Antigenic subtyping and epitopes' competition analysis of porcine circovirus type 2 using monoclonal antibodies

Porcine circovirus type 2 (PCV2) strains have been classified into two major genotypes (PCV2a and PCV2b) and 8 genetic clusters: PCV2b-1A to PCV2b-1C and PCV2a-2A to PCV2a-2E. To date, no studies have been performed to antigenically subtype PCV2 strains enclosing eight PCV2 clusters. The present study aimed to antigenically subtype PCV2 and perform epitopes' competition analysis using monoclonal antibodies (mAbs). Fourteen PCV2 strains representative for eight clusters were tested with 20 mAbs (fifteen of them were generated against PCV2a strain Stoon-1010 and 5 of them against PCV2b strain 1147) in immunoperoxidase monolayer assays. Four mAbs reacted to all 14 PCV2 strains and one mAb reacted with all strains except for a PCV2a-2C strain. One mAb reacted with all PCV2a strains, except for a PCV2a-2C strain and one mAb reacted with all PCV2b strains, except for a PCV2b-1C strain. Nine mAbs reacted with the strains of PCV2b-1A/1B, PCV2a-2A and PCV2a-2E. Three mAbs only reacted with the strains of PCV2a-2A and PCV2a-2E. One mAb reacted specifically with the strains of PCV2b-1A/1B. This suggests that discrete antigenic differences exist between different PCV2 genetic clusters and that these clusters can be discriminated by the use of a panel of universal and cluster-specific mAbs. Six mAbs were selected for cross-competition analysis by a competitive ELISA using PCV2 strain Stoon-1010. Six overlapping epitopes were identified on the PCV2 capsid protein. The universal mAbs recognized larger epitopes than the cluster-specific mAbs. These findings are helpful in the development of diagnostic tests and new generation vaccines against PCV2.