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13 Cards in this Set

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The thymus also possesses a dendritic like cell population known
nurse cells
Also have macrophages and variety of epithelial cells. These support cells express These cells also provide the thymocytes with a variety of
-high levels of both class I and II chains for peptide presentation to the maturing T cell’s TCR complex.
-T cell promoting compounds that help these cells proliferate (growth factors, etc).
1.The most immature cells of thymus do not possess CD3 (and thus TCR) but do express other markers including
Thy-1.
The first observed change is that these cells begin their TCR rearrangement pathway.
Gamma/delta chains re-arrange first. In a second lineage of T cells, alpha/beta next. Most available data suggests that there are two distinct lineages of T cells: one that express alpha/beta, the second with gamma/delta
Once the TCR genes start rearranging,
the transcription of the CD3 components is stimulated such that all of the primary components of the CD3/TCR complex are made together.
what lets a t cell survive?
So correct engagement of the TCR actually induces the cells to survive
Instructional model.
Epithelial cells that are part of the thymus framework express both class I and II.
Concept is that the double positive cells will bind to either I or II MHC with TCR.
If get close enough match with TCR, the CD4 or 8 chains engage as well.
This leads to the loss of the un-utilized chain (either CD4 or CD8) and enrichment of the TCR that binds self.
Stochastic model
Utilizes concept that the double positive cells randomly lose the expression of either the CD4 or CD8 chain. This loss then leaves the cell as TCR/CD8 or TCR/CD4. Must engage a class I or class II bearing cell correctly or the T cell dies.
a) if the naïve T cell is activated in the presence of IL-4
will commit to a TH2 lineage
b) if the naïve T cell is activated in the presence of IL-12,
will commit to a TH1 lineage
TH1 cells primarily produce which drives
IFN-gamma
-the antibacterial, inflammatory response: production of opsonizing isotypes of antibody (bound by Fc receptor and efficient at complement activation), activation of macrophages, enhanced CTL, NK and neutrophil killing.
TH2 cells primarily product IL-5 leads to
IL-4, with IL-5 and IL-10. Isotypes are neutralizing and part of the allergic response,
-eosinophil proliferation and activation, and macrophages are pushed into an anti-inflammatory status.
, TH1/TH2 phenotypes can also be ascribed to
CTL, dendritic cells, mast cells, e