Dendritic cell and T cell. Computer illustration of a dendritic cell (small, top) passing information to a T cell (large, bottom). Dendritic cells are protective cells of the human immune system. They process foreign antigens and present them on the cell surface to the T cells of the immune system. Dendritic cells are present in those tissues that are in contact with the external environment. Those found in the upper layer of the skin (the epidermis) are known as histiocytes or Langerhans cells. In the central nervous system they are known as microglia, and in the liver as Kupffer cells.