Characterization of a lung-cancer-associated auto-antigen

An antigen, protein X (Px), was purified from immune complexes isolated from malignant pleural effusions from patients with adenocarcinoma of the lung by EDTA treatment, PEG 8000 precipitation, protein A affinity chromatography, and Sephadex G-200 separation in the presence of 3 M NaCl. The purified antigen had a M(r) 17,000 by SDS-PAGE, and consisted of isoelectric species of pI 6.3 and 6.6. Purified Px recombined with Ig isolated from pleural fluids from patients with lung adenocarcinoma, but not with Ig from patients with breast carcinoma. Using an autologous human and heterologous chicken antibody, Px was found, by immunohistology, in the cytoplasm of some of the well-differentiated lung adenocarcinoma cells, but was not seen in normal lung or a variety of other malignant tissues. A liquid-phase competitive-inhibition RIA was developed. Over 30 ng/ml of Px were found in 9 of 15 pleural fluids from patients with lung carcinoma, none of 20 from patients with breast, ovary, stomach or colon cancer, and in 3 of 15 patients with unknown primary tumor. Our data suggest that Px may be a lung-cancer-associated autoantigen which can elicit a host humoral response in vivo.