| MHC Class II | |
|---|---|
 Schematic representation of MHC class II | |
| Identifiers | |
| Symbol | MHC Class II |
| Membranome | 63 |
MHC Class II molecules are a class of major histocompatibility complex (MHC) molecules normally found only on professional antigen-presenting cells such as dendritic cells, macrophages, some endothelial cells, thymic epithelial cells, and B cells. These cells are important in initiating immune responses.
The antigens presented by class II peptides are derived from extracellular proteins (not cytosolic as in MHC class I).
Loading of a MHC class II molecule occurs by phagocytosis; extracellular proteins are endocytosed, digested in lysosomes, and the resulting epitopic peptide fragments are loaded onto MHC class II molecules prior to their migration to the cell surface.
In humans, the MHC class II protein complex is encoded by the human leukocyte antigen gene complex (HLA). HLAs corresponding to MHC class II are HLA-DP, HLA-DM, HLA-DOA, HLA-DOB, HLA-DQ, and HLA-DR.
Mutations in the HLA gene complex can lead to bare lymphocyte syndrome (BLS), which is a type of MHC class II deficiency.