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T/F: All nucleated cells can present Antigen (peptides) to T-cells?
T: but, only APC can activate the T-cell through presentation
How and where do antigens come into contact with T-cells?
- Afferent lymphatics to Lymph Nodes.
- Carried by Dendritic APC cells
T/F: each MHC molecule is specific for one protein to be presented?
False, as long as the protein peptide fits in the cleft it can be presented to T-cells
What is the diff b/t histocompatible/incompatible MHC?
- During transplantation, if the MHC molecules from donors do not match = histoincompatible = rejection
- If MHC from donor and patient match = histocompatible = acceptance
What are the two steps in attaching peptides to MHC molecules?
- 1) Process: protein degraded into peptides
- 2) Present: Peptide binds to MHC and is presented
What MHC molecule is produced by the Cytosolic and Endocytic pathways?
- Cytosolic: MHC I, endogenous
- Endocytic: MHC II, exogenous
Describe the Cytosolic MHC I Pathway?
- 1) phagocytose
- 2) Ubiquitinate for proteosome
- 3) pass protein through proteosome
- 4) insert peptides into RER via TAP proteins
- 5) Bind peptide to MHC and transfer from RER - Golgi - vesicles - exocytosis
Why is TAP deficiency problematic?
TAP helps bring peptides into the RER so they can be prepared to interact with Tc cells
A patient deficient in TAP cannot attack intracellular microbes (viruses) or tumors and will have lots of immunity problems
Describe the endocytic MHC II pathway?
- Phagocytose protein
- breakdown in lysosome
- prepare MHCII in RER + invariant chain
- transport MHCII + invariant chain to endosome
- Release Invariant chain, leaving behind CLIP
- Insert DM to release CLIP and to help with peptide-MHCII rxn
- release through exocytosis to TH cells
What is the function of the invariant chain in the endocytic MHCII pathway?
inhibit binding of MHC I peptides since MHC I and MHC II are both made in the RER
Can exogenous peptides be presented to MHCI molecules?
Yes, but just during special viral cases when Dendritic cells come in contact with viruses