Hepatitis C virus single-stranded RNA induces innate immunity via Toll-like receptor 7.
OBJECTIVE
Innate immune responses to HCV infection are triggered through host recognition of pathogen-associated molecular patterns. Interferons are critical for the protection against HCV infection. However, the pathways linking virus recognition to IFN induction remain poorly understood.


METHODS
Immune cells and Huh-7 cells were infected with HCV cell culture (HCVcc) or transfected with HCV-derived immunostimulatory RNA oligonucleotides (ORNs), and immune activation was assessed.


RESULTS
We found that HCVcc suppressed immune responses because the HCVcc protein impaired the PBMC and pDC responses. However, HCVcc genomic RNA had an immunostimulatory effect. HCV encodes G/U-rich ssRNA TLR7 ligands that significantly activate innate immunity, and induced IFN-alpha production. Moreover, HCV-derived ORNs also activated IRF7 and NF-kappaB in Huh-7 cells. In particular, the HCV 3'-UTR strongly induced cytokine production. Different lengths of polyuridine tract in the 3'-UTR of different HCV strains induced IFN-alpha production. These data demonstrate that the HCV-specific G/U fragment is a motif sequence, and is recognized by TLR7 as a PAMP. The requirement for TLR7 to recognize HCV RNA was confirmed using specific inhibitors, RNAi and by TLR7overexpression.


CONCLUSIONS
These results provide an insight into the development of immune adjuvant for vaccines and for the production of new antiviral drugs.
Zhang
Yi-Liang
YL
Department of Medical Genetics, Second Military Medical University, 800 Xiang'Yin Road, 200433 Shanghai, China.
Guo
Ying-Jun
YJ
Bin Li
Sun
Shu-Han
SH
D000276:Adjuvants, Immunologic / Q000494:pharmacology*; D002478:Cells, Cultured; D016174:Hepacivirus / Q000235:genetics*; D006801:Humans; D007113:Immunity, Innate / Q000187:drug effects*; D016898:Interferon-alpha / Q000096:biosynthesis; D016328:NF-kappa B / Q000378:metabolism; D009841:Oligonucleotides / Q000494:pharmacology; D011072:Poly U / Q000494:pharmacology; D012367:RNA, Viral / Q000494:pharmacology*; D051199:Toll-Like Receptor 7 / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis
D000276:Adjuvants, Immunologic; D016898:Interferon-alpha; D016328:NF-kappa B; D009841:Oligonucleotides; D012367:RNA, Viral; C495348:TLR7 protein, human; D051199:Toll-Like Receptor 7; D014409:Tumor Necrosis Factor-alpha; D011072:Poly U