【论文】正常衰老和与衰老相关疾病的NK细胞

Hindawi Publishing Corporation

Journal of Biomedicine and Biotechnology

Volume 2012, Article ID195956, 8 pages

doi:10.1155/2012/195956

Review Article

NK Cells in Healthy Aging and Age-Associated Diseases

正常衰老和与衰老相关疾病的NK细胞

Xavier Camous,¹ Alejandra Pera,² Rafael Solana,²  and Anis Larbi¹

¹Singapore Immunology Network (SIgN) , Biopolis, Agency for Science, Technology and Research, Singapore138648

² Department of Immunology, School of Medicine, Reina Sofia University Hospital, IMIBIC, 14004 Cordoba, Spain

Correspondence should be addressed to Anis Larbi, anis_larbi@immunol.a-star.edu.sg

Received 10 August 2012; Accepted 10 September 2012

Academic Editor: Thomas Liehr

Copyright©2012 Xavier Camous et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

NK细胞在免疫系统中表现出很高的细胞毒性。 更改其数量或活性可能会对整体免疫力产生深远影响。 他的降低让老年人群变得更容易受到感染、患癌、自身免疫疾病和神经退行性疾病等。 随着全世界老年人比例的增加，人们迫切需要更好地了解免疫系统的老化，以预防和治愈他的老化。 为此，需要更好地了解不同免疫细胞及其子集的功能和表型。 我们在这里回顾NK细胞在健康老龄化以及各种年龄相关疾病中的功能和表象。

NK cells exhibit the highest cytotoxic capacity within the immune system. Alteration of their number or functionality may have a deep impact on overall immunity. This is of particular relevance in aging where the elderly population becomes more susceptible to infection, cancer, autoimmune diseases, and neurodegenerative diseases amongst others. As the fraction of elderly increases worldwide, it becomes urgent to better understand the aging of the immune system to prevent and cure the elderly population. For this, a better understanding of the function and phenotype of the different immune cells and their subsets is necessary. We review here NK cell functions and phenotype in healthy aging as well as in various age-associated diseases.

1、细胞衰老 Cellular Senescence

衰老，在整个生物体范围内，是一个非常复杂的过程，涉及许多不同的机制。研究正常的衰老过程也很复杂，因为我们长期被病原体包围，生活习惯不同，承受的压力不同，这些都会影响衰老过程。衰老生物学始于Hayflick 和 Moorhead博士^[1]于1961年。当时，细胞被认为是体外不朽的，死亡的发生是由于非最佳条件。他打破了这一教条，声称细胞在进入复制衰老状态(细胞停止分裂)之前，会经历一定次数的分裂。1971年，Olovnikov发现这种现象是由于每个分裂都发生了DNA缩短^[2,3]。随后，端粒在1978年首次在嗜热四膜菌^[4]中被研究，几年后在人类^[5]中被研究。端粒长度可能是衰老原因的第一个暗示来自于观察，每个组织^[6]的端粒长度不相同。一年前，Greider和Blackburn博士发现了端粒酶^[7]，海弗利克现象可以用端粒酶活性和端粒长度可能是正常衰老^[8]的主要作用因素来解释。在这里，我们将重点关注人体的重要部分，免疫系统，特别是自然杀伤(NK)细胞亚群的衰老。

Aging, at the whole organism scale, is a very complex process, involving many different mechanisms. Studying the normal senescence process is also complex as we are permanently surrounded by pathogens, have different lifestyle habits, and exposed to different levels of stress which all influence the senescence process. Senescence biology really started in 1961 with Drs. Hayflick and Moorhead^[1]. At this time, cells were supposed to be immortal invitro and death occurring because of nonoptimal conditions. He shattered this dogma by stating that cells were programmed to divide a certain number of times before entering a replicative senescence state, where cells stop to divide. In 1971, Olovnikov discovered that this phenomenon was due to a DNA shortening, occurring at each division^[2,3]. Then, telomeres were studied first in 1978 in Tetrahymena thermophila ^[4] and few years later in human ^[5]. The first hints that telomere length could be a cause of senescence came from the observation that its length was not the same in every tissue ^[6]. One year before, Drs. Greider and Blackburn discovered the telomerase ^[7] , and Hayflick phenomenon could be explained by the fact that telomerase activity and telomere length could be the main actors of normal senescence ^[8] . Here, we will focus on the senescence of averyimportant part of the human body, the immune system, and especially the natural killer (NK) cells subsets.

2.NK Cell Biology NK细胞生物学

NK细胞是非常重要的细胞毒性细胞群，其连接先天和细胞免疫。它们起源于常见的淋巴祖细胞，如B细胞和T细胞，在进入血液循环之前在淋巴组织（脾脏，骨髓，扁桃体）中成熟^[9]。与淋巴细胞的主要差异是它们缺乏CD3，BCR或TCR表达。它们可以定义为CD3^-CD56 ⁺ CD16 ⁺细胞。这些细胞在刺激后可以非常快地反应，比T细胞更快，因为它们可以直接杀死缺乏MHC- I类分子的“缺失自身”细胞，而不需要先前的致敏，抗体结合或肽呈递^[10]。这些细胞在抗病毒和抗肿瘤反应中非常重要。这种非常快速和有效的杀戮能力仍然受到严格监管。 NK细胞通过测量其表面抑制和激活受体所接收的信号之间的平衡来决定杀死，抑制作用占主导地位^[11]。这些信号由2族受体，Ig样和C型凝集素传递。在Ig样抑制性受体中，有KIR（杀伤细胞免疫球蛋白样受体）识别HLA分子并发送强抑制信号^[9]和LIR（白细胞抑制受体）也与I类HLA结合。关于抑制性C型凝集素，Ly49和异二聚体CD94 / NKG2A-B，识别HLA-E分子^[9]能够阻止NK细胞杀死。活化受体也是这两个家族的一部分。 NCR（天然细胞毒性受体）如CD16（FcγIIIA），允许抗体介导的毒性，或NKp46，NKp30和NKp44属于Ig样家族。 CD94 / NKG2C-E（识别HLA-E）以及NKG2D（识别非经典HLA）是激活C型凝集素受体。它们在先天性和适应性免疫接口中的作用的一部分受到它们表达的CD56和CD16水平的影响^[12-14]。 CD56^dimCD16 ⁺是终末分化的细胞毒性细胞，其作用更像先天免疫，尽管它们也是细胞因子产生者。另一方面，CD56^brightCD16^-细胞的分化程度较低，细胞因子分泌细胞能够维持先天性和适应性免疫^[15]。还有第三个NK细胞亚群，CD56^-CD16 ⁺，最初描述于HIV-1 +患者^[16]，也描述于乙型肝炎和丙型肝炎^[17]，具有较差的增殖和细胞毒性能力，细胞因子产生较少，以及高趋化因子产生^{[ 18}。 CD56^brightCD16^-细胞被认为是CD56^dimCD16 ⁺细胞的未成熟细胞前体^[19,20]。然而，CD56^-CD16 ⁺细胞与其他NK细胞群之间的关系尚不清楚。

