Identification of two new antigen epitopes on the putative capsid protein encoded by torque teno sus virus type 1 ORF1

Torque teno sus virus type 1 (TTSuV1) ORF1 is considered to encode the viral capsid (Cap) protein, which is crucial for the induction of TTSuV1-specific antibodies and protective immunity in the host. Eight monoclonal antibodies (mAbs) directed against the Cap protein were generated and biologically characterized. The immunoreactivity of the Cap protein expressed in transfected 293T cells for these mAbs was determined with an immunoperoxidase monolayer assay. The antigen epitopes of the Cap protein were mapped using these mAbs and truncated Cap proteins expressed in Escherichia coli. Fine epitope mapping was then performed with a panel of synthesized polypeptides. All the mAbs reacted with the Cap protein C fragment expressed in E. coli. One antigenic epitope of the Cap protein, which reacted with seven mAbs, had the polypeptide sequence 536HPKYAGQGGGYTT548, whereas another epitope recognized by the 1E9 mAb had the polypeptide sequence 549EIGHQGITAASLR561. It is interesting that the two new epitopes are adjacent, but mutually independent. This study should facilitate further investigation of the antigenic differences and enable the differential diagnosis of the virus.