A model of the human immuno-deficiency virus (HIV) on display at the Smithsonian Museum of Natural History in Washington, D.C.
HIV causes acquired immunodeficiency syndrome (AIDS).
HIV infects helper T cells, macrophages, and dendritic cells -- all of which are critical in helping the body fight off infections. HIV kills infected cells, causes cells to die faster than they should, and turns the bodies CD8 cytotoxic lymphocytes against the helper T cells. When the number of helper T cells falls below a certain level, the body becomes defenseless against even the most minute infections. It is these infections which kill the person.