Reliable confirmation of antibodies to bovine respiratory syncytial virus (BRSV) by enzyme-linked immunosorbent assay using BRSV nucleocapsid protein expressed in insect cells.

The nucleocapsid (N) protein of bovine respiratory syncytial virus (BRSV) in the baculovirus expression system was evaluated as a source of antigen in an enzyme-linked immunosorbent assay (ELISA) for the detection of respiratory syncytial virus (RSV) antibodies. The recombinant N protein was purified from infected-cell extracts by sucrose gradient centrifugation and used in the ELISA for the detection of antibodies to various RSV strains. The ELISA was compared with the virus neutralization (VN) test for determining BRSV antibodies in 10 consecutive serum samples from four calves vaccinated with a live modified BRSV vaccine and from two nonvaccinated control calves. The ELISA compared favorably with the VN test for detecting serological responses. All serum samples which were positive in the VN test were also positive in the ELISA. None of the serum samples collected from the two nonvaccinated calves reacted in the ELISA. To determine the usefulness of the ELISA for epidemiological studies, 58 cattle serum samples were tested in the ELISA and the VN test. Approximately 94% (42 of 45) of field serum samples which were positive in the ELISA were also positive in the VN test. No case was found in which the ELISA result was negative and the VN test result was positive. Thirteen of the serum samples were negative in both methods. Our results indicate that the ELISA with the baculovirus-expressed N protein as an antigen is an efficient, sensitive, and specific method for detecting serum antibodies to RSV.