Dendritic Cell

Dendritic cells (DC) are a type of cell found in the skin, mucous membranes, and some internal organs. They function as part of the immune system by taking up antigens, processing them, and presenting them to lymphocytes. DCs can also induce immunity against infections and tumors. There are two main types of dendritic cells: myeloid dendritic cells (MDCs) and plasmacytoid dendritic cells (PDCs). MDCs are found in most tissues, while PDCs are found mainly in the blood and lymph nodes.

Dendritic cells were first described in 1873 by German physician Paul Langerhans as he was studying the structure of the pancreas. He observed that some of the pancreatic cells had long processes extending from their surfaces. These were later named “dendrites” after their tree-like appearance. It wasn’t until 1963 that it was realized that dendritic cells were part of the immune system. In 1974, Ralph Steinman discovered that dendritic cells could take up antigens, process them, and present them to lymphocytes. This discovery led to Steinman being awarded the Nobel Prize in Physiology or Medicine in 2011.

Dendritic cells play an important role in both innate and adaptive immunity. Innate immunity is our first line of defense against infection and is non-specific, meaning it does not target a particular pathogen. Adaptive immunity is specific to a pathogen and can be either acquired or innate (born with it). Dendritic cells are involved in both forms of immunity by taking up antigens from infected or damaged tissues and presenting them to lymphocytes so they can mount an immune response. This process is known as antigen presentation.

There are two main types of dendritic cell: myeloid dendritic cells (MDCs) and plasmacytoid dendritic cells (PDCs). MDCs are found throughout the body including in the skin, mucous membranes, airways, gut lining, liver, spleen, bone marrow, and blood vessels while PDCs circulate mainly in the blood but can also be found in lymph nodes where they form a network around B-cells . Both types of DC have similar functions but differ in how they develop and mature .

Mature MDCs express high levels CD1a , HLA-DR , CD14 , CD40 , CD80/86 , CCR7 whereas mature PDCs express high levels BDCA-2 , BDCA-4 , HLA-DR , TLR9 . The surface proteins expressed on DC determine what type of T helper cell will be activated; Th1 for proinflammatory cytokines IL-12 production leading to cell mediated immunity or Th2 for antiinflammatory cytokines IL-10 production promoting humoral immunity . Cytokines secreted by Th help guide B -cells maturation into plasma effector or memory B -cells depending on whether continuous antigen stimulation is required . Naive T -cells become activated when encountering peptide fragments bound to major histocompatibility molecules displayed on professional antigen presenting APC like DC during immunosurveillance . After initial activation naive T -cell proliferate into effector T -cells which differentiate into various subtypes such as cytotoxicCD8+Tc  helperTh17or regulatoryTregbased on transcription factors induced by different combinations offactorsto produce diverse range offunctionalcytokines for host defence mechanisms