Analysis of the Lewisx epitope in human pancreas and pancreatic adenocarcinomas

Abstract

The Lewisx epitope (Gal beta 1-4[Fuc alpha 1-3]GlcNAc-R) can be detected in most ductal pancreatic carcinomas. However, few data pertain to its expression in normal exocrine pancreas and its biochemistry. We compared the expression of the Lewisx epitope in normal pancreas with its expression in pancreatic adenocarcinomas and tumor cell lines and to further characterize the nature of the antigens bearing this epitope with immunochemical methods. On frozen tissue sections of normal pancreas, the Lewisx epitope was detected focally in acinar cell granules; sialosyl-Lewisx was detected in centroacinar cells and the cytoplasm of intralobular ducts. Sixteen of 19 pancreatic carcinomas expressed the Lewisx antigen on tissue sections; however, there was no correlation with prognostic parameters, such as tumor grade or stage. Eighteen of 19 tumor specimens were positive for sialosyl-Lewisx. Analysis of pancreatic carcinoma cell lines (CAPAN-1, CAPAN-2, and DAN-G) revealed intracytoplasmic expression of sialosyl-Lewisx epitopes in these cells, and cell surface reactivity was detected on flow cytometry for sialosyl-Lewisx. Lectin-affinity chromatography of cytoplasmac preparations showed that Lewisx-positive antigens of normal human pancreas bind to SBA and UEA-I lectins but have little or no affinity to WGA, GS-I, or DBA lectins, indicating the presence of Fuc and Gal oligosaccharide residues. It was concluded that the Lewisx and sialosyl-Lewisx antigens are nonpolymorphic carbohydrate determinants that are present in secretory granules of acinar cells, ductules, and pancreatic secretions. This makes the Lewisx antigen suitable for the analysis of the secretory process in the exocrine pancreas and the study of secretory differentiation antigens in ductal pancreatic carcinoma.