Skin damage immune response. Cutaway computer artwork showing the body's immune response to a skin wound (upper centre). A blood vessel is shown across bottom. Bacteria (blue, rod-shaped) enter the wound, causing an infection; mast cells (blue and purple, left hand side) detect the bacteria and release cytokines (signalling chemicals, small dots) into the bloodstream, which attract other immune cells; macrophages (white blood cells, blue and purple, right hand side) migrate to the site of infection and engulf (phagocytose) the bacteria; hormones then stimulate the production of wound healing materials, such as platelets and fibrin.