Narrator: Listen to part of the lecture in a biology class.

旁白：听一篇生物学科讲座。

Professor: So that's the overview of the human immune system.

教授：所以那就是我们对人类免疫系统的回顾。

But we have a few minutes left.

但我们距离下课还有几分钟时间。

Any questions? George?

还有问题吗？乔治？

Student: Yes. You talked about T-cells, naive T-cells.

学生：你提到了T细胞，也就是初始T细胞。

Can you go over that part again?

您能再讲解一下那个部分吗？

And also why do we call them that anyway?

以及我们究竟为什么那样命名他们？

Professor: All right. They're... they're known as T-cells because they develop in the thymus.

教授：好的。它们……它们之所以被称为淋巴细胞是因为它们成长于胸腺中。

Student: The what?

学生：什么？

Professor: Thymus. That's T-H-Y-M-U-S.

教授：胸腺。拼法是T-H-Y-M-U-S。

It's a small organ in the body.

这是身体中的一个小器官。

Anyway, that's why we call them that.

无论如何，那就是我们如此命名淋巴细胞的原因。

They come from the thymus.

它们来自于胸腺中。

And T-cells are a part of body's immune system.

而淋巴细胞是身体免疫系统的一部分。

They can recognize and eliminate cells from outside the body that might cause disease.

它们可以辨识并消灭那些来自体外，可能会引起疾病的细胞。

Student: But why naive? I mean, we might call people naive if they don't have enough experience to know about the dangers of the world.

学生：但是为什么幼稚？我的意思是，我们会说人幼稚，如果他们没有足够感知世界危险的经验的话。

But how can you call a cell naive?

然而你怎么可能说一个细胞幼稚呢？

Professor: Well... when this type of immune cell encounters a cell from outside the body, like maybe a bacterium.

教授：恩……当这种类型的免疫细胞碰到一个来自体外的细胞，比如可能是一个细菌。

It interacts with that bacterium and learns to recognize it.

它会和那个细菌互动并学会辨识对方。

So whenever the immune cell runs into that kind of bacterium in the future, it'll attack and kill it.

所以，无论这个免疫细胞将来何时碰到那种细菌，它都会攻击并消灭它。

At that point we call it a memory T-cell because it's learned to recognize a protein marker that identifies this particular kind of bacterium.

到那时，我们就称它为记忆淋巴细胞，因为它已经学会辨识一种可以认出这种特定细菌的蛋白质标记了。

But before it's learned to recognize any particular protein from outside the body, we call it naive. Okay?

但在它学会辨认体外的任一特定蛋白质之前，我们称它为幼稚。明白了吗？

Student: Yeah, I get it.

学生：是的，我懂啦。

Professor: There is a lot of biochemistry involved that we'll get into in the next lecture.

教授：这当中涉及到很多生物化学的内容，我们下次讲座会进行讲解。

But your question reminds me about a study that some of my colleagues are doing.

但是你的问题使我想起了我的一些同事正在做的一项研究。

It relates to caloric restriction.

有关于卡路里限制的研究。

Student: Caloric? Like calories in the food we eat?

学生：卡路里？就像我们吃的食物中的卡路里？

Professor: Exactly! We are talking about the sugars, carbohydrates, fats that our bodies burn to get energy which we measure in calories.

教师：完全正确！我们现在要讨论的正是我们的身体可以用来燃烧获取能量的糖、碳水化合物、脂肪，而能量是以卡路里为单位计算的。

Okay, let's back up a little.

好的，我们回到刚才的话题。

Back in the 1930s, a nutritionist at Cornell University put mice on a severely restricted diet.

回到20世纪30年代，一位康奈尔大学的营养学家为老鼠制定了一个极为严格的饮食习惯。

He gave each mouse in one group thirty percent less food, or more precisely, thirty percent fewer calories than the mice in the other group which ate a normal amount.

他少给了一组中的每只老鼠30%的食物，或者说得更准确一点，比另一组正常食量的老鼠少30%的卡路里。

And the result, the underfed mice lived much longer than the normally fed ones.

结果是，未给予足够食物的老鼠比正常喂养的老鼠寿命要长很多。

Student: Wow! Does that just go for mice?

