NATURAL KILLER 自然杀手細胞NK

NK (Natural Killer) cells are lymphocytes that act as soldiers against cancer cells. Literally, it's called a "natural killer" that attacks abnormal cells, such as cancer cells or infected cells, when they are found. These cells are highly aggressive, accounting for 10 to 30 percent of lymphocytes and killing abnormal cells.

Studies have shown that the normal body produces hundreds of cancerous cells every day, but they are all wiped out by the legions of immune cells before cancer lesions are formed. In these immune cell corps, natural killer cells (NK cells) are the most important cells in the natural immune system and play an important role.

Although they can defend quickly and attack tumor cells directly, unfortunately NK cells are only a small part of the immune system, accounting for only 10% of white blood cells. And the study found that after the age of 25, the immunity of human beings decreased, the number of NK cells became less, tumor patients and tumor patients after surgery, the number and activity of NK cells in the body have changed, can not play a very effective anti-cancer role.

Compared with other cancer immune cells, such as cytotoxic T cells or synthesized cells, NK cells kill tumors and virally infected cells more effectively and effectively. Its activation does not depend on the surface antigens of tumor cells, nor does it need to go through the antigen identification response of the immune system to determine the "attack" target, as T cells do. NK cell wandering in the whole body blood vessels to exercise immune surveillance function, it can be found and activated in the first time immune defense function, quickly kill lesions, cancer cells, so it is recognized by the medical community as the first line of defense against cancer.

Normal people metabolize millions of cells a day, hundreds of which can cause cancer. Healthy people's NK cell immunity is strong enough to clean up cancerous cells in a timely manner. But for cancer patients, on the one hand, the growth of tumors hinders the differentiation and maturity of NK cells in the bone marrow, on the other hand, because of the cancer cells, the remaining NK cells in the body are extremely weak, the prevalence of low immune function, can not effectively identify and kill cancer cells. Therefore, healthy NK cells are more active and lethal than when they get sick.

The medical community found that it takes 5-20 years for individuals to develop cancer from exposure to risk factors in the body, during which time NK cells and cancer cells in the body "disappear", constantly "game", the occurrence of confrontation. In the process, NK cells are reduced in activity, lethality, and number of cancers. It can be said that the human body's NK cells are a non-renewable resource, is very precious. NK cells in patients in the middle and late stages of cancer are often severely damaged, unable to destroy tumor cells, resulting in the recurrence and metastasis of the cancer.

How do NK cells recognize normal and abnormal cells? Dr. Maresha, of the University of Maryland, revealed the problem in the journal Nature: NK cells, like "molecular patrols," travel around the bloodstream, and once foreign or mutant cells that lose their self-identification, known as MHC, the NK cell's subjects immediately signal, rush to the target's cell membrane, release toxic particles into it, quickly dissolve the target cells, and kill cancer cells within five minutes.

It is important to understand that the absolute number of NK cells in the blood does not represent the size of immune function, it is important that NK cell activity, that is, the ability to destroy and identify cancer cells. Numerous studies have shown that people with low NK cell activity are prone to cancer or virus infection, while cancer patients with low NK cell activity are prone to metastasis or recurrence.

Dexter cell vaccine therapy cultures T cells in lymphocytes and induces lymphocytes in the body that only work for cancer to attack specific killer cells. However, cancer cells may hide a cancer marker (MHC molecule) to escape attack on the cell, in which case they may escape from the T-cell attack. Complementary to this is NK cells. NK cells have the properties to attack cancer cells, which have hidden cancer markers (MHC molecules) from cancer cells. Think and start attacking. Therefore, by using a tree protrusion cell vaccine therapy and NK cell therapy together, the differences in cell response in lymphocytes can be compensated and higher invasiveness is expected for cancer.


