以小鼠模式探討第一型輔助型T細胞和IFN-γ在原發性膽道硬化症的角色

Abstract

原發性膽道硬化症（Primary biliary cirrhosis；PBC）為膽道受破壞導致膽汁鬱積甚至肝硬化的慢性肝臟自體免疫疾病。先前研究指出PBC病人血清中IFN-γ表現比起健康的人顯著增加，肝臟內亦可測得PDC-E2專一性輔助性T細胞浸潤。在不同PBC動物模式下也證實Th1細胞及IFN-γ參與在PBC病程，但如何作用於PBC尚未清楚。本研究探討Th1細胞和IFN-γ在PBC所扮演的角色及其作用機轉。我們使用先前實驗室建立的2-OA-OVA誘發PBC之小鼠模式，分析Th1細胞和IFN-γ在此PBC小鼠模式之表現，發現PBC小鼠肝臟中IFN-γ基因表現量以及PBC小鼠第四週血清IFN-γ的表現量均明顯升高。以細胞內染色方法分析PBC小鼠肝臟單核細胞分泌細胞激素的表現亦發現分泌IFN-γ的CD4 T細胞（Type I helper T cell；Th1）百分比顯著增加。為了釐清IFN-γ及Th1如何調控PBC免疫反應，我們將攜帶IFN-γ基因的Adeno-asoociated virus（AAV）給予小鼠同時誘發小鼠產生PBC，再測量其PBC疾病程度。結果顯示大量IFN-γ會增加PBC小鼠肝臟內免疫細胞浸潤，包括CD4+ T、CD8+ T、B、NK與NKT細胞以及增加屬於Th1且與組織發炎相關的TNF-α基因的表現。同時發現IFN-γ也會使PBC小鼠肝臟抗原呈獻細胞數增加且其MHC class II表現增強，而且Th1細胞數量也顯著增加。由以上實驗結果暗示Th1參與在PBC病程，且IFN-γ會增加抗原呈獻細胞並加強其MHC class II之表現以及促進更多CD4 T細胞分化成Th1細胞並製造更多IFN-γ以引起更多免疫反應，例如活化CD8+ T、B、NK與NKT細胞，最後使PBC肝臟門脈發炎情況變得更嚴重。

Primary biliary cirrhosis (PBC) is a slowly progressive liver-specific autoimmune disease caused by the destruction of small intra-hepatic bile ducts, which leads to cholestasis or even cirrhosis. In patients with PBC, the serum levels of IFN-γ are much higher than healthy people and PDC-E2 specific autoreactive helper T cells could be found in their livers. Previous studies showed that IFN-γ and Th1 cells regulate the immune responses in PBC, but the mechanism remains unclear. By using our previous established 2-OA-OVA immunized mouse model of PBC, we found that liver and serum levels of IFN-γ expression were significantly increased in PBC mice while IL-4 and IL-17 were undetectable. In addition, the percentage of IFN-γ-producing CD4 T cells (Th1 cells) in the liver of PBC mice was significantly increased. To study the effects of Th1 cells and IFN-γ on PBC, we intravenously injected IFN-γ expressing adeno-associated virus (AAV-IFN-γ) to 2-OA-OVA immunized PBC mice and measured the features of PBC in these mice. Results showed that administration of IFN-γ significantly increased liver mononuclear cells including CD4+ T, CD8+ T, B, NK and NKT cells and TNF-α expression. Increased numbers of antigen-presenting cells (APCs) with a higher MHC class II expression were also found in AAV-IFN-γ injected PBC mice. Moreover, the frequency and number of IFN-γ producing Th1 cells were also increased. These results suggest that IFN-γ producing Th1 cells play a role in the pathogenesis of PBC. IFN-γ promotes a higher antigen-presenting capability of APCs and Th1 cell differentiation. Th1 cells produce more IFN-γ to augment immune responses such as activating CD8+ T, B, NK and NKT cells, which then exacerbates portal inflammation of PBC.