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23 Cards in this Set

  • Front
  • Back
thymus
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
circulation
- T cells comprise the majority of blood lymphocytes in most spp: 40-80%
- long lived: can recirculate for months-years
secondary lymphoid tissue
T cells encounter Ag and undergo differentiation in secondary lymphoid tissues
subsets
subsets are defined by the specific surface molecules they express and the functions they perform
TCR
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
clonal expansion
clonal expansion:
- all subsequent progeny from a mature T cell express the same TCR and thus will have the same antigenic specificity
CD3 gen
CD3:
- expressed on all mature T cells
- associated with TCR
CD3 fx
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
co-stimulators
co-stimulators:
- binding of TCR to a peptide-MHC complex is usually insufficient to trigger a T cell response
- need other co-stimulatory signals
T helper cells
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
naive lymphocyte
naive lymphocyte:
- mature lymphocyte that has not yet interacted with the Ag it can recognize with its TCR
naive Th cells
naive Th cells fx:
- exogenous antigen trapped and processed by dendritic cells is presented to naive Th cells in the secondary lymphoid organs
non- naive Th cells
- 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
Th cells proliferation
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
Th cells fx
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
CD4 T cell interaction
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
inactivation of T cell
at some point, signals inactivate the T cell
- otherwise, Th will continually make cytokines
CD4 T cell activation
~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
Th 1 cells
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 !!!!
Th 2 cells
Th 2 cells:
1. secrete IL-4 and 5
2. stimulate B cell proliferation and Ab secretion, promoting resistance to extracellular pathogens
*Humoral Immunity !!!!!
CTLs gen
CTLs:
- recognize Ag in the context of MHC I: on all nucleated cells, endogenous Ag such as virus, tumor
- CD8 binds the MHC I
-
CTLs recognize and kill
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
CTL molecule expression
CTLs express:
- molecules similar to CD4
- adherence: integrins, selectins
- co-signaling: CD40L