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37 Cards in this Set

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  • Back
Lymphocytes (progenitor T-cells) destined to become T-cells migrate from the bone marrow to what primary lymphoid organ?
Thymocytes originate from what type of cells?
Bone marrow stem cells
What are the two lineages of T-cells?
alpha:beta and gamma:kappa
Thymocytes develop cell-surface proteins related to _________ function.
What do thymic epithelial cells secrete that assists with progenitor T-cells migration to the thymus?
A chemotactic factor which attracts the progenitor T-cells

T-cell precursors have antigen receptors, CD3, CD4, and CD8 molecules on their cell surface.

They lack these.

The developmental process of T-cells is similar to B-cell maturation

Assembly of a functional gene is required for each T-cell receptor chain.
Each productive T-cell receptor gene is expressed as soon as it is made, and it it assembled into one of which 2 receptor complexes?
Either a pre T-cell receptor (TCR) or a final TCR

TCR is a membrane-bound glycoprotein that resembles a single, antigen-binding arm of an immunoglobulin (antibody) molecule.
TCR is composed of what 2 different polypeptide chains?
Variable region and constant region
How many antigen binding sites are there on the TCR?
What produces the differences in the variable regions of TCR?
Gene rearrangements

Once T-cell is stimulated with antigen, no further changes occur in the antigen binding site and/or class switching of constant regions (as in immunoglobulins [B-cells])
When progenitor cells enter the thymus and interact with thymic stromal cells, this signals what?
Signals progenitor cells to proliferate
The double negative phase of T cell development is characterized by the absence of what?
T-cell coreceptors CD4 and CD8

also no expression of TCR complex
Double negative thymocytes first express what?

Then what?

then CD25
After progenitor cells enter thymus and proliferate, they express what T-cell specific adhesion molecule?
During T-cell development, expression of CD44 (decreases/increases) when TCR genes begin rearrangement.
Which T-cell lineage is more common?
There is a race between the different loci of of the TCR gene rearrangements.
a) If the gamma or delta chain rearrangements are completed before a productive beta chain rearrangement, what cell lineage do you get?
b) What about if beta occurs before gamma and delta?
a) gamma:delta TCR

b) alpha:beta TCR
If a productive beta chain is rearranged first, the beta chain is assembled with a surrogate alpha chain (pTalpha), forming what?
a) Which loci, if formed, halt gene rearrangements and cause cells to start proliferating?

b) Once gene recombination is reactivated, which gene loci can form?
a) beta, gamma, and delta

b) alpha, delta, or gamma
In most cases, a chain receives productive rearrangement first. For example: alpha:beta TCR -> alpha:beta T-cell lineage.

How can the T-cell become committed to the gamma:delta lineage after already having started out with a beta chain?
If gamma or delta gene loci achieve rearrangement before the alpha chain does

There is only one chance during T-cell development for a T-cell to become a gamma:delta cell.

It can occur during either of the gene loci rearrangement times
What happens to thymocytes that fail to achieve productive rearrangements?
They die by apoptosis and are phagocytosed by thymic macrophages
a) What receptor is expressed on "double negatives?"

b) What receptor is this similar to?
a) Pre-T cell receptor

b) Pre-BCR expressed by developing precursor B-cells
What do the pre-T cell receptors do?
Induce development of the precursor T-cells to the "double positive" phase
The "double positive" phase is characterized by what?
The T-cells express both CD4 and CD8
What are the 2 possible paths for double-negative thymocytes?
1. Become large, active "double positive" thymocytes, with CD3, CD4, CD8 and pTalpha:beta

2. Become gamma:delta with CD3, but without CD4 and CD8
What are the 2 reasons for "double positive" cells to be destroyed?
1. Those bearing antigen receptors for "self" antigens are destroyed by programmed cell death (apoptosis). This prevents an autoimmune reaction.

2. Those that do not react well with MHC antigens are also destroyed
What 2 features are required for an effective immune response by T cells?
T-cells must not react with "self" antigens and must react well to "self" MHC proteins
What are "single-positive" thymocytes characterized by? Where do they go?
They have EITHER CD4 or CD8, not both. They are exported to the periphery
The survival of thymocytes whose TCRs recognize antigens bound to "self" MHC molecules is called what?
Positive selection
The deletion of thymocytes whose TCRs recognize "self" antigens is called what?
Negative selection

Negative selection is critical in determining whether a double-positive T-cell will become a CD4 or CD8 cell.

POSITIVE selection is critical in determining this.
Double-positive thymocytes interact through the alpha:beta receptor with a peptied:MHC complex.
a) With MHC-I, which T-cell co-receptor is recruited and which is excluded?
b) With MHC-II, which T-cell co-receptor is recruited and which is excluded?
a) MHC-I -> CD8 recruited, CD4 excluded
b) MHC-II -> CD4 recruited, CD8 excluded