Characterization of a Tumor Cell Surface Protein with Heterologous Antisera to a Spontaneous BALB/c Lung Carcinoma1

Line 1, a spontaneous alveolar carcinoma from a BALB/c mouse, is highly metastatic and weakly antigenic in the syn geneic host. Sera and enriched antibody preparations were made specific for line 1 cells by in vitro and in vivo absorptions. By lactoperoxidase-catalyzed radioiodination of cell surface protein followed by precipitation with specific antibodies, a protein with a molecular weight of about 180,000 (designated TSP-i 80) was identified that was present on line 1 cells but not on normal lung cells or Moloney sarcoma tumor cells. Studies of competition for immune precipitation of TSP-i 80 by unlabeled protein preparations from various sources indicate that (a) TSP-i 80 is present in tumor cells of various culture passage levels, (b) tumor cells grown i.m. also contain TSP 180, and (c) normal lung proteins compete weakly, and only at very high protein concentrations. A protein similar to TSP-i 80 was detected on Madison 109 carcinoma and on three other lung carcinomas adapted to culture. Experiments with specific antisera show that TSP-i 80 is not lactoperoxidase, fetal bovine serum protein, large external transformation-sensitive protein, or an antigen related to murine leukemia virus proteins.