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 B4 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.