HBV相关慢性肝病T细胞调控

StephenW

Hepatology Snapshot
T cell regulation in HBV-related chronic liver disease

    Carlo Ferrari, , , Carolina Boni, Marzia Rossi, Andrea Vecchi, Valeria Barili, Diletta Laccabue, Paola Fisicaro, Gabriele Missale

    Unit of Infectious Diseases and Hepatology, Laboratory of Viral Immunopathology, Azienda Ospedaliero-Universitaria di Parma, and Department of Medicine and Surgery, University of Parma, Via Gramsci 14, 43126 Parma, Italy

    Received 23 August 2016, Revised 3 October 2016, Accepted 3 October 2016, Available online 8 February 2017

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        http://doi.org/10.1016/j.jhep.2016.10.002
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HBV-specific T cell dysfunction is believed to play a central role in the pathogenesis of chronic HBV persistence [1] ;  [2]. HBV-specific T cells are more dysfunctional within the liver than in the periphery [3] as a result of the inhibitory effect of different mechanisms. They are likely to be active simultaneously within the inflamed liver together contributing to T cell functional impairment [4] ;  [5]. Some of them have been directly characterized in HBV infection, while others are assumed to be relevant because of their general importance within the liver.
Panel A. Persistent exposure to high antigen load within the liver and in the periphery can cause HBV-specific T cell exhaustion and deletion

High antigen loads and high frequencies of infected liver cells are constantly detectable in chronically HBV infected patients [1] resulting in persistent antigen exposure, which is a key feature of T cell exhaustion in chronic HBV infection. Chronic antigen stimulation is associated with sustained expression of programmed death 1 (PD-1) and other co-inhibitory molecules on HBV-specific T cells, including TIM-3, CTLA-4, 2B4, CD160, LAG-3, etc., [1]; [2] ;  [3]. Although co-inhibitory molecules can be weakly and transiently expressed on functionally efficient T cells as a result of activation, their high and sustained expression is the hallmark of T cell exhaustion [6]. Upregulation of the corresponding ligands has been observed on liver resident and infiltrating cells during chronic liver inflammation [1]; [2] ;  [7]. Thus, constant T cell receptor stimulation and continuous exposure to inhibitory ligands can contribute to T cell exhaustion.

Once HBV-specific T cells reach the liver, they are subjected to the inhibitory effect of the hepatic microenvironment where an excess of arginase and indoleamine 2,3-dioxygenase (IDO) can induce depletion of important nutrients needed for T cell proliferation and function, as well as an accumulation of toxic metabolites which can further impair T cell responses [4] ;  [7].

StephenW

肝病快照
HBV相关慢性肝病T细胞调控

    卡罗法拉利，，卡罗莱纳州博尼，马齐亚·罗西，安德烈·维奇，瓦莱里亚·巴利里，Diletta Laccabue，Paola Fisicaro，Gabriele Missale

    传染病与肝病学单位，病毒免疫病理学实验室，Azienda Ospedaliero-Universitaria di Parma，以及帕尔马大学医学与外科学系，Via Gramsci 14,43126 Parma，Italy

    收到2016年8月23日，2016年10月3日修订，2016年10月3日接受，可在线于2017年2月8日

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        http://doi.org/10.1016/j.jhep.2016.10.002
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HBV特异性T细胞功能障碍被认为在慢性HBV持久性发病机制中起着关键作用[1]。 [2]。由于不同机制的抑制作用，HBV特异性T细胞在肝脏内比在周边更具功能障碍[3]。它们可能在发炎肝脏中同时起作用，共同促进T细胞功能障碍[4]; [5]。其中一些已被直接描述为HBV感染，而其他人被认为是相关的，因为它们在肝脏中的一般重要性。
面板A.持续暴露在肝脏和外围的高抗原负荷可导致HBV特异性T细胞耗竭和缺失

慢性乙型肝炎病毒感染患者的高抗原负荷和高频感染肝细胞不断检测[1]，导致持续性抗原暴露，这是慢性HBV感染中T细胞耗尽的关键特征。慢性抗原刺激与HBV特异性T细胞（包括TIM-3，CTLA-4,2B4，CD160，LAG-3等）的程序性死亡1（PD-1）和其他共抑制分子的持续表达有关， [1]; [2]; [3]。尽管协同抑制分子可以作为活化的结果在功能有效的T细胞上弱和瞬时表达，但其高而持续的表达是T细胞耗竭的标志[6]。在慢性肝脏炎症过程中，肝脏和浸润细胞上观察到相应配体的上调[1]。 [2]; [7]。因此，恒定的T细胞受体刺激和连续暴露于抑制性配体可能导致T细胞衰竭。

一旦HBV特异性T细胞到达肝脏，就会受到肝微环境的抑制作用，其中过量的精氨酸酶和吲哚胺2,3-双加氧酶（IDO）可以诱导T细胞增殖和功能所需的重要营养物质的消耗，以及可能进一步损害T细胞应答的有毒代谢物的积累[4]; [7]。

