Inside 您r body there is a mechanism designed to defend 您 from millions of bacteria, microbes, 病毒, toxins 和 parasites. VioletaStoimenova /盖蒂图片社
Inside 您r body there is an amazing protection mechanism called the 免疫的 系统. It is designed to defend 您 against millions of bacteria, microbes, 病毒, toxins 和 parasites that would love to invade 您r body. To understand the power of the 免疫的 系统, all that 您 have to do is look at what happens to anything 上ce it dies. That sounds gross, but it does show 您 something very important about 您r 免疫的 系统.
什么时候 something dies, its 免疫的 系统 (along with everything else) shuts down. In a matter of hours, the body is invaded 通过 all sorts of bacteria, microbes, parasites... None of these things are able to get in when 您r 免疫的 系统 is working, but the moment 您r 免疫的 系统 stops the door is wide open. Once 您 die it 上ly takes a few weeks for these organisms to completely dismantle 您r body 和 carry it away, until all that's left is a skeleton. Obviously 您r 免疫的 系统 is doing something amazing to keep all of that dismantling from happening when 您 are alive.
的 免疫的 系统 is complex, intricate 和 interesting. And there are at least two good reasons for 您 to know more about it. First, it is just plain fascinating to understand where things like fevers, hives, inflammation, etc., come from when they happen inside 您r own body. 您 also hear a lot about the 免疫的 系统 in the news as new parts of it are understood 和 new drugs come 上 the market -- knowing about the 免疫的 系统 makes these news stories understandable. In this 文章, we will take a look at how 您r 免疫的 系统 works so that 您 can understand what it is doing for 您 each day, as well as what it is not.
什么时候 您 get a cut, all sorts of bacteria 和 病毒 恩 ter 您r body through the break in the 皮肤. 什么时候 您 get a splinter 您 also have the sliver of wood as a foreign object inside 您r body. 您的 免疫的 系统 responds 和 eliminates the invaders while the 皮肤 heals itself 和 seals the puncture. In rare cases the 免疫的 系统 misses something 和 the cut gets infected. It gets inflamed 和 will often fill with pus. Inflammation 和 pus are both side-effects of the 免疫的 系统 doing its job.
什么时候 a mosquito bites 您, 您 get a red, itchy bump. That too is a visible sign of 您r 免疫的 系统 at work.
Each day 您 inhale thousands of germs (bacteria 和 病毒) that are floating in the air. 您的 免疫的 系统 deals with all of them without a problem. Occasionally a germ gets past the 免疫的 系统 和 您 catch a cold, get the flu or worse. A cold or flu is a visible sign that 您r 免疫的 系统 failed to stop the germ. 的 fact that 您 get over the cold or flu is a visible sign that 您r 免疫的 系统 was able to eliminate the invader after learning about it. If 您r 免疫的 系统 did nothing, 您 would never get over a cold or anything else.
Each day 您 also eat hundreds of germs, 和 again most of these die in the saliva or the acid of the stomach. Occasionally, however, 上e gets through 和 causes food poisoning. 的re is normally a very visible effect of this breach of the 免疫的 系统: vomiting 和 diarrhea are two of the most common symptoms.
让我们从头开始。有人说什么意思"I feel 生病 today?" What is a disease? By understanding the different kinds of diseases it is possible to see what types of disease the 免疫的 系统 helps 您 handle.
什么时候 您 "get 生病", 您r body is not able to work properly or at its full potential. 的re are many different ways for 您 to get 生病 -- here are some of them:
机械损伤 - If 您 break a bone or tear a ligament 您 will be "sick"（您的身体将无法发挥其全部潜能）。问题的原因是一些易于理解和看到的东西。
维生素或矿物质缺乏 - If 您 do not get 恩 ough vitamin D 您r body is not able to metabolize calcium properly 和 您 get a disease known as rickets. People with rickets have weak bones (they break easily) 和 deformities because the bones do not grow properly. If 您 do not get 恩 ough vitamin C 您 get scurvy, which causes swollen 和 bleeding gums, swollen joints 和 bruising. If 您 do not get 恩 ough iron 您 get anemia, 和 so 上.
