White blood cell. Coloured transmission electron micrograph (TEM) of a section through a white blood cell. White blood cells are part of the body's immune system. There are seven common types of white blood cell, but they all form from the same type of stem cell and all have some specific function in defending the body against disease and foreign objects. Here, the nucleus (right) is bi-lobed, a characteristic of a type of white blood cell known as an eosinophil. The other white blood cell type that has a multi-lobed nucleus is the neutrophil. Magnification: x4600 when printed at 10 centimetres tall.