1. Antigen presentation to T cells Zheng W. Chen, M.D., Ph.D

2. Intracellular compartments in APC for generation of TCR ligands (MHC-peptide complexes) Cytosol; the compartment for MHC class I Ag presentation pathway; viruses and some bacteria can replicate in cytosol. Their Ag peptides bound to MHC class I and presented to TCR on CD8 T cells. Vesicular system – MHC class II Ag presentation pathway; extracellular material (microbes) is taken out by endocytosis into endosomes, which then move to lysosome for degradation, bond to MHC class II, and presented to TCR on CD4 T cells

3. Ag presentation pathways

4. Typical MHC class I pathway for antigen peptide processing and presentation (occuring in ER)

5. MHC class II pathway for antigen peptide processing and presentation (occurring in the vesicle)

6. MHC class II molecules in the ER cannot bind to peptides in the ER because newly- synthesized MHC class II molecules are associated with the invariant chain (Ii) that fills and blocks their peptide-binding groove.

7. Peptides that bind to MHC class II molecules are generated in acidified endocytic vesicles.

8. An patient with influenza virus infection was found to have viremia and influenza virus-infected dendritic cells. The patient would have A. viral peptide-specific antibodies only B. viral peptide-specific CD8 T cells only C. viral peptide-specific CD4 T cells only D. both viral peptide-specific CD4 and CD8 T cells Question