title: Inhibition of cytotoxic T cell lysis by anti-CD8 monoclonal antibodies: studies with CD3-targeted cytolysis of nominal antigen-negative targets.
abstract: The function of the CD8 molecule in lympholysis mediated by cytotoxic T cells was investigated by examining possible contributions of ligands on the target cell to the inhibition of lysis observed with CD8-specific mAb. In order to evaluate a variety of target cells, including those not expressing the nominal Ag (NA) for which the CTL was specific, lysis was effected by cross-linking the CTL and the target cells with anti-CD3 mAb. Such CD3 redirected cytotoxicity was demonstrated to be inhibited by anti-CD8 mAb when low anti-CD3 mAb concentrations were used. The possibility that inhibition by anti-CD8 mAb resulted for competition for the FcR between the anti-CD3 mAb and anti-CD8 mAb was eliminated by targeting TNP-modified cells with an antibody heteroconjugate prepared from Fab fragments of anti-CD3 and anti-DNP antibodies. Inhibition of the lysis of target cells not expressing NA including those deficient in class I expression, demonstrated that neither NA nor class I expression was required for anti-CD8 mAb inhibition. Whether the anti-CD8 mAb inhibition required CD8 Ag interaction with any ligand on the target cell was further investigated by measuring exocytosis of enzyme granule from CTL activated with CD3-coated poly-styrene beads. CD8-specific mAb inhibited such CTL activation in this target cell-free system. A CD8(+), MHC class II-specific CTL clone, was used to show differential inhibition by anti-CD8 mAb, depending on the target cell, therefore providing evidence that anti-CD8 mAb binding does not generate an absolute off signal. These data are consistent with the hypothesis that anti-CD8 mAb affect the lytic process independent of the recognition of a ligand on the target cell by CD8.
authors: Experimental Immunology Branch, National Cancer Institute, Bethesda, MD 20892.
authors: R R
authors: RR
authors: Quinones
authors: D M
authors: DM
authors: Segal
authors: P
authors: P
authors: Henkart
authors: P
authors: P
authors: Perez
authors: R E
authors: RE
authors: Gress
mesh_terms: D000911:Antibodies, Monoclonal / Q000502:physiology*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology*; D001667:Binding, Competitive; D002474:Cell-Free System; D003594:Cytoplasmic Granules / Q000502:physiology; D003601:Cytotoxicity Tests, Immunologic; D003602:Cytotoxicity, Immunologic; D000939:Epitopes / Q000276:immunology; D000949:Histocompatibility Antigens Class II; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D046911:Macromolecular Substances; D011948:Receptors, Antigen, T-Cell / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000502:physiology
chemical_list: D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D007140:Immunoglobulin Fab Fragments; D046911:Macromolecular Substances; D011948:Receptors, Antigen, T-Cell