From the Guidelines
MHC class I and class II molecules are distinct in their structure, distribution, and function, with MHC class I presenting peptides from inside the cell to CD8+ T cells and MHC class II presenting peptides from extracellular pathogens to CD4+ T cells. The main difference between MHC class I and class II lies in their expression, antigen presentation, and the type of T cells they interact with.
Key Differences
- MHC class I molecules are expressed on nearly all nucleated cells and present endogenously synthesized peptides to CD8+ T cells, as noted in the study 1.
- MHC class II molecules are primarily expressed on professional antigen-presenting cells and present exogenously derived peptides to CD4+ T cells, also discussed in 1.
Structural Differences
- MHC class I consists of an alpha chain paired with β2-microglobulin, whereas MHC class II has both alpha and beta chains, as described in 1.
- The peptide-binding groove of MHC class I is closed, accommodating shorter peptides, whereas MHC class II has an open groove that can bind longer peptides, as explained in 1.
Functional Implications
- These differences enable the immune system to monitor both intracellular and extracellular environments for potential threats, highlighting the importance of both MHC classes in immune surveillance, as discussed in the context of disease associations in 1.
- The highly polymorphic nature of the MHC locus, including both class I and class II genes, contributes to its significant role in disease susceptibility and immune response, as outlined in 1.
From the Research
Overview of MHC Class 1 and MHC Class 2
- MHC (Major Histocompatibility Complex) molecules are peptide receptors that present peptides to T cells, with MHC class I presenting to CD8+ T cells and MHC class II presenting to CD4+ T cells 2.
- The MHC gene complex encodes two major classes of molecules, MHC class I and class II, which have distinct functions in adaptive immunity 2, 3.
Differences in Antigen Presentation
- MHC class I molecules present peptides from proteins produced by the cell's own translational machinery, while MHC class II molecules present peptides from proteins that are funneled into the endo-lysosomal vesicular system 3.
- The binding groove of each MHC allelic variant has structural features that influence the peptide repertoire presented, with peptide editors such as tapasin for class I and HLA-DM for class II contributing to the shaping of the presented peptidome 3.
Expression and Regulation
- MHC class I and II expression can be modulated by interferon gamma, with increased expression of MHC class I, beta-2 microglobulin, and class II observed in renal cell carcinoma cell lines after incubation with IFN-gamma 4.
- The regulation of MHC class I and II gene transcription involves distinct regulatory elements, with some elements shared between the two classes 2.