Chapter 7 end of chapter questions

Which cells, that populate in the thymus or circulate through it, express MHC class II molecules? Do they play a role in mediating positive and/or negative selection?

Macrophages, dendritic cells, and thymus epithelial cells. Cortical thymic epithelial cells participate in positive selection. (Cortical and medullary thymic epithelium may also participate in negative selection.) Thymic epithelium, circulating macrophages, and dendtric cells participate in negative selection.

Do delta:gamma T cells rearrange their Ag receptor genes in the periphery?

No.

Do delta:gamma chains in T cells pair with pT-alpha at any stage in their development?

No.

MHC restriction is best described as...

T cell recognition of a peptide antigen only when it is bound to a particular form of MHC molecule.

The following is true of T-cell development:

1) Delta and Gamma rearrangements may occur at 2 different stages. Once at the committed double-negative stage and again at the uncommitted double-negative stage. 2) Neither delta nor gamma chains associate with pT-alpha 3) T-cell development is biased in favor of alpha:beta lineage commitment 4) a max of 4 attempts can be made to produce a functional beta chain 5) delta:gamma T cells are not subject to positive or negative selection processes in the thymus

These are all true of the successive rearrangement of alpha-beta TCRs.

1) Unproductive rearrangement to the C-beta-1 locus can be rescued by a second rearrangement to the C-beta-2 locus. 2) Unproductive rearrangements between V-alpha and J-alpha can be rescued by a second rearrangement between upstream V-alpha and downstream J-alpha segments. 3) When the alpha chain undergoes a seccessive gene rearrangement, the unproductive intervening rearranged gene segments are deleted. 4) The delta chain locus is permanently deleted as an extrachromosomal circle when the alpha chain gene rearranges.

Generally, in healthy individuals and in the absence of infection, a mature naive T cell that encounters a self antigen outside of the thymus may...

1) be surpassed by a regulatory T cell 2) undergo activation-induced cell death 3) be rendered anergic

What proteins do delta:gamma T cells require for cell-surface expression of their Ag receptors?

CD3

What comprises the minority subpopulation of T lymphocytes?

Delta:gamma T cells

When does positive selection of a CD8 T cell occur?

If a T-cell receptor on a double-positive thymocyte binds to a self-peptide: self-MHC class I complex with low affinity.

Where does positive selection occur and what does it involve?

It happens in the cortex and involves double-positive thermocytes.

Name the two checkpoints in the early developmental stages of alpha-beta T cells in the thymus that must be satisfied to permit progression of their development.

The first checkpoint occurs after the rearrangement of the beta-chain locus and the second checkpoint occurs after the rearrangement of the alpha-chain locus.

What are the cell types that express MHC class II molecules?

The professional antigen-presenting cells (Cells, macrophages, and dendritic cells); thymic epithelial cells, neural microglia, and activated T cells.

What are characteristics of regulatory T cells?

They express: CD25 CD4 FoxP3 (the transcriptional repressor) MHC class II-restricted T-cell receptors specific for self antigen

Do delta:gamma T cells originate from the same bone marrow-derivived precursor that gives rise to an alpha:beta T cell?

Yes.

What is the underlying cause for the disease APECED?

a breakdown in the development of normal immune tolerance

Describe the developmental pathway for T cells

bone marrow---> thymus--->lymph nodes

It would be detrimental for non-circulating cells that populate tissues and glands to express MHC class II molecules because...

can result in autoimmunity

An adult who has been thymectomized will have a T cell repertoire that does what?

is self-renewing and long-lived and does not require replenishment from the thymus

During positive selection, if the selecting MHC molecule is class I, then...

the thymocyte is committed to the CD8 lineage.