Definition of a novel binding site on CD8 cells for a conserved region of the MHC class 1b molecule Qa-1 that regulates IFN-gamma expression

Natural killer (NK) cells and activated CD8 cells both express cytotoxic ac tivity and produce substantial levels of IFN-gamma in response to viral and bacterial infections. In the case of NK cells, cellular activation and IFN -gamma expression are regulated by an interaction between NK receptors and MHC class Ib molecules, including HLA-E/Qa-1. We have used soluble tetramer ic complexes of the murine class Ib molecule Qa-1 to define the significanc e of this interaction for CD8 cells. We find that all CD8 cells express a r eceptor for Qa-1 and that ligation of this receptor by Qa-1 results in up-r egulation of IFN-gamma production.