Antibody to the 32K structural protein of infectious bursal disease virus neutralizes viral infectivity in vitro and confers protection on young chickens.

Chicken sera containing IgG antibodies specific for the 32 000 (32K) mol. wt. structural polypeptide of infectious bursal disease (IBD) virus, as assessed by Western blotting, neutralized the in vitro infectivity of tissue culture-adapted IBD virus. When injected into young chickens, the serum passively protected them from challenge with pathogenic IBD virus. Chickens immunized with the 32K structural polypeptide of IBD virus, prepared by electroelution from SDS-PAGE gels, produced antibody detectable by ELISA and the virus neutralization assay, while chickens immunized with the 37K or 41.5K viral polypeptides synthesized antibody detectable by ELISA, but only very low levels of virus-neutralizing antibody. The immunoglobulin fraction of sera obtained from chickens immunized with the 32K polypeptide, but not the 41.5K polypeptide, passively protected chickens from infection with IBD virus. It is concluded that the 32K polypeptide is a major protective immunogen of IBD virus.