Red and white blood cells, coloured scanning electron micrograph (SEM). Polymorphonuclear white blood cell (leucocyte) surrounded by red blood cells (erythrocytes). Red blood cells are biconcave, disc-shaped cells that transport oxygen throughout the body. Polymorphonuclear leucocytes are any of several types of white blood cells produced in the bone marrow, which form 70% of human white blood cells. They play an important role in the immune system, migrating to areas of tissue damage and engulfing foreign bodies such as bacteria. Magnification unknown.