When somebody gets infected with HIV,” states Dr. Hasham, “the virus gets into the bloodstream and attacks certain immune cells and for our purposes, let us call it the CD4 cell. What happens is that the virus attaches onto receptors that are on the top of these immune cells. It binds onto that cell and releases its genetic material into this cell which will then find its way to the powerhouse of the cell (the cell nucleus). This starts the process of integrating into the DNA and replicating the virus, eventually coming out of the nucleus, exiting the cell, and infecting another cell.
When it exits the cell to get back into the bloodstream in order to go and infect another cell, it bursts out of that CD4 cell and that cell is dead. And what happens is you get such a huge viral response in the early stage of the infection because these viruses are replicating very, very quickly, so cell numbers will drop. Over time, the immune system does start to kick in and it will try and kind of tame the situation, and you almost level off with the viral number.
During this time, the immune system is just trying to keep up, but eventually it will tire out and then the immune system will drop again. And that is when you risk your T cells (white blood cells also known as your CD4 cells) reaching a certain number, or on the lower end. Once you reach that point, then you are looking at having AIDS. There are other criteria for AIDS as well but lowering the number down to the point where it cannot quiet a lot of the infection is also criteria for the AIDS definition.