Characterization by Western blotting of the immunogens of infectious bursal disease virus.

The Australian isolate of infectious bursal disease (IBD) virus (002/73) was purified from infected bursae by rate-zonal and density-equilibrium centrifugation and characterized by polyacrylamide gel electrophoresis. Two major polypeptides having approximate mol. wt. of 32 000 (32K) and 37K and three other polypeptides of approximate mol. wt. 29K, 41.5K and 91.5K were present in all preparations of virus having a buoyant density of 1.33 g/ml. Western blotting of the polypeptides of IBD virus showed that the initial antibody response of chickens infected with live virus or injected with an inactivated oil-emulsion vaccine was directed primarily towards the 32K polypeptide. Only sera obtained late in the response to live virus or following hyperimmunization contained antibodies recognizing the 29K, 37K and 41.5K polypeptides. An antibody response to the 91.5K polypeptide was not detected routinely by this technique. It was concluded that the 32K polypeptide is a major immunogen of IBD virus.