Human blood cells. Light micrograph of blood cells at a site of inflammation, showing red blood cells (erythrocytes, red) surrounded by many granulocytes (blue), macrophages (with lighter purple nuclei) and plasma cells (with darker purple nuclei). Granulocytes and macrophages are types of phagocyte, which means they are specialised white blood cells that ingest and destroy foreign matter, such as microorganisms or debris. They therefore protect the body against the invasion of foreign pathogens in the blood and lymph. Plasma cells are cells of the immune system that secrete large amounts of antibodies. Erythrocytes are carriers of oxygen and carbon dioxide to and from other cells in the body.