NK cells are a very important population of cytotoxic cells linking innate and cellular immunities. They originate from common lymphoid progenitors, like B and T cells, and mature in lymphoid tissues (spleen, bone marrow, tonsil) before entering the blood circulation [9]. A major difference with lymphocytes is their lack of CD3, BCR, or TCR expression. They can be defined as CD3⁻CD56⁺CD16⁺ cells. These cells can react very quickly upon stimulation, faster than T cells, as they can kill directly “missing-self”cells that lack MHC class-I molecules without any need of previous sensitization, antibody binding, or peptide presentation ^[10]. These cells are very important in antiviral and antitumoral responses. This very fast and efficient ability to kill is still very strictly regulated. The NK cell takes the decision to kill by measuring the balance between signal received by its inhibitory and activating receptors expressed at its surface, inhibition being dominant ^[11]. These signals are transmitted by 2 families of receptors, the Ig-like and the C-type lectins. Among Ig-like inhibitory receptors there are KIRs ( killer-cell immunoglobulin-like receptors) recognizing HLA molecules and sending a strong inhibitory signal ^[9] and LIR (leucocyte inhibitory receptor) also binding to class-I HLA. Concerning inhibitory C-type lectins, Ly49 and the heterodimer CD94/NKG2A-B, recognizing HLA-E molecules ^[9] are able to prevent NK cells to kill. The activating receptors are also part of these 2 families. The NCR (natural cytotoxicity receptors) such as CD16 (FcγIIIA), allowing antibody-mediated toxicity, or NKp46, NKp30, and NKp44 belong to the Ig-like family. CD94/NKG2C-E (recognizingHLA-E) as well as NKG2D (recognizing nonclassical HLA) are activating C-type lectins receptors. A part of their role at the interface of innate and adaptive immunities is influenced by the level of CD56 and CD16 they express [12–14]. CD56dimCD16+ are terminally differentiated cytotoxic cells that act more like innate immunity, although they are also cytokine producers. On the other hand CD56^brightCD16⁻ cells are less differentiated, cytokine secreting cells able to sustain innate and adaptative immunity ^[15]. There is a third NK cell subpopulation, CD56⁻CD16^+, originally described in HIV-1+ patients ^[16], also described in hepatitis B and C ^[17], with poor proliferative and cytotoxic capacity low cytokine production, and high chemokine production ^[18]. CD56^brightCD16⁻ cells are considered immature cell precursors of CD56^dimCD16⁺ cells ^[19,20]. However, it is not clear the relationship between CD56⁻CD16⁺cells and the other NK cell populations.

3.Aging and Overall Immunity 衰老与免疫

免疫衰老被定义为通过衰老逐渐丧失免疫功能，并且涉及所有类型的免疫细胞。造血干细胞（HSCs）由于端粒缩短和DNA代谢产生的自由基在其代谢过程中的积累而变得越来越不能更新血细胞群^[21]。巨噬细胞失去其杀菌能力，其数量减少^[22]。产生抗体的B细胞数量减少并导致较小的免疫球蛋白多样性和效率^[23]。树突状细胞抗原呈递功能随着年龄的增长而降低，引起细胞免疫的深刻变化^[24]。随着越来越少的免疫细胞被创造，淋巴细胞的体内平衡被修改，记忆群开始失去其功能，导致对病原体和癌症的更大易感性^[25]。为了估计免疫衰老，将T细胞活性用作生物标志物，因为几乎所有的功能都通过衰老进行修饰。它们产生较少的细胞因子^[26]，谱系多样性降低^[27]，稳态被修饰^[26]，它们的增殖受损^[26]，它们的细胞内信号转导能力被解除调节^[28]，它们的细胞毒性较低^[29]。 

Immunosenescence is defined as the progressive loss of immune functions through aging, and all types of immune cells are concerned. Hematopoietic stem cells (HSCs) become less and less able to renew the blood cells populations due to the shortening of telomeres and the accumulation of DNA lesionsdue to free radical created during their metabolism ^[21]. Macrophages lose their bactericidal capacities and their number decreases ^[22]. Antibody-producing B cell number decreases and leads to a smaller immunoglobulin diversity and affinity ^[23]. Dendritic cells antigen presenting function decreases with age causing profound changes in cellular immunity ^[24]. The lymphocytes homeostasis is modified as less and less na¨ıve immune cells are created, and memory populations start to lose their functions, leading to a greater susceptibility to pathogens and cancers ^[25]. To estimate the immunosenescence, T cells activity is used as a biomarker as nearly all of their functions are modified by aging. They produce less cytokines [26], the repertoire diversity decreases^[27], the homeostasis is modified^[26], their proliferation is impaired^[26], their intracellular signal transduction capability is deregulated^[28], and they are less cytotoxic^[29].

