Dendritic cells

A still-screen from a video of a Dendritic Cell
A still-screen from a video of a Dendritic Cell

Dendritic cells (DCs) are considered the most influential type of antigen-presenting cells (APCs) and are found in all tissues of the body. They have an unique role in initiating immunity against threatening antigens (anything that causes an immune response). Dendritic cells are especially abundant in places that form a barrier between the outside and the inside of the body (eg; skin, gastric tract, nasal cavity). The life cycle of the DC has 2 distinct developmental stages termed 'immature' and 'mature' .
Immature dendritic cells
They form a network throughout the body in an immature ‘antigen-capturing’ state, checking surrounding for invading pathogens. The immature DCs have the ability to recognize pathogen-associated molecular patterns (components of pathogen membranes) and damage-associated molecular patterns (released by damaged or tumorous cells of our body). These are recognized with a variety of pattern recognition receptors on the DC's membrane surface, which include toll-like receptors, cell-surface C-Type Lectins and intracytoplamic NOD-like receptors. Once the DC finds and recognises a cell displaying pathogen-associated molecular patterns or damaged-associated patterns, it will avidly endocytose (a process in which a cell engulfs a molecule or antigen) the antigen, fulfilling its role as an antigen-capturing cell. It now begins an irreversible change from an immature DC to a mature DC termed 'maturation'

Mature Dendritic Cells
Immature DCs change from antigen-capturing into mature antigen-presenting cells. This change induces the expression of MHC molecules on the cell membrane and the secretions of co-stimulating signals (that will be discussed later). Inside the cell the captured antigen is 'processed' into smaller protein chains which is then displayed on the MHC II complexes. The mature DCs then travels from the site of invasion through the lymphatic system to the lymph nodes. Mature DCs also play a role in killing faulty T-cells that may otherwise go to cause autoimmunity.

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Contributed by Jess Youngberry