Identification of a tumor-related protein antigen in immune complexes derived from pleural effusions of patients with bronchial carcinoma.

Pleural effusions from 15 patients with advanced primary bronchial carcinoma, from 2 patients with metastatic lung cancer and from 6 patients with nonmalignant disease were studied. Immune complexes were found in examined fluids in amounts corresponding to 2.5-210 mg/100 ml of aggregated IgG by means of ELISA solid phase anti C3 and 125ICIq binding radioimmunoassay. Following determination of protein content and salting out by ammonium sulfate of examined fluids, the sediments were subjected to subsequent chromatographic procedure including molecular sieving (Sephadex G-200, Sepharose 4B) and affinity chromatography on Protein A-Sepharose CL-4B. The yield--apparently pure immune complexes--was then split by means of chaotropic agent 2.5 M KSCN. It permitted to obtain 2 fractions: one contained IgG while the other was a non-Ig protein of m. w. = 150 000. The latter isolated from malignant effusions possessed antigenic activity in the leukocyte migration inhibition (LMI) assay. It resulted in inhibition of migration of allogenic peripheral blood leukocytes from lung cancer patients in 87% of cases. It had no activity against leukocytes from nonmalignant disease patients. LMI activity of the final second fraction derived from malignant effusion was significantly different from that of other fractions obtained both from malignant and nonmalignant fluids.