Dengue

Activation of Toll-Like Receptor 3 Impairs the Dengue Virus Serotype 2 Replication through Induction of IFN-b in Cultured Hepatoma Cells
Zhaoduan Liang1,2., Siyu Wu1,2., Yuye Li1,2, Li He1,2, Minhao Wu1,2, Lifang Jiang2,3, Lianqiang Feng1,2, Ping Zhang1,2*, Xi Huang1,2*
1 Department of Immunology, Institute of Immunology, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-senUniversity, Guangzhou, China, 2 Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou, China, 3 Department of Microbiology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China

Abstract
Toll-like receptors (TLRs) play an important role in innate immunity against invading pathogens. Although TLR signaling has been indicated toprotect cells from infection of several viruses, the role of TLRs in Dengue virus (DENV) replication is still unclear. In the present study, we examined the replication of DENV serotype 2 (DENV2) by challenging hepatoma cells HepG2 with different TLR ligands. Activation of TLR3 showed an antiviral effect, while pretreatment of other TLR ligands (including TLR1/2, TLR2/6, TLR4, TLR5 or TLR7/8) did notshow a significant effect. TLR3 ligand poly(I:C) treatment prior to viral infection or simultaneously, but not post-treatment, significantly down-regulated virus replication. Pretreatment with poly(I:C) reduced viral mRNA expression and viral staining positive cells, accompanying an induction of the type I interferon (IFN-b) and type III IFN (IL-28A/B). Intriguingly, neutralization of IFN-b alonesuccessfully restored the poly(I:C)-inhibited replication of DENV2. The poly(I:C)-mediated effects, including IFN induction and DENV2 suppression, were significantly reversed by IKK inhibitor, further suggesting that IFN-b is the dominant factor involved in the poly(I:C) mediated antiviral effect. Our study presented the first evidence to show that activation of TLR3 is effective in blockingDENV2 replication via IFN-b, providing an experimental clue that poly(I:C) may be a promising immunomodulatory agent against DENV infection and might be applicable for clinical prevention.
Citation: Liang Z, Wu S, Li Y, He L, Wu M, et al. (2011) Activation of Toll-Like Receptor 3 Impairs the Dengue Virus Serotype 2 Replication through Induction of IFN-b in Cultured Hepatoma Cells. PLoS ONE 6(8):e23346. doi:10.1371/journal.pone.0023346 Editor: Dong-Yan Jin, University of Hong Kong, Hong Kong Received April 21, 2011; Accepted July 15, 2011; Published August 4, 2011 Copyright: ß 2011 Liang et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided theoriginal author and source are credited. Funding: This work was supported in part by NSFC (National Natural Science Foundation of China) U0832006, 30972763, GRPCRG (Guangdong Recruitment Program of Creative Research Groups), Doctoral Fund of Ministry of Education of China 20100171110047, Guangdong Natural Science Foundation 10251008901000013. The funders had no role in study design, data collection andanalysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: huangxi6@mail.sysu.edu.cn (XH); zhangp36@mail.sysu.edu.cn (PZ) . These authors contributed equally to this work.

Introduction
Dengue virus (DENV), a group of prevalent arthropod-borne viruses, belongs to the Flavirvirus genus of the familyFlaviviridae. There are four related but distinct serotype viruses (DENV-1 to 4) [1]. While most DENV infections are asymptomatic or cause a self-limited Dengue fever (DF), some infections lead to severe and potentially lethal diseases, such as Dengue hemorrhagic fever (DHF) and Dengue shock syndrome (DSS) [1,2]. Dengue becomes a leading infectious disease with more than 50 million cases of DF,...