器官退化 -在某些情况下，器官被损坏或削弱。例如，一种形式的"heart disease" is caused 通过 obstructions in the blood vessels leading to the 心 muscle, so that the 心 does not get 恩 ough blood. One form of "liver disease"称为肝硬化，是由肝细胞受损引起的（喝酒过多是原因之一）。
什么时候 a virus or bacteria (also known generically as a germ) invades 您r body 和 reproduces, it normally causes problems. Generally the germ's presence produces some side effect that makes 您 生病. For example, the strep throat bacteria (Streptococcus) releases a toxin that causes inflammation in 您r throat. 的 polio virus releases toxins that destroy nerve 细胞s (often leading to paralysis). Some bacteria are benign or beneficial (for example, we all have millions of bacteria in our intestines 和 they help digest food), but many are harmful 上ce they get into the body or the bloodstream.
关于免疫系统的有趣事情之一是，它一直在您体内的整个生命中起作用，但您可能几乎一无所知。例如，您可能知道胸部内部有一个叫做"heart". Who doesn't know that they have a 心? 您 have probably also heard about the fact that 您 have 肺 和 a liver 和 kidneys. But have 您 even heard about 您r thymus? 的re's a good chance 您 don't even know that 您 have a thymus, yet its there in 您r chest right next to 您r 心. 的re are many other parts of the 免疫的 系统 that are just as obscure, so let's start 通过 learning about all of the parts.
的 most obvious part of the 免疫的 系统 is what 您 can see. For example, 皮肤 is an important part of the 免疫的 系统. It acts as a primary boundary between germs 和 您r body. Part of 您r 皮肤's job is to act as a barrier in much the same way we use plastic wrap to protect food. Skin is tough 和 generally impermeable to bacteria 和 病毒. 的 epidermis contains special 细胞s called Langerhans 细胞s (mixed in with the 黑色素细胞 in the basal layer) that are an important early-warning component in the 免疫的 系统. 的 皮肤 also secretes antibacterial substances. 的se substances explain why 您 don't wake up in the morning with a layer of mold growing 上 您r 皮肤 -- most bacteria 和 spores that land 上 the 皮肤 die quickly.
您的 nose, mouth 和 eyes are also obvious 恩 try points for germs. Tears 和 mucus contain an 恩 zyme (lysozyme) that breaks down the 细胞 wall of many bacteria. Saliva is also anti-bacterial. Since the nasal passage 和 肺 are coated in mucus, many germs not killed immediately are trapped in the mucus 和 soon swallowed. Mast 细胞s also line the nasal passages, throat, 肺 和 皮肤. Any bacteria or virus that wants to gain 恩 try to 您r body must first make it past these defenses.
人们最熟悉淋巴系统，因为医生和母亲经常检查"swollen lymph nodes" in the neck. It turns out that the lymph nodes are just 上e part of a 系统 that extends throughout 您r body in much the same way 您r blood vessels do. 的 main difference between the blood flowing in the circulatory 系统 和 the lymph flowing in the lymph 系统 is that blood is pressurized 通过 the 心, while the lymph 系统 is passive. 的re is no "lymph pump" like there is a "blood pump" (the 心）。相反，液体会渗入淋巴系统，并被正常的身体和肌肉运动推向淋巴结。这非常类似于社区中的供水和下水道系统。水被主动加压，而污水是被动的，并因重力而流动。
Lymph nodes contain filtering tissue 和 a large number of lymph 细胞s. 什么时候 fighting certain bacterial infections, the lymph nodes swell with bacteria 和 the 细胞s fighting the bacteria, to the point where 您 can actually feel them. Swollen lymph nodes are therefore a good indication that 您 have an infection of some sort.
的 thymus lives in 您r chest, between 您r breast bone 和 您r 心. It is responsible for producing T细胞 (see the next section), 和 is especially important in newborn babies - without a thymus a baby's 免疫的 系统 collapses 和 the baby will die. 的 thymus seems to be much less important in adults - for example, 您 can remove it 和 an adult will live because other parts of the 免疫的 系统 can handle the load. However, the thymus is important, especially to T 细胞 maturation (as we will see in the section 上 白血细胞 below).
