Development and characterization of monoclonal antibody against the critical loop structure of african swine fever virus P72 protein.

African swine fever (ASF) is a highly infectious and lethal viral disease caused by the African swine fever virus (ASFV). The four prominent loop structures on the surface of the primary structural protein P72 are considered to be key protective epitopes. In this study, the four critical loops (ER1-4) of the ASFV p72 protein were individually fused to hepatitis B virus core particles (HBc) and self-assembled into nanoparticles to preserve the natural conformation of the loop structure and enhance its immunogenicity. Then, four recombinant proteins were obtained in E. coli expression system and monoclonal antibodies (mAbs) were developed and characterized. All 10 mAbs obtained were able to react with P72 protein and ASFV with potencies up to 1:204 800. Amino acids 250-274, 279-299 and 507-517 of the P72 protein were identified as linear epitopes and highly conserved. The mAb 4G8 showed the highest inhibition rate of 84% against ASFV positive sera. Importantly, neutralization experiments illustrated that mAb 4G8 has a 67% inhibition rate, indicating that its corresponding epitopes are potential candidates for ASFV vaccine. In conclusion, highly immunogenic nanoparticles of the ASFV P72 key loop were constructed to induce the production of highly effective mAbs and clarify their epitope information for the diagnosis and prevention of ASFV.