title: Fas involvement in cytotoxicity mediated by human NK cells.
abstract: Lysis of target cells (TC) by cytolytic lymphocytes involves the secretion of cytoplasmic granules containing perforin and serine esterases by the effector cell (EC). Recently, a granule-independent cytolytic mechanism involving the interaction of the apoptosis-triggering Fas antigen (CD95) with Fas ligand (FasL) has been revealed in T cells. However, whether the Fas lytic pathway also functions in NK cells has not been established. We purified human peripheral NK cells (> 98% CD56+) and found that PMA and ionomycin treatment upregulated FasL message and stimulated the NK cells to lyse a Fas+ TC. This lysis was partially inhibited by the anti-Fas-blocking antibody M3 or by Fas.Fc fusion protein. We also found that FasL is constitutively expressed on the human NK-like leukemia cell line YT-INDY and that YT-INDY utilizes a Ca(2+)-independent Fas lytic pathway, as well as the granule pathway. We have previously shown that CD28/B7 interactions are involved in TC recognition by YT-INDY. K562 cotransfected with Fas and B7-1 (K562/Fas/B7) was lysed by YT-INDY at a higher level than a vector-transfected K562 line, whereas K562 transfected with Fas alone was not. Lysis of K562/Fas/B7 cotransfectants was partially Fas-mediated, as indicated by the presence of Ca(2+)-independent, M3-inhibitable lysis. Ca(2+)-independent, Fas-mediated lysis of several TC by YT-INDY was inhibited by anti-CD28 antibody. Anti-LFA-1 also inhibited Fas-mediated cytotoxicity in YT-INDY. Thus, fresh human NK cells and the human NK-like cell line YT-INDY are capable of using the Fas lytic pathway. In YT-INDY, CD28/B7 and LFA-1/ICAM interactions appear to influence the Fas lytic pathway.
mesh_terms: D018122:B7-1 Antigen / Q000502:physiology; D001483:Base Sequence; D018106:CD28 Antigens / Q000502:physiology; D002469:Cell Separation; D003602:Cytotoxicity, Immunologic; D053222:Fas Ligand Protein; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000502:physiology; D007694:Killer Cells, Natural / Q000276:immunology* / Q000502:physiology; D004915:Leukemia, Erythroblastic, Acute; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology; D008562:Membrane Glycoproteins / Q000378:metabolism; D008969:Molecular Sequence Data; D014162:Transfection; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000032:analysis / Q000502:physiology*
chemical_list: D018122:B7-1 Antigen; D018106:CD28 Antigens; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D016169:Lymphocyte Function-Associated Antigen-1; D008562:Membrane Glycoproteins; D019014:fas Receptor; D018799:Intercellular Adhesion Molecule-1