Macrophage engulfing TB bacteria. Coloured scanning electron micrograph (SEM) of a macrophage white blood cell (red) engulfing a tuberculosis (Mycobacterium tuberculosis) bacterium (yellow). 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: x750 when printed at 10 centimetres tall.