Gastroenterology

Gastroenterology

Volume 133, Issue 5, November 2007, Pages 1627-1636
Gastroenterology

Basic–Liver, Pancreas, and Biliary Tract
Viral and Host Factors Induce Macrophage Activation and Loss of Toll-Like Receptor Tolerance in Chronic HCV Infection

https://doi.org/10.1053/j.gastro.2007.08.003Get rights and content

Background & Aims: Persistent inflammation contributes to progression of liver damage in chronic HCV (cHCV) infection. Repeated exposure to toll-like receptor (TLR) ligands results in tolerance, a protective mechanism aimed at limiting inflammation. Methods: Monocytes/macrophages were repeatedly stimulated via proinflammatory cytokine-inducing TLRs and evaluated for activation markers. Results: Unlike monocytes of controls or patients with nonalcoholic steatohepatitis, the monocytes of cHCV patients were hyperresponsive and failed to show homo- or heterotolerance to TLR ligands, manifested by elevated tumor necrosis factor (TNF)-α production. Serum levels of interferon (IFN)-γ, endotoxin (TLR4 ligand), and HCV core protein (TLR2 ligand) were elevated in cHCV patients suggesting potential mechanisms for in vivo monocyte preactivation. Treatment of normal monocytes with IFN-γ resulted in loss of tolerance to lipopolysaccharide (LPS) or HCV core protein. Furthermore, we found increased levels of MyD88-IRAK1 complexes and nuclear factor (NF)-κB activity both in monocytes of cHCV patients and in normal monocytes that lost TLR tolerance after IFN-γ + LPS pretreatment. In vitro differentiation of TLR non-tolerant cHCV monocytes into macrophages restored their capacity to exhibit TLR tolerance to LPS and HCV core protein, and this could be reversed by administration of IFN-γ. cHCV patients exhibited increased TNF-α in the circulation and in the liver. In cHCV livers, we found Kupffer cell/macrophage activation indicated by increased CD163 and CD33 expression. Conclusions: We identified that host-derived factors (IFN-γ and endotoxin) and viral factors (HCV core protein) act in tandem to induce and maintain monocyte/macrophage activation, thus favoring persistent inflammation in patients with cHCV infection.

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Reagents

LPS was from List Biological Laboratories (Campbell, CA), peptidoglycan (PGN) from Fluka (Milwaukee, WI), Pam2CSK4 and Pam3CSK4 from EMC Microcollections (Tuebingen, Germany), Gardiquimod from Invivogen (San Diego, CA), fetal calf serum (FCS) from HyClone (Logan, UT), RPMI 1640 from Gibco (Grand Island, NY), recombinant HCV core protein (genotype 1A aa 2–192) from Biodesign (Saco, MN).

Patients and Cells

The study was approved by the Committee for the Protection of Human Subjects in Research at the University of

Monocytes of cHCV Patients Lack Tolerance to TNF-α-Inducing TLR Ligands

We have previously reported that monocytes of cHCV patients produced significantly higher levels of TNF-α both at baseline and upon stimulation with TLR4 and TLR2 ligands compared with controls.6 Production of TNF-α by immune cells contributes to the efficient control of invading pathogens, whereas excessive and uncontrolled production may lead to systemic chronic inflammation.2, 3 Tolerance to TLR ligands is one of the protective mechanisms against chronic inflammation.10 Considering the

Discussion

This study has provided 3 key observations related to the inflammatory cell activation during cHCV infection. First, we identified that monocytes, the precursors of tissue macrophages, are preactivated in patients with chronic HCV infection. Second, we demonstrated that in vivo occurring concentrations of IFN-γ, endotoxin, and HCV core protein modulate monocyte functions and favor the increased frequency of MyD88/IRAK complexes, elevated NF-κB activation, and excessive TNF-α production seen in

References (30)

  • S. Ward et al.

    Cellular immune responses against hepatitis C virus: the evidence base 2002

    Clin Exp Immunol

    (2002)
  • M.G. Neuman et al.

    Kinetics of serum cytokines reflect changes in the severity of chronic hepatitis C presenting minimal fibrosis

    J Viral Hepat

    (2002)
  • K. Takeda et al.

    Toll-like receptors

    Ann Rev Immunol

    (2003)
  • M.A. Dobrovolskaia et al.

    Induction of in vitro reprogramming by Toll-like receptor (TLR) 2 and TLR4 agonists in murine macrophages: effects of TLR “homotolerance” versus “heterotolerance” on NF-κB signaling pathway components

    J Immunol

    (2003)
  • J.M. Cavaillon et al.

    Endotoxin tolerance: is there a clinical relevance?

    J Endotoxin Res

    (2003)
  • Cited by (0)

    Supported by NIAAAA grant AA11576 (to G.S.), PHS grant AA12862, UMass CFAR grant 5P30 AI42845, and PHS grant DK32520.

    The authors have no conflicts of interest to disclose.

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