NK细胞在HBV感染中的作用研究

Study the change of NK cells in HBV infection

目的自然杀伤（natural killers, NK）细胞是淋巴细胞的重要组成，属于固有免疫的一部分。在乙型肝炎病毒（hepatitis B virus, HBV）感染过程中，NK细胞既发挥抑制病毒复制的作用，同时又可引起肝组织损伤。对于NK细胞在HBV感染过程中的具体作用，目前还存在很大争议。方法该研究比较了49例慢性HBV感染免疫清除期（immune clearance phase，IC）、32例急性乙型肝炎（acute hepatitis B，AHB）、30例慢性HBV感染免疫耐受（immune tolerance phase，IT）患者及13例健康对照（health control, HC）的外周血NK细胞、CD56bright群、CD56dim群和NK细胞表面受体IFNAR2、NKp46的表达情况以及细胞因子IL-10、TGFβ1、IFNα2、IFNγ的含量，并分析了它们与ALT、HBV DNA的关系。结果IC和AHB组CD3-CD56＋NK细胞频数降低，主要发挥细胞毒作用的CD56dim群的频数也减少，而主要分泌IFNγ的CD56bright群却升高。不一致的，外周血IFNγ含量却没有相应升高，相反，还明显降低。与HC组比，在IT组并没有发现NK细胞及其亚群频数的明显改变。可抑制NK细胞产生IFN-γ的IL-10在IC和AHB组升高，同样升高的还有另一种抑制性细胞因子TGFβ1。IC组IFNα2分泌增加而且NK细胞IFNAR2的表达上调。IT组虽然NK细胞IFNAR2表达上调，但是外周血IFNα2分泌量明显不足。AHB组IFNα2分泌水平和健康对照相近。ALT与HBV DNA在IC患者呈负相关，在AHB组呈正相关。IC组HBV DNA含量与IFNAR2的表达水平呈正相关。结论NK细胞在免疫清除期患者和急性乙型肝炎患者受到抑制，这种抑制可能有助于减轻肝脏损伤。在免疫清除期患者和急性乙型肝炎患者NK细胞的细胞毒性功能被保存，但分泌细胞因子能力受损。免疫耐受期患者可能是IFNα2分泌不足，不能有效的激活NK细胞，导致HBV长期存在。急性乙型肝炎患者HBV的清除可能依赖非IFNα2途径。ALT可作为评估免疫清除期患者免疫清除HBV水平的指标。急性HBV感染时，病毒的快速扩增可能是导致肝脏损伤的机制。另外，在免疫激活时，HBV可能刺激NK细胞上IFNAR2的表达。

Objective Background Natural killer （NK） cells is an important component of lymphocytes, part of the innate immunity. In hepatitis B virus （HBV） infection, NK cells can not only inhibit the replication of virus, but also can cause liver damage. Now, the specific mechanism of NK cells to clear HBV is still controversial. Methods The study compared the peripheral blood NK cells, CD56 bright subsets, CD56dim subsets, the expression of surface receptors IFNAR2 and NKp46 on NK cells and the level of IL-10, TGF-β1, IFNα2, IFNγ and their correlation with ALT and HBV DNA among the patients of chronic HBV infection immune clearance phase （ n = 49） , acute hepatitis B （ n = 32） , chronic HBV infection immune tolerance phase （ n = 30） and healthy controls （ n = 13）. Results We found that the frequency of CD3-CD56 ＋ NK cells is reduced in HC and AHB. The frequency of CD56dim subsets playing an important role of cytotoxicity is reduced too. However, the frequency of CD56bright subsets which mainly secretes IFNγ, increases. Inconsistently the level of the IFNγ is reduced significantly in the peripheral blood. We found that there is no obvious difference of the frequency of CD3-CD56＋ NK ceils and their subsets between IT and HC. The level of IL-10 which can inhibit NK ceils to produce IFNγ increases in IC and AHB, TGF-β1, another inhibitory cytokine, increases too. The level of IFNα2 increases and the expression of the surface receptor IFNAR2 on NK cells is up-regulated in IC. However in IT, the expression of the surface receptor IFNAR2 of NK cells is up-regulated but the level of IFNα2 is reduced. The level of IFNα2 in AHB and HC is similar. There is a positive correlation in IC and a positive correlation in AHB between ALT and HBV DNA. HBV DNA and the expression of IFNAR2 on NK cells have a positive correlation in IC. Conclusions In IC and AHB, NK cells are inhibited which may contribute to reducing liver damage. And the cytotoxicity of NK cells is retained, but the function to secrete cytokines is damaged. The insufficient secretion of IFNα2 can＇ t activate NK ceils effectively which may contribute to HBV long-standing in IT. It may not depend on IFNα2 to clear HBV in AHB. ALT can be used to evaluate the level of clearance HBV in IC. The rapid expansion of the virus may be the mechanism of liver damage in AHB. In addition, when immune response of the host is activated, HBV may stimulate NK cells to up-regulate the surface receptor IFNAR2.