进入聚光灯：乙型肝炎表面抗原特异性B细胞

StephenW

Entering the spotlight: hepatitis B surface antigen–specific B cells
Christoph Neumann-Haefelin and Robert Thimme

First published September 17, 2018 - More info
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Loghman Salimzadeh, … , Patrick T.F. Kennedy, Antonio Bertoletti
Categories: Research Article Hepatology Infectious disease
Circulating and intrahepatic antiviral B cells are defective in hepatitis B
Alice R. Burton, … , Nadege Pelletier, Mala K. Maini
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    Abstract

    Hepatitis B virus–specific (HBV-specific) T cells have been identified as main effector cells in HBV clearance. In contrast, B cells producing neutralizing antibodies against the HBV surface antigen (HBsAg) have been studied in little detail, mainly due to methodical limitations. In this issue of the JCI, two reports use a new technique to specifically detect and characterize HBsAg-specific B cells ex vivo. Indeed, these cells are present, but show phenotypic alterations and impaired function during acute and chronic HBV infection. Thus, HBsAg-specific B cells are a novel attractive target for antiviral strategies toward functional cure of chronic HBV infection.

    Hepatitis B surface antibody in history and treatment

    A fourth of the world’s population has been infected with hepatitis B virus (HBV), and an estimated 250 million people are chronically infected, putting them at risk for progressive liver disease, liver cirrhosis, liver failure, and hepatocellular carcinoma. Of adults infected with HBV, 95% clear the virus spontaneously, while 90% of newborns develop chronic infection. Since HBV infection does not induce an interferon response, HBV is a stealth virus with respect to the innate immune system (1, 2). Therefore, HBV clearance depends on a successful adaptive immune response. Indeed, a multispecific and vigorous HBV-specific CD8+ T cell response has been associated with viral clearance (3, 4), while HBV-specific CD8+ T cell exhaustion is a hallmark of persistent infection (5–7). Less attention, however, has been paid to the role of neutralizing antibodies targeting the envelope protein of HBV, the HBV surface antigen (HBsAg). Indeed, the hepatitis B surface antibody (anti-HBs) is only detectable in the blood of HBV-infected individuals after the loss of HBsAg, either upon the resolution of acute infection or in case of the rare event of spontaneous or drug-induced clearance of chronic HBV infection. Thus, anti-HBs is seen as not playing a major role in HBV clearance. Anti-HBs, on the other hand, has been established as a diagnostic tool, indicating protective immunity after acute-resolving HBV infection or vaccination as well as “functional cure” of chronic HBV infection (HBsAg to anti-HBs seroconversion). There are, however, several clinical observations that argue against such a minor role of anti-HBs. First, anti-HBs contained in hepatitis B immunoglobulin (HBIG) is well known to prevent vertical HBV transmission from infected mothers to newborns as well as reinfection of liver transplants in previously HBV-infected hosts. Second, B cell–depleting drugs used in oncology and rheumatology, such as the anti-CD20 antibody rituximab, induce HBV reactivation in HBV carriers and even in patients with “resolved” HBV in whom nuclear HBV cccDNA persists as a viral reservoir for decades (8). These clinical observations indicate that anti-HBs has a more prominent role than previously acknowledged. Indeed, anti-HBs can block HBV cell entry, either by blocking the binding site of HBsAg for the cell receptor recently identified to be sodium taurocholate cotransporting polypeptide (NTCP) or by binding to the “antigenic loop” of HBsAg that is involved in interaction with heparan sulfate proteoglycan (HSPG) in a prereceptor step of cell entry. In addition to direct inhibition of cell entry, anti-HBs also mediate endocytosis and subsequent neutralization of virions as well as Fc-mediated phagocytosis and killing of infected cells. In addition, anti-HBs, HBsAg, and additional components build immune complexes that can activate HBV-specific T cells (9).

StephenW

进入聚光灯：乙型肝炎表面抗原特异性B细胞
Christoph Neumann-Haefelin和Robert Thimme

首次发布于2018年9月17日 - 更多信息
相关文章：
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Loghman Salimzadeh，......，Patrick T.F.肯尼迪，安东尼奥贝托莱蒂
分类：研究论文肝病学传染病
循环和肝内抗病毒B细胞在乙型肝炎中有缺陷
Alice R. Burton，......，Nadege Pelletier，Mala K. Maini
分类：研究文章免疫学传染病

    抽象

    已经将乙型肝炎病毒特异性（HBV特异性）T细胞鉴定为HBV清除中的主要效应细胞。相反，已经很少详细地研究了产生针对HBV表面抗原（HBsAg）的中和抗体的B细胞，这主要是由于方法上的限制。在本期JCI中，两篇报道使用一种新技术来特异性地检测和表征体外HBsAg特异性B细胞。实际上，这些细胞存在，但在急性和慢性HBV感染期间表现出表型改变和功能受损。因此，HBsAg特异性B细胞是用于慢性HBV感染功能性治愈的抗病毒策略的新型有吸引力的靶标。

