COMPARISON OF NEUTRALIZING EPITOPES AMONG INFECTIOUS BURSAL DISEASE VIRUSES USING RADIOIMMUNOPRECIPITATION

Monoclonal antibodies (MAbs) were used to analyze the relatedness of n eutralizing epitopes of infectious bursal disease virus (IBDV) strains . The MAb B69 neutralized the homologous D78 virus but not the MD and Del-A variant strains of IBDV. MAbs 33E8 and R63 neutralized D78 and v ariant strains MD and Del-A. A cDNA clone consisting of a 1000-base-pa ir fragment of the VP2 gene from the Del-A IBDV strain was translated using an in vitro system. Six peptides were observed following transla tion, which represented a full-length product (35.5 kilodaltons) and f ive truncated products. The translated peptides were radioimmunoprecip itated using MAbs B69, 33B8, and R63. Only MAb R63 immunoprecipitate t he in vitro translation products from Del-A. MAbs B69 and 33E8 did not immunoprecipitate the in vitro-translated VP2 peptides. The D78 and D el-A viruses were radiolabeled in vivo using S-35-methionine. Proteins from these viruses were examined by radioimmunoprecipitation with MAb s B69, 33B8, and R63. Although the background made interpretation of t he results difficult for MAb B69, this MAb clearly immunoprecipitated VP2 of D78. MAb 33B8 immunoprecipitated the D78 VP3 protein, and R63 i mmunoprecipitated the VP2 protein. MAb R63 also immunoprecipitated the S-35-methionine-labeled VP2 protein from Del-A. It was concluded that the neutralizing epitope represented by 33B8 was located on VP3 and t hat the epitope represented by R63 is located on both classic and vari ant viruses in the region of VP2 that is generally thought to contain sequence variability among IBDV strains.