Antigen Processing and Presentation

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Antigen Processing and Presentation

• Cytosolic (endogenous) pathway
• Endocytic (exogenous) pathway

Ag processing degradation of proteins into
peptides
Ag presentation binding of peptide by MHC
molecule and displaying the complex on the cell
surface
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Two compartments of the cell
Cytosol continuous with nucleus Vesicular
system (ER, golgi, endosomes, lysosomes)
continuous with extracellular fluid
Extracellular pathogens Endocytic
vesicles (exogenous) Class II CD4 T cells
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Cytosolic pathway

1. Site of peptide generation
2. Site of membrane protein synthesis
3. Transport of peptides into ER
4. Loading of peptide onto nascent class I molecules
   in ER
5. Display the complex on the cell surface

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Cytosolic pathway
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Pathogen exploitation
Plasma membrane
nucleus
ER
Golgi
vesicle

• Human Cytomegalovirus (HCMV)
• US2 and US11 bind and remove nascent class I a
  chain from ER

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Endocytic pathway

1. Site of peptide generation
2. Site of MHC class II synthesis
3. Loading of peptide into class II molecules
4. Surface expression

Plasma membrane
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Endocytic pathway
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Influenza A Virus

• Segmented RNA virus
• 8 RNAs
• 10 proteins

• 15 HA
• 8 NA
• H5N1

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HA and NA are highly variable
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Interferons inhibit protein synthesis and
therefore virus replication
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Role of T and B cells in responses to influenza
virus infection
CD8 CD4 B Clearance (days) Survival
7-10 100
- 10-14 100
- 10-14 90
- 10-14 35-85
- - gt20 0
- - gt20 0
- - gt14 20
- - - gt20 0
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Host-Influenza Virus Interaction Host Influenz
a virus 5 triphosphate 5 cap TLR7,
RIG-I dsRNA, NS1 APOBEC NK
cells Antibody HA and NA (antigenic
shift) CTL Epitope change (antigenic drift)
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• Principles of adaptive immunity
• TCR recognition
• Antigen presentation and processing
• Host defense against viruses