Viral and Host Factors Induce Macrophage Activation and Loss of Toll-Like Receptor Tolerance in Chronic HCV Infection

Abstract

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. Monocytes/macrophages were repeatedly stimulated via proinflammatory cytokine-inducing TLRs and evaluated for activation markers. 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)-alpha production. Serum levels of interferon (IFN)-gamma, 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-gamma 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)-kappaB activity both in monocytes of cHCV patients and in normal monocytes that lost TLR tolerance after IFN-gamma + 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-gamma. cHCV patients exhibited increased TNF-alpha in the circulation and in the liver. In cHCV livers, we found Kupffer cell/macrophage activation indicated by increased CD163 and CD33 expression. We identified that host-derived factors (IFN-gamma 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.