    乙型肝炎表面抗体的病史和治疗方法

    世界上四分之一的人口已感染乙型肝炎病毒（HBV），估计有2.5亿人患有慢性感染，使他们面临进行性肝病，肝硬化，肝功能衰竭和肝细胞癌的风险。在感染HBV的成年人中，95％的人自发清除病毒，而90％的新生儿患有慢性感染。由于HBV感染不会诱发干扰素反应，因此HBV是一种与先天免疫系统相关的隐形病毒（1,2）。因此，HBV清除取决于成功的适应性免疫应答。实际上，多特异性和有活力的HBV特异性CD8 + T细胞反应与病毒清除有关（3,4），而HBV特异性CD8 + T细胞衰竭是持续感染的标志（5-7）。然而，较少关注靶向HBV包膜蛋白HBV表面抗原（HBsAg）的中和抗体的作用。实际上，乙型肝炎表面抗体（抗-HBs）只有在HBsAg丧失后才能在HBV感染个体的血液中检测到，无论是在急性感染消退后，还是在罕见的自发或药物诱导清除的情况下慢性HBV感染因此，抗HBs被认为在HBV清除中没有起主要作用。另一方面，抗HBs已被确立为诊断工具，表明在急性解决HBV感染或接种疫苗后的保护性免疫以及慢性HBV感染的“功能性治愈”（HBsAg至抗HBs血清转换）。然而，有一些临床观察结果反对抗HBs的这种次要作用。首先，众所周知，乙型肝炎免疫球蛋白（HBIG）中含有的抗-HBs可防止感染母亲向新生儿的垂直HBV传播以及先前HBV感染宿主中肝脏移植的再感染。其次，用于肿瘤学和风湿病学的B细胞耗竭药物，例如抗CD20抗体利妥昔单抗，在HBV携带者中诱导HBV再激活，甚至在具有“解决的”HBV的患者中，其中核HBV cccDNA作为病毒库持续数十年（ 8）。这些临床观察表明，抗HBs的作用比以前承认的更为突出。实际上，抗-HBs可阻断HBV细胞进入，阻断最近被鉴定为牛磺胆酸钠协同转运多肽（NTCP）的细胞受体的HBsAg结合位点或通过结合参与相互作用的HBsAg的“抗原环”。硫酸乙酰肝素蛋白多糖（HSPG）在细胞进入的预先受体步骤中。除了直接抑制细胞进入外，抗HBs还介导内吞作用和随后的病毒粒子中和以及Fc介导的吞噬作用和杀死感染细胞。此外，抗HBs，HBsAg和其他成分可构建可激活HBV特异性T细胞的免疫复合物（9）。

StephenW

   specific T cells (9).

    HBsAg-specific B cells in acute and chronic HBV infection

    Given these important antiviral functions of anti-HBs, a main open issue in HBV immunobiology is the reason for the lack of detectable anti-HBs in both acute and chronic HBV infection prior to HBsAg loss. To date, two plausible hypothetical explanations for the lack of anti-HBs have been put forth. First, it was suggested that anti-HBs is produced by HBsAg-specific B cells in acute and chronic HBV infection, but is depleted by the large number of circulating HBsAg-containing subviral particles that outnumber complete virions by an order of magnitude. This hypothesis was supported by the finding that complexes of anti-HBs with circulating HBsAg are not recognized by current diagnostic assays, but can be detected in chronically infected patients using highly sensitive immunoassays (10). Additionally, there were early and have been more recent reports of HBsAg-specific B cell dysfunction, especially in chronic HBV infection. Indeed, B cells isolated from patients with chronic HBV infection showed a reduced proliferative capacity and were not able to produce anti-HBs upon stimulation. This functional defect reverted after the rare event of HBsAg loss during chronic infection (11, 12). In the current issue of the JCI, Salimzadeh and Le Bert et al. from the Bertoletti laboratory (13) and Burton et al. from the Maini laboratory (14) addressed the issue of lack of anti-HBs during acute and chronic HBV infection by making use of a new technique to detect HBsAg-specific B cells. Specifically, they utilized fluorochrome-labeled recombinant HBsAg as “bait” to detect and characterize HBsAg-specific B cells by FACS analysis ex vivo. Strikingly, by using a similar approach independently, the two groups came to the very same results (Figure 1): first, HBsAg-specific B cells are present in acute, chronic, and resolved HBV infection in similar frequencies. Second, HBsAg-specific B cells isolated from patients with acute as well as chronic, but not resolved, HBV infection are unable to mature into anti-HBs–secreting cells in vitro. Third, in phenotypical analyses, these HBsAg-specific B cells in acute and chronic HBV infection resemble “atypical memory B cells” that are characterized by low expression of CD21 and CD27, but high expression of inhibitory markers, such as PD-1, and the transcription factor T-bet (15). Fourth, Burton et al. demonstrated that these HBsAg-specific atypical memory B cells accumulate in the liver, the site of infection and inflammation of HBV-infected patients. Fifth, this phenotype and functional impairment are not restricted to HBsAg-specific B cells, but also affect the global B cell population in HBV-infected patients, a finding with so far unclear implications that needs further clarification. Sixth, the function of HBsAg-specific B cells can be partially restored in vitro by specific culture conditions, such as PD-1 blockade (13, 14) or the addition of IL-2, IL-21, and CD40 ligand–expressing (CD40L-expressing) feeder cells (13).
   

