Computer enhanced micrograph of HIV. HIV (Human Immunodeficiency Virus) causes AIDS (Acquired Immune Deficiency Syndrome) by damaging T-cells - white blood cells that play a crucial role in the immune system. Like other viruses, it reproduces by planting its genes in the host cell's DNA. These take over the cell, turning it into a virus producing machine. The resulting damage to the immune system exposes the victim to a range of opportunistic infections, leading ultimately to death.