Changes

[[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===

===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 α2, β1 and β2. 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; each chain is 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.