学生：哇哦！这个结果只适用于老鼠吗？

Professor: Apparently not. Similar results have come from experiments on other animals from roundworms to most recently Rhesus monkeys.

教授：显然不是。关于其他动物的实验，不管是针对蛔虫还是最近对恒河猴的实验，都得到了相似的结果。

These monkeys, two groups of them, were given all the vitamins and minerals and other nutrients they needed, except that one group got thirty percent fewer calories.

这些猴子被分成两组后，被给予了它们所需要的所有维生素、矿物质及其他营养，除了其中一组获得了少于另一组30%的卡路里。

And now after thirty years or so, about an average lifetime for a monkey, it's clear that the monkeys that have been on the calorie restricted diet are doing a lot better than the ones on that we consider a normal healthful diet.

而现在，过了30几年左右的时间之后，大概是一只猴子平均寿命的时间，结果明显表明， 那些严格限制卡路里的猴子们比那些我们认为饮食正常健康的猴子们状况要好得多。

Like in terms of blood pressure and lots of other measures, the calorie restricted monkeys are much healthier and they just look and act younger than the monkeys in the normal diet group.

比如在血压和很多其他测试方面，限制卡路里摄入的猴子比正常饮食的那组猴子要健康得多，并且它们外表上和行动上就是比较年轻。

And as a group, they are living longer.

作为一个组群，它们的寿命更长。

Student: Interesting. But what's the connection?

学生：有趣。但有什么关联吗？

Professor: Oh, with the immune system?

教授：哦，和免疫系统吗？

Well, it is been shown that the immune system becomes much less effective as animals age.

恩，实验表明，随着动物变老以后，其免疫系统的效率会降低很多。

That's true in humans too.

这也同样适用于人类。

We think those naive T-cells just get used up.

我们认为那些初始淋巴细胞只是被用尽了。

I mean it is not like the body's always making lots of new ones.

我的意思是，身体并不是总会制造很多新的细胞。

And over the course of a lifetime, as T-cells encounter more and more strange bacteria or whatever, the naive T-cells get turned into memory T-cells.

而经过一生的过程，随着淋巴细胞遇到越来越奇怪的细菌或者其他的东西，初始淋巴细胞转变成了记忆淋巴细胞。

So later on in life, there are fewer and fewer of these naive T-cells left to deal with any new disease- causing organisms that might attack, which means less immunity, and the animal or person is more likely to get sick.

所以在生命的后期，身体里剩下的能够处理任何新疾病的初始淋巴细胞会越来越少，导致器官遭受攻击，意味着免疫能力降低，而动物或人更容易生病。

But caloric restriction, it kind of shocks the system, and one result is, well, those monkeys on the calorie-restricted diet had lots more naive T-cells left than you'd expect in monkeys that old.

但是卡路里限制会有些冲击到免疫系统，结果之一就是，那些限制卡路里的猴子体内剩余的初始淋巴细胞数量会比 你们预想的那么老的猴子体内剩余的细胞数量要多很多。

The expected drop in naive T-cells, apparently the shock of getting thirty percent fewer calories really slows that down.

预期中的幼稚淋巴细胞数量下降，显然减少30%卡路里摄入对免疫系统的冲击真的可以减缓细胞数量的减少。

And after many years, with so many more naive T-cells still in reserve, these monkeys are a lot better at fighting off new infections than normally fed monkeys of the same advanced age.

多年之后，这些仍然留下了这么多的幼稚淋巴细胞的猴子会比那些同样年老但正常喂养的猴子更能够打败新的传染病。

Student: And that's why they live longer?

学生：那就是它们寿命更长的原因吗？

Professor: Well, it's got be one reason.

教授：呃，这肯定是原因之一。

This is all pretty complex though with lots of details yet to be worked out.

但这一切都很复杂，还有很多细节有待研究。

Student: But are results the same for humans?

学生：但对于人来说，结果是一样的吗？

Professor: Hard to say. A good study would take decades.

教授：很难讲。一个好的研究，需要花费几十年的时间。

And it's not easy finding people who'd want to take part, would you?

要找到愿意参与研究的人并不容易，你会参加吗？

Student: And eat thirty percent less?

学生：要少吃30%的食物？

That would be tough.

这比较困难。

Professor:You bet it would.

教授：你说对了。