Macrophage engulfing e.coli bacteria. Coloured composition scanning electron micrograph (SEM) of a macrophage white blood cell engulfing e.coli bacteria (pink). This process is called phagocytosis. Macrophages are cells of the body's immune system. They phagocytose and destroy pathogens, dead cells and cellular debris. Magnification: x5000 when printed at 10 centimetres wide.