Table showing molecular comparison of MHC class I and class II molecules

	Class I MHC	Class II MHC
Structure	MHC encoded chain, beta-2 microglobulin	MHC encoded chain, MHC encoded beta-chain
Antigen binding groove*	Closed	Open
Peptide length	9 to 10 amino acids	12 to 28 amino acids
Source of antigen	Intracellular	Extracellular
Expression	All nucleated cells	B cells, macrophages, dendritic cells
Antigen presented to:	CD8+ T cells	CD4+ T cells

MHC: major histocompatibility complex.
* The length of peptide and the conformation of the antigen binding groove differs between class I and II molecules. In the class I MHC molecule, the distal ends of the -helical regions meet, and so the antigen binding cleft is completely enclosed apart from the uppermost surface. In contrast, the -helical regions of the class II MHC molecule do not meet. Thus, the molecule is able to present a longer peptide.

Graphic 70970 Version 4.0

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Table showing molecular comparison of MHC class I and class II molecules