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Human dendritic cell, scanning electron micrograph (SEM). Dendritic cells (also known as histiocytes or Langerhans cells in the epidermis) are part of the human immune system. They are macrophage cells that are found in the body's tissues. In the central nervous system dendritic cells are known as microglia, and in the liver as Kupffer cells. The long extensions projecting from the cell help them to move. Dendritic cells recognize and engulf foreign cells and proteins (antigens). Dendritic cells act as antigen presenting cells (APCs) that present the digested parts of phagocytosed pathogens to other immune system cells to enhance the immune response. Once activated, the dendritic cells migrate to the lymphoid tissues where they interact with T cells and B cells to initiate and shape the adaptive immune response. Magnification: x600 when shortest axis printed at 25 millimetres. (KEYSTONE/SCIENCE PHOTO LIBRARY/DENNIS KUNKEL MICROSCOPY/SCIENCE PHOTO LIBRARY)