Th1 Disabled Function in Response to TLR4 Stimulation of Monocyte-Derived DC from Patients Chronically-Infected by Hepatitis C Virus

BackgroundLack of protective antibodies and inefficient cytotoxic responses are characteristics of chronic hepatitis C infection. A defect in dendritic cell (DC) function has thus been suspected, but this remains a controversial issue.Methods and FindingsHere we show that monocyte-derived DC (MoDC) from chronically-infected patients can mature in response to TLR1/2, TLR2/6 or TLR3 ligands. In contrast, when stimulated with the TLR4 ligand LPS, MoDC from patients show a profound defect in inducing IFN�� secretion by allogeneic T cells. This defect is not due to defective phenotypic maturation or to the presence of HCV-RNA in DC or monocytes but is correlated to reduced IL-12 secretion by DC. Restoration of DC ability to stimulate IFN�� secretion can be obtained by blocking MEK activation in DC, indicating that MEK/ERK pathway is involved in the Th1 defect of MoDC. Monocytes from HCV patients present increased spontaneous secretion of cytokines and chemokines, especially MIP-1��. Addition of MIP-1�� on healthy monocytes during differentiation results in DC that have Th1 defect characteristic of MoDC from HCV patients, suggesting that MIP-1�� secretion by HCV monocytes participates in the Th1 defect of DC.ConclusionsOur data indicate that monocytes from HCV patients are activated in vivo. This interferes with their differentiation into DC, leading to deficient TLR4 signaling in these cells that are enable to induce a Th1 response. This specific defect is linked to the activation of the MEK/ERK pathway.背景：慢性丙型肝炎感染的典型特征为保护性抗体缺失与细胞毒性应答低效。此前学界曾推测树突状细胞（dendritic cell, DC）功能存在缺陷，但该议题迄今仍颇具争议。 材料与方法及结果：本研究证实，慢性丙型肝炎感染者的单核细胞衍生树突状细胞（monocyte-derived DC, MoDC）可在Toll样受体（Toll-like receptor, TLR）1/2、TLR2/6或TLR3配体的刺激下完成成熟。与之相反，当以TLR4配体脂多糖（lipopolysaccharide, LPS）刺激时，感染者的MoDC在诱导同种异体T细胞分泌干扰素γ（interferon-γ, IFN-γ）方面存在显著缺陷。该缺陷并非源于表型成熟障碍或DC与单核细胞内存在HCV-RNA，而是与DC分泌白细胞介素12（interleukin-12, IL-12）减少相关。通过阻断DC中的丝裂原活化蛋白激酶激酶（mitogen-activated protein kinase kinase, MEK）激活，可恢复DC刺激IFN-γ分泌的能力，这表明MEK/细胞外调节蛋白激酶（extracellular signal-regulated kinase, ERK）通路参与了MoDC的Th1型应答缺陷。丙型肝炎患者的单核细胞会出现细胞因子与趋化因子自发分泌增多的情况，尤以巨噬细胞炎症蛋白1α（macrophage inflammatory protein-1α, MIP-1α）为著。在健康单核细胞的分化过程中添加MIP-1α，可使其分化得到的DC呈现出与HCV感染者MoDC一致的Th1型应答缺陷特征，这提示HCV患者单核细胞分泌的MIP-1α参与了DC的Th1型应答缺陷。 结论：本研究数据表明，丙型肝炎患者体内的单核细胞已被活化。这会干扰单核细胞向DC的分化过程，导致这些细胞的TLR4信号通路功能缺陷，无法诱导Th1型应答。该特异性缺陷与MEK/ERK通路的激活密切相关。