HIV destroys CD4 T-cells, which are white blood cells that help the body fight off infection. The more CD4 T-cells the virus kills, the weaker an HIV-positive person’s immune system grows. Medical providers make an AIDS diagnosis when the number of CD4 T-cells in an individual’s blood (also known as the CD4 T-cell count) falls too low.
The Purpose of CD4 T-Cells
CD4 T-cells attack viruses in the blood. They coordinate the immune system’s response to these infections by activating other immune cells, including CD8 T-cells, B-cells, and macrophages. These cells work together to clear viruses from the body.
HIV’s Effect on CD4 T-Cells
Unfortunately, CD4 T-cells cannot attack HIV successfully. Instead, HIV weakens the immune system by destroying CD4 T-cells. As the CD4 T-cell count decreases, the individual becomes less capable of fighting off infections and infection-related cancers.
A CD4 T-cell count of 200 or fewer cells per cubic millimeter of blood indicates the onset of AIDS in an HIV-positive person. For comparison, a person with a healthy immune system typically has about 500 to 1,500 cells per cubic millimeter of blood. Without treatment, a person with AIDS will survive for about three years.
The best way for people with HIV to maintain their CD4 T-cell levels is to use antiretroviral therapy (ART), which reduces viral load (the amount of HIV in the blood). With less HIV present, fewer CD4 T-cells get destroyed and the immune system doesn’t weaken as dramatically. A lower viral load also decreases the risk of transmitting HIV to a partner during sex.
ART must be taken every day to be effective. It’s best to start taking it as soon as possible after an HIV diagnosis. You still need to practice safe sex if you’re on ART. In addition, you can encourage HIV-negative partners to consider taking PrEP to reduce their risk of getting HIV.