Characterization of the Antigenicity and Immunogenicity of the Escherichia Coli Produced RNase Domain of the Classical Swine Fever Virus Glycoprotein E

E^rns is a highly glycosylated envelope protein of classical swine fever virus (CSFV) with RNase activity. E^rns can induce neutralizing antibodies and provide immune protection against CSFV infection. In this study, the RNase domain of the E^rns was produced in Escherichia coli. Its reactivity with CSFV-positive sera and its ability to induce antibodies and to provide protective immunity were then investigated. The serological tests showed that the prokaryotically expressed RNase domain of the E^rns retained its antigenicity and induced high titers of humoral responses. However, only partial protection and a limited amount of neutralizing antibodies were demonstrated by an in vitro neutralization test and an immunization/challenge test. The results suggest that other essential factors rather than simply enhancing the immunogenicity of E^rns should be taken into consideration when E^rns is enrolled as one of the components of a candidate vaccine.