的 spleen filters the blood looking for foreign 细胞s (the spleen is also looking for old 红细胞 in need of replacement). A person missing their spleen gets 生病 much more often than someone with a spleen.
骨髓 produces new blood 细胞s, both red 和 white. In the case of 红细胞 the 细胞s are fully formed in the marrow 和 then 恩 ter the bloodstream. In the case of some 白血细胞, the 细胞s mature elsewhere. 的 marrow produces all blood 细胞s from 干细胞。他们叫"stem 细胞s" because they can branch off 和 become many different types of 细胞s - they are precursors to different 细胞 types. Stem 细胞s change into actual, specific types of 白血细胞.
抗体 (also referred to as immunoglobulins 和 gammaglobulins) are produced 通过 白血细胞. 的y are Y-shaped proteins that each respond to a specific 抗原 （细菌，病毒或毒素）。每种抗体都有一个特殊的部分（位于Y的两个分支的末端），该部分对特定抗原敏感并以某种方式与其结合。当抗体与毒素结合时，称为抗毒素（如果毒素来自某种形式的毒液，则称为抗毒素）。结合通常使毒素的化学作用失效。当抗体结合到病毒颗粒的外衣或细菌的细胞壁上时，它可以阻止它们通过细胞壁移动。或者大量抗体可以与入侵者结合，并向补体系统发出信号，告知需要将其移除。
什么时候ever 您 see an abbreviation like IgE in a medical document, 您 now know that what they are talking about is an antibody.
的 complement 系统, like antibodies, is a series of proteins. 的re are millions of different antibodies in 您r blood stream, each sensitive to a specific 抗原. 的re are 上ly a handful of proteins in the complement 系统, 和 they are floating freely in 您r blood. Complements are manufactured in the liver. 的 complement proteins are activated 通过 和 work with (complement) the antibodies, hence the name. 的y cause lysing (bursting) of 细胞s 和 signal to phagocytes that a 细胞 needs to be removed.
您 are probably aware of the fact that 您 have "red blood 细胞s" 和 "white blood 细胞s" in 您r blood. 的 白血细胞 are probably the most important part of 您r 免疫的 系统. And it turns out that "white blood 细胞s" are actually a whole collection of different 细胞s that work together to destroy bacteria 和 病毒. Here are all of the different types, names 和 classifications of 白血细胞 working inside 您r body right now:
Learning all of these different names 和 the function of each 细胞 type takes a bit of effort, but 您 can understand scientific 文章s a lot better 上ce 您 get it all figured out! Here's a quick summary to help 您 get all of the different 细胞 types organized in 您r brain.
All 白血细胞 are known officially as 白细胞。白细胞与人体内的正常细胞不同，它们实际上就像独立的，活着的单细胞生物，能够自行移动和捕获事物。白细胞的运动非常像变形虫，可以吞噬其他细胞和细菌。许多白细胞不能自行分裂和繁殖，而是在体内某个地方产生白细胞。那家工厂是骨髓。
Monocyte - 单核细胞 make up 7% or so of all 白细胞. 单核细胞 evolve into 巨集phages.
All 白血细胞 start in bone marrow as 干细胞. Stem 细胞s are generic 细胞s that can form into the many different types of 白细胞 as they mature. For example, 您 can take a mouse, 照射 it to kill off its bone marrow's ability to produce new blood 细胞s, 和 then inject 干细胞 into the mouse's blood stream. 的 干细胞 will divide 和 differentiate into all different types of 白血细胞. A "骨髓移植"只需将供体的干细胞注入血流即可完成。干细胞几乎神奇地进入骨髓，并在那里安家。
Each of the different types of 白血细胞 have a special role in the 免疫的 系统, 和 many are able to transform themselves in different ways. 的 following descriptions help to understand the roles of the different 细胞s.
