Identification of three distinct antigenic sites in parapoxviruses

Monoclonal antibodies (Mabs) were generated in BALB/c mice immunized with gradient-purified particles, envelopes and cores of intracellular mature orf virus D-1701. Three distinct antigenic sites were identified in this virus strain. Their topographical relationships was determined by pairwise epitope specificity studies in competition ELISAs. One MAb (class IgM) neutralized virus infectivity. Four μg/ml purified IgM gave a 50% reduction of 100 PFU of orf virus D-1701. As shown by immunogold electron microscopy (ELMI), all MAbs reacted with epitopes localized on the virus surface. Western blotting analysis demonstrated that two proteins of a Mr of 39kDa and 22kDa were the main targets for the Mabs. Cross-reactivity studies of several parapoxviruses (PPV) differentiated stomatitis papulosa virus strains from orf virus and milker’s node virus (MNV) by a missing antigenic site.