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At some point, like, if you've donated blood, you might have been asked about your blood type.
有时候，比如捐血的时候，你会被问到血型。
And even if you don't know what yours is, you're probably aware that you could have A, B, AB or O blood,
即便你不知道自己的血型，你也应该知道自己的血型可能是A、B、AB或O型血，
and that your blood can be positive or negative.
并且你的血可能是阴性或阳性的。
But that's not the whole story, because there are potentially millions of blood types out there.
但这还不是故事的全部，因为世界上存在百万种血型。
There are so many possible blood types because of the way blood types are defined.
由于血型的定义方式不同，所以可能有很多种血型。
You see, your blood type is defined by the antigens present in your blood.
你看，你的血型是由你血液中的抗原决定的。
Antigens are anything that can elicit a response from your body's self-defense system,
抗原是任何可以引起你身体自卫系统反应的物质
though your immune system normally ignores the ones that belong to you.
虽然你的免疫系统通常会忽略掉那些属于你的物质。
And you can find antigens on cells throughout your body,
你可以在全身的细胞中发现抗原，
with different cells having different combinations of antigens.
不同细胞的抗原组合也不同。
The ones that matter for blood classification are found on the surfaces of your body's red blood cells.
血型分类的重要因素被发现于红细胞的表面。
Simply put, your particular blood type depends on which antigens are or aren't there.
简单来说，你的血型取决于哪些抗原在或不在红细胞表面上。
Like, if you have AB blood, that means you have both the A and B antigens in the ABO blood group.
比如，如果你是AB型血，这意味着你的ABO血型系统中现存A和B抗原。
You could be just A, or just B, or if you're O, you don't have either.
你可以只是A型或B型，或者如果你是O型，那么两者你都没有。
But those ABO antigens are just two of over 600 blood antigens identified by the International Society of Blood Transfusion,
但那些ABO抗原只是国际输血协会鉴定的六百多种抗原中的两种，
and the list hasn't stopped growing yet. Many of these antigens fit into blood group systems,
并且这份名单还在增长。其中很多抗原符合血型系统，
like ABO, each of which is defined by a gene at a single site or by multiple genes that are closely related.
比如ABO，其中每一种都有单一点的一个基因或与之紧密相关的多基因所定义的。
And all of us have these genes—your type for a particular group depends on
我们所有人都有这些基因—你是哪种血型取决于
how your genes translate into the antigens that end up on the outside of your blood cells.
你的基因如何转化成血细胞外端的抗原。
There are 36 blood group systems currently recognized. So your full blood type, if written out,
目前已知的血型系统有36种。所以如果全写出来的话，你的血型
would include all 36 of these groups and the variants you have or don't have for all of those 600-plus antigens.
将包括所有这36种系统以及所有600多种有或没有的变异抗原。
Which is why we can say that there are millions of potential blood types.
所以我们可以说世界上存在百万种潜在血型。
Of course, there are only 8 common ones, and that's because many of these antigens are found in practically everyone,
当然，常见的只有8种，这是因为其中很多抗原发现于几乎每个人身上，
while others are present in only a few individuals.
而另一些只存在于少数个体中。
For example, the SARA antigen has only ever been seen in two families, while 99.96% of people have the Vel antigen.
例如，SARA抗原只存在于两个家族，而99.96%的人都有Vel抗原。
And blood groups can get really complicated, too. Just look at the Rh blood group.
血型真的也可以很复杂。看看Rh血型就知道了。
That's the group that gives you a positive or negative blood type—like, if you're AB+,
这种血型分阴性和阳性，比如如果你是AB+，
the positive part generally means you have the Rh antigen called Rh(D).
阳性的部分通常意味着你有被称为Rh(D)的Rh抗原。
But, to make things more confusing, whether your blood is considered positive or negative
但让事情更复杂的是，你的血是阴还是阳性
may depend on how much of the antigen you have in your system,
可能取决于你的系统中存在多少这种抗原，
since that can impact what sorts of antibodies your immune system makes to protect you.
因为这影响了你的免疫系统需要制造什么样的抗体来保护你。
And D is just one of over 60 million antigens in the Rh group.
D只是Rh血型中6千多万个抗原之一。
So positive or negative doesn't even begin to capture your overall Rh blood type.
所有阴性或阳性甚至不能反映出你的整体Rh血型。
In fact, one of the rarest blood types in the world occurs if you have none of the antigens in the Rh group.
事实上，如果你没有Rh血型中的任何抗原，就会出现世界上最罕见的血型之一。
If you're one of the about 50 people with this blood type, which is known as Rh null
这种血型（Rh null）概率是五十分之一，如果你是其中之一
your body will reject the blood from practically anyone else.
那么你的身体会排斥其他任何人的血液。
And the Rh group isn't the only blood group where having no antigens can be a matter of life or death.
Rh血型并不是唯一一个没有抗原的血型，没有抗原是生死攸关的问题。
Another example is the Diego group.
另一个是Diego血型。
Its antigens are proteins that help the lungs and kidneys perform essential functions.