StephenW

特异性T细胞（9）。

    HBsAg特异性B细胞在急性和慢性HBV感染

    鉴于抗HBs的这些重要的抗病毒功能，HBV免疫生物学中的一个主要开放问题是在HBsAg丢失之前急性和慢性HBV感染中缺乏可检测的抗HBs的原因。迄今为止，已经提出了关于缺乏抗HBs的两种似是而非的假设性解释。首先，有人提出抗HBs是由HBsAg特异性B细胞在急性和慢性HBV感染中产生的，但是由于大量循环的含HBsAg的亚病毒颗粒数量超过完整病毒颗粒一个数量级而耗尽。这一假设得到以下发现的支持：抗HBs与循环HBsAg的复合物未被当前的诊断分析识别，但可以使用高灵敏度免疫分析在慢性感染患者中检测到（10）。此外，早期和最近有关于HBsAg特异性B细胞功能障碍的报道，尤其是慢性HBV感染。实际上，从患有慢性HBV感染的患者中分离的B细胞显示出增殖能力降低并且在刺激时不能产生抗HBs。在慢性感染期间罕见的HBsAg丢失事件后，这种功能缺陷恢复（11,12）。在最新一期的JCI中，Salimzadeh和Le Bert等人。来自Bertoletti实验室（13）和Burton等人。来自Maini实验室（14）通过利用新技术检测HBsAg特异性B细胞，解决了急性和慢性HBV感染期间缺乏抗HBs的问题。具体而言，他们利用荧光染料标记的重组HBsAg作为“诱饵”，通过离体FACS分析检测和表征HBsAg特异性B细胞。引人注目的是，通过独立使用类似的方法，两组得出了相同的结果（图1）：首先，HBsAg特异性B细胞以相似的频率存在于急性，慢性和解决的HBV感染中。其次，从急性和慢性但未解决的HBV感染患者中分离的HBsAg特异性B细胞不能在体外成熟为抗HBs分泌细胞。第三，在表型分析中，急性和慢性HBV感染中的这些HBsAg特异性B细胞类似于“非典型记忆B细胞”，其特征在于CD21和CD27的低表达，但是抑制标记物如PD-1的高表达，和转录因子T-bet（15）。第四，Burton等。证明这些HBsAg特异性非典型记忆B细胞在肝脏，HBV感染患者的感染部位和炎症部位积聚。第五，这种表型和功能障碍不仅限于HBsAg特异性B细胞，而且还影响HBV感染患者的全球B细胞群，这一发现目前尚不明确，需要进一步澄清。第六，HBsAg特异性B细胞的功能可以通过特定的培养条件在体外部分恢复，如PD-1阻断（13,14）或添加IL-2，IL-21和CD40配体表达（表达CD40L的饲养细胞（13）。
    HBV感染的HBsAg特异性B细胞。图1

    HBV感染的HBsAg特异性B细胞。 （A）荧光染料标记的HBsAg与HBsAg特异性B细胞的HBsAg特异性B细胞受体（BCR）结合，允许它们直接在体外进行检测和表征。使用这种方法，确定了急性和慢性感染与解决感染中HBsAg特异性B细胞之间的表型和功能差异。 （B）在急性和慢性感染中，与其在解决的感染中的存在相比，HBsAg特异性B细胞以相似的频率存在;然而，它们显示CD21和CD27的低表达（与非典型记忆B细胞一致）以及抑制性受体的高表达，例如PD-1，BTLA，CD22，FcγRIIB和FcRL5。它们还高度表达转录因子T-bet，并且不能分化成分泌抗HBs的浆细胞。这些表型改变在肝脏中富集。然而，它们不限于HBsAg特异性B细胞，而是影响急性或慢性HBV感染患者的全球B细胞区室。