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Major Histocompatability Complexes (view source)

Revision as of 17:12, 27 September 2010

74 bytes removed , 17:12, 27 September 2010

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==MHC II==

[[Image:MHC II presentation.jpg|thumb|200px|right|'''MHC II presentation, courtesy of Janeway, et al. 2008''']]

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===Structure===

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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.

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~~===Structure===~~

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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.

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* MHC class II is expressed mainly on [[Macrophages|macrophages]], [[T cell differentiation#Antigen Presentation by Dendritic Cells|dendritic cells]] and [[Lymphocytes#B Cells|B-lymphocytes]]

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* MHC class II consists of membrane-associated α and β chains

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** Each chain is a transmembrane glycoprotein

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** The extracellular parts of each chain have two Ig-like domains

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*** α1 and 7alpha;2, β1 and β2

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**** The outer domains (α1 and β1) are variable-like

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**** The inner domains (α2 and β2) are constant-like

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* The 3-dimensional structure of MHC class II is similar to MHC class I

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** The outer domains of the α and β chains fold in a similar way to the α1 and α2 domains of class I

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*** 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]]

===Presentation Pathway===

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*MHC II presents '''exogenous''' (~~that is, derived from the~~ ECF) peptides

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MHC II presents '''exogenous''' (ECF) peptides. Endocytosed antigen interacts with MHC II in the cytoplasm to form a complex:

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*Endocytosed antigen interacts with MHC II in the cytoplasm to form a complex:

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*Antigen is endoycotsed from the ECF

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**Antigen is endoycotsed from the ECF

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*Lysosomes fuse with primary endosomes to digest the antigen to peptides

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**Lysosomes fuse with primary endosomes to digest the antigen to peptides

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*MHC II is meanwhile being produced by the endoplasmic reticulum, along with an invariant chain chaperone

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**MHC II is meanwhile being produced by the endoplasmic reticulum, along with an invariant chain chaperone

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*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.

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**These pathways (endoytotic and secretory) merge to allow interaction between the antigen and MHC II:

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*Foreign antigen then replaces the CLIP peptide

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***The invariant chain is digested, leaving a CLIP peptide in the binding groove

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*The MHC II-antigen complex is then secreted to the cell surface for presentation to [[T_cells#Helper_CD4.2B|CD4+ T-cells]]

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***Foreign antigen then replaces the CLIP peptide

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*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=

Suzannah.stacey

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