BIIC Immunology Lecture 1_MHC Molecules and Antigen Presentation Flashcards
What is the main role of MHC?
To bind peptide fragments and present them to T and B cells to induce the addaptive immune response.
How does MHC class 1 effect the activity of NK cells?
NK cells kill any cell not expressing MHC class 1
What cells express MHC class 1 and what kind of immune cells does it present to?
MHC class one is expressed on nearly all nucleated cells. It presents antigens to CD8 T cells
What kind of cells express Class II MHC and what kind of immune cells does it present to?
MHC class II is expressed on “professional” antigen presenting cells. MHC class 2 activates CD4 T cells
What is the role of lymph nodes in the immune response?
Cells expressing lots of MHC (class 1 or 2) will migrate to lymph nodes (they follow a gradient of chemokine released by the b and t cells). Because T Cells congragate in the lymph nodes, this greatly increases the probability that a MHC complex will find the antigen specific T and B cells.
What causes APCs to travle to lymph nodes
Inflammatory signals cause APCs to express CCR7 wich binds to the chemokines being secreated in the lymph nodes
How do MHC class I bind to peptide fragments
They bind specific anchor residues (same amino acids at several defined points) which bind tightly into the binding site like a baseball in a glove.
How do MHC class II bind peptide fragments?
The cleft is open at both ends and binds a “conserved motif”
What kind of antigens are MHC class 2 effective against? Why?
MHC class 2 are effective against extra cellular antigens. This is because MHC class 2 activates CD4 T cells which activate B cells which release antibodies
What kind of antigens are MHC class 1 effective against?
Intracellular antigens. This is becase they present to CD8 T cells which the kill the presenting cell. This eliminates the host for viruses and such
What are the steps of MHC class I presentation?
1) antigen protein gets ubiquitinated and munched up by proteosomes
2) Peptide fragments are transported into the ER by TAP
3) peptide fragments bind MHC class 1 and the complex is transported to the cell surface through the golgi
NOTE: MHC class 1 presents intracellular protein
What are the steps of MHC class II peptide loading?
1) MHC class II exists on the surface of the cell held together by the inveriant chain
2) Extra cellulatr protein gets endocytosed with the MHC class II
3) Protein gets munched up in the vacule and displaces the inveriant chain.
4) Loaded MHC class II is reexpressed on the surface of the cell
What does the accumulation of protein in a cell lead to?
Apoptosis. There are anti cancer drugs that suppress proteasome activity specifically to allow this accumulation and subsequent cell death,
What is cross penetration and what is it’s purpose?
Cross presentation is a when peptides derived
from the extracellular environment, or from
within endosomes/lysosomes, get redirected
into the Cytosolic Pathway for presentation by
MHC Class I. This stimulate both the helper T and killer/cytotoxic T cell populations.
What are the PAIR diseases and what HLA pre disposes people to them?
Psoriasis, ankylosing spondylitis, IBS, and reactive arthritis. they are all associated with HLA B27
