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

We have previously shown that glycophorin A (GPA), inserted by electropulsation into the membrane of K562 cells, protected them from natural killer (NK) cell-mediated cytotoxicity and the unique N-linked oligosaccharide of GPA was essential for resistance to occur. The present study demonstrates that the protection level conferred by GPA is similar to the resistance induced by HLA-Cw3 expressed by transfected K562 cells. A monoclonal antibody against NKG2-A, an NK inhibitory receptor interacting with HLA class I antigens and belonging to the C-type lectin receptor, was able to restore the ability of NK cells to lyse K562 cells expressing HLA-Cw3 at the cell membrane but not electroinserted-GPA, suggesting that the N-linked oligosaccharide of 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-mediated lysis, the other was susceptible to cytotoxic CD8+ T-lymphocyte (CTL)-mediated cytotoxicity. The electroinserted GPA protected the target cells from NK-mediated cytotoxicity, whereas it did not modify the cell susceptibility to lysis by CTL. Endoglycosidase F treatment abolished the resistance towards NK cell-mediated lysis, suggesting that N-linked glycans could inhibit mechanisms used by NK cells to exert their cytotoxic function in agreement with our previous results.