Identification of novel monoclonal antibodies specific for the conserved epitopes in the E2 protein of genotype 2 classical swine fever virus: implication for differential diagnosis

Since the last century, the spread of the genotype 2 classical swine fever virus (CSFV) has caused significant issues for the pig breeding industries. Ideal strategies for controlling CSFV include vaccination and keeping farms free of CSFV. For vaccination, several attenuated CSFV viruses originating from genotype 1 are widely used; for the latter, accurate diagnosis is required for detection of the CSFV infection. Nucleic acid testing for CSFV usually uses tonsil samples, which requires an inconvenient sampling operation that injures pigs. Commercial serological tests for CSFV antibodies or antigens are unable to distinguish the genotype for originating virus. In this study, 20 mAbs were developed from the mice hybridoma cells. Four of the mAbs were identified to have the ability to only recognize the peptides derived from sub-genotype 2.1 strain, and two of them, MM1 and MM5, were further studied to identify critical binding sites (epitopes) on the E2 protein of CSFV. A total of 353 genotype 2 collections were made worldwide in GeneBank, 90.9% of which contained MM1 or MM5 epitopes. Moreover, 95.1% of sub-genotype 2.1 isolations contained MM5 epitope. Therefore, MM1 and MM5 have the potential to be developed as a diagnostic tool for detection of genotype 2 virus antigen by indirect ELISA or antibodies by competitive ELISA.