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Major Histocompatability Complexes (view source)
Revision as of 15:29, 28 August 2008
, 15:29, 28 August 2008no edit summary
|pagetype =Blood
|pagetype =Blood
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=Introduction=
T-cells rely on Major Histocompatability Complexes (MHC) to present antigen fragments for their recognition. MHC has evolved to form two classes to present antigen: '''MHC I''' presents digestion fragments from antigen in '''cellular cytoplasm''', and '''MHC II''' presents digestion fragments from antigen in the '''tissue fluid'''. As such, MHC I tends to bind slightly smaller peptides (~9 amino acids) than MHC II (~15 amino acids).
=Classes=
=Classes=
==MHC I==
==MHC I==
[[Image:MHC I.jpg|thumb|200px|right|'''MHC I presentation pathway, courtesy of B. Catchpole, 2008''']]
===Structure===
===Structure===
* MHC class I is expressed on virtually all nucleated cells
* MHC class I is expressed on virtually all nucleated cells
**** This limits the size of epitope seen by the T-cell receptors
**** This limits the size of epitope seen by the T-cell receptors
===Function===
===Presentation Pathway===
*Viral proteins are broken down to peptides by the proteasome and transferred to the endoplasmic reticulum via TAP (Transporters associated with Antigen Processing) molecules
*In the ER< peptides are processed with empty MHC I molecules and exported to the cell surface for presentation
* MHC class I molecules bind antigenic peptides derived from within the cell and present these to the T-cell receptors of '''CD8+ T-cells'''
* MHC class I molecules bind antigenic peptides derived from within the cell and present these to the T-cell receptors of '''CD8+ T-cells'''
* Endogenously produced proteins are produced in the cell cytoplasm
* Endogenously produced proteins are produced in the cell cytoplasm
** Intracellular pathogens utilise this cellular metabolic machinery for protein synthesis
** Intracellular pathogens utilise this cellular metabolic machinery for protein synthesis