Inhibition of natural killer cell cytotoxicity by a monoclonal antibody directed against adhesion-mediating protein gp 90 (CD18).

Contact is required between the effector natural killer (NK) or cytotoxic killer T cell and its corresponding target in order for efficient lysis to occur. Several surface molecules of different types are involved in this process. Here we could show that Fab fragments from a murine monoclonal antibody reacting with gp 90, the human leucocyte common antigen CD18, are extremely efficient in blocking human NK of killer T cells, regardless of whether the target has or does not have the antigen. In contrast, no impact of the antibody was observed when the effector cells were of murine origin, again regardless of whether the target cell did or did not display the leucocyte common antigen. The inhibition could be shown to occur at the level of blockage of target-conjugate formation. This means that the functional display of effector/target gp 90 on the effector but not the target cell is necessary for efficient lysis to occur both in NK and killer T cell systems.