Purification and Characterization of a Human Lung Tumor-Associated Antigen

A human lung tumor-associated antigen was purified from a saline extract of a lung adenocarcinoma. The antigen was demonstrated In extracts of lung tumors with the use of an absorbed antiserum by double-diffusion immunoprecipltation. The antiserum did not react with extracts of normal lung or other normal tissues, and the antigen was immunologically distinct from other tumor-associated antigens. Purification was achieved by antibody affinity chromatography and preparative polyacrylamide gel electrophoresis. Isolation procedures were monitored by immunoreactivity with absorbed monospecific antiserum. The antigen was labeled with 125I and judged homogeneous by 1) polyacrylamide gel electrophoresis In detergent and non detergent gels, 2) molecular sieve chromatography, 3) ion exchange chromatography, and 4) sucrose gradient sedimentation analysis. A molecular weight of 77,000 was calculated from the S20.w value of 4.248 and from the D20.w value of 5.0×10-7 cm2/sec. Sodium dodecyl sulfate gel electrophoresis indicated a subunit molecular weight of 42,000. The Stokes radius of the antigen was 40 Å and the frictional ratio was 1.42, indicating a nonspherical molecule. The purified radioiodinated antigen could be quantitatively precipitated with specific antiserum.