Characterization of lymphocyte receptors for glycosaminoglycans

This paper describes attempts to isolate and characterize glycosaminoglycan (GAG)-binding molecules on the surface of lymphocytes and lymphoma cell lines and relate their expression to splenic and lymph node homing capacity. Initial binding studies with radiolabelled GAG and rosetting studies with GAG-coupled erythrocytes revealed that there are receptors on lymphocytes for the major classes of GAG (i.e. hyaluronic acid, chrondroitin sulfates, heparin), but lymphocytes bind heparin much more avidly than other GAG species. Analysis of the binding of solubilized radiolabelled cell-surface molecules to immobilized GAG revealed cell-type specific expression of GAG-binding molecules. Thus, each of four lymphoma cell lines tested gave a characteristic pattern of GAG-binding molecules, some molecules being unique to a particular cell line and others being shared by some of the lines. Similarly, splenocytes expressed at least 10 distinct GAG-binding molecules with molecular weights (MW) ranging from 10,000 to 100,000, whereas thymocytes expressed additional GAG-binding proteins of 190,000 and 250,000 MW. Furthermore, splenocytes differed from thymocytes by possessing a unique family of cell-surface molecules which reacted with each GAG. Immunoprecipitation studies demonstrated that the GAG-binding molecules on splenocytes did not correspond to any of the cell-surface antigens tested, notably the cell adhesion molecules MEL-14, CD11/CD18 and CD44, although CD8 bound weakly to heparin. Four lymphoma cell lines with well-characterized migration properties were examined for GAG-binding molecules which may control lymphocyte migration. It was found that no one GAG-binding protein could be correlated with the entry of cells into a particular lymphoid organ. Nevertheless, the role of GAG-binding molecules in the subsequent positioning of lymphocytes within lymphoid organs requires further investigation.