The Importance of Lectin Binding Sites and Carcinoembryonic Antigen with Regard to Normal, Hyperplastic, Adenomatous, and Carcinomatous Colonic Mucosa

Summary

Using fluorescence microscopy a higher content of lectin binding sites was observed in the mucosubstances of transitional mucosa adjacent to colonic carcinomas than in normal mucosa. The lectin binding pattern of adenomas was similar to that of the transitional mucosa. However, in proliferating parts and areas with cell atypia the amount of lectin receptors was generally reduced. In colonic carcinomas the occurrence of lectin receptors was correlated with the morphological degree of differentiation: well differentiated carcinomas showed more lectin binding sites than undifferentiated ones. Often a concomitant occurrence of FYTC-Ricinus communis agglutinin with carcinoembryonic antigen was found; the latter is known to be a glycoprotein with a high carbohydrate content. Of special interest was the peanut agglutinin receptor that was only demonstrable in transitional mucosa and carcinomas but was absent in normal mucosa of the colon. The importance of this receptor is discussed with respect to the occurrence of blood group antigens and immunotherapeutical considerations in colonic carcinomas.

The histopathology and classification of tumours of the colon is well established (survey by Morson and Sobin [17]; also [6]). However, in future the morphological differentiation alone may not be adequate for the characterisation of these tumours. With respect to new therapeutical considerations, therefore, further investigations are needed that give more detailed information about the metabolism of tumour cells. This development in oncology requires a more sensitive microscopical diagnosis with histochemical methods that allow the demonstration of distinct cell components. In this context the analysis of the mucins in the epithelial cells of the colon seems to be of great importance [3, 4, 7, 10, 12, 13, 16, 18]. There is still much, to be learned about the role of the different monosaccharides to determine the significance of mucins in the physiology and pathology of the bowel.

In this study different carbohydrate structures have been investigated by fluorescence microscopy in normal, hyperplastic, adenomatous, and carcinomatous colonic mucosa. Lectins that are well known for their carbohydrate specificity (survey by Sharon and Lis [21]), were used for visualisation of these sugar components; the lectins were labelled by conjugation with fluorescein isothiocyanate (FITC). Additionally, in our histochemical investigations the occurrence of lectin receptors was compared with the localisation of carcinoembryonic antigen (CEA), a tumour marker that possesses a high content of carbohydrates [15].