Indirect ELISA based on truncated N protein for detecting Porcine deltacoronavirus-specific IgA antibodies

Porcine deltacoronavirus (PDCoV) is a porcine intestinal coronavirus that causes severe diarrhea in piglets and is extremely harmful to the pig industry. Rapid and accurate detection of antibody levels is necessary for effective prevention of the disease. We previously demonstrated that PDCoV and porcine epidemic diarrhea (PEDV) N protein have serum cross-reactivity. Therefore, in this study, we first constructed and expressed five recombinant truncated PDCoVN proteins ( N1-N5). Through the reactivity of these proteins to porcine PDCoV positive serum and porcine PEDV positive serum and the established ELISA method, the truncated proteins with less cross-reaction between PDCoV and PEDV serum were selected, and these recombinant truncated N proteins and PDCoVS1 proteins were used to establish an indirect enzyme-linked immunosorbent assay ( ELISA) for IgA detection. The ELISAs with S1 protein or truncated protein N3（aa1-122） as the coating antigen had the highest sensitivity and specificity(S1-ELISA: sensitivity 75%, specificity 86%; N3-ELISA: sensitivity 75%, specificity 86%). The two methods showed > 90% consistency in detecting anti-PDCoV-specific IgA levels in a total of 63 colostrum and serum samples. Although S1-ELISA and N3-ELISA have the same sensitivity and specificity, the N protein is more stable than the S protein in coronavirus. Our ELISA therefore can be applied to detect anti-PDCoV specific IgA after natural infection or vaccination. Our findings provide an important basis for antigen selection in the future establishment of a specific clinical rapid diagnosis method for PDCoV.