A mouse
IgG2a monoclonal antibody, SWA20, defining a
tumor-associated
cell surface antigen on
small cell carcinoma of the lung (SCC) was generated. The reactivity of the antibody with cell lines was examined by indirect immunofluorescence staining and solid phase radioimmunoassay and the reactivity with tissues by immunoperoxidase staining. The antibody reacts with a proportion of
small cell carcinoma cell lines (4 of 8) and tissues (7 of 12), but not with other pulmonary or extrapulmonary cell lines (0 of 30) or
tumor tissues (0 of 78). The antibody was unreactive with primary cultures of normal bronchial epithelial cells, RBC, and WBC. Immunoperoxidase staining of normal tissues showed rare
antigen-positive cells in suprabasal layers of bronchial epithelium and less than 10% of positive cells in colon epithelium. Immunoblots of SCC extracts demonstrated antibody reactivity with a doublet band at Mr 40,000, a broader band at Mr 100,000, and a band at Mr 180,000. The
antigen was not present in crude
lipid extracts of SCC cells. Solid phase radioimmunoassays and immunoblots showed binding competition with the
lectin Triticum vulgaris, sensitivity of the
antigen to
neuraminidase, and a partial sensitivity to treatment with
periodate. The
antigen was coexpressed on SCC cell lines with the
antigen sGP90-135 defined first by antibody LAM8 (R. Waibel, C. J. O'Hara, and R. A. Stahel.
Cancer Res., 47:3766-3770, 1987) but differed from it by lack of reactivity with Lea-positive saliva and partial resistance to
periodate treatment. There was no binding competition between radiolabeled
antibodies SWA20 and LAM8 to SCC target cells. The
IgG2a antibody SWA20 identifies a previously undescribed
tumor-associated surface membrane
antigen, sGP100, expressed selectively on a proportion of SCC.