MHC Class 1 and 2 Antigen Presentation

MHC Class 1 and 2 Antigen Presentation

• APCs use MHC to present linear peptides to T cells.
• The MHC complex is composed of 2 alpha and 2 beta chains forming a peptide-binding groove.
• The MHC gene region on chromosome 6 is the most diverse in the genome.
• "Crossing over" (in meiosis) occurs only 2% of the time in the MHC region.
• Individuals inherit a solid block of MHC genes from each parent rather than recombined versions.
• MHC II has 5 isotypes (HLA-DQ, HLA-DP, and HLA-DR).
• MHC II α and β chains are referred to as A and B.
• Different MHC II complexes lead to varied peptide presentation.
• Variation is primarily focused on the binding groove of the β chain.
• APCs take up proteins/antigens and break them down into smaller linear peptides.
• Proteases are used to degrade 3-D protein into linear peptides.

MHC II Complex Function

• The invariant chain blocks the peptide-binding groove in the MHC II complex until the antigen is processed.
• The invariant chain is removed, and the binding groove is available for peptides.
• HLA-DM facilitates the peptide exchange for CLIP (class II associated invariant chain peptide).

MHC I Complex Function

• MHC I has one heavy chain and Beta 2 microglobulin.
• It exhibits peptide-binding groove variability.
• MHC I complex in ER needs an escort to transport peptides into the complex
• Chaperone proteins (like Calnexin) assist the MHC I assembly process
• A peptide delivered by TAP binds to the heavy chain to form the mature MHC I molecule.
• MHC I complex then exports from ER to cell surface.
• ERAP enzyme removes N-terminal amino acids of peptides to make the peptides 8-10 residues.

T Cell Interaction with MHC

• MHC I interacts with CD8 T cells.
• MHC II interacts with CD4 T cells.
• CD8 T cells check cells for intracellular organisms.
• CD4 T cells need co-stimulation for proliferation/ activation.
• CD8 T cells directly kill infected host cells.

Mechanisms of Cellular Killing

• Granules in CD8 T cells contain perforin to create pores in target cells.
• Granules also contain granzymes that enter the pores to initiate apoptosis.

NK Cell Function

• NK cells detect MHC I on healthy cells, killing cells lacking MHC I.
• Activating receptors on NK cells recognize stress proteins on infected cells.
• Inhibitory receptors check MHC I presence.

Explore the intricate mechanisms of MHC Class 1 and Class 2 antigen presentation in this detailed quiz. Learn about the structure and diversity of MHC molecules, their role in T cell activation, and the process by which antigens are processed and presented. Test your knowledge on key concepts and functions related to MHC complexes.