CD45 molecule cross-linking inhibits natural killer cell-mediated lysis independently of lytic triggering.
The fact that certain CD45 [anti-leucocyte common antigen (LCA)] monoclonal antibodies (mAb) inhibit natural killer (NK) cell non-major histocompatibility complex (MHC)-restricted cytolysis led to the suggestion that these mAb block a 'trigger' for NK cell lytic activity. However, the discovery that the intracytoplasmic portion of the leucocyte common molecule has protein tyrosine phosphatase activity raises the possibility that the mAb initiate a direct inhibitory signal, independent of the triggering apparatus. To clarify this, we have tested the ability of CD45 antibodies to trigger NK cells and redirect cytotoxicity against mAb-producing hybridoma cells and autologous monocytes, an approach which has identified other cytotoxic trigger molecules. Peripheral blood NK cells failed to kill the CD45 antibody-producing hybridomas, although a CD3 antibody expressing hybridoma was susceptible to cytotoxic T-cell lysis. Furthermore, the CD45 mAb CMRF-12 + 26, 13.3 and HuLyM4 did not redirect lysis of autologous monocytes by NK cells, whereas the isotype-matched CD16 mAb did so. Bivalent CD45 antibody was necessary to block NK lysis of K562, as F(ab')2 but not F(ab') fragments of CMRF-12 + 26 antibody inhibited killing. Capping of the LCA appeared to correlate with the ability of the CD45 mAb to block killing, suggesting that cross-linking of LCA molecular isoforms on the NK cell surface is required for CD45 mAb to inhibit non-MHC-restricted cytolysis.
Starling
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GC
Department of Haematology, Christchurch Hospital, New Zealand.
Hart
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DN
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000943:Antigens, Differentiation / Q000276:immunology*; D001667:Binding, Competitive / Q000276:immunology; D003602:Cytotoxicity, Immunologic; D006649:Histocompatibility Antigens / Q000276:immunology*; D006801:Humans; D007152:Immunologic Capping; D007694:Killer Cells, Natural / Q000276:immunology*; D017493:Leukocyte Common Antigens; D008214:Lymphocytes / Q000276:immunology; D009000:Monocytes / Q000276:immunology; D011961:Receptors, Fc / Q000276:immunology
D000911:Antibodies, Monoclonal; D000943:Antigens, Differentiation; D006649:Histocompatibility Antigens; D011961:Receptors, Fc; D017493:Leukocyte Common Antigens