Changes

==MHC II==

==MHC II==

[[File:MHC Class II Presentation.png|thumb|right|200px|MHC Class II Presentation pathway - RJ Francis, RVC, 2012]]

[[Image:MHC II Structure.jpg|thumb|right|200px| Structure of MHC II molecule - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]]

 

===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 α and β chains with each chain being a transmembrane glycoprotein. The extracellular parts of each chain have two Ig-like domains - α1 and α2, β1 and β2. The β2 domain is responsible for the activation of [[T cells|T helper cells]] through the interaction with the CD4⁺ on the cell surface of the T helper cells. The outer domains (α1 and β1) are variable and the inner domains (α2 and β2) 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 α and β chains with each chain being a transmembrane glycoprotein. The extracellular parts of each chain have two Ig-like domains - α1 and α2, β1 and β2. The β2 domain is responsible for the activation of [[T cells|T helper cells]] through the interaction with the CD4⁺ on the cell surface of the T helper cells. 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.

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.

===Presentation Pathway===

===Presentation Pathway===

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

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

*Antigen is endoycotsed from the ECF