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Dendritic cell. Coloured scanning electron micrograph (SEM) of a dendritic cell, part of the human immune system. It is a macrophage cell that is found in the body's tissues. The long projections seen on the cell's surface help it to move. The cells recognise and engulf foreign cells. They may then display the foreign antigen as a warning of the infection to other cells. Dendritic cells found in the upper layer of the skin (the epidermis) are known as histiocytes or Langerhans cells. In the central nervous system dendritic cells are known as microglia, and in the liver as Kupffer cells. Magnification: x2130 when printed 10 cm wide. (KEYSTONE/SCIENCE PHOTO LIBRARY/EYE OF SCIENCE)