Abstract
The A antigen, detectable in cultures of Marek's Disease Virus (MDV) grown in suitable cells, was isolated, concentrated, purified and characterised. Virulent virus was propagated in cultures of both chick kidney and duck embryo fibroblast, the supernatants harvested, and A antigen was extracted by various means such as salt precipitation and membrane ultrafiltration. A antigen was also prepared from skins and feathers of chickens infected with MDV, and it was found that this material was immunologically identical with that obtained from cell culture fluids. In order to monitor concentration and purification procedures, an assay technique for the antigen was devised based on single (radial) immunodiffusion. The antigen was found to be a protein of relatively low molecular weight (30,000 to 60,000 daltons), stable to marked changes in pH and temperature, and to be an entity quite distinct from the virus particle. It was also found that the herpesvirus of turkeys (HVT) induced the production of A antigen in cultures of chick embryo fibroblast, and a serological test was devised which distinguished this type of infection from that caused by MDV. The possible functions of the A antigen in virus/cell relationships, and its counterpart in other herpesviruses, are discussed.