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Dendritic cell, coloured scanning electron micrograph (SEM). This cell is a cell type found in the human immune system. Dendritic cells are a type of macrophage, and one of their functions is to recognise and engulf foreign cells in a process that is called phagocytosis. Dendritic cells are being studied for use in vaccinating against certain forms of cancer. Magnification: x4700 when printed at 10 centimetres across. (KEYSTONE/SCIENCE PHOTO LIBRARY/EYE OF SCIENCE/SCIENCE PHOTO LIBRARY)