An indirect enzyme-linked immunosorbent assay using a recombinant truncated capsid protein of Porcine circovirus-2

Abstract

Porcine circovirus-2 (PCV-2) serology is commonly used for PCV-2 herd status determination and optimal timing of PCV-2 vaccination programs. The objectives of the current study were to develop an in-house indirect enzyme-linked immunosorbent assay (ELISA) using a recombinant nuclear localization signal truncated capsid (rntCap) protein expressed in an Escherichia coli system and to determine the diagnostic performance of the developed rntCap indirect ELISA in comparison with immunoperoxidase monolayer assays (IPMAs). Based on a receiver operating characteristic (ROC) curve analysis of the rntCap indirect ELISA (n = 90), an optimum cutoff optical density (OD) of 0.330 was determined, which resulted in diagnostic sensitivity, diagnostic specificity, and accuracy of 98.33%, 93.33%, and 96.67%, respectively. Average OD values of the positive (n = 8) and negative sera (n = 8) tested by either purified glutathione-S-transferase (GST) protein or the rntCap protein as the coating antigen revealed that the mean OD values tested by the rntCap indirect ELISA were significantly different from using GST alone (P < 0.005). The correlation between the established rntCap indirect ELISA and the IPMA results demonstrated as the linear regression (Spearman correlation coefficient = 0.772, P < 0.005) indicated that the OD ratio obtained from the rntCap indirect ELISA could be used to predict the levels of the IPMA titers. More samples are needed for enhancing the diagnostic sensitivity, specificity and accuracy. In conclusion, the establishment of the rntCap indirect ELISA could be used as a serodiagnostic assay for large-scale detection of PCV-2 antibodies in swine and has the capability to be produced commercially for routine use in diagnostic laboratories.