Human blood cells. Light micrograph of erythrocytes (red) surrounding two granulocytes (purple). Erythrocytes are red blood cells and granulocytes are a type of white blood cell (leukocyte) that have an irregular nucleus and grainy appearance. Red and white blood cells are the two main cell components of blood. Erythrocytes are carriers of oxygen and carbon dioxide to and from other cells in the body. Granulocytes are involved in the immune system's defence mechanisms, protecting the body against the invasion of foreign pathogens in the blood and lymph. Magnification: x1000 when printed 10cm wide.