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10 Cards in this Set
- Front
- Back
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Where in thymus does positive selection occur? Negative selection?
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Positive selection = Cortical epithelial cells
Negative selection = Medullary epithelial cells (via macs and dendritic cells) |
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Process of T cell recognition to differentiation
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1) Recognition of antigen on APC in lymphnode by T Cell
2) T cell expresses IL-2 receptors and secretes IL-2 3) Autocrine and paracrine effects > clonal expansion 4) Differentiation into an effector or memory T cell |
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What cell is most important APC for initial T cell activation
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Dendritic cells
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Molecules involved in T cell activation
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1) TCR binds MHC and antigen
2) CD4/8 binds MHC w/ TCR (co-receptor) -Leads to a bit of signal transduction 3) CD3s associate with TCR > TCR complex -Lots of signal transduction 4) Adhesion molecules hold APC and Tcell together 5) C28 binds B7 allowing activation |
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Super Antigen
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Indiscriminately binds TCR to an MHC regardless of antigen causing over activation of t cells and cytokine release resulting in the illness. Employed by microbes.
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ITAMs
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Immunoreceptor Tyrosine based activation motif. Found on tails of CD3 molecules. Upon assocaiation with TCR during antigen recognition, leads to tyrosine phosphorylation which leads to transcription factors which leads to differentiation.
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How does IL-2 work as a costim molecule?
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1) CD8 binds an APC with a legit antigen. However, because of lack of costim receptors on APC, will not respond.
2) CD4 binds same APC, becomes activated, and secretes IL-2 3) IL-2 compensates for lack of costim from APC, inducing clonal expansion of CD8 |
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TH1
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Defense against intracellular microbes > Inflamation
Secretes IF-gama which activates macs to eat more, activates b cells to a certain isotype, and increases APC expression of MHC-1 |
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TH2
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Host defense against helminths (parasitic worms) > allergic Rx. Secretes:
IL-4 - activates B cells to a different isotype than IF-gama (like IgE) IL -13 and 5 - Activate tissue repair macs and also eosinophils. One of the cytokines also stims mast cells. |
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What determines whether a helper T differenciates into a Th1or2
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The cytokine environment at time of activation, which will be specific for a certain type of infection.
Bacterial/viral infection (phagocytic infection) > lots of macs > lots of IL-12 > TH1 Helminth infections or allergins (not phagocytic) > lack of IL-12 > TH2 |
