CD4 cells, also known as helper T-cells, are a type of lymphocyte , which is a white blood cell that plays an important role in the immune system.
Lymphocytes control the body's ability to recognize and fight infections and cancers.
CD4 lymphocytes help to identify, attack, and destroy specific bacteria, fungi, and other germs that infect the body. CD4 cells are produced in the spleen, lymph nodes, and thymus gland, and they circulate throughout the body in the bloodstream. HIV binds to the surface of CD4 cells, enters them, and either reproduces immediately, killing them in the process, or remains in a resting state, reproducing when the cell becomes active. Although the body attempts to produce new lymphocytes in order to replace the ones that have been destroyed, the number of CD4 cells in the blood gradually declines as HIV disease progresses. Normal CD4 counts in adults range from 500 to 1500 cells per cubic millimeter of volume.