Dendritic cells are a type of white blood cell. They typically begin their lives as monocytes. Monocytes are produced in the bone marrow and circulate throughout the bloodstream. When an infection or inflammation triggers a response, the monocytes can leave the bloodstream and enter other tissues and organs in the body. After leaving the bloodstream, monocytes develop into dendritic cells or macrophages.
Once monocytes have evolved into dendritic cells, they assist a part of the immune system known as the adaptive immune system. This is also referred to as "acquired immunity." Dendritic cells don't destroy invading bacteria and other microbes directly. Instead, they identify something as foreign and present this information to other immune cells called B-cells and T-cells. This helps the T- and B-cells learn to recognize the foreign invader and respond more strongly to destroy it the next time it is encountered.
Dendritic cells also are called antigen presenting cells (APCs) because of their ability to present information from foreign particles and microbes to B- and T-cells. Antigen is the word used to describe the information that is presented and results in the immune response.