the pestiviruses CSFV and bovine viral diarrhoea virus (BVDV). Almost 100% inhibition of
infection of porcine kidney cells with CSFV was produced by 100 microg/ml E(rns). After removal of the virus no E(rns) was needed in the overlay medium (growth medium) to maintain this level of inhibition. In contrast, 100% inhibition of
infection of porcine kidney cells with CSFV by 10 microg/ml E2 was only achieved when E2 was added to the overlay medium. When E2 was omitted, a maximum of 50% inhibition was achieved. This indicated that after the virus and E2 were removed from the cells,
infection still occurred, by virus particles which were still bound to the cell surface. Treatment with 100 microg/ml E(rns) released these particles from the cell surface. Furthermore, E(rns) bound irreversibly to the surface of cells susceptible or unsusceptible to
pestivirus infection and cell-to-cell spread of CSFV was completely inhibited by E2 but not by E(rns). These results demonstrated that E(rns) and E2 interacted with different
cell surface receptors. Inhibition of BVDV
infection of porcine and bovine cells by CSFV E2 suggested that CSFV E2 and BVDV E2 share an identical receptor. BVDV strain 5250 isolated from pigs was efficiently inhibited by CSFV E(rns), whereas several BVDV strains isolated from cattle were not, suggesting that the conformation of E(rns) plays a role in host tropism.