The genomic region coding for the antigenic structure responsible for the induction of neutralizing antibodies was localized in the central variable region of the VP2 gene by comparing the nucleotide sequence of five escape mutants derived from the standard infectious bursal disease virus strain Cu-1. Exchange of a single amino acid at one of the prominent hydrophilic parts of this region proved to be sufficient for altering the neutralizing properties. The reactivity of neutralizing antibodies with peptides expressed in vitro encompassing both hydrophilic areas suggests that the entire variable region is engaged in the formation of this conformationdependent antigenic site. VP2-specific, non-neutralizing monoclonal antibodies directed against the sequencedependent epitope of the serotype I strain Cu-1 and the serotype II strain 23/82 cross-reacted with peptides located towards the carboxy terminus of VP2; no reaction occurred with peptides derived from the aminoterminal side adjacent to the variable region.

No abstract