ABSTRACT
An enzyme-linked immunosorbent assay (ELISA) using a fragment of the infectious bursal disease virus (IBDV) VP2 gene expressed in baculovirus was developed. A 944-bp portion of the VP2 gene from the Del-A strain of IBDV was ligated into the pAc360 transfer vector and transfected into baculovirus, Recombinant baculoviruses were identified by dot blot hybridization. The recombinant baculovirus 9A5 expressed a 57-kDa VP2 fusion protein, which was immunoprecipitated. This baculovirus-expressed VP2 was used as an antigen in an ELISA (Ohio State University [OSU]-ELISA). Titers of sera from specific-pathogen-free chickens infected with different strains of IBDV in our laboratory were determined by the OSU-ELISA, commercial ELISAs, and a virus neutralization assay. The results indicate that all sera from the specific-pathogen-free chickens infected with IBDV strains contained high titers of neutralizing antibodies. Each of these antisera also tested positive with the commercial ELISA kits. The OSU-ELISA did not detect antibodies to all strains of IBDV tested. This ELISA detected antibodies to the antigenically similar Delaware variant strains Del-A, Del-E, and GLS but did not detect or detected very poorly antibodies to antigenically heterologous classic IBDV strains STC, D78, and BVM. Although the antiserum to the IN strain of IBDV contained a virus-neutralizing antibody titer, the OSU-ELISA did not detect antibodies in this serum, suggesting IN is antigenically heterologous to Del-A. Titers to the IN strain were detected with the commercial ELISA kits. The OSU-ELISA detected antibodies to the SAL strain, suggesting this virus is antigenically similar to Del-A, which is supported by previously reported vaccination and challenge studies. In conclusion, the OSU-ELISA could be used to detect antibodies to a subgroup of IBDV strains, while commercially available ELISA kits detected antibodies to all the antigenic subtypes of IBDV tested.
