Blocking of cytotoxic T cell function by monoclonal antibodies against the CD45 antigen (T200/leukocyte-common antigen).

Cytotoxic T cells are important effectors in graft rejection and antiviral immunity. A full identification of the functional surface molecules used by these cells may help in determining the best strategies for the therapeutic control of rejection responses. Many T cell surface molecules have been implicated in cytotoxic function through the ability of specific monoclonal antibodies to inhibit T cell activity in vitro. Such measures of "inhibition" must be affected by the avidity of interaction of antibody with the particular surface molecule, as well as the avidity of that surface molecule for any physiological ligand. We show that the introduction of an antiglobulin step substantially amplifies the inhibitory effects of certain CD3 and CD8 monoclonal antibodies, presumably by conferring multivalency. In addition the "antiglobulin" approach has permitted, for the first time, the demonstration that monoclonal antibodies to the "common" determinants of the leukocyte-common antigen family (CD45/LCA/T200) prevent cytotoxic T cell function.