谁知道关于英语AIDS的严重性！！谢谢！急用！

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Why is HIV dangerous?
The immune system is a group of cells and organs that protect your body by fighting disease. The human immune system usually finds and kills viruses fairly quickly.

So if the body's immune system attacks and kills viruses, what's the problem?

Different viruses attack different parts of the body - some may attack the skin, others the lungs, and so on. The common cold is caused by a virus. What makes HIV so dangerous is that it attacks the immune system itself - the very thing that would normally get rid of a virus. It particularly attacks a special type of immune system cell known as a CD4 lymphocyte.

HIV has a number of tricks that help it to evade the body's defences, including very rapid mutation. This means that once HIV has taken hold, the immune system can never fully get rid of it.

There isn't any way to tell just by looking if someone's been infected by HIV. In fact