Sialic acids on the surface of caprine arthritis-encephalitis virus define the biological properties of the virus.

The lentivirus caprine arthritis-encephalitis virus (CAEV) is a pathogen of goats. It is transmitted in milk and causes a persistent infection in goats, which often fail to produce neutralizing antibodies to the virus. Native CAEV particles are remarkably resistant to digestion with proteinase K and are neutralized extremely slowly by immune sera. Our studies showed that the virus particles are heavily sialylated. Studies with highly specific sialyltransferase enzymes identified penultimate carbohydrate linkages typical of O- and N-linked oligosaccharides on the virus and suggested that the virus may be more heavily sialylated on O-linked than on N-linked oligosaccharides. Removal of sialic acids from the virus by neuraminidase treatment did not reduce infectivity of the particles. However, desialylation rendered the virus more susceptible to proteolysis by proteinase K. Desialylation also enhanced the kinetics of neutralization of the virus by goat antibodies. These results suggest that the carbohydrates on the viral surface are important both in protecting viral proteins from digestion by proteases and in protecting the virus from rapid neutralization by antibodies.