This 640 x 401 pixel image depicts that the course of HIV infection typically runs many years, during most of which the patient has no symptoms. Strikingly, the body's defenses--as indicated by levels of antibodies, killer T cells and helper T cells in the blood--remain strong throughout much of the asymptomatic period, eradicating almost as much virus as is produced. At some point, however, the immune defenses lose control of the virus, which replicates wildly and leads to collapse of the immune system.