Of all blood 细胞s, 巨集phages 是最大的（因此得名"macro"). 单核细胞 are released 通过 the bone marrow, float in the bloodstream, 恩 ter tissue 和 turn into 巨集phages. Most boundary tissue has its own devoted 巨集phages. For example, alveolar 巨集phages live in the 肺和keep the 肺 clean (by ingesting foreign particles like smoke 和 dust) 和 disease free (by ingesting bacteria 和 microbes). 巨噬细胞 are called langerhans 细胞s when they live in the 皮肤. 巨噬细胞 also swim freely. One of their jobs is to clean up dead neutrophils -- 巨集pghages clean up pus, for example, as part of the healing process.
T 细胞s, 上 the other hand, actually bump up against 细胞s 和 kill them. T 细胞s known as Killer T 细胞s can detect 细胞s in 您r body that are harboring 病毒, 和 when it detects such a 细胞 it kills it. Two other types of T 细胞s, known as 救命er 和 Suppressor T 细胞s, help sensitize killer T 细胞s 和 control the 免疫的 response.
Because 白血细胞 are so important to the 免疫的 系统, they are used as a measure of 免疫的 系统 health. 什么时候 您 hear that someone has a "strong 免疫的 系统" or a "免疫系统受抑制"，一种确定方法是对血液样本中的不同类型的白细胞进行计数。正常的白细胞计数为每微升血液4,000至11,000个细胞。每个抑制器T细胞有1.8至2.0个辅助T细胞是正常的。正常的绝对中性粒细胞计数（ANC）在每微升1,500至8,000个细胞的范围内。像这样的文章 血液学概论 can help 您 learn more about 白血细胞 in general 和 the different types of 白血细胞 found in 您r body.
A vaccine is a weakened form of a disease. It is either a killed form of the disease, or it is a similar but less virulent strain. Once inside 您r body 您r 免疫的 系统 mounts the same defense, but because the disease is different or weaker 您 get few or no symptoms of the disease. Now, when the real disease invades 您r body, 您r body is able to eliminate it immediately.
人y diseases cannot be cured 通过 vaccines, however. 的 common cold 和 Influenza are two good examples. 的se diseases either mutate so quickly or have so many different strains in the wild that it is impossible to inject all of them into 您r body. Each time 您 get the flu, for example, 您 are getting a different strain of the same disease.
Sometimes 您r 免疫的 系统 is not able to activate itself quickly 恩 ough to outpace the reproductive rate of a certain bacteria, or the bacteria is producing a toxin so quickly that it will cause permanent damage before the 免疫的 系统 can eliminate the bacteria. In these cases it would be nice to help the 免疫的 系统 通过 killing the offending bacteria directly.
Antibiotics work 上 bacterial infections. Antibiotics are chemicals that kill the bacteria 细胞s but do not affect the 细胞s that make up 您r body. For example, many antibiotics interrupt the machinery inside bacterial 细胞s that builds the 细胞 wall. Human 细胞s do not contain this machinery, so they are unaffected. Different antibiotics work 上 different parts of bacterial machinery, so each 上e is more or less effective 上 specific types of bacteria. 您 can see that, because a virus is not alive, antibiotics have no effect 上 a virus.
有时免疫系统会犯错误。一种错误称为 自身免疫: the 免疫的 系统 for some reason attacks 您r own body in the same way it would normally attack a germ. Two common diseases are caused 通过 免疫的 系统 mistakes. Juvenile-onset diabetes is caused 通过 the 免疫的 系统 attacking 和 eliminating the 细胞s in the pancreas that produce insulin. Rheumatoid arthritis is caused 通过 the 免疫的 系统 attacking tissues inside the joints.
的 last example of an 免疫的 系统 mistake is the effect the 免疫的 系统 has 上 transplanted tissue. This really isn't a mistake, but it makes organ 和 tissue transplants nearly impossible. 什么时候 the foreign tissue is placed inside 您r body, its 细胞s do not contain the correct identification. 您的 免疫的 系统 therefore attacks the tissue. 的 problem cannot be prevented, but can be diminished 通过 carefully matching the tissue donor with the recipient 和 通过 using immunosuppressing drugs to try to prevent an 免疫的 系统 反应. Of course, 通过 suppressing the 免疫的 系统 these drugs open the patient to opportunistic infections.