Basophil white blood cell. Transmission electron micrograph (TEM) of section through a circulating basophil cell. Basophils are the smallest and least common of the white blood cells. Like all white blood cells (leucocytes), basophils are part of the body's immune system, involved in allergic and inflammatory reactions. They secrete the chemicals heparin and histamine, which are stored in granules (dark circles) in the cell's cytoplasm. Magnification: x22,000 when printed at 10 centimetres wide.