Dendritic cells are antigen-presenting cells of the mammalian immune system. Antigen are any substance that starts an immune response, such as a virus or bacteria. The dendritic cells ingest and degrade pathogens in a process called phagocytosis. Once the pathogen in broken down the dendritic cell presents the pathogen to other immune cells. The dendritic cell's main function is to process antigen material and present it on the cell surface to the T cells of the immune system. They act as messengers between the innate and the adaptive immune systems.

Dendritic cells are present in tissues that are in contact with the external environment, such as the skin and the inner lining of the nose, lungs, stomach and intestines. They can also be found in an immature state in the blood.