4.NK Cells in Healthy Aging 正常衰老的NK细胞

在衰老过程中，像淋巴细胞一样，NK细胞的数量、功能和表型都被调节和修饰。几项研究表明,在老年人中NK细胞亚群的数量和重新分布增加，CD56明显群体减少，更不成熟，CD56^dim成熟细胞增加，,尤其是那些表达CD57高度分化,以及CD56⁻CD16 ⁺细胞^[34]。虽然CD56^bright细胞表型在健康衰老过程中没有变化，但与年轻个体^[30]相比，晚期分化的CD56^dim人群HLA-DR和CD95 (Fas)表面表达水平较高，CD69 (c型凝集素和早期活化抗原)表达水平较低。在健康老年人中检测NK细胞细胞毒性时，发现年龄对^[35]无影响，但血液中CD56^dim人群的增加与整体细胞毒性的增加无相关性(图1)。这假设NK细胞在单细胞水平上的细胞毒性活性受损，尽管未发现与靶点结合或穿孔蛋白含量^[36]的缺失。这种内在的细胞毒性降低的原因仍在研究中。

During aging, like for lymphocytes, NK cell number functions and phenotype are modulated and modified. Several studies indicate that in the elderly there is an increase in number and a redistribution of NK cell subpopulations, with a decrease of CD56bright population, more immature, and an increase of CD56dim mature cells, particularly those highly differentiated who express CD57, as well as the CD56−CD16+ cells ^[30–34]. While the CD56bright cells phenotype does not change during healthy aging, the terminally differentiated CD56dim population displays higher levels of HLA-DR and CD95 (Fas) surface expression and a decrease in CD69 (a C-type lectin and early activation antigen) compared to young individuals ^[30]. When NK cells cytotoxicity was tested in healthy elderly individuals, it was noted that age does not affectit ^[35], but the increase of CD56dim population in blood does not correlate with an increase of overall cytotoxicity (Figure1). This supposes an impairment in NK cells cytotoxic activity at the single-cell level although no default was identified in binding to target or in perforin content ^[36]. The explanation for this intrinsic reduced cytotoxic activity is still under investigation.

Figure1:NK cell phenotype and functions in healthy aging. Increase and decrease in the NK-related parameters during aging are depicted. For example, NK cell proliferation is reduced.

图1：正常衰老的NK细胞表型和功能。 描述了老化期间NK相关参数的增加和减少。 例如，NK细胞增殖减少。

NK细胞最重要的细胞因子之一是IL-2，因为它结合适应性免疫应答和NK细胞。用细胞因子如IL-2，IL-12，IFN-γ和IFN-α处理NK细胞增加了它们的杀灭能力并使它们能够杀死通常“NK抗性的细胞。在健康的老年人中，如果细胞因子刺激没有受到损害，杀死“NK抗性”细胞的能力261仍然下降^[35] .IL-2也可以增殖，但是，在老年人中，反应强度越小，从非常轻微的减少到几乎没有增殖^[30]。 IL-2还修饰了老年人细胞因子分泌的NK谱，与年轻人相比，IL-2诱导的IFN-γ和TNY-α降低，而IL-1，IL 4，IL-6，IL.8， IL-10和TNF-α增加^[37]。来自老年人的NK细胞在IL-2刺激时也产生较少的IFN-γ，而穿孔素和TNF-α未被修饰^[36] .Almeida-Oliveira等人最近做了一个关于NK标志物在整个生命过程中从儿童到死亡的调节研究非常有趣^[38]。他们注意到CD56群体的扩大和收缩（i） n和数量的CD56^bright在老年人中增加细胞毒性细胞，同时减少细胞因子的NK CD56明显量，如IFN-γ，TNF-α，GM-SCE或IL-10和IL-13（图1）。此外，活化的NK细胞分泌较少的IFN-γCD56^bright细胞来自儿童和老年受试者表达更多的KIR受体，并且在他们的队列中，大多数仅表达抑制性KIR或同时抑制和激活同时关于NCR，他们发现下降NKp30和NKp46在老年人中的表达已知NKP30参与与树突细胞的串扰，导致先天性和适应性反应之间的联系^[39]。他们还发现，两个NK亚群中的老年人和仅儿童CD56^dim细胞中CD94表达下降。有趣的是，他们发现NKG2D表达在儿童和老年人中都没有下降。这可能是适应缺乏的适应性免疫系统的一种形式，因为在衰老过程中它变得不那么有效，而在童年期间，它对于抗原应答大多是天然的。

One of the most important cytokines for NK cells is IL-2 as it binds adaptive immune response and NK cells. Treating NK cells with cytokines such as IL-2, IL-12, IFN- γ, and IFN-α increases their killing aptitudes and allows them to kill cells usually "NK resistant. In healthy elderly people, if cytokine stimulation is not impaired, the ability 261, to kill " NK resistant" cells still decreases [35]. IL-2 can also s proliferation, but, in elderly people, the less intensity of the response varies from a very slight decrease to nearly no proliferation [30]. IL-2 also modifies the NK profile for cytokine secretion in elderly, compared to young people, IL-2 induction of IFN-γ and TNY-α is decreased whereas IL-1, IL 4, IL-6, IL. 8, IL- 10, and TNF-α increase [37]. NK cells from elderly also produce less IFN-γ upon IL-2 stimulation whereas perforin and TNF-α were not modified [36]. Almeida-Oliveira et al. recently did a very interesting in study about the modulation of NK markers throughout life, from childhood to death [38]. They noticed an expansion of the CD56 population and shrinkage (in and number) of CD56bright in elderly people, increasing cytotoxic cells while diminishing the NK CD56bright amount of cytokine like IFN-γ, TNF-α, GM-SCE or IL-10 and IL-13 (Figure 1). Moreover, activated NK cells secrete less IFN-γ CD56bright cells from children and elderly subjects express more KIR receptors, and in their cohort, most of them express only inhibitory KIR or both inhibitory and activating at the same time Concerning NCR, they find a decline in the expression of NKp30 and NKp46 in elderly people. NKP30 is known to participate in the crosstalk with dendritic cell leading to the link between innate and adaptive response [39] They also found a decline in CD94 expression in elderly people in both NK subsets and only in CD56dim cells in children. Interestingly, they found no decline in NKG2D expression neither in children nor in elderly. This could be a form of adaptation to a deficient adaptive immune system as during aging it becomes less effective while during childhood it is mostly naive regarding antigen encounter.

