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How do the Major histocompatibility complex class I and II molecules differ in function?
They differ in their cellular distribution, the antigenic peptide fragments they present, and the type of T cell that recognizes and responds to the complex they present.
Function of Major Histocompatibility Complex Class I and II Molecules
| MHC Class I | MHC Class II | |
|---|---|---|
| Cellular distribution | All nucleated cells and platelets | Antigen-presenting cells:• B cells• Monocytes/macrophages• Dendritic cells• Thymic epithelial cellsSome activated T cells Some cells in which MHC Class II is induced, particularly during chronic inflammation:• Endothelial cells• Synovial cells |
| Antigen size | 8–13 amino acids in length | 13–25 amino acids in length |
| Antigen type | Antigen peptides found inside the cell (self-peptides, intracellular pathogens, or tumor antigens) | Phagocytosed or receptor-mediated endocytosed antigen taken into the lysosome (extracellular pathogens) |
| T-cell recognition | CD8+ T cells | CD4+ T cells |
| T-cell response | Cell-mediated cytotoxicity of the cell presenting the antigen on MHC class I | T cell coordinated phagocytic and/or antibody response to eradicate the presented antigen |
