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chapter_5 - Chapter 5 Antigen Presentation to T Lymphocytes...

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Chapter 5 Antigen Presentation to T Lymphocytes Review: Two antigen-specific receptors: the TCR and the BCR. TCR “sees” antigens that were inside cells and that are displayed on the surface by MHC molecules. *Antigen Processing is the modification of native proteins into peptides for presentation by MHC MHC class I presents processed proteins* that were in the cytosol. MHC class II presents processed proteins* that were in endocytic vesicles. MHC class I presented-antigens are recognized by CD8 + T cells (CTL). MHC class II presented-antigens are recognized by CD4 + T cells (T H ).
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Basic cell structure (ER )
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Inside of a cell, pathogens and their products are found in either the cytosol or in vesicles Mostly viruses but some bacteria Mostly bacteria, common bacterial products (less likely to be toxins and viruses), self junk Bacteria, bacterial products, viruses (anything that is antigenic) and more (see chpt. 2) after recognition by an appropriate T cell Dendritic cell This slide is missing the very important antigen presentation by dendritic cells : Degrade in vesicles; peptides bind to MHC II, presented to naïve CD4 T cells, activates naïve CD4 T cells
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How do cytosol peptides get associated with MHC class I (and not with MHC class II)? Peptides (made from proteins by proteosomes; next slide) are pumped from the cytosol into the endoplasmic reticulum (ER) by t ransporters a ssociated with antigen p rocessing ( TAP ) molecules
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In the cytosol, proteins are degraded into peptides by proteasomes Proteasomes are multicatalytic protease complexes made of ~28 subunits 2004 Nobel Prize in chemistry for the role of ubiquitin in protein recycling
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Peptides are made from proteins in the cytosol, transported into the ER, loaded into MHC class I and transported to the surface of the cell Which cells do this? peptide MHC class I
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Some viruses evade the immune system by inhibiting or blocking antigen presentation by MHC class I
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Peptides that are destine for MHC class II are taken up from the outside of the cell and are degraded into peptides in acidified endocytic vesicles
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Cl ass II-associated i nvariant-chain p eptide ( CLIP ) The invariant chain
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The invariant chain prevents MHC class II from acquiring peptides too soon Which cells do this?
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