immunogenetics

• What is MHC class I made up of?


  A heavy chain non-covalently liked to β2m - b2microglobulin
• How many domains does the heavy chain of MHC class I have?


  Three domains: α1, α2, α3
• What forms the peptide binding site in MHC class I?


  The folding of α1 and α2
• What supports the peptide binding groove in MHC class I?


  The Ig-like α3 domain and β2m
• Where is the gene encoding β2m located?


  Outside the MHC
• What does MHC class II consist of?


  Two non-identical transmembrane chains - a +b
• How many domains does each chain of MHC class II contribute to the peptide binding site?


  One domain

  the two domains farthest from the membrane from the peptide binding site
• What type of domains do α2 and β2 in MHC class II represent?


  Ig-like supporting domains
• What is the overall function of MHC class I and II?


  To present peptide to T cells
• What type of antigens do MHC class I molecules present?


  Peptide antigens derived from pathogens that replicate inside the cell — eg viruses and some bacteria

  • present endogenous foreign molecules - produced by the cell
• MHC class II molecules 


  • restricted to groups of cells- present peptides from pathogens and antigens that are present outside the cell - exogenous- are taken up by endocytosis vesicles of phagocytic cells
• Where is the Major Histocompatibility Complex located?


  A cluster of genes -On the short arm of chromosome 6

  all vertebrate have MHC
• What do MHC molecules encode?


  A set of polymorphic membrane glycoproteins called MHC molecules
• What is the function of MHC molecules?


  Presenting short peptide antigens to T cells
• What are the key structural features of MHC class I and II?


  MHC class I:

  • Heavy chain + β2m
  • Three domains: α1, α2, α3
  • Peptide binding site from α1 + α2

  
  

  MHC class II:

  • Two non-identical chains (α + β)
  • Each chain contributes one domain
  • Similar 3D structure
• Compare the antigen presentation of MHC class I and II.


  MHC class I:

  • Presents intracellular antigens
  • Derived from pathogens inside the cell

  
  

  MHC class II:

  • Presents extracellular antigens
  • Derived from pathogens outside the cell
• classes of MHC molecules are expressed differently on cells


  • MHC class I cells are expressed on nucleated Cells
  • MHC class II Cells are expressed on antigen presenting cells ( presenting to T cells) - dendritic cells, macrophages and B cells.
• routes of infection 


  • in the circulation
  • once virus inside cell antibody is ineffective - cannot cross membrane
  • viral particles can only be identified by MHC - stimulates immune response - kills viral particles by cytotoxic T cellls