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Costimulatory activity of dendritic cells - Essay Example

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Summary
T cell activation is a highly regulated event involving complex receptor-ligand interactions, ultimately leading to downstream signaling events.Optimal activation of naïve T cells requires at least two signals, antigen recognition and co stimulation.The first signal requires engagement of an antigen receptor by foreign antigen.
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Costimulatory activity of dendritic cells
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Costimulatory activity of dendritic cells

Download file to see previous pages... T cell activation is a highly regulated event involving complex receptor-ligand interactions, ultimately leading to downstream signaling events (Annu Rev Immunol. 2002). Optimal activation of naïve T cells requires at least two signals, antigen recognition and co-stimulation (Bretscher and Cohn 1970).The first signal requires engagement of an antigen receptor by foreign antigen. Professional antigen presenting cells (APCs) such as dentritic cells, macrophages and B-lymphocytes play a major role in this. They present different sets of antigens and serve to activate T cells at different points during immune response. These cells on encountering foreign antigens such as bacteria, engulf and destroy them. The major histocompatible cell (MHC) present in the APCs binds to a piece of this antigen and displays the antigen to the cell surface. This MHC molecule that displays the antigen is recognized by a compatible T cell receptor (TCR). Thus, these APCs communicate with a T cell (Understanding Autoimmune Diseases. How Does the Immune System Work? 2007).For a T cell to respond to a foreign antigen on the MHC, a second signal is required. (P.Anton van der Merwe.2000).This second signal or co-stimulation is an antigen-independent signal required for sustained cell proliferation, effector/memory cell generation and prevention of energy or apoptosis. APC participation is required in the second signaling also. In addition to antigen presentation, these cells provide co stimulatory signals. ...
Provide the co-stimulatory signal necessary for T cell activation. When a

naive T cell binds to its specific peptide: MHC complex, the CD28 on the T

cell's surface binds to the B7 molecules on the APC (Fig.1). These two

signals together lead to the production of several cytokines.



Fig.1: T cell activation by two-signal pathway. [Online] Available at http://www.clinsci.org.

Dendritic cells are the most effective stimulators of T cell activation. They

continuously express high levels of co stimulatory B7 (Fig 2). Upon
recognition of infectious particles, these cells migrate through the
lymphatics to the nearest lymph node. In the follicles of the lymph node, they
come into close contact with the nave T cells where it begins expression of
the B7 molecules. Once the T cells are activated, they will leave the lymph
node and travel to the sites of inflammation.
Macropohages, in the absence of infection, express low levels of MHC II
and almost no co stimulators (B7). In the case of infection, however
macrophages poses certain types of receptors that recognize differential
carbohydrate patterns on foreign cells. They also have receptors for specific
bacterial products such as lippolysaccharide endotoxin. When these
molecules bind with their ligands, they stimulate the macrophages to
up regulate MHC II and B& providing these cells with strong antigen

presenting properties. They also start to secrete cytokines that aid in their
functions. It is at this point that antigen presentation by MHC II will activate
T cells.












Macrophage
Dendritic Cell
B cell
MHC-II Expression
Low levels. Induced by Bacteria and/or Cytokines
Always Expressed.
Always Expressed.
Inducible upon ...Download file to see next pagesRead More
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