Development of a Highly Specific Monoclonal Antibody-Based Sandwich ELISA for Rapid Detection of Porcine Circovirus...

Porcine circovirus type 3 (PCV3), initially identified in the United States in 2016, is associated with multisystemic inflammation, myocarditis, reproductive failure in sows, and growth retardation in piglets, posing a significant economic threat to the swine industry. In this study, prokaryotic-expressed recombinant PCV3 Cap protein was used to immunize mice and rabbits. A monoclonal antibody (mAb 4G1) was generated through hybridoma technology, targeting a novel linear epitope (³⁷DYYDKK⁴²) within the first β-sheet of the Cap structure. This epitope exhibits high conservation (99.35%, 1239/1247) based on sequence alignment analysis, and residues 39 and 42 are critical residues affecting mAb binding. Subsequently, using rabbit polyclonal antibody (pAb) as the capture antibody and mAb 4G1 as the detection antibody, a double antibody sandwich ELISA (DAS-ELISA) method was developed. The assay demonstrates a cut-off value of 0.271, a detection limit for positive pig serum is 1:800, and shows no cross-reactivity with other swine pathogens. Intra- and inter-assay coefficients of variation were <10%, with a linear detection range for Cap protein down to 3.4 ng/mL. The coincidence rate between the DAS-ELISA and qPCR was 93.33% (70/75) for PCV3 detection in serum, with a kappa value of 0.837. This study establishes a simple, sensitive, and operationally efficient DAS-ELISA and provides a reference for monitoring PCV3 infection in swine herds.