title: Perforin, Fas/Fas ligand, and TNF-alpha pathways as specific and bystander killing mechanisms of hepatitis C virus-specific human CTL.
abstract: In chronic hepatitis C, Fas expression is up-regulated in the hepatocytes, especially near liver-infiltrating lymphocytes, and Fas ligand is expressed on the lymphocytes. The presence of hepatitis C virus (HCV)-specific CTLs has been demonstrated both in peripheral blood and among liver-infiltrating lymphocytes of patients with chronic hepatitis C. We studied the killing mechanisms of HCV-specific human CTLs using target cells that were sensitive or resistant to agonistic anti-Fas Abs and TNF-alpha. We show that HCV-specific CTL clones kill non-Ag-bearing bystander cells as well as Ag-bearing cells, although the bystander killing is less efficient than the specific target cell killing, and the efficacy of the bystander killing of anti-Fas- and soluble TNF-alpha-sensitive cells is greater than that of resistant cells. We also show that the killing of Ag-presenting, sensitive cells is mediated by Fas ligand and TNF-alpha as well as perforin, although the latter plays a major role in the killing at a low E:T ratio, and that the killing of sensitive bystander cells is primarily mediated by Fas ligand and TNF-alpha on CTLs expressed upon specific Ag stimulation, which may be relevant to the bystander lysis by HCV-specific CTLs of uninfected hepatocytes, in which Fas expression is up-regulated. Activated CTLs also kill bystander cells by the perforin-based mechanism, although it requires a high E:T ratio. The effective bystander killing requires a close intercellular contact between CTLs and target cells, although TNF-alpha released from the CTLs mediates lysis of the bystander cells without a close cell-cell contact.
authors.affiliation: Hepatology Division, Jichi Medical School, Kawachi-gun, Tochigi, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ando
authors.forename: K
authors.initials: K
authors.lastname: Hiroishi
authors.forename: T
authors.initials: T
authors.lastname: Kaneko
authors.forename: T
authors.initials: T
authors.lastname: Moriyama
authors.forename: Y
authors.initials: Y
authors.lastname: Muto
authors.forename: N
authors.initials: N
authors.lastname: Kayagaki
authors.forename: H
authors.initials: H
authors.lastname: Yagita
authors.forename: K
authors.initials: K
authors.lastname: Okumura
authors.forename: M
authors.initials: M
authors.lastname: Imawari
mesh_terms: D017951:Antigen Presentation; D003602:Cytotoxicity, Immunologic; D016174:Hepacivirus / Q000276:immunology*; D006526:Hepatitis C / Q000276:immunology*; D006801:Humans; D008562:Membrane Glycoproteins / Q000276:immunology*; D054353:Perforin; D052899:Pore Forming Cytotoxic Proteins; D015398:Signal Transduction; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000821:virology; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology*; D019014:fas Receptor / Q000276:immunology*
chemical_list: D008562:Membrane Glycoproteins; D052899:Pore Forming Cytotoxic Proteins; D014409:Tumor Necrosis Factor-alpha; D019014:fas Receptor; D054353:Perforin