How does the HIV virus work?

HIV is different from other viruses because it gets inside your immune system cells. The immune cells are called CD4 cells, also known as T4 cells. The job of CD4 cells is to watch out for viruses that get into your body. CD4 cells send a message to the rest of the immune system to help fight the virus.

But when HIV takes over the CD4 cells they can't do their job. This means your body doesn't have part of its immune system and can't work as hard as it should, so you are at a much higher risk of getting sick.

When HIV gets into a CD4 cell, it takes control of that cell, so the cell starts making new copies of HIV. This process is called replication.

Basically, the HIV goes into the CD4 cell and sets up a little factory. In that factory it starts making more HIV. Then the new HIV leaves the CD4 cell (the factory) to go and infect (set up other factories in) other CD4 cells. HIV uses an enzyme called protease to make its coat before it leaves the cell.

A doctor can use a blood test to count the number of CD4 cells per cubic millimeter (mm3) in your blood. The CD4 count is important because it shows how much damage has been done to your immune system. Another blood test counts the number of HIV cells in your blood. This is called your viral load.