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Major Histocompatability Complexes (view source)
Revision as of 17:12, 27 September 2010
, 17:12, 27 September 2010→MHC II
==MHC II==
==MHC II==
[[Image:MHC II presentation.jpg|thumb|200px|right|'''MHC II presentation, courtesy of Janeway, et al. 2008''']]
[[Image:MHC II presentation.jpg|thumb|200px|right|'''MHC II presentation, courtesy of Janeway, et al. 2008''']]
===Structure===
MHC class II is expressed mainly on [[Macrophages|macrophages]], [[T cell differentiation#Antigen Presentation by Dendritic Cells|dendritic cells]] and [[B Cells|B-lymphocytes]]. MHC class II consists of membrane-associated α and β chains; each chain is a transmembrane glycoprotein. The extracellular parts of each chain have two Ig-like domains - α1 and 7alpha;2, β1 and β2. The outer domains (α1 and β1) are variable and the inner domains (α2 and β2) are constant.
The 3-dimensional structure of MHC class II is similar to MHC class I; the outer domains of the α and β chains fold in a similar way to the α1 and α2 domains of class I to produce the antigen-binding groove.
[[Image:MHC II Structure.jpg|thumb|right|200px| Structure of MHC II molecule - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]]
[[Image:MHC II Structure.jpg|thumb|right|200px| Structure of MHC II molecule - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]]
===Presentation Pathway===
===Presentation Pathway===
MHC II presents '''exogenous''' (ECF) peptides. Endocytosed antigen interacts with MHC II in the cytoplasm to form a complex:
*Antigen is endoycotsed from the ECF
*Lysosomes fuse with primary endosomes to digest the antigen to peptides
*MHC II is meanwhile being produced by the endoplasmic reticulum, along with an invariant chain chaperone
*These pathways (endoytotic and secretory) merge to allow interaction between the antigen and MHC II and the invariant chain is digested, leaving a CLIP peptide in the binding groove.
*Foreign antigen then replaces the CLIP peptide
*The MHC II-antigen complex is then secreted to the cell surface for presentation to [[T_cells#Helper_CD4.2B|CD4+ T-cells]]
*The MHC II-antigen complex is then secreted to the cell surface for presentation to [[Lymphocytes#Helper CD4+|CD4+ T-cells]]
=Interaction of MHC With Antigen=
=Interaction of MHC With Antigen=