DON FAWCETT / SCIENCE PHOTO LIBRARY DON FAWCETT / SCIENCE PHOTO LIBRARY
T-lymphocyte. Coloured transmission electron micrograph (TEM) of a section through a T-lympho- cyte white blood cell. At centre, the large nucleus is seen (brown) with chromatin (yellow). Characteristic of normal T-lymphocytes are long microvilli which project from the cell surface. Mitochondria (brown) are seen in the cell cytoplasm (orange). T-lymphocytes are cells of the human immune system, produced in bone marrow and which mature in the thymus gland. They help to protect the body against invasion by bacteria, viruses and other foreign substances. T-cells are attacked by the human immunodeficiency virus (HIV) which causes AIDS.
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