5.Age_Associated Diseases 年纪相关的疾病

无数的疾病都与衰老有关，所以在本文中，我们将讨论与NK细胞相关的最常见和免疫相关的疾病。以惊人的速度出现的阿尔茨海默氏症(AD)肯定与衰老有关，除了早发性先天性阿尔茨海默氏症可以在任何时候发生。

Countless diseases are correlated with aging, so in this present paper, we will talk about the most common and immune-related diseases to link up with NK cells. Emerging at alarming speed is certainly Alzheimer's disease (AD) that is associated with aging, with the exception of the early onset congenital form that can occur at any time.

通常这种疾病在65岁后被诊断出来并且正在成为世界范围内的一个真正的问题，因为在2006年，有2660万患者，预计到2050年全球将有8500万人受到影响^[40]。除了先天性形式外，阿尔茨海默氏症的原因尚不清楚。已经提出了几种假设来解释这种疾病。其中，淀粉样蛋白假说假定淀粉样β（Aβ）积聚，在脑中形成斑块，是阿尔茨海默氏症的致病因子^[41]。这得到了几个事实的支持：唐氏综合症患者需要额外的21号染色体，携带Aβ相关基因APP，并在40岁前发展为阿尔茨海默氏症 ^[42]。最后，载脂蛋白E 4基因（APOE4）是已知的阿尔茨海默氏症相关标记，因为APOE基因中的不同基因型导致Aβ在脑中的不同积累^[43]。非斑块Aβ寡聚体也可能非常重要，因为它们可以结合神经元表面受体和破坏突触^[44]。此外，这些受体中的一种可能是朊病毒，导致Creutzfeldt-Jakob病^[45]。2009年，该理论被修改，表明Aβ的邻居，而不一定是蛋白质本身，可能是Aβ的主要致病因子。这种病。 N-APP，相同酶的片段。 N-APP通过与称为DR6（死亡受体6）的神经元受体结合来触发自毁途径^[46]。 DR6在受AD影响最大的大脑部分高度表达。 N-APP / DR6途径可能在衰老的大脑中被劫持而导致损伤。在这个模型中，Aβ只扮演副作用。另一个假设是Tau假设^[47]。 Tau蛋白是稳定中枢神经系统和神经元中丰富的微管的因子。已经表明，过度磷酸化的tau蛋白可以聚集在一起并形成神经原纤维缠结，通过分解微管并导致细胞死亡来破坏神经元转运系统^[48-50]。

Usually this disease is diagnosed after 65 years and is becoming a real problem worldwide, as in 2006, there were 26. 6 million Patients, and it is predicted to affect I in 85 people globally by 2050 ^[40]. The causes of AD are still unknown, except for the congenital form. Several hypotheses have been proposed to explain the disease. Among them, the amyloid hypothesis postulates that amyloid β (Aβ) accumulation, forming plaques in the brain, is the causative agent of AD ^[41]. This is supported by several facts: Down syndrome patients gut an extra chromosome 21, bearing the Aβ-related gene APP ,and develop AD before 40 [42]. Finally, apolipoprotein E 4 gen (APOE4) is a known AD-associated marker as different genotypes in the APOE gene lead to differential accumulation of Aβ in the brain ^[43].Nonplaque Aβ oligomer may also be very important as they can bind neuron surface receptor and disrupt synapses^[44]. Moreover, one of these receptors may be the prion, responsible for Creutzfeldt-Jakob disease ^[45].In 2009, this theory was modified, suggesting that a neighbor of Aβ, and not necessarily the protein itself, could be a major causative agent of the disease. N-APP, a fragment of the same enzymes. N-APP triggers the self-destruct pathway by binding to a neuronal receptor called DR6(Death Receptor 6) ^[46]. DR6 is highly expressed in the part of the brain that is the most affected by AD. It is possible that the N-APP/DR6 pathway might be hijacked in the ageing brain to cause damage. In this model, Aβ only plays a side role. One of the other hypotheses is the Tau hypothesis ^[47]. Tau protein is a factor that stabilizes microtubules abundant in central nervous system and neurons. It has been shown that hyperphosphorylated tau proteins can cluster together and form neurofibrillary tangles shattering neuron transport system by disintegrating microtubules and leading to the death of the cell ^[48-50].

有几种癌症与衰老有关，因此，我们将在这里讨论经常发生的癌症和大多数老年人。 根据美国国家癌症研究所（NIC）的数据，经过65年的研究，癌症病例数比以前增加了10倍，并且在40岁之后发生癌症的可能性增加^[51]。 老年人中最常见的癌症是前列腺癌，乳腺癌，结肠癌，胰腺癌，膀胱癌，胃癌，肺癌和直肠癌。 它主要发生在老年人身上的原因尚不清楚，但可以提供一些解释。 首先，一些癌症发展缓慢是由于它们内在的攻击潜能，或者是由于免疫系统的控制。由于某些原因，免疫系统在经过多年或数十年的持续免疫监测后会出现缺陷。

Several cancers have been linked to aging so, tar and we will discuss here those occurring frequently and in the majority of elderly people. According to the US National Cancer Institute (NIC), after 65 years, there are 10 times ore cancer cases than before, and the probability to develop a cancer rises after 40 years of age ^[51]. The most common cancers in elderly people are prostate, breast, colon, pancreas, bladder, stomach, lung, and rectum. The reasons why it happens mainly in elderly are not clear, but some explanations can be provided. First, some of the cancers develop slowly due to their intrinsic aggressive potential or by its control by the immune system that for some reasons becomes deficient after years or decades of constant immune surveillance.

