Elsevier

Immunobiology

Volume 210, Issues 2–4, 19 August 2005, Pages 237-247
Immunobiology

Subversion of plasmacytoid and myeloid dendritic cell functions in chronic HCV infection

https://doi.org/10.1016/j.imbio.2005.05.018Get rights and content

Abstract

Insufficient elimination of the hepatitis C virus (HCV) during acute infection results in chronic disease in the majority of patients due to weak virus-specific immune responses. Dendritic cells (DC) play a central role in recognition of HCV and in induction of innate and adaptive immune responses. In this study, we evaluated the frequency and functions of plasmacytoid dendritic cells (PDC) and myeloid dendritic cells (MDC) in patients with chronic HCV infection. We found that both the numbers and IFNα production capacity of blood PDC were significantly reduced in patients with chronic HCV infection compared to normal controls. While the frequency of MDC was not affected in chronic HCV, the allostimulatory capacity of monocyte-derived MDC was significantly decreased compared to normals. Lipopolysaccharide (LPS)-induced maturation improved the allostimulatory capacity of HCV infected patients’ MDC that still remained significantly lower compared to normal controls. Our experiments revealed that MDC defects can be induced by HCV core and NS3 proteins suggesting virus-induced mechanisms for the DC defects in HCV infection. Finally, using toll-like receptor 2 (TLR2) and TLR4 deficient or mutant mice, we demonstrated that TLR2 but not TLR4 was critical in recognition of HCV core and NS3 proteins by innate immune cells. Further, TLR2 recognition of HCV core and NS3 was not augmented by co-expression of the TLR co-receptor, CD14. These data demonstrate that both PDC and MDC functions are impaired in patients with chronic HCV infection and DC defects are likely related to interaction of HCV viral products with innate immune cells.

Introduction

Hepatitis C virus (HCV) infection affects more than 170 million people worldwide and 4 million in the US. Unlike other hepatitis viruses, HCV results in chronic infection in about 85% of the cases leading to chronic hepatitis and over decades result in liver fibrosis, cirrhosis, liver failure and hepatocellular carcinoma (Afdhal, 2004). Increasing evidence suggests that insufficient immune activation during acute infection is associated with viral persistence. Invading pathogens, such as the HCV virus, are normally recognized by cells of the innate immune system including monocytes and dendritic cells (DC) (Andrews et al., 2005; Kanto and Hayashi, 2004). DC uptake and process pathogens and have a unique capacity to activate CD4 and CD8T lymphocytes in an antigen-specific manner (Mellman and Steinman, 2001). Depending on the co-stimulatory environment and signals, DC can induce T activation, T cell anergy or tolerance (Steinman et al., 2000; Banchereau et al., 2003). Mounting of a vigorous CD4+ and CD8+ T cell response and predominant Th1-type immune activation in acute HCV infection are associated with viral clearance (Kamal et al., 2004; Lechner et al., 2000; Thimme et al., 2001; Shoukry et al., 2004; Heller and Rehermann, 2005). While HCV-specific T cell activation can be detected in patients with chronic HCV infection, HCV-specific CD4+ and CD8+ T cell frequency and responses are weak and insufficient for viral elimination (Shoukry et al., 2004; Rehermann and Nascimbeni, 2005). CD4+ and CD8+ T cell activation is largely dependent on signals derived from antigen presenting cells (Steinman et al., 2000; Iwasaki and Medzhitov, 2004). DC, the most efficient inducers of all immune responses, have two major phenotypes based on their precursors, plasmacytoid dendritic cells (PDC) and myeloid dendritic cells (MDC). While PDC and MDC share common functional features related to antigen uptake, processing and presentation, each type expresses unique sets of receptors that enables them to specifically recognize and respond to different pathogens (Colonna et al., 2004; Larsson et al., 2004; Iwasaki and Medzhitov, 2004). For example, all DC and cells of the innate immune system express evolutionally preserved pattern recognition receptors, toll-like receptors (TLRs). Of the 10 functional TLRs in humans identified to date, viral pathogens can be sensed by TLR3 (double stranded RNA), TLR7 or TLR8 (single-stranded RNA), bacterial lipopolysaccharide and some viral proteins by TLR4, bacterial CpG sequences in DNA by TLR9 and flagellin by TLR5. TLR2 has a broad recognition profile that includes Gram-positive peptidoglycans and di- and triacetylated lipopeptides as well as selected viruses (Iwasaki and Medzhitov, 2004). Recently identified TLR11 is activated by uropathogenic bacteria and Toxoplasma gondii in mice (Zhang et al., 2004; Yarovinsky et al., 2005), while no equivalent of TLR11 was found in other species. It remains to be evaluated which TLRs are exactly involved in HCV recognition. PDC express TLR7 and TLR9 that are pivotal in recognition of viruses and bacteria while MDC express TLR2, TLR4, and TLR3 and monocytes express a broad profile of TLRs including TLR2, 3, 4, and 5 (Hornung et al., 2002).

