MHC class I and II molecules and the antigen processing and presentation pathways tested on USMLE Step 1.
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- What is the human gene locus that encodes MHC molecules called?
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The human leukocyte antigen (HLA) complex- On which human chromosome is the HLA complex located?
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Chromosome 6- What cell types express MHC class I molecules?
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Nearly all nucleated cells- What cell types express MHC class II molecules under normal conditions?
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Professional antigen presenting cells: dendritic cells, macrophages, and B cells- What T cell type recognizes antigen presented on MHC class I?
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CD8+ cytotoxic T cells- What T cell type recognizes antigen presented on MHC class II?
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CD4+ helper T cells- What are the three classic MHC class I gene loci in humans?
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HLA-A, HLA-B, and HLA-C- What are the three classic MHC class II gene loci in humans?
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HLA-DP, HLA-DQ, and HLA-DR- What is the source of peptides typically presented on MHC class I?
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Endogenous (cytosolic) proteins, including viral proteins synthesized within the cell- What is the source of peptides typically presented on MHC class II?
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Exogenous proteins taken up from outside the cell via phagocytosis or endocytosis- What proteolytic complex degrades cytosolic proteins into peptides for MHC class I loading?
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The proteasome- What transporter moves peptides from the cytosol into the endoplasmic reticulum for loading onto MHC class I?
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TAP (transporter associated with antigen processing)- Where does MHC class I peptide loading occur?
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In the endoplasmic reticulum- What cellular compartment degrades exogenous proteins into peptides for MHC class II loading?
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The phagolysosome (endosomal/lysosomal compartment)- What invariant chain-derived peptide occupies the MHC class II peptide groove before final antigen loading, and what removes it?
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CLIP (class II-associated invariant chain peptide), which is removed by HLA-DM to allow antigenic peptide loading
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