其次，随着年龄的增长，免疫系统开始减弱，降低了我们抵御癌症的天然屏障^[52]。第三，从逻辑上讲，较长的寿命与暴露于致癌物质(如污染、吸烟、化学品或紫外线)的风险较高有关。最后，参与细胞解毒的机制在衰老的细胞中受损，这些细胞表现出它们的能力来阻止(抗氧化水平)和修复DNA损伤或蛋白质修饰(例如。最终导致功能缺陷的细胞死亡或细胞转化^[53,54]。

Secondly, with advancing age the immune system starts to weaken, lowering our natural shield against cancer ^[52] Thirdly, a longer lifespan is logically associated to higher risks of exposition to carcinogens like those due to pollution, smoking, chemicals or UV. Finally, the mechanisms involved in cellular detoxification are impaired in aged cells rendering their capacity to prevent (antioxidant levels) and repair DNA damage or protein modifications (e. g., chaperones such as heat shock proteins) that ultimately lead to faulty functions cell death, or cell transformation ^[53,54]. 

骨骼和关节相关疾病降低了老年人的生活质量，使他们这些疾病更加重要。最痛苦的与年龄有关的疾病之一是关节炎，这是一个涵盖100多种疾病的通用术语。最常见的关节炎形式是骨关节炎(或退行性关节炎)，占美国病例的70%患骨关节炎。它包括关节软骨的丢失，导致骨间摩擦增加，导致疼痛和渐进性残疾^[55]。该区域的炎症经常被注意到，而骨骺的损伤迫使补偿性骨生长，从而阻止自然运动。这是有关系的，但不是由衰老引起的。最令人担心的身体部位是手和膝盖。骨质疏松症是一种与年龄有关的骨质疏松症，骨质疏松导致骨折的风险增加。在疾病期间，骨密度降低，内部结构受损，使骨骼更加脆弱。1型骨质疏松女性绝经后发生骨质疏松症，而2型骨质疏松症在75岁(女性为2:1)后男女均有发生。这种疾病的主要问题是跌倒的风险增加，再加上骨折会使老年人严重残疾。骨质疏松症最常见的骨折是髋关节骨折，往往导致髋关节置换。

Bone and joint-associated diseases reduce the quality of life of the elderly population rendering them more dependent. One of the most painful age-related diseases is arthritis, which is a generic term covering more than 100 pathologies. The most common form of arthritis is osteoarthritis (or degenerative arthritis) and is predominant in 65+ people (70% of cases in USA). It consists in a loss of cartilage in joints leading to an increased friction between bones inducing pain and a progressing disability [55]. Inflammation of the area is often noted, and the epiphyses damages force a compensatory bone growth that can prevent natural movements. It is related but not caused by aging. The most concerned body parts are hands and knees. Osteoporosis is and age-related condition where bones become porous, leading to an increased risk for fractures [56]. During the disease, bone mineral density is reduced, and the inner architecture is impaired making the bone much more fragile. It occurs in women, after menopaused for type 1 osteoporosis while type 2 osteoporosis is prevalent for both genders after 75 (2:1 ratio for female). The main problem of this disease is the increased risk of fall plus the fact that fracture can severely disable elderly people [57]. The most common fracture related to osteoporosis is the hip fracture often leading to hip replacement.

心血管疾病，如动脉粥样硬化或高血压，也与年龄有关，在55岁以后，中风的风险每10年就会翻一番。部分原因可能是血管壁失去了部分弹性，对血压的控制起着重要作用。此外，胆固醇水平会随着年龄的增长而增加，它的积累会阻碍血液在冠状动脉等小动脉中的流动。动脉粥样硬化是一种更为复杂的疾病，因为它涉及免疫成分^[59]。它是一种脂质在血管壁的堆积，通常靠近血流中有湍流的区域。由于单核细胞在“泡沫细胞”中积累和转化，导致斑块(或动脉粥样硬化)越来越厚，从而引发炎症。这种复合物的破坏可能导致血液中产生血栓的分子释放，从而导致凝血。它通常是无症状的，但往往与心脏病发作或猝死有关。

Cardiovascular issues like atherosclerosis or high blood pressure are also correlated with age, and the risk of stroke doubles very decade after 55 years of age [58]. It could be partly explained by the fact that the vascular wall loses part of its elasticity, which plays a great role in the control of blood pressure. Moreover, cholesterol levels increase with age, and its accumulation hinders blood flow in small arteries like coronaries. Atherosclerosis is a much more complicated disease as it involves an immunological component ^[59]. It consists in an accumulation of lipids in the vascular wall generally close to area where there are turbulences in blood flow. It induces an inflammation due to monocyte accumulation and transformation in "foam cells" that make the plaque, or atheroma, growing thicker and thicker. Disruption of this complex may lead to release of thrombogenic molecules in the blood causing clotting. It is usually asymptomatic but often associated with heart attack or sudden death.

为了总结与年龄有关的疾病，我们将讨论一些破坏性的眼病，如青光眼、白内障和与年龄有关的黄斑变性(AMD)。青光眼由压力增加引起的，导致视神经受压并破坏视网膜细胞，如果不治疗，可导致失明。在50岁及以下的人群中，每200人中就有1人患病，80岁以上的人群中，每10人中就有1人患病。它是仅次于白内障的全球第二大致盲原因。白内障是在晶状体或晶状体囊中形成的一种浑浊物，会导致完全失明。老年性白内障发生在老年人身上，开始时晶状体混浊，然后肿胀，最后萎缩，完全失去透明度。此外，随着时间的推移，白内障皮质液化形成乳白色液体，如果晶状体囊泄漏，可引起严重炎症^[61]。年龄是老年性白内障的重要危险因素，常表现为老年性黄斑变性，表现为黄斑区视网膜受损，导致(中央)视力逐渐丧失。大约有10%的66-74人会患上AMD。在75-85岁的老年人中患病率增加到30%^[62]。

To conclude our presentation of age-related diseases, we will discuss about destructive eye diseases like glaucoma, cataract, and age-related macular degeneration (AMD) which are causing severe disruption in daily life. Glaucoma s induced by an increase in pressure leading to the optic nerve compression and destructing of retinal cells and, if left untreated, to blindness [60]. It affects 1 in 200 people aged 50 and younger and 1 in 10 over the age of 80. It is the second cause of blindness worldwide after cataract. Cataract consists in a clouding that develops in the crystalline lens or the lens capsule of the eye and induces a loss of vision that can be complete. The senile cataract, occurring in the elderly, begins with a clouding of the lens followed by its swelling, and finally it shrinks with a complete loss of transparency. Moreover, with time, the cataract cortex liquefies to form a milky white fluid which can cause severe inflammation if the lens capsule leaks [61]. Age is an important risk factor for senile cataract and is often present with AMD which manifests by damages to the retina in the macula area, leading to a progressive loss of (central) vision. Around 10% of 66-74 people will develop AMD. The prevalence increases to 30% in 75-85 elderly [62].

