Lentiviral-mediated delivery of classical swine fever virus Erns gene into porcine kidney-15 cells for production of recombinant ELISA diagnostic antigen

Classical swine fever virus (CSFV), a member of the Pestivirus genus within the Flaviviridae family causes contagious fatal disease in swine. Antibodies against E2, Erns and NS3 proteins of virus can be detected in infected animals. Development of an ELISA coating antigen to improve the sensitivity of detecting Erns-specific antibodies in pig sera is always desirable for diagnosis as well as for differentiation of infected from vaccinated animals. In present study, a lentivirus-based gene delivery system was used to develop a stable PK-15 cell line expressing Erns (PK-Erns) for production of diagnostic antigen. The Lenti-Erns virus was purified from the supernatant of co-transfected 293LTV cells and used to transduce PK-15 cells. The homogenous PK-Erns cell line was produced by single cell cloning by monitoring eGFP expression. The Erns gene in the genomic DNA and RNA transcripts in total RNA isolated from PK-Erns cells were detected by PCR and RT-PCR, respectively. Expression of 45 kDa Erns glycoprotein was detected in western blot using CSFV-specific hyperimmune sera. The use of PK-Erns cell lysate as antigen in serial dilution and single dilution ELISAs with known positive and negative pig sera was investigated. The PK-Erns ELISA revealed sensitivity equivalent to commercial HerdChek ELISA kit. The sensitivity, specificity and accuracy of the PK-Erns ELISA was 95%, 100% and 96.66%, respectively compared to ELISA using purified CSFV as coating antigen. When field pig sera (n = 69) were tested in PK-Erns ELISA, a significant correlation between the titers from serial dilution and single dilution ELISA was observed. This indicated that PK-Erns cell line can serve as continuous source of ELISA diagnostic antigen for detection of CSFV-specific antibodies in pig sera.