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 (BR SV) in the baculovirus expression system was evaluated as a source of antigen in an enzyme-linked immunosorbent assay (ELISA) for the detect ion of respiratory syncytial vims (RSV) antibodies. The recombinant N protein was purified from infected-cell extracts by sucrose gradient c entrifugation and used in the ELISA for the detection of antibodies to various RSV strains. The ELISA was compared with the virus neutraliza tion (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 favorab ly with the VN test for detecting serological responses. All serum sam ples which were positive in the VN test were also positive in the ELIS A. None of the serum samples collected from the two nonvaccinated calv es reacted in the ELISA. To determine the usefulness of the ELISA for epidemiological studies, 58 cattle serum samples were tested in the EL ISA and the VN test. Approximately 94% (42 of 45) of field serum sampl es 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 t est result was positive. Thirteen of the serum samples were negative i n both methods. Our results indicate that the ELISA with the baculovir us-expressed N protein as an antigen is an efficient, sensitive, and s pecific method for detecting serum antibodies to RSV.