6.NK cells in Age-Related Diseases 与年纪相关的NK细胞

在本文描述的年龄相关性疾病样本中，NK细胞发挥一定作用，但其在相应疾病中的意义存在差异(图2)。在阿尔茨海默病中，NK细胞IL-2介导的细胞毒性活性升高，与认知状态呈负相关^[63]。同一团队的另一项研究显示,这可能是由于放松管制的蛋白激酶C(PKC),监管在NK胞外分泌酶发挥作用和细胞毒性反应后感应IL- 2和IFN-β^[64]。细胞毒性刺激- 2后增加了102%和132%相比,阿尔茨海默病患者IFN-γ后控制(健康老年人和年轻人)。IL- 2和IFN-γ刺激后,胞质降低生理观察PKC浓度在控制而不是广告的病人,和皮质醇(免疫抑制剂)没有减少PKCaactivation广告组。最后,被证明IL- 2诱导释放IFN-γ和AD患者TNF-α控制(健康老人)相比,这里也释放负相关,认知状态^[65]。综上所述，这些数据表明，NK细胞的细胞毒性活性和整体功能在阿尔茨海默病期间观察到的与神经退行性变相关的神经炎症中起着积极的作用。甚至有人建议使用NK活性作为阿尔茨海默病进展的生物标志物^[66]。

Among the samples of age-related diseases described in this present paper, NK cells play a role but with differences in their implication in the corresponding diseases (Figure 2). In Alzheimer’s disease, NK cells have an increased IL-2 mediated cytotoxic activity that is negatively correlated with cognitive status [63]. Another study from the same team showed that it may be due to a deregulation of protein kinase C(PKC), a regulatory enzyme playing a role in NK exocytosis and cytotoxic response after induction by IL-2 and IFN-β ^[64]. Cytotoxicity increased by 102% after IL-2 stimulation and 132% after IFN-γ in AD patients compared to controls (healthy elderly and younger people). After IL-2 and IFN-γ stimulation, a physiological decrease in cytosolic PKC concentration was observed in controls but not in AD patients, and cortisol (as immunosuppressor) did not decrease PKCａactivation in the AD cohort. Finally, IL-2 was shown to induce a greater release of IFN-γ and TNF-α in AD patients compared to controls (healthy elderly), and here also the releases were negatively correlated with cognitive status ^[65]. Altogether, these data suggest that NK cell cytotoxic activity and overall functionality participate actively in neuroinflammation related to neurodegeneration observed during AD. It was even suggested to use NK activity as a biomarker of AD progression ^[66].

与年龄有关的癌症和NK细胞功能，一些进化成NK逃逸过程。前列腺癌就是一个完美的例子。肿瘤细胞可以分泌可溶性的NKG2D，通过与真实的NKG2D竞争结合在受体位点上，通过抑制MHC-I表达^[10]，在80%的NK细胞上表达NKG2D，从而逃避CD8识别，从而诱导假NK反应。这个事实说明了癌症是如何从一个重要的群体——NK细胞中进化出来的。对于胰腺癌来说，主要的问题是肿瘤被纤维化的屏障所包围，很少有细胞能够到达核心。在这些肿瘤浸润细胞中，仅观察到少量NK细胞^[67]。但用自体NK细胞局部治疗本病可能与支持治疗有关，因为凋亡的胰腺肿瘤细胞是NK和T细胞很好的激活剂^[68]。此外，肿瘤来源RNA脉冲树突状细胞刺激NK细胞可逆转胰腺癌细胞的耐药^[69]。对于结肠癌，NK细胞活性降低与结肠癌转移有关，NK反应正常的患者未发生转移，而NK反应低的患者复发[70]。NK活性可作为结直肠进展的标志，并有助于识别转移风险较高的患者。在结直肠癌组织中，尽管趋化因子和细胞因子水平较高，但肿瘤浸润NK细胞非常少见[71]。肿瘤的逃逸机制尚未被阐明，但它也促进了NK细胞的重要作用，似乎在疾病的早期就存在。此外，结直肠癌组织中NK细胞的存在与患者的年龄呈负相关，这可能与粘附分子表达的年龄有关^[72]。激活受体NCR和DNAM-1的表达下降不仅见于健康个体>65，也见于年轻的急性髓系白血病患者[31,73]。这是由于CD122和CD155 (DNAM-1配体)在白血病细胞[34]中的表达增加所致。考虑到DNAM-1在NK识别/杀伤癌细胞中的相关性，其在AML患者NK细胞上表达的减少可能是肿瘤逃逸的另一种机制。对于胃癌，NK细胞的活性与肿瘤大小、淋巴和血管受累、淋巴结转移等临床病理参数相关。NK组(~95%)5年生存率高于NK组(72%)^[74,75]。此外，NK活性可能是肿瘤体积、播散和预后的良好标志。在肺癌中，一项研究表明，肿瘤浸润的NK细胞主要是CD56^bright，能够分泌细胞因子，但不能杀伤肿瘤细胞^[76]。肿瘤细胞CD56^bright和CD16-高富集，但细胞毒性低于外周血NK细胞。它们也存在于肿瘤间质，不直接与肿瘤细胞接触。瘤内NK细胞表现出明显的表型改变，如NK细胞受体表达减少。这些缺陷导致受损脱粒和细胞因子的分泌,像IFN-γ。肿瘤表达激活和抑制NK细胞配体，似乎是肿瘤的NK逃逸机制，正因为如此，NK细胞与患者的临床疗效无关^[77]。

