Hepatitis C Lipo-Viro-Particle from Chronically Infected Patients Interferes with TLR4 Signaling in Dendritic Cell

BACKGROUND Hepatitis C virus (HCV) can be purified from serum of chronically-infected patients in the form of Lipo-Viro-Particles (LVP), which are triglycerid-rich lipoprotein-like particles containing viral RNA and proteins. Since LVP is a constant feature of chronically infected patients, we asked whether purified LVP could interfere with the immune response by acting directly on dendritic cell (DC) function. METHODS AND FINDINGS We have analyzed the impact of LVP on the maturation monocyte-derived DC induced by TLR3 or TLR4 ligands. Following incubation with LVP, immature DC supported weak transient HCV-RNA replication and type I IFN synthesis. This, however, did not lead to viral particle production nor to maturation of DC. LVP-treatment prior to TLR3 stimulation by polyI:C only enhanced the secretion of IL-12, IL-6 and TNFalpha yielding typical mature DC. In contrast, LVP-treated DC activated by the TLR4 ligand LPS yielded phenotypically mature DC with reduced capacity to secrete both pro- and anti-inflammatory cytokines. Their ability to stimulate allogeneic T lymphocytes was strongly affected since activated T cells produced IL-5 and IL-13 instead of IFNgamma. Addition of IFNalpha prevented the effect of LVP on DC function. Restoration of IFNgamma secretion by T cells was obtained by blocking ERK activation in DC, while induction of IL-5 and IL-13 secretion was inhibited by blocking the p38-MAPK pathway in DC. CONCLUSIONS LVP can interfere with TLR4-triggered maturation of DC, inducing a shift in DC function that stimulates Th2 cells instead of Th1, by a mechanism that is ERK- and p38-MAPK-dependent. The effect of LVP on DC polarization was reversed by IFNalpha, providing an additional rationale for the interferon therapy of chronically-infected patients. By acting on TLR4 pathway with LVP, HCV may thus exploit a natural protective mechanism of the liver and the intestine normally used to control inflammation and immunity to commensal microorganisms.