N-linked oligosaccharides can protect target cells from the lysis mediatedby NK cells but not by cytotoxic T lymphocytes: role of NKG2-A

We have previously shown that glycophorin A (GPA), inserted by electropulsa tion into the membrane of K562 cells, protected them from natural killer (N K) cell-mediated cytotoxicity and the unique N-linked oligosaccharide of GP A was essential for resistance to occur. The present study demonstrates tha t the protection level conferred by GPA is similar to the resistance induce d by HLA-Cw3 expressed by transfected K562 cells. A monoclonal antibody aga inst NKG2-A, an NK inhibitory receptor interacting with HLA class I antigen s and belonging to the C-type lectin receptor, was able to restore the abil ity of NK cells to lyse K562 cells expressing HLA-Cw3 at the cell membrane but not electroinserted-GPA, suggesting that the N-linked oligosaccharide o f GPA cannot be a ligand for NKG2-A. GPA was then electroinserted into the membrane of two lymphoblastoid B-cell lines: one was sensitive to NK cell-m ediated lysis, the other was susceptible to cytotoxic CD8(+) T-lymphocyte ( CTL)-mediated cytotoxicity. The electroinserted GPA protected the target ce lls from NK-mediated cytotoxicity, whereas it did not modify the cell susce ptibility to lysis by CTL. Endoglycosidase F treatment abolished the resist ance towards NK cell-mediated lysis, suggesting that N-linked glycans could inhibit mechanisms used by NK cells to exert their cytotoxic function in a greement with our previous results.