Macrophage and virus. Computer artwork of a macrophage white blood cell (purple) phagocytosing (engulfing) a virus (red). Macrophages are immune system cells that phagocytose and destroy pathogens, dead cells and cellular debris. After phagocytosis they display fragments of a pathogen's proteins on surface receptors to direct other cells to attack the pathogen. The virus has antibodies (green) bound to it. These proteins recognise foreign bodies and bind to them, flagging them for destruction