美科学家新发现：人体内有“天然杀手”能“猎癌”http://www.sina.com.cn 2009年02月06日17:44 青年参考
本报特约撰稿李月
美国科学家的一项新发现，让我们对人体免疫系统“如何排兵布阵”有了新认识。以前被认为是“有勇无谋”的“天然杀手”细胞(naturalkiller，简称NK细胞，也称“自然杀手”细胞)，其实被低估了。如果好好开发它们的潜能，艾滋病和癌症的恶魔就可能束手就擒。
人体的第一道防线
这项最新研究刊登在1月11日出版的英国《自然》杂志上。该研究负责人、美国加州大学的微生物学家路易斯·拉尼尔说，人类的免疫反应通常分为两类——先天免疫和适应性免疫。人们在出生时便具有先天免疫功能，主要由一些“屏障” 如皮肤和黏液，以及一些免疫细胞如NK细胞等构成。
NK细胞大约在1970年被发现，是一种大粒状淋巴细胞。其之所以被称为“天然杀手”，是因为它们不像毒素细胞T细胞一样，要经过免疫系统的抗原辨识反应才确定目标“出击”。NK细胞能主动出击，杀死肿瘤或被病毒感染的坏细胞。在1986年美国夏威夷举办的国际免疫学座谈会上，这种不需通过抗原辨识即可攻击“入侵者”的细胞，正式被命名为“ 天然杀手(NK)”细胞。
与先天免疫不同的适应性免疫，主要由T细胞和B细胞及其他免疫细胞来实施。它们大概要花费数周时间才能培育出对抗入侵病毒的抗体。
NK细胞是人体的“忠勇卫士”，是人体的第一道防线，感染首次发生时，NK细胞会率先“查杀”。T细胞和B细胞能从上一次病原体入侵中学习经验，提高防御能力，为应对病原体的二次入侵做好准备。
T细胞和B细胞都有“记忆功能”，免疫记忆可保存很长时间，能摧毁数年甚至数十年后的相同入侵者。我们使用的各种病毒疫苗，就是利用了适应性免疫细胞的记忆功能，但此前科学家们认为，NK细胞不具有类似记忆功能，因而难以在病毒疫苗研发中“挑大梁”。
NK细胞其实有记性
加州大学的微生物学家拉尼尔说：“以前我们一直以为NK细胞在猎杀入侵者时是盲目的，对付每一次感染的免疫反应都视如首次，毕竟NK细胞的寿命很短，只有两三周。但试验结果让我们大吃一惊。”拉尼尔的研究小组在老鼠身上注射一种细胞巨化病毒(这类病毒在人类身上很常见，可以导致水痘和性病等)，此后，老鼠体内的NK细胞立刻产生反应，其表面产生大量受体并锁定和查杀遭病毒感染的细胞。数周后，研究人员发现，部分对病毒产生受体的NK细胞隐藏在淋巴组织内。
研究人员将这部分NK细胞提取出来，注射到未感染过细胞巨化病毒的第二批试验老鼠身上，这些老鼠的T细胞和B 细胞等已被破坏。结果，在不到一周的时间里，第二批老鼠的体内产生了大量具有专杀细胞巨化病毒特性的NK细胞，数量惊人，在脾和肝中的这种细胞，分别是正常情况的100倍甚至1000倍。拉尼尔表示：“通过实验我们发现，NK细胞对病原体具有一定的免疫记忆，能有针对性地提供更高效的免疫措施。”
拉尼尔表示，新发现有助于疫苗的研发。“既然NK细胞也具有记忆功能，那么，疫苗的研发也可以把NK细胞的功能发挥出来。它还可能对艾滋病毒疫苗的研究起到启发作用。先前的研究发现，某些人对HIV(艾滋病毒)具有更强的抵抗力，感染后历经更长时间才会发病。这是否与NK细胞有关？如果能更好的了解NK细胞，我们就能找到控制艾滋病病毒的方法。”
哈佛大学医学院免疫学家范·安德瑞安认为：“现行教科书上对NK细胞的解释也许是错误的，越来越多的发现让我们了解了NK细胞，对人类免疫系统的认知也进了一步。”范·安德瑞安2006年曾在《自然》杂志上发表文章指出，实验显示，部分NK细胞的寿命有数月之久。
有望在抗癌上大显神通
除了对艾滋病研究的期待，今天，NK细胞的研究已经体现在抗癌研究上。
据了解，通常人体每天都会产生数千个癌细胞，我们的免疫系统通过血液循环全天候监控。NK细胞对癌细胞有极强的查杀作用，一旦发现癌细胞，会立刻与其结合，5分钟内就会破坏癌细胞将其杀死，是高效的“猎癌专家”。近年来，科学家利用NK细胞的特性，研发对抗癌症的药物和方法。
日本的医学家曾把癌症患者的NK细胞在体外培养，达到一定数量后，再注入患者体内。具体来说，首先抽取20～ 30毫升的病人静脉血，从中分离出极少量的NK细胞，再用各种增长因子刺激并活化。经过两周的培养后，这些原本极少量且活性不强的NK细胞数量增加到10～60亿个，再通过静脉用点滴方式注入患者体内。一般而言，一个健康人体内的NK 细胞约有1～5亿个，注入体内的NK细胞，极大增强了对癌细胞的杀伤能力。NK疗法完全采用患者自身的细胞，所以没有痛苦，也没有副作用和排斥反应，是一种直接有效的抗癌方法，但目前成本非常高。随着技术进一步成熟，成本大大降低，就完全可以走进寻常百姓家来对付癌魔。
NK细胞活性不足会致病
NK细胞的活力和数量是人体健康的重要保证。美国疾病控制中心(CDC)去年的报告显示，几乎所有疾病的产生都与NK细胞的活性明显不足有关。
加州大学微生物学家拉尼尔说，“人们患有疾病时，无论是慢性的、偶发性的或是急性的，NK细胞的活性都在平均水平以下。让NK细胞恢复到高水平的活性，是最好的治疗疾病方法。”