StephenW

Panel B. Liver suppressive environment: Increased arginase activity

The main source of arginase can be from damaged hepatocytes and liver infiltrating cells, such as myeloid-derived suppressor cells. These are expanded particularly in those chronic patients with high HBV replication levels and a lack of overt immunopathology [8]. An excess of arginase results in the depletion of the amino acid arginine. Deprivation of arginine is reflected by the downregulation of CD3ζ and leads to the suppression of functional T cells proliferation.
Panel C. Liver suppressive environment: Increased IDO/TDO expression

A number of liver infiltrating cells, including monocytes, macrophages and dendritic cells upon IFN-γ stimulation can produce IDO [3]; [4] ;  [6], which can cause tryptophan depletion with subsequent inhibition of T cell proliferation and function. Tryptophan metabolism can also give rise to toxic compounds, such as kynurenines, which are responsible for T cell apoptosis and differentiation of CD4 cells in Treg cells [9].
Panel D. Liver suppressive environment: Hyperexpression of regulatory cytokines

Expanded regulatory T cells (Treg) cells contribute to create a local intrahepatic suppressive cytokine milieu by secreting interleukin (IL)-10 and transforming growth factor beta (TGF-β). These suppressive soluble mediators can also be produced by other cell types. Stellate cells can secrete TGF-β while dendritic cells, Kupffer cells and B cells secrete IL10 [3] ;  [4].
Panel E. Mechanisms of Treg expansion within the liver

Expansion of Treg cells can inhibit T cell responses either by direct cell-cell contact or by secretion of suppressive cytokines. This expansion can also be caused by plasmacytoid dendritic cells (pDC) through an IL27-based circuit, which can lead to PD-L1 expression, with subsequent Treg proliferation. Treg cell expansion can be also stimulated by IFN-γ activated liver sinusoidal endothelial cells (LSEC) and stellate cells in a PD-L1 independent manner [3] ;  [4].

StephenW

B组肝脏抑制环境：精氨酸酶活性增加

精氨酸酶的主要来源可来自受损的肝细胞和肝脏浸润细胞，如骨髓来源的抑制细胞。特别是在那些具有高HBV复制水平和缺乏明显免疫病理学的慢性病患者中尤其如此。过量的精氨酸酶导致氨基酸精氨酸的消耗。精氨酸的去除被CD3ζ的下调所反映，并导致功能性T细胞增殖的抑制。
面板C.肝脏抑制环境：增加IDO / TDO表达

在IFN-γ刺激下，许多肝脏浸润细胞，包括单核细胞，巨噬细胞和树突状细胞可产生IDO [3]。 [4] [6]，其可以导致色氨酸消耗，随后抑制T细胞增殖和功能。色氨酸代谢也可引起毒性化合物，如犬尿胆碱，这是造成T细胞T细胞凋亡和CD4细胞分化的原因[9]。
面板D.肝脏抑制环境：调节性细胞因子的过表达

扩增的调节性T细胞（Treg）细胞通过分泌白介素（IL）-10和转化生长因子β（TGF-β）有助于产生局部肝内抑制性细胞因子环境。这些抑制性可溶性介体也可以由其他细胞类型产生。星状细胞可以分泌TGF-β，而树突细胞，枯否细胞和B细胞分泌IL10 [3]; [4]。
图E.肝内Treg扩张的机制

Treg细胞的扩增可以通过直接的细胞 - 细胞接触或分泌抑制性细胞因子来抑制T细胞的反应。这种扩增也可以通过基于IL27的电路的浆细胞样树突状细胞（pDC）引起，其可以导致PD-L1表达，随后的Treg增殖。 Treg细胞扩增也可以通过IFN-γ活化的肝窦内皮细胞（LSEC）和星状细胞以PD-L1独立的方式刺激[3]; [4]。

StephenW

Panel F. Activated natural killer (NK) cells can delete HBV-specific T cells in chronic HBV infection

The intrahepatic suppressive cytokine milieu can impair not only the T cell function but also NK cells, which are abundant within the liver and barely able to produce IFN-γ in chronic HBV patients [10]; [11] ;  [12]. Instead, NK cells can show efficient cytolytic activity and upregulate the death ligand TNF-related apoptosis-inducing ligand (TRAIL) [11] ;  [12]. TRAIL can engage with the upregulated TRAIL-R2 receptor on liver cells, thereby amplifying liver damage [11] ;  [12]. TRAIL positive NK cells can also interact with TRAIL-R2 positive HBV-specific T cells and delete them, thereby contributing to HBV-specific T cell attrition [11] ;  [12]. T cell susceptibility to apoptotic death can be amplified by the upregulation of the pro-apoptotic BIM molecule in HBV-specific T cells (see panel A) [7].
Panel G. Myeloid cell plasticity

