Our body is protected by the immune system made up of white blood cells or WBC. These WBC have only one job and that is to keep us healthy. We could say that they are our body's army or police force.
We are surrounded by all kinds of viruses and germs that attack our body and make us ill. The WBC fights these viruses and diseases, usually manage to keep us healthy and protect us from disease. Sometimes though, in the case of more serious illnesses such as pneumonia or tuberculosis (TB), we need medication to help the white blood cells destroy these diseases. However, these white blood cells, with the help of the medication would normally get us healthy again.
HIV is totally different. It does not attack the body but it attacks the white blood cells that protect us. So what happens is that HIV slowly but surely kills our whole army or police force. After some years, our body will not have enough WBC left to protect itself; which means that it has no defenses against all the other diseases such as pneumonia, TB, cancer and skin infections that can make us ill. When that starts happening, we say that someone has AIDS. He now has an acquired immune deficiency syndrome.
But if he dies, what does he die of? Not of AIDS. Yes, he may have AIDS but that only means that his body no longer has an army or police force to protect itself. That is why he will become ill easily, and why it is diseases such as pneumonia, TB or cancer that will ultimately kill him.
For much deeper explanation, your blood contains different types of white blood cells: T-lymphocytes, B-lymphocytes, killer T-cells and macrophages. The most important WBC in the body is the T-lymphocyte or the CD4 cell. The CD4 cell or T-lymphocyte basically acts as the commanding officer or commander of the body's army. If any virus or germs arrives in the body, it is the CD4 cells that identify these viruses. They emit a chemical signal which activates all the other WBC. The other WBC reacts to the chemical signal of the CD4 cell and destroys the viruses or germs.
The HI virus is different. The moment it enters the body, it begins to attack the T-lymphocytes or CD4 cells. It penetrates the CD4 cell and uses them as a factory where it manufactures hundreds of new viruses. These new viruses are then released into the blood, in the process destroying the CD4 cells.
The longer a person is HIV positive, the more rapidly the HI viruses multiply, and the more CD4 cells are destroyed. Your body is constantly manufacturing new CD4 cells, but the virus multiplies so rapidly that there ultimately comes a time when the CD4 cells are destroyed more quickly than your body can manufacture new ones.
This process can take up to 8-10 years, but it means that the body's defense system is gradually being worn down. In other words, the commanders of the army, the ones that give the command to attack are being destroyed. The body's alarm system is being switched off. All the other WBC are still there and they can still do their job, but now there is no one to tell them to attack. So the body's immune system is neutralized.
Your body is now susceptible to all kinds of diseases, because there is no longer a defense system to protect you. Now all the other diseases can cause chaos in the body. This condition is AIDS. In other words, your body is susceptible to all sorts of opportunistic infections that will eventually become so serious that you will probably die of them.
A normal person has between 800-1200 T-lymphocytes or CD4 cells per milliliter of blood. When an HIV positive person has fewer than 200, there are no longer enough CD4 cells to set off the chain reaction. The person falls ill easily. By definition, this person now has AIDS.
Note: Information was excerpt from the "Channels of Hope" manual.