Why Are CD4 Cells Important in HIV?
When HIV infects humans, the cells it infects most often are CD4 cells. The genetic code of the virus becomes part of the cells. When CD4 cells 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. 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 (see Fact Sheet 500).
HIV most often infects CD4 cells. The virus becomes part of the cells, and when they multiply to fight an infection, they make more copies of HIV. When someone is infected with HIV but has not started treatment, the number of CD4 cells they have 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. 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 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 (see Fact Sheet 500).