Myeloid cells also play a key regulatory role within the liver because they can differentiate from monocytes into macrophages, monocyte-derived dendritic cells or myeloid suppressor cells, thanks to their functional plasticity. During liver inflammation, inflammatory monocytes can be recruited into the liver as a result of intercellular adhesion molecule 1 (ICAM-1 [CD54]) expression on LSEC [4]. They can then differentiate into myeloid-derived suppressor cells by a CD44-dependent mechanism driven by activated stellate cells [4]. On the other hand, TLR-9 signaling can drive monocyte differentiation towards anti-viral protection by causing the formation of inflammatory monocyte aggregates, called iMATEs, where virus-specific CD8 cells can expand upon OX40 and CD28 signaling released from inflammatory dendritic cells of monocyte origin [13].
Panel H. T cell activation by liver antigen presenting cells (APC) is suboptimal and can promote tolerance

Several liver cell types, including LSEC, stellate cells and Kupffer cells can serve as APC to activate naive T cells [14]. Interestingly, CD8 T cells can extend protrusions through fenestra in LSEC to sample HBV antigens on hepatocytes [15]. T cell activation within the liver can be however suboptimal with tolerance induction because most of these hepatic APC show very poor expression of co-stimulatory molecules in the steady state, express increased levels of the co-inhibitory molecules PD-L1 and PD-L2 upon IFN stimulation and can produce immune regulatory cytokines, including IL10 and TGF-β.
Financial support

This work was supported by a grant from Regione Emilia-Romagna, Italy (Programma di Ricerca Regione-Università 2010-2012; PRUa1RI-2012-006) and by a FIRB grant (RBAP10TPXK) from the Italian Ministry of University and Research.
Conflict of interest

Carlo Ferrari: research grants from Gilead, Roche and Janssen, served as advisor/consultant for Gilead, Merck, Abbvie, BMS and Arrowhead.

Gabriele Missale: served as consultant for Bayer.

StephenW

F.激活的天然杀伤（NK）细胞可以删除慢性HBV感染中的HBV特异性T细胞

肝内抑制性细胞因子环境不仅可以损害T细胞功能，而且可以损害肝脏内丰富的NK细胞，并且在慢性HBV患者中几乎不能产生IFN-γ[10]。 [11] [12]。相反，NK细胞可以显示有效的细胞溶解活性和上调死亡配体TNF相关的凋亡诱导配体（TRAIL）[11]。 [12]。 TRAIL可以与肝细胞上调的TRAIL-R2受体结合，从而扩大肝损伤[11]。 [12]。 TRAIL阳性NK细胞也可以与TRAIL-R2阳性HBV特异性T细胞相互作用并将其删除，从而有助于HBV特异性T细胞的消耗[11]。 [12]。可以通过HBV特异性T细胞中促凋亡BIM分子的上调来扩增T细胞对凋亡死亡的敏感性（见图A）[7]。
骨髓细胞可塑性

骨髓细胞在肝脏中也起着关键的调节作用，因为它们可以从单核细胞分化为巨噬细胞，单核细胞衍生的树突状细胞或骨髓抑制细胞，这归功于其功能可塑性。在肝脏炎症期间，由于细胞间粘附分子1（ICAM-1 [CD54]）在LSEC上的表达，炎性单核细胞可以被引入肝脏[4]。然后，它们可以通过由激活的星状细胞驱动的CD44依赖性机制来分化成骨髓来源的抑制细胞[4]。另一方面，TLR-9信号可以通过引起称为iMATE的炎性单核细胞聚集体的形成来驱动单核细胞分化成抗病毒保护，其中病毒特异性CD8细胞可以在从单核细胞的炎性树突状细胞释放的OX40和CD28信号传导起源[13]。
通过肝脏抗原呈递细胞（APC）的T细胞激活是次优的，可以促进耐受性

几种肝细胞类型，包括LSEC，星状细胞和枯否细胞可以作为APC激活天真T细胞[14]。有趣的是，CD8 T细胞可以通过LSEC中的窗口延伸突起，以在肝细胞上采样HBV抗原[15]。然而，肝脏内的T细胞活化可能不是最佳的耐受性诱导，因为这些肝脏APC中的大多数在稳态中表现出共刺激分子的非常差的表达，表达共抑制分子PD-L1和PD-L2的增加的水平IFN刺激并可产生免疫调节细胞因子，包括IL10和TGF-β。
经济支持

这项工作得到意大利艾米利亚 - 罗马涅地区（2010-2012年度计划大学，PRUa1RI-2012-006）和意大利大学和研究部的FIRB拨款（RBAP10TPXK）的资助。
利益冲突

卡罗法拉利：来自吉利德，罗氏和扬森的研究资助，担任吉利德，默克，阿维，BMS和箭头的顾问/顾问。

Gabriele Missale：担任拜耳顾问。