How bones make blood - Melody Smith

翻译人员: Wanting Zhong 校对人员: Haylin Qin

At any given moment, trillions of cells are traveling through your blood vessels,

在任何时刻，你的血管内 有几万亿细胞经过，

sometimes circling the body in just one minute.

有时候能在一分钟内 在身体里循环一周。

Each of these cells has its origins deep in your bones.

这些细胞中的每一员 都起源于你的骨头深处。

Bones might seem rock-solid, but they’re actually quite porous inside.

骨头看上去和石块一样坚固， 但它们中心其实有相当多孔。

Large and small blood vessels enter through these holes.

大小血管从这些洞里进入。

And inside most of the large bones of your skeleton is a hollow core

而你骨骼中的大骨头大多数是空心的，

filled with soft bone marrow.

其中填满了柔软的骨髓。

Marrow contains fat and other supportive tissue,

骨髓中含有脂肪和其它支持组织，

but its most essential elements are blood stem cells.

但它最重要的成分是造血干细胞。

These stem cells are constantly dividing.

这些干细胞一直在进行分裂。

They can differentiate into red blood cells,

它们可以分化成红细胞、

white blood cells, and platelets,

白细胞和血小板，

and send about hundreds of billions of new blood cells

每天能将数千亿新生的血细胞

into circulation every day.

投入人体循环。

These new cells enter the bloodstream

这些新细胞

通过骨髓里小毛细血管上的洞 进入血液循环。

through holes in small capillaries in the marrow.

Through the capillaries,

通过毛细血管，

they reach larger blood vessels and exit the bone.

它们可以抵达更大的血管， 离开骨头。

If there’s a problem with your blood,

如果你的血液出了问题，

there’s a good chance it can be traced back to the bone marrow.

这个问题很有可能 可以追溯回骨髓。

Blood cancers often begin with genetic mutations in the stem cells.

血癌往往是由干细胞中 的基因突变开始的。

The stem cells themselves are not cancerous,

干细胞本身并没有癌变，

but these mutations can interfere with the process of differentiation

但这些突变会干扰 分化的过程，

and result in malignant blood cells.

产生恶性的血细胞。

So for patients with advanced blood cancers like leukemia and lymphoma,

因此，对于重症血癌， 例如白血病或淋巴癌的患者来说，

the best chance for a cure is often an allogeneic bone marrow transplant,

最有可能治愈的手段 通常是异体骨髓移植，

which replaces the patient’s bone marrow with a donor’s.

能将患者的骨髓替换成捐献者的骨髓。

Here’s how it works.

以下是它的原理：

First, blood stem cells are extracted from the donor.

首先，从供者的体内采集造血干细胞。

Most commonly,

最常见的做法是，

blood stem cells are filtered out of the donor’s bloodstream

通过将血液循环通过机器

by circulating the blood through a machine

将其分离成不同成分，

that separates it into different components.

从而将造血干细胞 从供者的血液中过滤出来。

In other cases, the marrow is extracted directly

另外的做法是，用针直接从供者

from a bone in the hip, the iliac crest, with a needle.

髋部的骨头髂嵴中抽取骨髓。

Meanwhile, the recipient prepares for the transplant.

与此同时，受者将为移植做准备。

High doses of chemotherapy or radiation kill the patient’s existing marrow,

用高剂量的化疗或放射线照射 杀死患者现存的骨髓，

destroying both malignant cells and blood stem cells.

将癌细胞与造血干细胞同时破坏掉。

This also weakens the immune system,

这也会弱化患者的免疫系统，

making it less likely to attack the transplanted cells.

降低其攻击移植细胞的几率。

接下来，供者的细胞将通过静脉注射输注给患者。

Then the donor cells are infused into the patient’s body through a central line.

They initially circulate in the recipient’s peripheral bloodstream,

这些细胞先在受者的外周血液中循环，

but molecules on the stem cells, called chemokines, act as homing devices

不过干细胞上被称为“趋化因子“的分子 起到归巢作用，

and quickly traffic them back to the marrow.

引导这些干细胞快速迁移回骨髓中。

Over the course of a few weeks,

在几个星期的时间里，

they begin to multiply and start producing new, healthy blood cells.

它们的数量开始增长， 并开始制造新的健康血细胞。

Just a small population of blood stem cells

只需要少许造血干细胞，

can regenerate a whole body’s worth of healthy marrow.

就能再生整个身体所需的健康的骨髓。

A bone marrow transplant can also lead to something

一次骨髓移植也可以产生

called graft-versus-tumor activity,

所谓的“移植物抗肿瘤”效应，

when new immune cells generated by the donated marrow

即移植骨髓产生的新免疫细胞

can wipe out cancer cells the recipient’s original immune system couldn’t.

能够抹杀受者原来的免疫系统 无法杀灭的癌细胞。

This phenomenon can help eradicate stubborn blood cancers.

这个现象能帮助患者 清除顽固的血癌细胞。

But bone marrow transplants also come with risks,

但是骨髓移植也伴随风险，

including graft-versus-host disease.

包括移植物抗宿主病。

It happens when the immune system generated by the donor cells

这种病症会让由供体细胞生成的免疫系统

attacks the patient’s organs.

攻击患者的器官。

This life-threatening condition occurs in about 30–50% of patients

这种危机生命的病症 会发生在约 30% - 50% 那些

who receive donor cells from anyone other than an identical twin,

没有从同卵双胞胎获得 供体细胞的患者身上，

particularly when the stem cells are collected

尤其是在干细胞

from the blood as opposed to the bone marrow.

是从血液中而不是从骨髓中采集的情况下。

Patients may take immunosuppressant medications

通过让患者服用免疫抑制药，

or certain immune cells may be removed from the donated sample

或者将特定免疫细胞 从捐献的样本中移除，

in order to reduce the risk of graft-versus-host disease.

可以降低移植物抗宿主病的风险。

But even if a patient avoids graft-versus-host disease,

然而即使患者躲过了移植物抗宿主病，

their immune system may reject the donor cells.

他们的免疫系统 还是有可能排斥供体细胞。

So it’s crucial to find the best match possible in the first place.

因此，在第一步找到尽可能 匹配的捐献者至关重要。

Key regions of the genetic code determine how the immune system

遗传基因中有关键区域

决定免疫系统如何识别外来细胞。

identifies foreign cells.

If these regions are similar in the donor and the recipient,

如果供者和受者的这些区域比较相似，

the recipient’s immune system is more likely to accept the donor cells.

受者的免疫系统就更有可能接受供者的细胞。

Because these genes are inherited, the best matches are often siblings.

因为这些基因是遗传的， 最好的配型一般是兄弟姐妹。

But many patients who need a bone marrow transplant

但是很多需要骨髓移植的患者

don’t have a matched family member.

并没有匹配的家庭成员。

Those patients turn to donor registries of volunteers

这些患者转而求助于愿意捐献骨髓的

willing to offer their bone marrow.

志愿者资料库。

All it takes to be on the registry is a cheek swab to test for a genetic match.

想成为骨髓捐献者， 只需用棉签刮口腔进行基因配型。

And in many cases, the donation itself

大多数情况下，骨髓捐献本身

isn’t much more complicated than giving blood.

并不比献血麻烦多少。

It’s a way to save someone’s life

这种办法可以通过完全可再生的资源

with a resource that’s completely renewable.

拯救某个人的生命。