Concerning age-related cancers and NK cell function, some evolved an NK escaping process. The perfect example is prostate cancer. Tumor cells can secrete soluble NKG2D that will induce a fake NK response by competing with the true NKG2D for binding on the receptor site and at the same time evade CD8 recognition, as it is expressed on 80% of NK cells, by inhibiting MHC-I expression [10]. This is a fact that shows how cancers evolve to escape from an important population, the NK cells. Concerning pancreatic cancer the major problem is the tumor is surrounded by a fibrotic shield that allows very few cells to reach the core. Among these tumor-infiltrating cells, only a very small number of NK cells were observed [67]. But treating this disease locally with autologous NK cells may be relevant to support for the cure as it was showed that apoptotic pancreatic tumor cells are very good activator of NK and T cells [68]. Moreover, NK cells stimulated by dendritic cells pulsed with tumor-derived RNA can reverse the resistance of pancreatic carcinoma cells [69]. For colon cancer, NK cells reduced activity was showed to be related to colon cancer metastasis as patient with normal NK response remained free of metastasis whereas low NK response patient showed relapse [70]. NK activity could be used as a marker of colorectal progression and help to identify patients with higher risks of metastasis. In colorectal carcinoma tissue, despite high levels of chemokines and cytokines, tumor infiltrating NK cells are very rare [71]. The tumor escaping mechanism is not yet enlightened but it also promoted the important role of NK cells and seems to be present even in the early stages of the disease. Moreover, NK cells presence in colorectal carcinoma tissue has been negatively correlated with the age of the patients maybe due to an age-related decrease in adherence molecule expression [72]. The decreased expression of activating receptors NCR and DNAM-1 is not only seen in healthy individuals >65 but also in young acute myeloid leukemia patients [31,73]. This is attributed to increased expression of CD122 and CD155 (DNAM-1 ligands ) in leukaemic blasts [34]. Considering the relevance of DNAM-1 in NK recognition/killing of cancer cells, its reduced expression on NK cells from AML patients may represent another mechanism of tumor escape. For stomach cancer, NK cells activity has been correlated to clinic-pathological parameters including tumor size, lymphatic and vascular involvement, and lymph node metastases. The 5-year survival was higher in responding NK group (~95%) compared to nonresponding NK group (72%) [74,75]. Here also, NK activity could be a good marker for tumor volume and dissemination and prognosis. In lung cancer, a study showed that tumor-infiltrating NK cells are mainly CD56^bright and able to secrete cytokines but are unable to kill tumor cells [76]. Cells were CD56^bright and CD16^-, highly enriched in the tumor, but their cytotoxicity was lower than those from NK cells in peripheral blood. They were also found in the tumor stroma, not in direct contact with tumor cells. Intratumoral NK cells display great phenotypic alterations such as reduced NK cell receptor expression. These defects lead to an impaired degranulation and secretion of cytokines, like IFN-γ. AS tumor expresses activating and inhibiting NK cells ligands, it seems that it is a tumoral NK escaping mechanism, and because of this, NK cells are not correlated to the clinical outcome of patients [77].

Figure 2: NK cell phenotype and functions in age-ssociated diseases. The functionality of NK cells in the different diseasesis depicted.

图2:NK细胞在年龄相关性疾病中的表型和功能。描述了NK细胞在不同疾病中的功能。

在骨关节炎和假体周围炎症中，移除滑膜组织并进行研究以分析其免疫细胞组成^[78]。 已经表明，主要的浸润细胞是NK细胞，并且滑液中富含NK引诱剂，如CCL-4，CCL-5，CXCL-9，CXCL-10和凯莫瑞。 这些NK细胞表达受体与独有的CD56^bright表型一致（图2）。 它们还产生较少的外周NK细胞的IFN-γ，其不会阻止疾病的进一步发展，因为IFN-γ可以诱导破骨细胞分化并因此诱导骨修复。 这在骨质疏松症中也具有重要意义，因为老年人具有较少的分泌IFN-γ的NK细胞，但到目前为止尚未对此进行研究。

In osteoarthritis and periprosthetic inflammation, synovial tissue was removed and studied to analyze its immune cell composition [78]. It has been showed that the main infiltrating population was NK cells and that synovial fluid was very rich in NK attractants like CCL-4, CCL-5, CXCL-9, CXCL-10, and chemerin. These NK cells express receptor consistent with an exclusive CD56^bright phenotype (Figure 2). They also produce less IFN-γ that peripheral NK cells, which does not prevent further development of the disease as IFN-γ can induce osteoclast differentiation and thus bone repair. This can also have significance in osteoporosis, as elderly possess less IFN-γ secreting NK cells, but this has not been investigated so far.

NK细胞也与冠心病（CHD）有关^[79]。 与年龄匹配的对照相比，CHD患者具有较低的NK细胞毒活性，较少的CD56^dim细胞，较少的CD56^bright调节细胞和较少的IFN-γ分泌NK细胞。 在特发性肺动脉高压（PAH）中，还发现了NK细胞损伤^[80]。 他们发现PAH患者的NK细胞表型被修改。 他们表现出活化受体NKp46和KIRs水平降低，细胞因子MIP-1β分泌减少，以及与KIR3DL1表达降低相关的细胞溶解功能显着受损。 这些NK细胞对TGF-β反应更强，已知可降低KIR表达。 最近的假设表明先天免疫，TLR和心血管疾病之间的联系^[81]。 在心脏损伤期间，一些TLR配体可以通过TLR-2激活先天免疫细胞，如NK细胞，从而产生潜在的临界炎症。

NK cells have also been linked to coronary heart disease (CHD) ^[79]. CHD patients had lower NK cytotoxic activity, less CD56^dim cells, less CD56^bright regulatory cells, and less IFN-γ secreting NK cells than age-matched controls. In idiopathic pulmonary hypertension (PAH), NK cells impairments have also been identified ^[80]. They revealed that PAH patients’ NK cell phenotype was modified. They displayed decreased levels of the activating receptor NKp46 and KIRs, reduced secretion of the cytokine MIP-1β, and a significant impairment in cytolytic function associated with decreased KIR3DL1 expression. These NK cells were more responsive to TGF-β, known to decrease KIR expression. Recent hypotheses suggest the links between innate immunity, TLR, and cardiovascular diseases ^[81]. During cardiac injuries, some TLR ligands may activate innate immune cells, like NK cells through TLR-2, and thus creating a potentially critical inflammation of the heart. 

