Immunogenicity of subunit vaccine of E2 protein against atypical porcine pestivirus in pigs

Introduction: An atypical porcine pestivirus (APPV) causes congenital tremor (CT) type A-II in piglets and has caused considerable financial losses to the pig industry worldwide. This study aimed to develop an effective vaccine candidate against APPV. Methods: We constructed a prokaryotic expression system for the APPV E2 protein in Escherichia coli. The immunogenicity of the APPV E2 subunit vaccine, formulated with three different adjuvants (ISA 201VG, IMS 1313VG, and Gel 02), was evaluated in piglets. Assessment was based on E2-specific antibody levels measured by an in-house enzyme-linked immunosorbent assay (ELISA) and protection against an APPV challenge. Successful expression of the E2 protein was confirmed by western blot analysis. Results: The E2 protein was successfully expressed, and an E2-ELISA detection method was established. Vaccinated piglets mounted virus-specific IgG responses. The E2 protein emulsified with ISA 201VG and Gel 02 adjuvants induced significantly higher antibody levels than the formulation with IMS 1313VG adjuvant. The vaccine with ISA 201VG adjuvant yielded the highest antibody levels and provided protection against APPV infection. Histopathological examination confirmed normal organ morphology in vaccinated pigs, whereas the control group displayed significant pathological alterations. Discussion: The results demonstrate that the Escherichia coli-expressed E2 protein elicits an immune response in pigs. The E2 subunit vaccine is a potential candidate for preventing APPV infection, and ISA 201VG and Gel 02 adjuvants are suitable candidate adjuvants for vaccine preparation. This study provides a foundation for further APPV vaccine research.