Generation and immunogenicity analysis of recombinant classical swine fever virus glycoprotein E2 and E(rns) expressed in baculovirus expression system

Classical swine fever (CSF) caused by the classical swine fever virus (CSFV) is a highly contagious swine disease resulting in large economical losses worldwide. The viral envelope glycoprotein E2 and E(rns) are major targets for eliciting antibodies against CSFV in infected animals. In this report, the glycoprotein E2 and E(rns) were expressed using the baculovirus system and their protective immunity in rabbits were tested. Twenty CSFV seronegative rabbits were randomly divided into five groups. Each rabbit was intramuscularly immunized with CSFV-E2, CSFV-E(rns), or their combination (CSFV-E2 + E(rns)). Besides, a commercial CSFV vaccine (C-strain) and PBS were used as positive or negative controls, respectively. Four weeks after the second immunization, all the rabbits were challenged with 100 RID(50) of CSFV C-strain. High levels of CSFV E2-specific antibody, neutralizing antibody and cellular immune responses to CSFV were elicited in the rabbits inoculated with C-strain, CSFV-E2, and CSFV-E2 + E(rns). And the rabbits inoculated with the three vaccines received complete protection against CSFV C-strain. However, no neutralizing antibody was detected in the E(rns) vaccinated rabbits and the rabbits exhibited fever typical of CSFV, suggesting the E(rns) alone is not able to induce a protective immune response. Taken together, while the E(rns) could not confer protection against CSFV, E2 and E2 + E(rns) could not only elicit humoral and cell-mediated immune responses but also confer complete protection against CSFV C-strain in rabbits.