Cell surface glycoconjugates as possible target structures for human natural killer cells: evidence against the involvement of glycolipids and N-linked carbohydrate chains

Natural killer (NK) cells can spontaneously kill various malignant cells, but the susceptibility towards NK cells differs greatly among different types of tumour cells. The molecules, which are recognized by NK cells, have not yet been identified, but there is ample evidence that target cell surface glycoconjugates are involved in the interaction with NK cells. In this report, we show that the recognition of K562 target cells by human NK cells depends on the presence of protein-bound determinants, implying that glycolipids are not the primary target structures on K562 cells. The NK susceptibility of K562 cells was not altered by enzymic removal of various cell surface carbohydrates or oligosaccharides, mostly related to N-linked carbohydrate chains. Treatment of K562 cells with 1-deoxynojirimycin and 1-deoxymannojirimycin, inhibitors of N-glycan processing, resulted in drastic alterations in the carbohydrate phenotype of the cell surface, as could be shown by flow cytometric analysis of the lectin-binding properties of the cells. Despite these clear changes in N-glycosylation, the NK susceptibility of K562 cells remained unaffected. Summarizing, the results described in this report show that potential target structures for NK cells are protein bound, but the involvement of a specific (N-linked) carbohydrate determinant in the interaction between NK cells and target cells could not be established.