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23 Cards in this Set
- Front
- Back
thymus
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mature in thymus:
- TCR diversity is generated: somatic gene rearrangement - negative and positive selection - end result: vast repertoire of Ag receptors, foreign Ag will bind to at least one TCR - mature, but naive T cells leave to colonize the secondary lymphoid tissues and circulate in the blood |
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circulation
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- T cells comprise the majority of blood lymphocytes in most spp: 40-80%
- long lived: can recirculate for months-years |
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secondary lymphoid tissue
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T cells encounter Ag and undergo differentiation in secondary lymphoid tissues
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subsets
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subsets are defined by the specific surface molecules they express and the functions they perform
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TCR
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TCR:
- recognizes peptide displaye on an MHC molecule - each binds a single epitope - each T cell expresses many identical, unique TCRs once it leaves the thymus, which all bind the same epitope= same Ag specificity - membrane-anchored, never secreted |
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clonal expansion
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clonal expansion:
- all subsequent progeny from a mature T cell express the same TCR and thus will have the same antigenic specificity |
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CD3 gen
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CD3:
- expressed on all mature T cells - associated with TCR |
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CD3 fx
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CD3 fx:
1. TCR binds epitope being presented by another cell's MHC 2. CD3 on surface of T cell delivers signal to T cell: occurs after Ag binding 3. activates T cell: enters cell cycle, proliferates and secretes cytokines |
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co-stimulators
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co-stimulators:
- binding of TCR to a peptide-MHC complex is usually insufficient to trigger a T cell response - need other co-stimulatory signals |
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T helper cells
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T helper cells= Th cells:
- CD4 - provide help to both B cells and cytotoxic T cells (CTLs) - each has several thousand identical TCR on its surface |
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naive lymphocyte
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naive lymphocyte:
- mature lymphocyte that has not yet interacted with the Ag it can recognize with its TCR |
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naive Th cells
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naive Th cells fx:
- exogenous antigen trapped and processed by dendritic cells is presented to naive Th cells in the secondary lymphoid organs |
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non- naive Th cells
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- CD4 Th cells that have seen Ag before can be stimulated by Ag presentation by other APCs (B cells, macrophages) in addition to dendritic cells
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Th cells proliferation
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Th cells fx:
- if the TCR binds its Ag, Th will proliferate and differentiate - B cells and CTLs cannot respond to optimally to Ag without Th help |
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Th cells fx
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Th cells:
-can only respond to a foreign Ag when presented with MHC II on an APC: 1. CD4 molecule binds to MHC II on APC -and- 2. TCR binds the epitope within the groove of the MHC II molecule |
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CD4 T cell interaction
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TCR- CD4- MHC- epitope interaction:
1. leads to a signal through the CD3 2. signal causes the T cell to express CD40L which now interacts with CD40 on the APC 3. signals other molecules to be expressed on the APC and T cell, resulting in other interactions and activation of the T cell 4. active T cell can make and secrete cytokines that help B cells and CTLs |
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inactivation of T cell
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at some point, signals inactivate the T cell
- otherwise, Th will continually make cytokines |
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CD4 T cell activation
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~1000 TCR-MHC with peptide interactions are needed to activate one CD4 T cell
- highly regulated - # interactions needed depends on the costimulatory signals present - eg if CD 28 present, fewer needed |
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Th 1 cells
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Th 1 cells secrete:
1. IL2: activates other T, B and NK cells 2. interferon gamma: activate macrophages primarily thus stimulating CMI and resistance to intracellular pathogens *CMI !!!! |
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Th 2 cells
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Th 2 cells:
1. secrete IL-4 and 5 2. stimulate B cell proliferation and Ab secretion, promoting resistance to extracellular pathogens *Humoral Immunity !!!!! |
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CTLs gen
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CTLs:
- recognize Ag in the context of MHC I: on all nucleated cells, endogenous Ag such as virus, tumor - CD8 binds the MHC I - |
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CTLs recognize and kill
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CTLs recognize and kill:
1. infected cells: endo via MHC I 2. transformed cells: tumor Ag 3. MHC incompatible cells: foreign MHC eg poorly matched transplant |
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CTL molecule expression
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CTLs express:
- molecules similar to CD4 - adherence: integrins, selectins - co-signaling: CD40L |