Toll-like receptors (TLRs) 是一種pattern recognition receptors，不僅在先天性免疫系統中扮演重要角色，具有調節控制發炎反應，同時也可以進一步啟動後天性免疫作用。其中TLR8主要表現在細胞內的exndosome胞器的磷酯雙層膜上，負責辨識多種病毒的單股RNA，活化下游的訊息傳導，促使一些與發炎相關的細胞激素以及第一型干擾素基因表現。人類C型肝炎病毒(HCV)是一種單股RNA病毒，可以被TLR8辨識，但對於TLR8基因多型性是否影響慢性HCV感染之感受性，到目前為止仍未有文獻深入探討。因此，本研究的主要目標是探討TLR8遺傳基因多型性影響其功能上的變異，進而導致HCV感染之相關機轉。首先，我們藉由PCR-RFLP方式分析312位慢性HCV感染病患和298位健康者的TLR8基因型，結果發現TLR8 起始碼Met/Val與promoter -129位置C>G的變異之間具有鏈鎖不平衡的遺傳現象，並且在男性族群中， CA allele在HCV感染組出現的頻率明顯比對照組高(17.1%比10.0%; p=0.035)。在基因多型性之功能分析實驗中，我們也發現在帶有TLR8-129C/+1A男性自願者，血球細胞中TLR8 mRNA表現較多，體外誘導刺激後，發炎細胞激素之表現量也明顯較高。相反的，刺激後產生抗病毒作用的干擾素(IFN-alpha)，反而卻是在TLR8-129G/+1G基因型的男性中較高。除此之外，我們同時也證實了在TLR8-129G/+1G基因型TLR8 mRNA表現量少，是由於其產生的mRNA相對不穩定，以及在Raw264.7細胞轉染實驗中，發現TLR8-129G/+1G的promoter表現活性較低。總而言之，在我們的研究證實了TLR8基因多型性的確會影響其表現量與對於外來刺激後產生細胞激素能力，因此才可能導致TLR8多型性與HCV感染之間有相關聯存在。

Toll-like receptors (TLRs) are characterized as pattern recognition receptors that play pivotal roles in innate immunity system, controlling inflammation responses and further instructing development of adaptive immunity. Toll-like receptor 8 (TLR8) is situated in endosomes and activates downstream signals to induce inflammatory cytokines and type I interferon through recognizing single-stranded RNA derived from various viruses, including hepatitis C virus (HCV). However, very little is known about the influence of TLR8 polymorphisms on susceptibility to chronic HCV infection. The aims of the study were to investigate the association and functional alteration of TLR8 genetic variation with HCV infection. We genotyped a population of 312 chronic HCV-infection patients and 298 healthy control subjects for TLR8 polymorphisms by PCR-RFLP. The results demonstrated the frequency of the complete linkage disequilibrium of Met/Val change at start codon and -129C>G of TLR8 at promoter and the frequency of CA allele was significantly higher in HCV-infection male group (17.1% versus 10.0%; p=0.035). In functional examination of the polymorphisms, both TLR8 mRNA expression and ex vivo inflammatory cytokines were higher among male volunteers with TLR8-129C/+1A. In contrast, IFN-alpha with effective anti-viral activity was higher in TLR8-129G/+1G. We further demonstrated the lower mRNA expression level in the TLR8-129G/+1G genotype was due to the relative instability of mRNA and lower promoter activity in Raw264.7 cells. In conclusion, our study provided the direct evidence showing TLR8 functional variants modulated the expression as well as the responds after stimulation, which may contribute to the association between TLR8 polymorphisms and HCV infection.

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