Dendritic cells, computer illustration. Dendritic cells are protective cells of the human immune system. They process foreign antigens which then act like an alarm signal, alerting other immune cells of the body to the infection. 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.