Lymphocytes in AIDS. Transmission electron micrograph of active lymphocytes (white blood cells) from an enlarged lymph node of a man with AIDS (Acquired Immune Deficiency Syndrome). The orange and red structures are the cell nuclei. In the centre is a cell whose nuclear material has formed a crescent (brown) under the nuclear envelope. This is characteristic of apoptosis, where a cell self-destructs. Lymph nodes are clusters of white blood cells that filter fluid passing through body tissues to destroy infectious micro-organisms. In AIDS the lymphocytes become infected. Magnification: x2740 at 6x4.5cm size.