Most of us already know our blood type: whether it's A, B, AB or O, and whether it's positive or negative.
我们大多数人都知道自己的血型：A型、B型、AB型，或者是O型，还知道血是阳性还是阴性的。
But did you know that there is a blood type so rare that only 43 people on Earth have ever been reported to have it.
但你知道吗，有一种血型非常罕见，据报道，地球上只有43个人拥有这种血型。
This blood group is known as Rhnull and scientists are calling it the golden blood type.
这种血型名叫Rhnull血型，科学家们称之为黄金血型。
Things would be straightforward if we all had the same blood type.
如果我们的血型都一样，那事情就简单得多了。
But we don't.
然而事实并非如此。
On the surface of every one of our blood cells, we have hundreds of antigens which are the molecules that are capable of triggering the production of specialized proteins called antibodies.
我们每个血细胞的表面都有数百种抗原，这些抗原分子能够因触发而产生一种被称为抗体的特殊蛋白质。
It is the presence or absence of particular antigens that determines someone's blood type.
特定抗原的存在或缺失便决定了一个人的血型。
For example, you may have AB blood in the ABO blood group system, be Rh positive in the Rh system, as well as being K positive in the Kell system, and so on.
例如，你可能是ABO血型系统中的AB血型，或是Rh血型系统中的Rh阳性，也可能是Kell血型系统中的K阳性，等等。
Of the 32 blood group systems, the Rh system is the largest, containing 61 antigens.
在所有的32种血型系统中，Rh血型系统是最大的，包含了61种抗原。
Interestingly, 99.999 9994 percent of people in the world have blood with Rh antigens on their red blood cells.
有趣的是，世界上99。9999994%的人的血液红细胞上都有Rh抗原。
But, as the name implies, the Rhnull blood type is completely missing these Rh blood group antigens, which makes it the rarest blood type in the world.
但是，正如该血型名字所暗示的那样，Rhnull血型便没有这些Rh血型抗原，这使它成为世界上最罕见的血型。
Rhnull blood was first found in 1961 in an Australian woman.
1961年，Rhnull血型在一名澳大利亚妇女身上首次被发现。
Until then, doctors had assumed that an embryo missing all Rh blood cell antigens would not survive, let alone grow into a normal, thriving adult.
在此之前，医生们一直认为缺少所有Rh血细胞抗原的胚胎无法存活，更不用说成长为一个正常、茁壮的成年人了。
But, by 2010, nearly five decades later, some 43 people with Rhnull blood had been reported worldwide.
但是，在大约50年以后的2010年，世界范围内大约有43人拥有Rhnull血。
You might think these 43 people are very lucky, but that couldn't be further from the truth.
你可能会认为这43个人非常幸运，但事实并非如此。
In reality, because Rhnull blood is so rare, it is also extremely dangerous to live with.
在现实中，因为Rhnull血非常罕见，拥有这种血型也是一件极其危险的事。
Blood groups are inherited, and Rhnull is known to run in families.
血型是由遗传决定的，Rhnull血型同样如此。
But when researchers tried to find the genetic basis of this golden blood type in one of the subjects, they found that Rhnull blood was due to two completely different random mutations on pure chance, which is one reason why this blood type is so rare!
但当研究人员试图在其中一名受试者身上找到这种黄金血型的基因基础时，他们发现Rhnull血型是由于两种完全不同的随机突变而形成的，这便是该血型如此罕见的一个原因。
Your immune system naturally contains antibodies, which help to fight off any foreign material that your immune system doesn't recognize, such as viruses and bacteria.
你的免疫系统自然含有抗体，它有助于你的身体对抗任何自身免疫系统无法识别的外来物质，如病毒和细菌。
These antibodies can also attack antigens that aren't present in your natural blood type.
这些抗体也可以攻击在你的自然血型中并不存在的抗原。
For example, if you have type B blood and you receive a blood transfusion of type A blood, your antibodies will work to destroy the A antigens.
例如，如果你是B型血，却输了A型血，你的抗体就会破坏A型血抗原。
This can have life-threatening results.
这可能会造成危及生命的后果。
This means if you have the Rhnull blood type, receiving a transfusion of a blood type with any Rh antigens will cause your body to reject the blood.
这也就意味着，如果你是Rhnull血型，接受任何带有Rh抗原的血型输血都会导致你的身体排斥这种血液。
Because fewer than 50 individuals in the entire world have the Rhnull blood type, finding a blood donor for Rhnull individuals can be nearly impossible.
因为全世界只有不到50个人拥有Rhnull血型，为Rhnull血型的人找到一个献血者几乎是不可能的事情。
This is why people who have the golden blood type are encouraged to donate blood in case they ever need blood.
这就是为什么人们鼓励那些拥有黄金血型的人献血，那便是以备不时之需。
As Rhnull blood contains no Rh antigens to be rejected, it can be a universal donor for those with generally rare blood types.
由于Rhnull型的血液不含会被排斥的Rh抗原，它可以为那些拥有罕见血型的人提供通用供体。
Golden blood, therefore, can be both life-threatening and lifesaving.
因此，黄金血液既能危及生命，也能拯救生命。
And while your chances of having the rarest blood type are incredibly low, it's important that you know what your blood type is.
虽然一个人拥有这种最稀有血型的几率非常之低，但是弄清楚自己的血型仍然十分重要。
You never know when your life will need to be saved or when you could save someone else.
因为你永远不知道自己何时需要被拯救，抑或何时可以拯救别人。
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