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==MHC II==
 
==MHC II==
[[File:MHC Class II Presentation.png|thumb|left|200px|MHC Class II Presentation pathway - RJ Francis, RVC, 2012]]
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[[File:MHC Class II Presentation.png|thumb|right|200px|MHC Class II Presentation pathway - RJ Francis, RVC, 2012]]
 
===Structure===
 
===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 &alpha; and &beta; chains with each chain being a transmembrane glycoprotein. The extracellular parts of each chain have two Ig-like domains - &alpha;1 and &alpha;2, &beta;1 and &beta;2. The &beta;2 domain is responsible for the activation of [[T cells|T helper cells]] through the interaction with the CD4<sup>+</sup> on the cell surface of the T helper cells. The outer domains (&alpha;1 and &beta;1) are variable and the inner domains (&alpha;2 and &beta;2) are constant.
 
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 &alpha; and &beta; chains with each chain being a transmembrane glycoprotein. The extracellular parts of each chain have two Ig-like domains - &alpha;1 and &alpha;2, &beta;1 and &beta;2. The &beta;2 domain is responsible for the activation of [[T cells|T helper cells]] through the interaction with the CD4<sup>+</sup> on the cell surface of the T helper cells. The outer domains (&alpha;1 and &beta;1) are variable and the inner domains (&alpha;2 and &beta;2) are constant.
    
The 3-dimensional structure of MHC class II is similar to MHC class I; the outer domains of the &alpha; and &beta; chains fold in a similar way to the α1 and α2 domains of class I to produce the antigen-binding groove.
 
The 3-dimensional structure of MHC class II is similar to MHC class I; the outer domains of the &alpha; and &beta; 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]]
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[[Image:MHC II Structure.jpg|thumb|left|200px| Structure of MHC II molecule - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]]
    
===Presentation Pathway===
 
===Presentation Pathway===
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