事实上，NK细胞活性的降低是某些类型的压力导致的。当身体不能充分适应环境时，随之而来的就是身体功能下降。睡眠不足、工作过度、感情不顺利、缺少运动、营养不足、暴露在病菌毒素之下等，都会对身体造成压力。
据拉尼尔介绍：“在过度压力下，人体会产生有害的改变，尤其是免疫系统。研究显示，NK细胞的活性与感情压力之间有一定的互动关系。无法处理压力的人和行为举止失控的人，都有NK细胞活性不足的问题。”
即便是临时性的压力，也会导致NK细胞活性急性降低，但加以适当调整和休息，NK细胞活性就会提升。例如，太疲劳和营养不良时，只要好好休息几天，吃恰当的食物就可以恢复。然而，当我们持续处在压力和不和谐的生活环境下时，免疫系统被不断削弱，就可能导致癌症或其他慢性病的发生。U.S. scientists discovered: the human body has "natural killer" to "hunting and cancer" http://www.sina.com.cn 2009 on 06 day 02 years Cankao 17:44
Contributing writer Li Dong
American scientists found a new, let us on the body's immune system "How to排兵布阵" With the new understanding. Were previously considered to be "foolhardy" and "natural killer" cells (naturalkiller, referred to as NK cells, also called "natural killer" cells), in fact, been underestimated. If properly develop their potential, AIDS and cancer may Photo / Bill devil.
The body's first line of defense
The latest research published in the January 11 issue of the British "Nature" magazine. The people in charge of the United States University of California microbiologist路易斯拉尼尔said that the human immune response is usually divided into two types - innate immunity and adaptive immunity. People born with the innate immune function, mainly by the number of "barriers" such as skin and mucus, as well as some immune cells such as NK cells, etc..
NK cells, some were found in 1970, is a large granular lymphocytes. The reason why its called "natural killer" because they, unlike T cells, like cell toxin, to go through the immune system response to antigen recognition before deciding on target "attack." NK cells can take the initiative to kill tumor or virus-infected cells bad. HI in the United States in 1986 was the International Forum on immunology, the antigen recognition can be passed without attack "invaders" of cells, was officially named "natural killer (NK)" cells.
Different innate immunity and adaptive immunity, primarily by T cells and B cells and other immune cells to implement. They probably have to spend a few weeks time to produce antibodies against the invading virus.
