Expression of the porcine circovirus type 2 capsid protein subunits and application to an indirect ELISA

Porcine circovirus type 2 (PCV2) is considered to be associated with post-weaning multisystemic wasting syndrome (PMWS), which is a newly emerged economically important swine disease. The entire coding region of open reading frame 2 (ORF2), encoding the viral capsid protein (Cap), of PCV2 was cloned and sequenced from the clinical specimen obtained from PMWS-affected piglets. Six recombinant subunits, A-F, spanning the defined regions of Cap were produced by E. coli expression system and used as antigens for testing their reactivities with swine sera in the indirect ELISA. The recombinant Cap subunit-based ELISA was evaluated by examining a panel of 12 PCV2-negative and 26 PCV2-positive sera. When the positive/negative cut-off value was set at the mean value of negative sera plus 3 standard deviations, all subunits-based ELISA demonstrated 100% specificities. The N-terminal subunits, A and B, revealed poor reactivity with positive swine sera, whereas, greater immunoreactivity was observed for the C-terminal subunits of which subunits C and D demonstrated good sensitivities of 96.2% and 84.6%, respectively. The recombinant Cap subunits possessing defined antigenicity are easy to produce and the subunit-based ELISA was developed with a high specificity and sensitivity that may provide a useful method for routine serodiagnosis of PCV2 infection.