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.