HIV is a lot like other viruses, including those that cause the "flu" or the common cold. But there is an important difference – over time, your immune system can clear most viruses out of your body. That isn't the case with HIV – the human immune system can't seem to get rid of it. That means that once you have HIV, you have it for life.We know that HIV can hide for long periods of time in the cells of your body and that it attacks a key part of your immune system – your T-cells or CD4 cells. Your body has to have these cells to fight infections and disease, but HIV invades them, uses them to make more copies of itself, and then destroys them.Over time, HIV can destroy so many of your CD4 cells that your body can't fight infections and diseases anymore. When that happens, HIV infection can lead to AIDS, the final stage of HIV infection. Hoever, a person who is diagnosed with HIV and treated before the disease is far advanced can have a nearly normal life expectancy.