Natural killercells and cancer cell. Coloured scanning electron micrograph (SEM) show natural killer cells purified from a healthy donor's blood attacking a liver cancer cell line (HepG2). NK cells (white) have multiple finger-like protrusions for sensing danger and interacting with target cells and can kill their targets by punching holes in their surface. Natural killer (NK) cells are part of our body's battalion of immune soldiers, specialised at killing cancerous cells. They provide a powerful first line of defence against tumours and are being developed as immunotherapy for liver cancer, that is the second commonest cause of cancer deaths worldwide. Magnification x 7000 at 10cm wide. Specimen courtesy of the Maini Lab. UCL