A nonviral, virus strain-specific antigen expressed on rat cells transformed by avian sarcoma virus

Five of six rat sarcomas, induced by the Schmidt-Ruppin (SR) strain of avian tumor virus, expressed a Mr 60,000 tumor cell surface antigen (TSA), immunoprecipitable from non-ionic detergent extracts. Expression of the antigen was exclusive to rat cells transformed by the SR virus strain. Moreover, expression of TSA appeared restricted by cell type. The five TSA-positive SR-transformed rat cell lines tested were apparently of fibroblastic origin, but cultured rat cerebral endothelial cells (RCE-T1), transformed by SR virus, showed no expression of TSA. However, the antigen emerged on cultured tumors obtained after histoincompatible transplantation of these cells into newborn rats of another strain (tumor digest cells). Investigation of TSA for immunological relationship to viral structural antigens and the src gene product indicated that the TSA is distinct from any of these and more probably derives from a virus-directed alteration in a host molecule.