Credit: Nele Dieckmann and Nicola Lawrence. Super-resolution micrograph of a natural killer (NK) cell (left) examining a second cell (the less bright, slightly rounder cell on the right) for signs of disease. NK cells are part of the immune system and can recognise and destroy some infected or cancerous cells. The NK cell has docked onto the second cell and will release toxic chemicals (red) that will cause it to self-destruct. These chemicals are stored in specialised compartments (cytotoxic granules) inside the NK cell, so NK cells are always pre-armed and ready to kill. This image was created using 3D structured illumination microscopy, one type of super-resolution microscopy. Each cell is approximately 20 micrometres (0.02 mm) in diameter.