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Isolation of a ‘Speckled’ Nuclear Antigen Reactive with Autoantibodies in Patients with Cancer and Autoimmune Diseases

An antigenic substance reactive with autoantibodies found in patients with cancer and autoimmune diseases was isolated from calf thymus. The purification procedure included extraction of the tissues with acetone powder, batch and column chromatography on DEAE‐resins, ammonium sulfate precipitation, gel filtration on Sephadex G‐200, and affinity chromatography on antibody‐Sepharose 4B. Indirect immunofluorescence examination of cultured human embryo cells, using the serum of patients with nasopharyngeal cancer, showed a speckled nuclear pattern. The antigenic factor was a soluble acidic protein with a pI of 5.0 and a molecular weight of 250.000. The antigenic activities of this purified substance from calf thymus, and of the material on the cultured human embryo cells, were destroyed by proteases, ribonuclease, and alkaline phosphatase. The determinants were also sensitive to periodate oxidation. Thermal stability to 60°C and pH stability between 2.6 and 8.5 were demonstrated. Cross‐reactivity of the antigenic substance with antibodies isolated from individuals with cancer and autoimmune diseases was shown by immunofluorescence, with appropriate blocking and absorption controls.