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23 Cards in this Set
- Front
- Back
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Define the T cell functions for CD8+
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kills cells infected with intracellular pathogens
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Define the functions of a CD4+ T cell
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- B cell sitmulation to proliferate and secrete Ab
- Macrophage activation - cytokine secretion |
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What is required to activate a t cell?
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Processing of Ag by APC
cutting proteins to small peptides 9-20aa required as T cells cannot recognise large proteins, or proteins presented in a non linear form. |
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How are extracellular proteins transported into cells?
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endocytosis and phagocytosis
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What are the two antigen processing pathways?
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peptides can be endogenous or exogenous proteins
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What are the two systems of degrading proteins?
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lysosomes -
proteasomes - |
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Which class are peptides from the cytosol
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MHC class I
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How are MHC II peptides presentes
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Extracellular antigen from outside the cell which is engulfed via endocytosis, presented to CD4+ cells
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What is the structure of a MHC class I
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3 alpha chains 1 beta
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What is the structure of a MHC class II?
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2 alpha, 2 beta
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What are the genes on MHC I
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What are the genes presented on MHC II
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Explain the process of Antigen processing for MHC 1
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- virus proteins replicating in the cell
- virus porteins being synthesised in the cytosol - interfeurons are sent out (innate immunity) to warn other cells and to increase MHC1 expression and to increase proteosome activity - Ubiquitin a 76 aa who action requires ATP, makes the shreds viral proteins to a format which can be presented on MHC 1 and recognised by CD8+ cells - Ubiquitin does this by binding to the protein (lyseine residue) and tagging the protein for protease destruction. - this peptide is degraded in the proteosome and transported to the ER memrbane - in the ER, chaperone molecules guide TAP and MHC I (Transport associated Ag processor) to allow peptide fragments to bind. - peptide fragments are now able to penetrate ER to see if it binds to MHC-C1 with high affinity ( peptide editing) - stable binding of MHC 1 and peptide result in dissociation of TAP and chaperones - MHC 1 leaves ER to go to Golgi then to surface to be recognised |
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What do interfeurons do?
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increase proteosome activity
increasse MHC presentation |
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What about virus infected cells makes it easier to present to attact T cells?
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viruses overtake protein making machinery of the cell so only virus encofing proteins are made. This means +++ MHC1:virus complexes which far exceed the CD8+ activation limit - threshold for activation.
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What do normal cells need proteosomes for?
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used for old and damaged cells
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Describe ubiquitin
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- 76 aa
- Requires ATP - tags protein - binds to lysein - three types - reused |
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Describe the mechanisms of CTL killing through granules
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- CTL granules
- multiple binding occurs - perforin acts like C9 in MAC and installs pores where granzymes can travel and degrade and fragment nuclear material. |
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What is FAS?
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Fas is a receptor on virus infected cells which CD95 on CD8+ T cell (FasL) activates caspases, a type of protease) in the infected cell leading to apoptosis
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Describe the process of exogenous antigen processing
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- extracellular peptide
- engulfed by phagosome or endosome depending on cell type, where it is in an neutral pH until merges with lysosome which will break down peptide via pH or proteases - MHC II is made in the ER and is vound by the invariant chain, where cleavage leaves just CLIP portion in the binding region. This is to prevent self antigens binding - acidic pH releases CLIP from binding groove - Calnexin and Caltriculin keep keeps MHC-II in ER until loaded with peptide - MHC II travels via Golgi apparatus to the endo-lysosome - CLIP release and peptide loading in cytosol - in phagolysosome or endolysosome |
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Contrast MHC-I and MHC-II processing pathways
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List chaperones and their role. IFNgamma's role is what?
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Define cross presentation
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not all viruses will present to APC
epithelial cell ************* |
