Basic components of the immune system part 77

There are two forms of dendritic cells: immature and mature. The induction of an adaptive immune response begins when a pathogen is ingested by an immature dendritic cell. The cells reside in most tissues and are relatively  long-lived. They are derived from the same cell myeloid precursor as the macrophage. The immature cell carries receptors on its surface that recognize common features of many pathogens such as cell wall carbohydrates of bacteria. Once the bacterium is in contact with these receptors, the dendritic cell is stimulated to engulf  the pathogen and degrade it intracellularly. These cells also continue engulfing  extracellular material (both viruses and bacteria) by a receptor-independent mechanism of macropinocytosis. Once accomplished, the main function of the "activated" dendritic cell is to carry pathogenic antigens to the peripheral lymphoid organs  to present them  to T lymphocytes. Once arrived, the dendritic cell matures into an APC, which now permits it to activate pathogen-specific  lymphocytes. Another function of activated dendritic cells is to secrete  cytokines that influence both the innate and adaptive immune responses