Genetic evidence for the Lewis enzyme, which synthesizes type-1 Lewis antigens in colon tissue, and intracellular localization of the enzyme.

To determine whether the Lewis enzyme responsible for the Lewis blood type antigens on erythrocytes synthesizes the Lewis antigens on normal cells and cancer cells in colon tissue, we performed genotyping of the Lewis gene by the PCR-RFLP method and by immunohistochemical staining of Lewis antigens and the Lewis enzyme with specific monoclonal antibodies (mAbs) in colon tissues obtained from 100 colon cancer patients. Five of the 100 patients were identified as homozygotes for the mutant Lewis gene, i.e., the le/le genotype that cannot encode functional Lewis enzyme. The cells in both the normal and cancerous regions of colon tissue from these five le/le patients were completely devoid of staining with mAbs against Lewis antigens with the type 1 chain, i.e., Lewis a, Lewis b, and sialyl Lewis a. In contrast, the cells in cancerous regions of the colon tissue of the 95 patients with the Le/Le or Le/le genotype positively stained with all three mAbs, anti-Lewis a, anti-Lewis b, and anti-sialyl Lewis a. The cells in the cancerous regions of the colon tissue of the five le/le patients stained with DU-PAN-2 mAb, whose recognizing epitope is known to be sialyl Lewis c, a precursor structure of sialyl Lewis a. By immunohistochemical staining with FTA 1-16 mAb, which is directed at the human Lewis enzyme, we were able to demonstrate for the first time that the enzyme is localized in the Golgi area of the colon epithelial cells of patients with the Le/Le or Le/le genotype. No staining was observed in the Golgi area of the cells of the patients with the le/le genotype. From these results, we conclude that individuals with the Le/Le or Le/le genotype possess a functional Lewis enzyme synthesizing fucosylated type-1 Lewis antigens in the Golgi apparatus of the colon epithelial cells, but that individuals with the le/le genotype are devoid of the Lewis enzyme in the Golgi apparatus, resulting in an inability to synthesize Lewis antigens with the type-1 chain, and that it is inappropriate to use CA19-9, whose antigenic epitope is defined as sialyl Lewis a, as a tumor marker in patients with the le/le genotype.