False-colour transmission electron micrograph (TEM) of a single HIV-2 virus, the cause of AIDS. Here, the protein coat of the virus (green) has small surface spikes; central (orange) is the nucleoid which contains the viral RNA genetic material. HIV-2 (human immunodeficiency virus type 2) is more closely related to the simian immuno- deficiency virus (SIV) found in monkeys, than is HIV-1. However, both HIV viruses affect T-lympho- cytes (white blood cells) of the human immune system. This undermines the body's natural defence and patients with AIDS fall prey to opportunistic infections. Magnification: x74,000 at 6x7cm size.