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 (blue) with yellow chromatin. Characteristic of normal T-lymphocytes are long microvilli which project from the cell surface. Mitochondria (red) are seen in the cell cytoplasm (green). T-lymphocytes are cells of the human immune system, produced in bone marrow and which mature in the thymus gland. There are three major types of white blood cells: granulocytes, lympho- cytes and monocytes, which protect the body against invasion by foreign substances. T-cells are attacked by the HIV virus which causes AIDS.
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