Ch. 3 Antigen Capture and Presentation to Lymphocytes

Question 1

MHC restriction

Answer 1

an organism’s T-cells can only recognize peptides presented by self-MHC proteins

Question 2

Cross-presentation

Answer 2

• DC can take up an antigen from another cell (or a whole other cell) - this would be extracellular
• they can then present this antigen to CD8+ cells via their MHC-1
• normally MHC-1 present intracellular to CD8+
  (DC’s can present this same antigen on MHC-II to CD4+ helper cells)

Question 3

MHC - structure, expression

Answer 3

• N-terminus is where the peptide binds that is being presented
• they are polymorphic genes for each class, and they are co-dominantly expressed - both are expressed and function regardless of the other one.

Question 4

MHC-I

Answer 4

• a1 and a2 bind the antigen - variant domains for diff antigens
• a3 is the invariant domain that binds to CD8 co- receptor (MHC-1 = CD8)
• HLA -A, B, C genes = 6 MHC-1 per person
• Present on all nucleated cells

Question 5

MHC-II

Answer 5

• Peptide binds btw variant a1 and B1 regions
• B2 region is the invariant that binds to CD4 co-receptor
• DP, DQ, DR (PQR)
• present on APC - dendritic, macrophages, B-cells

Question 6

molecule that binds inactive MHC-II

Answer 6

• invariant chain = CLIP

Question 7

molecule that loads MHC-II with peptide by removing stabilizing molecule

Answer 7

DM

Question 8

Processing of MHC-II peptides

Answer 8

• Protein taken in f/ extracellular (endocy, phagocy)
• vesicle fuses with lysosome and degrades protein
• phagolysosome fuses with vesicle from ER contain MHC+clip
• DM unloads CLIP from MHC-II
• MHC-II tries to bind with one peptide from the protein (immunodominant epitope - other ones don’t bind the MHC)
• exocytotic vesicle puts MHC-II on the CD4+’s cell surface

Question 9

MHC-I processing

Answer 9

• Proteins in the cytoplasm (either from tumor, virus that used cell machinary, or phagocytized protein that escaped vesicle) is ubiquitinated and sent to the proteosome
• proteosome degrades protein into peptides
• peptides are pumped in the ER by TAP
• they are then incorporated to MHC-I and exocytosed into the CD8+ cell surface

Question 10

Molecule that is used in MHC-I transport processing

Answer 10

TAP - moves intracellular peptides into the ER where they bind with matching MHC-I complexes

Question 11

2nd signal

Answer 11

(first signal is the antigen presented with the self-MHC)

• 2nd signal is needed to stimulate naive T-cells
• it is the co-stimulator B7 that binds CD28 on T-cells
• Microbes induce APC cells to express the co-stimulator and to secrete cytokines to stimulate T-cells
• insures that even if some T-cells will recognize self or harmless non-microbial substances, they won’t respond b/c APC cells won’t be expressing co-stimulators