Histochemical study of expression of lectin-reactive carbohydrate epitopes and glycoligand-binding sites in normal human appendix vermiformis, colonic mucosa, acute appendicitis and colonic adenoma

Abstract

In a glycohistochemical analysis of human appendix vermiformis we report the assessment of lectin binding in cells of the Gut Associated Lymphoid Tissue of normal samples and in acute appendicitis using a panel of plant, invertebrate and mammalian lectins with specificity for a-L-Fuc (UEA-I), a-D-Gluc and a-DMan (Con A), a-D-GalNAc (DBA), GalNAc (SBA, HPA), B-Gal (RCA-I, 14 kDa=galectin-l) and a-, B-Gal (VAA). Moreover, we initiate the study of expression of carbohydrate-binding sites in this tissue and in colonic mucosa, employing several types of carrier-immobilized carbohydrate ligands as suitable probes for this purpose. Within the three populations of macrophages intralsubepithelial macrophages of the dome region, the lamina propria of the intercryptal region and the follicleassociated epithelium were apparently reactive with most of the lectins and also with mannose and fucose residues of the tested neoglycoproteins. Distinguishing features of germinal center macrophages in relation to intra-/subepithelia1 phagocytes were the lack of binding of UEA-I and DBA. In comparison to all other types of phagocytes, macrophages of the T-region displayed a rather restricted binding capacity only to Con A and RCA-I. Labeling of macrophages with SBA, HPA and VAA in this location was only rarely found. With respect to dendritic cells no consistently positive reaction was seen for follicular cells, whereas interdigitating cells of the T-region bound Con A, HPA and RCA-I, and, less frequently, SBA. Lymphocytes in all anatomical subsites of the Gut Associated Lymphoid Tissue, centrocytes, centroblasts and plasma cells had binding sites for Con A and RCA-I in common. Notably, a small number of lymphocytes mostly in the T-region but also in B-cell-rich areas expressed intranuclear binding sites for fucose and mannose residues. Intraepithelial lymphocytes and lymphatic cells of the T-region differed from lymphocytes in other regions by a more frequent expression of VAA-binding sites. The epithelium of appendix vermiformis and colonic mucosa not only presents lectin binding sites, but also has the capacity to bind carbohydrate structures, as shown by labeled glycoligand-exposing neoglycoproteins. In normal mucosa the extent of binding appeared to be associated with maturation of cells, the surface epithelium showing the most intense staining reaction. This pattern is not detectable in colonic adenoma which reveal increased intensity, when compared to normal mucosa. In contrast to development of hyperplasia, acute inflammation in appendicitis caused no detectable changes of neoglycoprotein binding. Taking our previous assessment on lectin binding in appendicitis into account, we conclude that glycosylation of goblet cell mucus, but not the capacity to bind certain sugar epitopes responds to inflammatory processes, whereas tumorigenesis of colonic adenoma can also affect the binding of neoglycoproteins.