NK cells are the body's "Jhongyong defender" is the body's first line of defense, when the first outbreak of infection, NK cells will take the lead in "Killing." T cells and B cells from the invasion of pathogens in the previous learning experiences, and boost its defense capabilities to cope with the invasion of secondary pathogens ready.
T cells and B cells have "memory function", immune memory can be stored for a long time, can destroy a few years or even decades after the same intruder. We use a variety of virus vaccines, is to take advantage of the adaptive immune cells and memory function, but after the scientists think, NK cells do not have a similar memory function, it is difficult to HIV vaccine research and development of "enough to undertake the projects."
In fact, NK cells have memory
University of California microbiologist Lanier said: "We always thought that NK cells in the hunt when the intruder is blind to deal with every infection the immune response are the first striker, after all, the life span of NK cells is very short, only 23 weeks. However, the results surprised us. "Lanier's research team injected mice a cytomegalovirus virus (this virus is common in humans, can cause chicken pox and sexually transmitted diseases, etc.) Since then, the rats NK cells in vivo respond immediately, a large amount of its surface receptor and has been locked and killing virus infected cells. After a few weeks, the researchers discovered that some viruses have a receptor on NK cells in the lymphoid tissue hidden within.
The researchers of this component of NK cells, extracted and injected into not infected with Cytomegalovirus in the second group of test mice, these mice T cells and B cells have been destroyed. As a result, less than a week's time, the second group of mice in vivo has generated a great deal of expertise to kill Cytomegalovirus characteristics of NK cells, the number of amazing, in the spleen and liver cells, which are normally 100 times or even 1,000 times. Lanier said: "We have found through experiments, NK cells to pathogens has certain immunological memory, has targeted to provide a more efficient immune measures."
Lanier said that the new findings contribute to vaccine research and development. "Since NK cells also have a memory function, then the vaccine R & D can also be the function of NK cells play. It is also possible for HIV vaccine research inspired role play. Previous studies found that some people on the HIV (AIDS drugs) have a stronger resistance to infection only after a longer period of time after onset. Is it related to NK cells? If we can gain a better understanding of NK cells, we can find ways to control HIV. "
Immunologist at Harvard Medical School范安德瑞安think: "The current textbook explanation for the NK cells might be wrong, more and more discoveries to help us understand the NK cells, the immune system of human cognition has also entered the step. "范安德瑞安in 2006 in" Nature "magazine published an article pointed out that the experiment showed that some NK cells, the life span of several months.
Expected to be on anti-cancer大显神通
In addition to expectations for AIDS Research, today, NK cells have been reflected in the anti-cancer research.
It is understood that the human body every day usually have thousands of cancer cells, our immune system through the blood circulation around the clock monitoring. NK cells in killing cancer cells have a strong role in cancer cells, once found, we would be immediately and their combination would damage within five minutes to kill cancer cells is highly efficient, "hunting and cancer experts." In recent years, scientists use the properties of NK cells, research and development of drugs against cancer and methods.
Japan's scientists had cancer in patients with NK cells in vitro, reaching a certain number, and then injected into the patient. Specifically, the first collected 20 to 30 ml of venous blood of patients, isolated from a very small number of NK cells, and then a variety of growth factor stimulation and activation. After two weeks after the training, which was originally a very small amount of activity is not very strong and the NK cell number increased to 10 ~ 6 billion, and then the way through the intravenous drip into the patient. In general, a healthy human body's NK cells, about 1 ~ 500 million, injected into the body's NK cells, which greatly enhanced the ability of anti-cancer cells. NK therapy in patients with completely their own cells, there is no pain, no side effects and rejection, is a direct and effective anticancer approach, but the current cost is very high. As the technology further matures, the cost of greatly reduced, it is entirely possible into ordinary癌魔home to deal with.
NK cell activity, under-pathogenic
NK cell viability and the number is an important guarantee for human health. The United States Centers for Disease Control (CDC) last year's report shows that almost all diseases are related to the emergence of NK cells activity was significantly less than relevant.
University of California microbiologist Lanier said, "People suffering from disease, whether it is chronic, episodic or acute, NK cells are below average. Allow NK cells to return to a high level of activity, is the best method of treatment of disease. "