Evaluation of a nucleoprotein-based enzyme-linked immunosorbent assay for the detection of antibodies against infectious bronchitis virus

As an immunogen of the coronavirus, the nucleoprotein (N) is a potential antigen for the serological monitoringof infectious bronchitis virus (IBV). In this report, recombinant N protein from the Beaudette strain of IBV wasproduced and purified from Eschevichia coli as well as Sf9 (insect) cells, and used for the coating of enzymelinkedimmunosorbent assay (ELISA) plates. The N protein produced in Sf9 cells was phosphorylated whereasN protein from E. coli was not. Our data indicated that N protein purified from E. coli was more sensitive toanti-IBV serum than the protein from Sf9 cells. The recombinant N protein did not react with the antisera toother avian pathogens, implying that it was specific in the recognition of IBV antibodies. In addition, the datafrom the detection of field samples and IBV strains indicated that using the recombinant protein as coatingantigen could achieve an equivalent performance to an ELISA kit based on infected material extracts as asource of antigen@). ELISAs based on recombinant proteins are safe (no live virus), clean (only virus antigensare present), specific (single proteins can be used) and rapid (to respond to new viral strains and strains thatcannot necessarily be easily cultured).