Questions and Answers
What areas are polymorphic in MHC Class I structure?
Alpha-2 and Alpha-3
What areas are polymorphic in MHC Class II structure?
Alpha-1 and Beta-1
MHC Class I structure is expressed on which cells?
All nucleated cells
MHC Class II structure is expressed on which cells?
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What is the peptide size for MHC Class I?
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What is the peptide size for MHC Class II?
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What are the unique differences between MHC Class I antigen processing and MHC Class II processing?
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What are the alternative pathways for antigen presenting?
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What is cross presentation?
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Study Notes
MHC Class I Structure
- Composed of an α chain with three MHC-encoded domains and β2-microglobulin (not encoded in MHC locus).
- Polymorphic regions: alpha-2 and alpha-3, which are the peptide binding domains.
MHC Class II Structure
- Composed of an α and a β chain, each with two structurally conserved, MHC-encoded domains.
- Polymorphic regions: alpha-1 and beta-1.
Cell Expression for MHC Class I
- Expressed on all nucleated cells, playing a crucial role in presenting antigens to CD8+ T cells.
Cell Expression for MHC Class II
- Expressed exclusively on antigen-presenting cells (APCs), including macrophages, dendritic cells, and B cells.
Peptide Size for MHC Class I
- Peptides are typically 8-11 amino acids long.
Peptide Size for MHC Class II
- Peptides are larger, ranging from 14-20 amino acids.
Differences in Antigen Processing
- MHC Class II processing involves an invariant chain that is degraded into CLiP in the Golgi vesicle before antigen loading.
- MHC Class I processing uses TAP1/TAP2 to transport peptides into the endoplasmic reticulum for loading onto MHC Class I.
- MHC Class I utilizes a proteasome for peptide cutting, while MHC Class II uses an endolysosome.
Alternative Pathways for Antigen Presentation
- Exogenous antigens can leak from endosomes to the cytosol and subsequently enter the MHC Class I pathway.
- Damage within the cell may lead to autophagy, routing these materials to the MHC Class II pathway via the MIIC compartment.
Cross-Presentation Mechanism
- B cells can express MHC Class I molecules, allowing them to present antigens to cytotoxic T cells.
- Antigens from infected cells are phagocytosed by APCs, processed, and loaded onto the APC's own MHC Class I, facilitating T-cell activation.
- This serves as an alternative mechanism to activate CD8+ T cells against foreign cells or antigens.
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Description
Test your knowledge on the structures and polymorphic areas of MHC Class I and Class II. This quiz focuses on key components and their definitions, enhancing your understanding of immune system functions. Ideal for students studying immunology or related fields.
