Topographical analysis of tumor-associated antigens on bovine leukemia virus-induced bovine lymphosarcoma

Tumor-associated antigens (TAAs) expressed on tumor cells from cattle with enzootic bovine leukosis were divided into three groups by using 13 monoclonal antibodies: common TAA; partially common TAA; and individually distinct TAA. TAA was extracted from tumor cells and purified by ion exchange chromatography on diethylaminoethyl-cellulose and isoelectric focusing. The common TAA, which was detected on all tumors tested, was eluted with 0.6 M KCl in ion exchange chromatography on diethylaminoethyl-cellulose, and the isoelectric point of the antigen was 6.8. The partially common TAA, which was detected on some (but not all) of the tumors tested, was eluted with 0.4 to 0.8 M KCl, and the isoelectric points of the antigen were 5.3, 5.8, and 6.4. The individually distinct TAA was present in the fractions eluted with 0.4 to 0.8 M KCl, and the isoelectric point of the antigen was 5.5. Results of competitive binding assay and Western blot analysis showed that the common TAA was a polypeptide with a molecular weight of 74,000; that it has at least two independent antigenic regions; that the partially common and individually distinct TAAs were a polypeptide with a molecular weight of 64,000; and that the antigenic determinants on the common TAA, partially common TAA, and individually distinct TAA existed independently from each other.