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<sup>+</sup> 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<sup>+</sup> 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. |