HCV is a single stranded positively charged RNA hepacivirus within the flaviviruses that encodes 10 proteins, including structural (core, envelopes 1 and 2), p7, and non-structural proteins (NS2, NS3, NS4, NS5) (Rosenberg, 2001). While HCV primarily replicates in hepatocytes, increasing evidence suggests that cells of the immune system can also harbor both positive and negative strands of HCV suggesting the presence of viral replication (Goutagny et al., 2003; Tsubouchi et al., 2004). HCV viral proteins, particularly core, NS3 and NS5 were found to interact with host cells and to modulate functions of hepatocytes and immune cells (Tellinghuisen and Rice, 2002). We have recently reported that HCV core and NS3 proteins can inhibit differentiation of monocyte-derived MDC and affect their potential to function as accessory cells (Dolganiuc et al., 2003). In this study, we evaluated whether TLR2 or TLR4, TLR previously reported to recognize viral proteins, were involved in the interaction of monocytes with HCV core and NS3 proteins in inducing altered MDC functions. Furthermore, we investigated the frequency and function of PDC in chronic HCV-infected patients.

Section snippets

Reagents

Lipopolysaccharide (LPS, Escherischia coli O111:B4, SIGMA, St Louis, MO), phenol-purified, lipoprotein-free LPS (pLPS, List Biologicals Laboratories Inc., Campbell, CA), proteoglycan (PGN, SIGMA, St. Louis, MO), fetal calf serum (FCS, HyClone, Logan, UT), culture media D-MEM, F12 and RPMI 1640 (Gibco, Grand Island, NY), recombinant IL-1β (Peprotech, Rocky Hill, NJ), R848 (InvivoGen, San Diego, CA). Recombinant hepatitis C core (aa 2-192) and NS3 (aa 1450-1643) proteins and β-galactosidase were

Reduced numbers of circulating plasmacytoid but not MDC in chronic HCV-infected patients

Recognition and elimination of pathogens is dependent on circulating and tissue-associated DC (Mellman and Steinman, 2001). Previous studies indicated the presence of abnormalities either in the function or frequency of DC of patients with chronic HCV infection (Dolganiuc et al., 2003; Kanto et al., 1999; Bain et al., 2001; Auffermann-Gretzinger et al., 2001; Goutagny et al., 2004; Murakami et al., 2004). Here we investigated the frequency of circulating PDC and MDC in patients with chronic HCV

Discussion

Recognition of invading pathogens by DC is critical in initiation of both innate immune responses and in activation of T cell-specific immune responses. In chronic HCV, HCV-specific immune responses and T cell activation are weak and insufficient for elimination of the virus. Here we report impairment in the function of both PDC and MDC in chronic HCV-infected patients. We also demonstrate that reduced allostimulatory capacity of monocyte-derived MDC can be induced by HCV core and NS3 proteins

Acknowledgments

The authors thank Drs. K. Thamma, L. Shick, and S. Mehta for recruitment of patients, Ms. K. Kodys for the support with graphics, and Drs. E. Kurt-Jones and D. Golenbock from UMass Medical School for providing us with the HEK cell lines and TLR deficient mice. This work was supported by NIH Grant #AA14372 from the National Institute of Alcohol Abuse and Alcoholism and its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIAAA.

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