NK（自然杀手）细胞是一种淋巴细胞，可充当攻击癌细胞的士兵。从字面上看，它被称为“天生的杀手”，一旦发现异常细胞，例如癌细胞或被病毒感染的细胞，便会发起攻击。这些细胞具有很高的攻击性，占淋巴细胞的10％至30％，并杀死异常细胞。  

研究表明正常人体每天都将产生上百个癌变细胞，但它们在形成癌症病灶前就已全部被免疫细胞军团消灭。在这些免疫细胞军团中，自然杀伤细胞（Natural killercell, NK细胞）是天然免疫系统中最重要的细胞，发挥着举足轻重的作用。  

尽管他们可以迅速进行防御并直接攻击肿瘤细胞，但遗憾的是NK细胞只是免疫系统的一小部分，仅占白细胞的10％。并且研究发现，人类到了25岁以后，免疫力下降，NK细胞数量变得更少，肿瘤患者及肿瘤术后患者体内NK细胞的数量及活性都发生了一定的改变，不能非常有效地发挥抗癌作用。  

与其他抗癌免疫细胞相比，如细胞毒性T细胞或树突状细胞，NK细胞杀灭肿瘤和病毒感染细胞的作用更强、更有效。它的激活不依赖于肿瘤细胞表面抗原，也不需要像T细胞一样，要经过免疫系统的抗原辨识反应才确定“攻击”目标。NK细胞游弋在全身血管行使免疫监视功能，它能在第一时间发现并启动免疫防御功能，迅速杀死病变、癌变的细胞，因此被医学界公认为抗癌第一道防线。  

正常人每天会新陈代谢数百万个细胞，其中上百个会产生癌变。健康人的NK细胞免疫功能足够强大，可以及时地清理癌变的细胞。但对于癌症患者来说，一方面，肿瘤的生长阻碍了NK细胞在骨髓内的分化、成熟；另一方面，因为癌细胞的侵害，身体中残存的NK细胞战斗力极弱，普遍存在免疫功能低下、不能有效识别、杀灭癌细胞的情况。所以，健康时的NK细胞比得病时的细胞活性更强、杀伤力更胜一筹。  

医学界发现，个体从接触危险因素到体内出现癌变需要5-20年的时间，在这个期间NK细胞与体内的癌细胞"此消彼长"，不断"博弈"，发生着对抗。NK细胞在此过程中，活性、杀伤力和数量会受到癌症的影响不断下降。可以说人体的NK细胞是一种不可再生资源，是非常珍贵的。

癌症中、晚期患者的NK细胞往往已经发生严重的受损，无法消灭肿瘤细胞，造成癌症的复发和转移。  

NK细胞如何识别正常细胞与异常细胞呢？美国马里兰大学的马瑞沙博士在《自然》杂志上揭示了这一问题：NK细胞像“分子巡逻队”一样，在血流中到处巡视，一旦发现失去自我标识（称为MHC）的外来细胞或变异细胞，NK细胞的受体立即就发出信号，冲到目标的细胞膜上，向它释放有毒的颗粒，迅速将靶细胞溶化，在5分钟之内使癌细胞死亡。  

需要理解的是，血液中NK细胞的绝对个数并不代表免疫功能的大小，重要的是NK细胞的活性，即消灭和识别癌细胞的能力。大量研究证明，NK细胞活性低的人，容易得癌症或感染病毒；而NK细胞活性低的癌症病人，则容易发生转移或复发。  

树突状细胞疫苗疗法DC-CIK可培养淋巴细胞中的T细胞，并诱导体内仅对癌症起作用的淋巴细胞攻击特定的杀伤细胞。但是，癌细胞可能会隐藏一种癌症标记（MHC分子），以逃避对该细胞的攻击，在这种情况下，它们可能会从T细胞攻击中逃脱。与之互补的是NK细胞。NK细胞具有攻击癌细胞的特性，这些癌细胞已从癌细胞中隐藏了癌症标记物（MHC分子）。思考并开始进攻。因此，通过一起使用树突状细胞疫苗疗法和NK细胞疗法，可以补偿淋巴细胞中细胞反应的差异，并期望对癌症具有更高的侵袭性。