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Most of us already know our blood type: whether it's A, B, AB or O, and whether it's positive or negative.
我们绝大多数人都知道自己的血型：A型、B型、AB型、O型，每一种血型又都有Rh阳性和Rh阴性血型。
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，整个地球上只有43人是这种血型。
This blood group is known as Rhnull, and scientists are calling it the "golden blood type".
这种血型就是“Rhnull血型”，科学家称其为“黄金血型”。
Things would be straightforward if we all had the same blood type. But we don't.
如果我们都有相同的血型，那事情就简单了。但可惜，事与愿违
On the surface of every one of our blood cells,
在我们每个血细胞的表面，
we have hundreds of antigens which are the molecules that are capable of triggering the production of specialized proteins called antibodies.
有数百种抗原，这些分子能够触发产生一种叫做抗体的特殊蛋白质。
It is the presence or absence of particular antigens that determines someone's blood type.
其中特定抗原的存在或缺失决定着一个人的血型。
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，你可能在ABO血型系统中是AB血型，在Rh血型系统中是Rh阳性，在Kell血型系统中是K+型，等等。
Of the 32 blood group systems, the Rh system is the largest, containing 61 antigens.
在32种血型系统中，Rh血型系统是最大的，拥有61种抗原。
Interestingly, 99.9999994 percent of people in the world have blood with Rh antigens on their red blood cells.
有趣的是，全世界99.99999994%的人的血液中，红细胞表面含有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，正如其名字所暗示的那样，Rhnull血型完全没有这些Rh抗原，这也使它成为了世界上最罕见的血型！
Rhnull blood was first found in 1961 in an Australian woman.
1961年，Rhnull血型首次在一个澳大利亚女性的血液中发现。
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，医生一直以为缺少Rh抗原的血细胞的胚胎是无法存活的，更不用说长成正常、健康的成年人了。
But by 2010, nearly five decades later, some 43 people with Rhnull blood had been reported worldwide.
但到了2010年，也就是近50年后，全世界大约有43人被报道是Rhnull血型。
You might think these 43 people are very lucky, but that couldn't be further from the truth.
你可能会想，这43个人真是太幸运了。但事实并非如此。
In reality, because Rhnull blood is so rare, it is also extremely dangerous to live with.
因为在现实中，因为Rhnull血型非常罕见，所以这些人的生存其实也是极其危险的。
Blood groups are inherited, and Rhnull is known to run in families.
血型是遗传的，因此Rhnull血型是会在家族内遗传的。
But when researchers tried to find the genetic basis of this golden blood type in one of the subjects,
但是，当研究人员试图找出这一黄金血型的遗传学基础时，
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.
她们发现Rhnull血型是由两种纯属巧合的随机突变形成的，而这就是为什么这种血型如此罕见的根本原因。
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.
人体的免疫系统天生就含有抗体，可以帮助你对抗免疫系统无法识别的外源性物质，比如病毒和细菌。
These antibodies can also attack antigens that aren't present in your natural blood type.
这些抗体也会攻击你自然血型中不存在的抗原。
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. This can have life-threatening results.
比如说，如果你是B型血，但是给你输了A型血，你的抗体就会破坏红细胞上的A抗原。结果可能会危及生命。
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.
这就意味着，如果你是Rhnull血型，输入了含有任何Rh抗原的血液，机体都会产生排斥反应。
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.
而因为全世界只有不到50人的血型是Rhnull，所以为Rhnull血的个体寻找血液捐献者几乎是不可能的。
This is why people who have the golden blood type are encouraged to donate blood in case they ever need blood.
这就是为什么要鼓励黄金血型的人献血，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.
不过也恰恰由于Rhnull血型不含会被机体排斥的Rh抗原，所以这种血液可以成为那些较为罕见血型的人的通用供体。
Golden blood, therefore, can be both life-threatening and life-saving.
因此，黄金血型既可以威胁生命，也可以拯救生命。
And while your chances of having the rarest blood type are incredibly low, it's important that you know what your blood type is.
虽然你拥有这种最稀有血型的几率非常之低，但搞清楚自己的血型是什么还是很重要的。
You never know when your life will need to be saved, or when you could save someone else's.
你永远不知道什么时候自己需要被救一命、什么时候自己可以救别人一命。
