E2 Glycoprotein of BVDV 1u Circulating in Qinghai Yaks: A Candidate for Serological Surveillance and Subunit-Vaccine Development With Neutralizing-Antibody Evaluation in Yaks.

Bovine viral diarrhea (BVD) virus (BVDV) is a globally distributed Pestivirus that severely affects the cattle industry, and Pestivirus bovis (formerly BVDV-1), subgenotype 1u is the predominant subtype circulating in yak populations of Qinghai, China. This study aimed to express the N-terminal fragment (amino acids 1-200) of the E2 glycoprotein of yak-origin BVDV 1u and identify its antigenic and immunogenic properties for potential application in serological surveillance and subunit-vaccine development. Using the purified truncated E2 antigen, an indirect ELISA was established for detection of BVDV-specific antibodies from yak sera. Immunogenicity for the recombinant protein was evaluated in BALB/c mice using Freund's adjuvant and Montanide ISA 201 VG by determining CD4+/CD8+ T-cell activation and the secretion of IFN-γ, TNF-α, and IL-6. Immunization was further performed in BVDV-naïve yak calves to assess BVDV 1u-specific neutralizing antibody responses. The established indirect ELISA achieved a diagnostic sensitivity of 99.0 % and specificity of 97.4 %, without detectable cross-reactivity against other common bovine pathogens; screening of 377 field yak serum samples yielded a BVDV seroprevalence of 21.48 %. Both adjuvant formulations elicited high antibody levels in mice, yet Montanide ISA 201 VG induced stronger T-cell activation and proinflammatory cytokine production. In immunized yak calves, the E2-ISA 201 vaccine antigen elicited BVDV 1u-specific neutralizing antibody titers that showed trends similar to those induced by commercial inactivated vaccines. Our findings demonstrate that the truncated BVDV 1u E2 serves as a feasible antigen for serological surveillance and a candidate subunit-vaccine development for BVDV. This study provides reliable experimental evidence for regional BVDV prevention and control in yak-rearing areas of China.