Preparation of Monoclonal Antibodies Against the NSP7 Protein of Porcine Reproductive and Respiratory Syndrome Virus and the Establishment of a Blocking ELISA Detection Method

Porcine reproductive and respiratory syndrome (PRRS) remains an important infectious disease of pigs, and serological assays are widely used to monitor antibody responses to the PRRS virus (PRRSV). This study aimed to develop and evaluate a blocking enzyme-linked immunosorbent assay (bELISA) targeting PRRSV nonstructural protein 7 (NSP7). Recombinant NSP7 was expressed in Escherichia coli, purified, and used to generate monoclonal antibodies. Monoclonal antibody 5E2 was selected to establish the bELISA. A cutoff of 40% inhibition was determined via receiver operating characteristic analysis of 198 serum samples classified using a commercial ELISA. No cross-reactivity was detected with the tested sera positive for pseudorabies virus (PRV), African swine fever virus (ASFV), classical swine fever virus (CSFV), or porcine circovirus type 2 (PCV2). Intra-assay and interassay coefficients of variation were below 10%, and agreement with the commercial ELISA was 95.74% among 94 clinical serum samples. The assay detected antibody responses in experimentally infected pigs. Samples from pigs given the tested inactivated vaccine were negative, whereas those from pigs given the tested live attenuated vaccine were positive. These findings support the potential of the NSP7-based bELISA as a complementary tool for PRRSV serology. The assay does not distinguish natural infection from live attenuated vaccination, and its performance across PRRSV genotypes requires further validation.