What are CD4 cells?

CD4 cells are a type of lymphocyte (white blood cell). They are an important part of the immune system. CD4 cells are sometimes called T-cells. There are two main types of T-cells. T-4 cells, also called CD4+, are “helper” cells. They lead the attack against infections. T-8 cells, (CD8+), are “suppressor” cells that end the immune response. CD8+ cells can also be “killer” cells that kill cancer cells and cells infected with a virus.

Why are CD4 cells important in HIV?

When HIV infects humans, the cells it infects most often are CD4 cells. The virus becomes part of the cells, and when they multiply to fight an infection, they also make more copies of HIV.

When someone is infected with HIV for a long time, the number of CD4 cells they have (their CD4 cell count) goes down. This is a sign that the immune system is being weakened. The lower the CD4 cell count, the more likely the person will get sick. Early in the course of the disease, the body can make more CD4 cells to replace the ones that have been damaged by HIV. Eventually, the body can’t keep up and the number of functioning T-cells decreases. As more and more CD4 cells become damaged, the immune system becomes more and more weakened.

There are millions of different families of CD4 cells. Each family is designed to fight a specific type of germ. When HIV reduces the number of CD4 cells, some of these families can be totally wiped out. You can lose the ability to fight off the particular germs those families were designed for. If this happens, you might develop an opportunistic infection.

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