Abstract
An epithelial cell surface antigen is described which is defined by monoclonal antibody HEA125 (IgG1). The antibody was raised against the colon carcinoma cell line HT-29. Under reducing conditions HEA125 immunoprecipitates a surface glycoprotein of Mr 34,000 which was designated Egp34. The antigen does not contain disulfide-linked subunits. A slightly different migration behavior under non-reducing conditions (Mr 39,000) may be due to intrachain disulfide bonds. After enzymatic cleavage of N-linked carbohydrate residues the apparent molecular weight of the antigen was 29,000. Egp34 is a major cell surface component of HT-29 cells (10(6) molecules per cell). No antigen could be detected in the sera of colorectal cancer patients. A panel of malignant cell lines and normal cells was studied for surface expression of the antigen. 17/17 carcinoma lines of 6 different origins expressed the antigen, whereas 16/16 melanoma, neuroblastoma, sarcoma and lymphoma/leukaemia were unreactive as it was the case for normal fibroblasts and blood cells. Immunoperoxidase staining of frozen tissue sections with HEA125 demonstrated the presence of Egp34 in almost all normal epithelia and tumours derived therefrom. No reactivity with non-epithelial tissues was observed. Undifferentiated carcinomas of various origins homogeneously expressed Egp34. Therefore, HEA125 may become a valuable tool for the immunohistochemical diagnosis of carcinoma.