Q: What does antigen presentation refer to?
A: Peptides presented within MHC class I/II clefts to the T-cell receptor (TCR).

Q: For T cell recognition of a foreign element, T cell will only recognize:
A: Peptides, linear sequences and the peptide in context.

Q: What is MHC restriction?
A:Specific T cells recognize foreign peptide sequences within the cleft of a self MHC molecule.

Q: Can MY T cells recognize a peptide in the cleft of YOUR class I/II proteins?
A: No, unless we have identical class I/II proteins.

Q: How has the immune system solved the problem of killing both extracellular and intracellular pathogens?
A: It kills infected cells with cytotoxic T cells, and produces antibodies to neutralize extracellular pathogens.

Q: What kind of cells have MHC class II molecules?
A: Antigen presneting cells (Accessory cells): B cells, Macrophages, Dendritic cells. 

Q: How do B cells take up protein? Is this method efficient?
A: Proteins is taken up through Ig complexes and complement receptors on the surface of the cell. This is very efficient, as Ig bind antigen with high affinity.

Q: What are Langerhans cell, and where are they located?
A: They are dendritic cells, and are located in the skin.

Q: What do dendritic cells do upon the uptake of antigen?
A: Process it and migrate from the periphery into lymph nodes for activation of T cells.

Q: What organelle is responsible for digestion of antigen into peptides for the exogenous pathway?
A: lysosome

Q: Which MHC molecule has an invariant chain prior to being loaded with a peptide?
A: MHC II

Q: Where is the MHC II loaded with peptides and, are these peptides derived from endogenous or exogenous proteins?
A: The MHC II is loaded in the vescle formed by the fusion of the lysosome with the MHC vesicle. The peptides are of exogenous origin.

Q: Where is the MHC I loaded with peptides, and what organelle generates these peptides?
A: The MHC I is loaded in the RER with peptides that have been generated from the proteasome.

Q: How long do peptide expressing MHC I/II exist on the cell surface?
A: MHC II lasts about 12 hours, MHC I has a half-life of 10-15 hours.

Q: MHC II is loaded with what peptides?
A: exogenous

Q: MHC I is loaded with what peptides?
A: endogenous

Q: What is the origin of most peptides found in the MHC I in a healthy person, and in a person with a cold? 
A: self proteins, viral proteins.

Q: What is the origin of most peptides found in the MHC II in a healthy person, and in a person with strep throat? 
A: self proteins, bacterial proteins.

Q: What cells express class I proteins?
A: virtually all cells.