Carbohydrate synthesis inhibitors decrease interleukin 1-stimulated lymphocyte binding to endothelial cells.

Lymphocyte extravasation (homing) is initiated when lymphocyte adheres to endothelial cells. All know protein structures involved in the lymphocyte binding located on the endothelial surface are heavily glycosylated. We asked therefore whether these carbohydrate motifs had a role in the lymphocyte homing. The relative importance of the N-linked chains on biological effects mediated by glycoproteins can be studied with specific inhibitors of carbohydrate processing, i.e. 1-deoxynojirimycin (DN), castonospermine (CAST), 1-deoxymannojirimycin (DMN) and swainsonine (SW), which produces different kinds of blocked carbohydrate chains. N-linked carbohydrate chains are modified in the Golgi apparatus and in the final glycoprotein they can be either of high-mannose-, hybrid- or complex-type motifs, having the same core structure but different terminal structures. We show here that when all N-linked carbohydrates were cleaved off from the cell surface glycoproteins by treating endothelial cells with N-glycosidase F interleukin 1-induced lymphocyte binding was reduced almost to non-stimulated control values. Treatment of endothelial cells with CAST led to generation of glycoproteins carrying high-mannose-type oligosaccharides, which are glucose capped with three glucose molecules on the chain. CAST treatment resulted in an 85% decrease in lymphocyte binding compared to interleukin 1-induced levels. DMN treatment, resulting in accumulation of high-mannose type oligosaccharides without any terminal glucoses on the cell surface, caused a similar inhibition of lymphocyte binding to that induced by CAST treatment. SW treatment, leading to accumulation of hybrid-type glycoproteins, decreased only slightly the lymphocyte binding. These results suggest that carbohydrates indeed have a role in lymphocyte binding to endothelial cells.