ROLE OF CONSERVED GLYCOSYLATION SITE UNIQUE TO MURINE CLASS-I MHC IN RECOGNITION BY LY-49 NK CELL-RECEPTOR

The recognition of class I MHC molecules on target cells by the Ly-49 family of receptors regulates NK cytotoxicity, Previous studies have s uggested that carbohydrates are involved in the recognition of class I MHC by Ly-49, although their precise role remains unclear, Here, we e xamined the role of asparagine-linked carbohydrates of the murine clas s I MHC in the binding to Ly-49A and Ly-49C. We have generated H-2D(d) mutants that lack the highly conserved glycosylation sites at amino a cid residues 86 in the alpha 1 domain and 176 in the alpha 2 domain, r espectively, These mutant D-d cDNAs were transfected into leukemic cel l lines, and the binding of the transfected cells to COS cells express ing Ly-49A or Ly-49C, as well as their susceptibility to lysis by Ly-4 9A(+) NK cells, was examined, Only the mutation of the alpha 2 domain glycosylation site significantly reduced the binding of D-d to Ly-49A and Ly-49C. Cells expressing D-d with the mutation at this site were p artially resistant to killing by Ly-49A(+) NK cells. These results sug gest that, white carbohydrates linked to residue 176 seem to function as a part of the ligand structure for the Ly-49 family of NK receptors , there are additional structural features involved in this recognitio n. This glycosylation site is highly conserved among murine class I MH C but is not found among those of other species, suggesting that its r ole is unique to the murine immune system. It further suggests that mu rine class I MHC and Ly-49 gene families may have evolved in concert.