其抗原是帮助肺和肾脏运行基本功能的蛋白质。
Like with the ABO group, there are two primary antigens, A and B, that determine a person's Diego blood type.
和ABO血型一样，有两种主要抗原A和B决定了一个人的Diego血型。
But unlike the ABO group, where "O" or the lack of antigens is most common,
但和ABO不一样的是，ABO中O或抗原的缺乏是最常见的，
there has only been one documented case of someone lacking both of these key Diego antigens.
仅有一项病例记录有人缺乏这两种Diego抗原。
Sometimes, though, having no antigens can help you out.
虽然有时没有抗原可以帮助到你。
For example, one of the malarial parasites uses antigens in the Duffy blood group to target and infiltrate cells,
例如，有一种疟原虫利用Duffy血型中的抗原瞄准并渗入细胞中，
so having no antigens from that group can make you more resistant to the disease.
所以如果没有来自那个血型的抗原可以让你对疾病更有抵抗力。
But it also means there's a chance that your body will attack another person's blood if you're given a transfusion,
但这也意味着，输血时，你的身体可能会攻击其他捐献者的血液，
since the cells you receive could have Duffy antigens on them that your body sees as foreign.
因为你接收血液中可能存在Duffy抗原，你的身体会视之为入侵者。
The good news is that despite all the potential blood types you could have,
好消息是，尽管你可能有很多潜在的血型，
for the most part, the ABO-Rh blood typing we're used to does a pretty good job of matching people's blood.
对大多数而言，我们习惯的ABO-Rh血型能够很好地匹配大家的血液。
With this system, if you receive blood from someone with the same ABO-Rh type,
在这个系统中，如果你从具有相同ABO-Rh血型的人那里接受血液，
there's a 99.8 percent chance your blood will be compatible with your donor's.
你的血液有99.8%的几率与捐赠者的血液相容。
For some reason, your body's immune system doesn't go after every antigen equally,
出于一些原因，你身体的免疫系统并不是对每一种抗原都一视同仁，
so you don't usually need to know what version of every single known antigen you have.
所以通常不需要知道自己体内的每个抗原。
And if you do want to be extra sure, there are ways that doctors can tell if you have a rare blood type.
如果你想知道，医生可以鉴别是你否拥有稀有血型。
For example, they can screen for unexpected antibodies that could potentially target donated red blood cells,
例如，他们可以筛查意想不到的抗体，这些抗体可能针对捐献的红细胞，
or perform crossmatching, where your blood is mixed with a donor's to see how the two react.
或是进行交叉配型，将你的血液与供者的血液混合，观察两者的反应。
Doing these two steps racks your safety margin up to 99.95 percent.
这两个步骤可以使你的安全边际达到99.95%。
And if you do happen to have a rare blood type like Rh null, don't fret.
如果你恰好拥有稀有血型，比如Rh null，也不要烦恼。
Efforts like the International Rare Donor Panel work hard to make sure you can get the blood you need,
国际稀有血型库会确保你能获得所需的血型，
no matter where in the world you are.
不管你在世界哪个地方。
One person needing a transfusion had a rare blood type delivered from the UK to Cameroon.
一名需要罕见血型的病人可以从英国被送往喀麦隆。
That's about four thousand miles away! So even if your blood is literally one in a million,
其间距离约有四千英里。所以即便你的血型真的是百万分之一，
you can be pretty confident that you'll be able to find someone whose blood matches yours.
你也能够找到匹配你血型的人。
And, I guess, you could say that's one of the parts of being human —
我猜你可能会觉得作为人类
having something in common with other people while being unique in your own special way.
大家即拥有共同之处，又在某一方面千差万别。
Blood types ultimately boil down to microscopic differences between red blood cells.
血型最终归结为红细胞之间的微观差异。
And if you were to zoom in to see those differences and really watch what goes on in your own bloodstream,
如果你将这些差异放大来看并真正观察你的血液里发生了什么，
you'd see a bustling and bizarre world.
你会看到一个热闹而奇异的世界。
In fact, when you look at pretty much anything under a powerful enough microscope,
事实上，当你在足够强大的显微镜下观察任何东西时，
all sorts of wonderfully fantastic lifeforms are revealed.
各种奇妙的生命形式都会被揭示出来。
And that's kind of the point of our new sister channel produced by Complexly: Journey to the Microcosmos.
这就是姐妹频道Complexly新推出的重点：《Journey to the Microcosmos》。
Journey to the Microcosmos is all about bringing you closer to the world of very, very small things in a relaxing way.
《Journey to the Microcosmos》会用一种放松的方式让你更接近那些细微之物的世界。
It pairs James Weiss's incredible microscopic footage with Hank Green's soothing narration
将詹姆斯·韦斯令人难以置信的微观镜头与汉克·格林令人宽慰的叙述
and Andrew Huang's meditative music, so you can just kick back and marvel at the microscopic realm.
以及Andrew Huang的冥想音乐相结合，你可以放松下来，惊叹于微观世界。
You can check it out for yourself at the link in the description. And as always, thanks for watching!
点击下方链接查看，感谢收看！
