Hepatitis C Virus (HCV) Evades NKG2D-Dependent NK Cell Responses through NS5A-Mediated Imbalance of Inflammatory Cytokines

• DOI: 10.1371/journal.ppat.1001184
• Publication Date: 2010-11-11T21:41:23Z
• Authors: Damien Sène; Franck Levasseur; Michal Abel; Marion Lambert; Xavier Camous; Céline Hernandez; Véronique Pène; Arielle R. Rosenberg; Evelyne Jouvin-Ma...; Patrice N. Marche; Patrice Cacoub; Sophie Caillat-Zu...
• Keywords: Adult; Cytotoxicity, Immunologic; Liver Cirrhosis; Male; 0301 basic medicine; QH301-705.5; Hepacivirus; Viral Nonstructural Proteins; Virus Replication; Monocytes; Young Adult; 03 medical and health sciences; [SDV.MHEP.MI]Life Sciences [q-bio]/Human health and pathology/Infectious diseases; Humans; Biology (General); Aged; Immunity, Cellular; RC581-607; Hepatitis C, Chronic; Middle Aged; Flow Cytometry; 3. Good health; Killer Cells, Natural; NK Cell Lectin-Like Receptor Subfamily K; [SDV.IMM]Life Sciences [q-bio]/Immunology; Cytokines; Female; Immunologic diseases. Allergy; Inflammation Mediators; Research Article

Understanding how hepatitis C virus (HCV) induces and circumvents the host's natural killer (NK) cell-mediated immunity is of critical importance in efforts to design effective therapeutics. We report here the decreased expression of the NKG2D activating receptor as a novel strategy adopted by HCV to evade NK-cell mediated responses. We show that chronic HCV infection is associated with expression of ligands for NKG2D, the MHC class I-related Chain (MIC) molecules, on hepatocytes. However, NKG2D expression is downmodulated on circulating NK cells, and consequently NK cell-mediated cytotoxic capacity and interferon-γ production are impaired. Using an endotoxin-free recombinant NS5A protein, we show that NS5A stimulation of monocytes through Toll-like Receptor 4 (TLR4) promotes p38- and PI3 kinase-dependent IL-10 production, while inhibiting IL-12 production. In turn, IL-10 triggers secretion of TGFβ which downmodulates NKG2D expression on NK cells, leading to their impaired effector functions. Moreover, culture supernatants of HCV JFH1 replicating Huh-7.5.1 cells reproduce the effect of recombinant NS5A on NKG2D downmodulation. Exogenous IL-15 can antagonize the TGFβ effect and restore normal NKG2D expression on NK cells. We conclude that NKG2D-dependent NK cell functions are modulated during chronic HCV infection, and demonstrate that this alteration can be prevented by exogenous IL-15, which could represent a meaningful adjuvant for therapeutic intervention.