Novel Linear B Cell Epitopes of ASFV p54: Screening and Fine-Scale Mapping

African swine fever (ASF) is an acute, febrile, and lethal pig disease induced by the African swine fever virus (ASFV). In the absence of an effective vaccine, early diagnosis is essential for the prevention and control of ASF disease. The p54 protein is important for ASFV diagnosis and vaccine design. In this study, ASFV p54 protein was constructed, expressed, purified, and used to generate three mAbs, namely 9A3, 5H2, and 2G6. Epitope mapping was performed using alanine mutants; the minimal linear epitope recognized by 9A3 and 5H2 was 56KKKAAAI62, and the minimal linear epitope recognized by 2G6 was 108TNRPATN114. Of these, 56KKKAAAI62 was identified as a new linear epitope for the first time. The epitopes were highly conserved in at least genotypes I and II. Alanine-scanning mutagenesis further revealed that residues 56K, 57K, 60A, 61A, 62L, 108T, 110R, 111P, 113T, and 114N were the core sites involved in antibody recognition. Overall, the mAbs and epitopes of the p54 protein identified in this study provide theoretical support for the development of ASFV vaccines based on the B cell epitope, the development of ASFV therapeutic antibody drugs, and the development of ASFV diagnostic tools.