Detection and biochemical characterization of antigens in human leukemic sera that cross-react with primate C-type viral proteins (Mr 30,000).

Antigens have been detected in 35 to 40% of sera from patients with leukemia that cross-react with the Mr 30,000 core proteins (p30) of baboon endogenous virus (BaEV) and/or of simian sarcoma-simian sarcoma-associated virus (SiSV) in a solid-phase enzyme immunoassay using anti-SiSV p30 and anti-BaEV p30 antisera. These antigens could not be found in sera from nonleukemic persons. Fetal calf serum; normal chicken, goat, rabbit, and rhesus sera; and normal human serum components like albumin, immunoglobulins, and transferrin did not react with the anti-SiSV p30 and anti-BaEV p30 antisera. The reactivity in the leukemic sera was abolished by treatment with protease, but not with glycosidases. The antigens purified by immunoaffinity chromatography showed essentially one band with an apparent molecular weight of 70,000 on sodium dodecyl sulfate: polyacrylamide gel electrophoresis. In competition enzyme-linked immunosorbent assays the leukemia-associated antigens competed out SiSV p30 in the anti-SiSV p30 system. Peptide mapping experiments with antigens from sera of two different leukemic patients showed that the two antigens were identical concerning numbers of peptides and their position. Eleven of 21 major peptides of SiSV p30 and 10 of 20 major peptides of BaEV p30 (50 to 60% of major peptides) showed mobilities identical with those of the major peptides of the human antigens. The data suggest the presence in human sera of retroviral antigens closely associated with leukemia.