LY-49 MEDIATES EL4 LYMPHOMA ADHESION TO ISOLATED CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX-MOLECULES

Ly-49 is a recently identified cell surface molecule expressed on a subpopulation of natural killer (NK) cells and certain T lymphomas. It has been suggested, based on gene transfection and antibody blocking studies, that Ly-49 is a negative regulator of NK lytic activity, possibly through an interaction with target cell class I molecules. However, it has not been demonstrated that class I molecules indeed serve as ligands for Ly-49. We have found that T lymphomas expressing Ly-49 bind isolated class I major histocompatibility complex (MHC) molecules but not class II molecules immobilized on plastic. Adhesion to class I molecules was not found with T lymphomas lacking Ly-49 expression. The Ly-49 expressing EL4 lymphoma bound D-d, D-k, and K-b, but not K-d, K-k, or D-b, thus demonstrating a restricted pattern of class I adhesion. The observed cell adhesion was class I density dependent, and binding to D-d and D-k was extensively inhibited by the A1 monoclonal antibody directed against Ly-49. These results provide direct evidence for Ly-49 serving as a receptor for a subset of class I MHC molecules.