Macrophage attack. Coloured scanning electron micrograph (SEM) of white blood cells (brown) attacking surgical thread (green). These are macrophages, cells of the immune system which recognise and engulf foreign bodies. The thread was removed from a patient two weeks after it was used to stitch together a wound, and the image was taken immediately. Those parts which were inside the body (as seen here) were densely covered with macrophages, which had recognised the thread as foreign and attacked it. The cells have been elongated into finger-like projections in an attempt to surround and engulf the thread. Magnification: x3200 at 6x6cm size.