Z Gastroenterol 2014; 52 - P_1_28
DOI: 10.1055/s-0033-1360872

Monocytes Affect Natural Killer cell Antiviral IFN-γ Production in HCV Infection via Inflammasome-mediated IL-18 Secretion

JM Werner 1, E Serti 1, MA Chattergoon 2, AL Cox 2, V Lohmann 3, B Rehermann 1
  • 1NIDDK, National Institutes of Health, Liver Diseases Branch, Bethesda, MD, USA
  • 2Johns Hopkins School of Medicine, Division of Infectious Diseases, Baltimore, MD, USA
  • 3University of Heidelberg, Department of Infectious Diseases and Molecular Virology, Heidelberg, Germany

IFN-γ production by Natural killer (NK) cells is attenuated in patients with chronic hepatitis C virus (HCV) infection. Here, we asked whether this impairment is NK cell-intrinsic or extrinsic.

Hepatoma cells expressing luciferase-tagged subgenomic HCV replicons (Huh7/HCV-replicons) or their HCV-negative counterparts (Huh7) were co-cultured with NK cells in the presence or absence of other PBMC subsets. Antiviral activity, cytotoxicity, and cytokine production were assessed.

NK cells exerted greater IFN-γ production (22% vs. 8% IFN-γ+ NK cells, p = 0.004; MFI 318 vs. 114, p < 0.05) when PBMC were co-cultured with Huh7/HCV-replicons rather than Huh7. Cytotoxicity was minimal (11% vs. 0.5%, p < 0.05) and neutralization of IFN-γ and TNF-α increased HCV replication (68% vs. 21.4%, p = 0.03), which suggested that the antiviral effect was cytokine-mediated. Amount of IFN-γ and antiviral function of NK cells were lower when isolated NK cells rather than PBMCs were co-cultured with Huh7/HCV-replicons (24% vs. 71% decrease in replication) suggesting that other PBMC subpopulations contributed to NK cell activation. Increased levels of multiple monokines implicated a role of activated monocytes in NK cell stimulation. Indeed, depletion of CD14+ monocytes (9% vs. 20.7% IFN-g+ NK cells, p < 0.0001; MFI 127 vs. 277, p = 0.002), siRNA knockdown of the monocyte NALP3 inflammasome (14% vs. 25.8% IFN-g+ NK cells, p = 0.031; MFI 304 vs. 440, p = 0.003) or neutralization of the inflammasome product IL-18 (22% vs. 43% IFN-g+ NK cells, p = 0.03; MFI 280 vs. 555, p = 0.031) decreased IFN-γ secretion and antiviral activity of NK cells. Finally, monocytes from chronic HCV patients were less effective than monocytes from healthy controls in stimulating the antiviral function of healthy blood donor NK cells (55% vs. 71% decrease in replication, p = 0.011). Vice versa, monocytes from healthy controls improved both HCV-specific cytokine production and antiviral activity of NK cells from chronic HCV patients (75% vs. 61% decrease in replication, p = 0.019).

Monocytes sense HCV-replicating cells and induce, via inflammasome-mediated IL-18 production, NK cell IFN-γ secretion and antiviral activity. An impaired monocyte function in chronic HCV infection contributes to the attenuated IFN-γ production of NK cells.