如所讨论的，肿瘤中的NK细胞分布相当低，表明防止其募集的机制或这些细胞与其它细胞相比不是最好的化学治疗细胞的可能性，至少对于某些组织而言。在像eye.com这样的网站上，报道很少，但现有的报道也表明NK细胞存在不足^[82]。这项罕见的研究还发现大量的IgG，IgA和IgE以及结缔组织基质和AMD患者新血管壁内的Clq，C3c和C3d补体成分。对于癌症和与年龄相关的黄斑变性的常见治疗是光动力疗法。如显示光动力疗法与其他促凋亡治疗如FasL和TRAIL之间的协同作用的研究^[83]，可以类似地治疗其他癌症。 AMD可以细分为湿性或干性AMD。湿性AMD指的是脉络膜新血管形成的后果。与使用KO小鼠（NK T细胞缺陷和Ja18缺陷）的玻璃体液实验中与先天免疫相关的细胞因子水平增加一起显示实验诱导的脉络膜新血管形成相关疾病的效果显着降低^[84]。体外实验证实，NK样细胞可以在与视网膜色素上皮细胞的共培养中产生VEGF ^[85]。这表明NK样家族可能参与了这种疾病（图2）。 HLA-Cw * 0701等位基因与抑制性KIR AA单倍型组合与AMD显着相关（P-0.006，OR = 4.35），这部分证实了这一点。这种基因型组合表明NK细胞确实参与了AMD的发病机制^[86]。

As discussed, NK cell distribution in tumors is fairly low suggesting mechanisms preventing their recruitment or the possibility that these cells are not the best chemoattractable cells compared to others, at least for certain tissue. In a site like the eye there have been very few reports but the existing noes also suggest a poor presence of NK cells [82]. This rare study also identified large amounts of IgG, IgA, and IgE as well as Clq, C3c, and C3d complement components in the connective stroma and within the new blood vessel walls in AMD patients. A common treatment for cancer and age-related macular degeneration is photodynamic therapy. Other cancers may be treated similarly as suggested by a study showing synergy between photodynamic therapy and other proapoptotic treatments such as FasL and TRAIL [83]. AMD can be subdivided in wet or dry AMD. The wet AMD refers to consequences of choroidal neovascularization. Together with increased levels of cytokines related to innate immunity in the vitreous fluid experiments using KO mice (NK T cell deficient and Ja18 deficient) show significant reduction of the effect of experimentally induced choroidal neovascularization-related diseases [84]. In vitro experiments confirmed the fact NK-like cells could produce VEGF in cocultures with retinal pigment epithelial cells [85]. This suggests that NK-like family may be involved in such disease (figure 2). This was partly confirmed by the fact HLA-Cw*0701 allele in combination with the inhibitory KIR AA haplotype was significantly associated with AMD (P-0.006, OR=4.35). This genotype combination suggests that NK cells are indeed involved in the pathogenesis of AMD [^86].

7.Conclusion结论

NK细胞是重要的免疫细胞，因为它们对攻击者提供快速和强烈的反应。 NK细胞表型与其功能之间的确切联系仍然知之甚少，应该继续进行以便更好地了解疾病，尤其是老年人，因为这些人群表现出缓慢但持续的免疫侵蚀。 NK细胞的免疫衰老越来越被认为是与年龄相关的病理和低反应性的主要参与者。虽然NK细胞的作用在某些病理学（癌症）中已明确确立，但它们在其他如自身免疫疾病或慢性传染病的免疫监视中的作用尚不确定。作为先天细胞，NK还通过使宿主具有合理的免疫监视和由CD8 + T细胞进行的细胞毒活性而参与具有适应性免疫的相互作用。因此，自然地，即随着衰老或在疾病期间改变NK细胞功能将不可逆地影响免疫。当两种因素都存在时（衰老和疾病），患者可能更有风险。在将NK细胞用作某些病理学的生物标志物之前，正如其他人所建议的那样，首先应该确定NK细胞衰老，因为在老年人群中可以看到NK所涉及的许多疾病。

NK cells are important immune cells as they provide a rapid and intense response to challengers. The exact link between NK cell phenotype and their function is still poorly understood and should be pursued to enable a better understanding of diseases, especially in the elderly as this population is showing slow but continuous immune erosion. Immunosenescence of NK cells is recognized more and more as a major player in age-related pathologies and hyporesponsiveness. While the role of NK cells is clearly established in certain pathologies (cancer), their role in other such as autoimmune diseases or immunosurveillance of chronic infectious diseases is less established. As innate cells, NK also participates in the interplay with adaptive immunity by leaving the host with reasonable immune surveillance and cytotoxic activity performed by CD8⁺T cells. Thus, altering NK cell functionality naturally, that is, with aging or during diseases, will irreversibly impact on immunity. When both factors are present (aging and diseases), the patients are probably even more at risk. Before NK cells to be used as biomarkers for certain pathologies, as suggested by other, one should first identify NK cell aging as many diseases where NK is involved are seen in the elderly population.

Acknowledgments致谢

这项工作得到了新加坡科学技术研究局（A * STAR）的支持。 这项工作部分得到了西班牙卫生部的Grants FIS PI06I320和PS09 / 00723（对R. Solana）的支持。 A. Larbi是ISAC的学者。

This work was supported by the Singapore Agency for Science Technology and Research (A*STAR). This work was partly supported by Grants FIS PI06I320 and PS09/00723 from Spanish Ministry of Health (to R. Solana). A. Larbi is an ISAC Scholar.

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