Isolation of a precipitating glycoprotein antigen from cell cultures persistently infected with bovine leukemia virus

A procedure was developed to isolate a glycoprotein with precipitating antigen activity from fluids from fetal lamb kidney cell cultures persistently infected with bovine leukemia virus (BLV). The antigen was precipitated by ammonium sulfate and subjected to affinity chromatography on concanavalin A Sepharose. The glycoprotein was eluted with alpha-methyl-D-mannoside and was further purified by gel filtration over Sephadex G-100. Antigen activity was determined by agar gel immunodiffusion (AGID) reactions with serum from cattle infected with the virus. The major portion of the AGID activity was eluted from the Sephadex G-100 in the 60,000-dalton elution region. In some experiments, identical AGID activity was also found in the 18,000-dalton elution region. The larger protein was discovered to have a molecular weight of 58,000 daltons by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its designation as a glycoprotein was confirmed by carbohydrate-positive staining. The isolated BLV glycoprotein antigen did not contain ovine or bovine proteins as indicated by gel immunodiffusion.