ENHANCEMENT IN ACCESSIBILITY TO MACROPHAGES BY MODIFICATION OF MUCIN-TYPE CARBOHYDRATE CHAINS ON A TUMOR-CELL LINE - ROLE OF A C-TYPE LECTIN OF MACROPHAGES

We investigated the role of mucin-type (O-linked) carbohydrate chains of tumor target cells in the recognition by macrophages through a Gal/GalNAc-specific calcium-dependent lectin. Binding of a soluble form of this lectin to P815 mastocytoma cells was increased by treatment with benzyl-GalNAc, which presumably inhibited the extension of mucin-type carbohydrate chains, The levels of cell surface expression of GalNAc residues were elevated after benzyl-GalNAc treatment, as revealed by the binding of Vicia villosa agglutinin B-4 and Dolichos biflorus agglutinin. Adhesion of treated P815 cells to this lectin immobilized on plastic surfaces also increased, Furthermore, the binding of P815 cells to macrophage-like RAW 264.7 cells and to peritoneal macrophages also increased after the same treatment, We concluded that elevated levels of cell surface terminal GalNAc in mucin-type carbohydrate chains increased accessibility of P815 cells to macrophages through Gal/GalNAc-specific calcium-dependent lectins.