Lectin-binding sites in the epithelium of normal

Abstract

By using histochemical methods, the binding pattern of various lectins in the epithelium of normal human appendix vermiformis was assessed. In addition to plant and invertebrate sugar receptors with nominal monosaccharide specificity for a-L-Fuc (UEA-1), a-DMan and a-D-Gluc (Con A), a-D-GalNAc (DBA), DGalNAc (SBA, HPA) B-D-Gal (RCA-I) and D-Gal (VAA), a mammalian B-galactoside-specific lectin (MW, 14 kDa) was included in the applied panel. The apical surface of enterocytes presented binding sites for RCA-1 on al1 cells, binding sites of UEA-1, DBA, SBA, HPA and VAA heterogeneously and no binding sites of Con A and 14 kDa. Binding sites of DBA, SBA, HPA, VAA and RCA-1 within enterocytes were located primarily focally in a supranuclear position, whereas Con A and 14 kDa bound to the cytoplasm both in apical and basa1 cell parts. In the follicle-associated epithelium more enterocytes expressed SBA- and VAA-binding sites than in the crypt epithelium. No differences between the lectin-binding pattern of M-cells and enterocytes were found in the follicle-associated epithelium. Intraepithelial macrophages were heterogeneously positive for the full panel of applied lectins. In contrast, intraepithelial lymphatic cells expressed binding sites only for RCA-1 and less prominently for Con A, VAA and 14 kDa. Goblet cell mucus contained lectin-binding sites in a heterogeneous manner: binding sites for Con A were not detected in goblet cells for DBA, SBA, VAA and 14 kDa in less than 20%, for UEA-1 in 20-40%, for HPA in 40-60% and for RCA-1 in 60-100% of the goblet cells. Secreted mucus differed in its lectin-binding capacity from intracellular goblet cell mucus selectively by an increase of UEA-1, SBA- and RCA-1-binding sites and a lack of 14 kDa-binding sites. Comparative study of lectin binding to goblet cell mucin in another region of the large intestine, namely the rectosigmoid, demonstrated that DBA, SBA and 14 kDa bound mainly to the dista1 colon, while UEA-1 and VAA labelling was selectively found in Oífprint reguests lo: Dr. Ulrich Brinck, M.D., Department of Pathology, University of Gottingen, Robert-Koch-Str. 40, D-37075 Gottingen, Germany apendiceal goblet cell mucin. Comparing the lectin-binding pattern in normal appendix epithelium and in appendicitis, the percentage of goblet cells expressing DBA- and SBA-binding sites in mucus globules was found to be about 4 times higher in appendicitis than in normal appendix. These results demonstrate that the expression of lectin-binding sites in appendiceal goblet mucin is specifically altered in appendicitis, indicating that there are selective changes of glycosylation of mucin in goblet cells mainly of the lower and middle crypt segment. Changes of lectinbinding pattern in appendicitis are discussed in connection with histochernical findings in inflammatory bowel disease.