Characterization of an Epithelial and a Tumor-associated Human Small Cell Lung Carcinoma Glycoprotein Antigen1

The small cell carcinoma (SCC) antigens recognized by LAM2 and I. \ MS antibody were characterized by comparison of their tissue expres sion and analysis of their biochemical composition. LAM2, but not I. \ MS antigen could be demonstrated in lipid extracts of SCC cells. By inininnohistochemical staining the SCC antigen LAM2 was shown to be an epithelial type membrane antigen. Immunoblotting experiments and com petition solid phase radioimmunoassays showed LAM2 antigen to be a native conformation of a glycoprotein with major bands at M, 100,000120,000 and a minor band at M, 210,000. L-Fucose was a dominant part of the epitope which appeared to be closely related to the carbohydrate epitope of the blood group antigen H(O). The tumor-associated mem brane antigen I \MS was shown to be a glycoprotein with major bands at M, 90,000-135,000 and a minor band at M, 200,000. Neuraminic acid was the predominant part of the carbohydrate epitope. I \ MS antibody recognized a structure in the saliva of Le*positive probands, but untreated and neuraminidase-treated SCC extracts were unreactive with anti-Le* antibody. Anti CA 19-9 (sialo-Le* antigen) and LAM2 antibodies did not compete for LAM8 binding in direct radioimmunoassays. The sialoGPM-D5 antigen recognized by LAM8 antibody therefore is likely to represent a novel tumor antigen.