Coloured transmission electron micrograph (TEM) of HIV particles (blue) budding from the membrane of a host cell. HIV (human immunodeficiency virus) attacks CD4+ T-lymphocytes (specialised white blood cells), which are crucial to the body's immune system. It enters the cell and makes many copies of itself, which then destroy the cell as they emerge through its membrane. This severely weakens the immune system, causing AIDS (acquired immunodeficiency syndrome). Magnification: x80,000 when printed at 10 centimetres wide.