T cell Development Flashcards
What are the steps in the life of a T cell?
- T cell progenitors develop in the bone marrow and migrate to the thymus
- Positive and negative selection in the thymus
- Mature T cells migrate to the peripheral lymphoid organs
- Active T cells migrate to sites of infection
What are Thymocytes?
Developing T cells within the thymus
Which type of T cells maintain Tissue Integrity?
gamma:delta T cells
Which type of T cell does not express CD8 or CD4 co-receptors?
Gamma:delta T cells
Which type of T cells interact with non-classical receptors?
gamma:delta T cells
Which type of T cells are considered Helper T cells?
CD4
What are the subtypes of a CD4 cell?
- Th1
- Th2
- Th17
- Tfh
- Treg
Which type of T cells regulate adaptive and innate immune function?
CD4 T cells
Which T cells are cytotoxic?
CD8 T cells
Which T cells have a direct effector function?
CD8 cells
What is the site of all T cell development?
Thymus
Selection of T cells happens as thymocytes move from ______ to ______ in the thymus.
- Cortex
2. Medulla
TCR development happens where?
Cortex of Thymus
What happens to the T cell production of the thymus with age?
It is reduced
T/F T cells have long half lives
True
What is the half life of a CD4 T cell?
4.2 years
What is the half life of a CD8 T cell?
6.5 years
T/F with the reduction of T cell production, T-cell mediated immunity is also greatly diminished
False, T cell-mediated immunity is not grossly affected
*probably because of the long half life
What is Notch1?
T cell transcription factor complex
What is Pax-5?
B cell transcription factor
T cell progenitors don’t commit until they reach what?
The thymus
When is the first checkpoint in T cell development?
Pre-T cell
When is the second checkpoint in T cell development?
Positive and Negative selection
Thymic location influences ________
T cell development
What dictates T cell lineage?
Gene rearrangement
What genes rearrange first?
Beta, Gamma, and Delta
T/F Gamma or Delta rearrangement enhances Beta and Alpha
False, is suppresses Beta and Alpha
Which T cells leave the thymus with little selection?
Gamma:Delta T cells
Beta chain production drives _________
CD4 and CD8 expression
*Double Positive
What would initiate an alpha:beta lineage?
B chain formation
Between Alpha and Beta, which chain is rearranged first?
Beta
How many attempts can be made to achieve a productive rearrangement of the Beta chain?
4 attempts
- Two attempts per locus - Two genes
What is the order of rearrangement on the Beta chain?
1st: Vb-Db-Jb -> Vb-DJb
2nd: Vb-DJb -> VDJb
T/F Beta chain locus is organized similar to immunoglobulin chains
False, it is organized differently
Alpha chain rearrangement occurs in _________
Pre-T cells
Alpha chain rearrangement follows what?
Proliferation and CD4/8 expression
Just before alpha chain rearrangement, what is still a possible fate for this cell?
May still develop into gamma:delta T cells
Once you have had Alpha chain rearrangement what is no longer possible?
gamma:delta T cells
What purpose does Positive selection serve?
Selects for a functional T cell receptor
What purpose does Negative Selection serve?
Ensures no self-antigen binding
Within T cell development, what are the stages in development for a mature double-positive cell?
- Poliferation and differentiation to double-positive CD3+ thymocytes
- Positive Selection
- Negative selectdion
- Entry to the circulation
What are the thymocyte location and characteristics at the time of proliferation and differentiation to double positive CD3+ thymocytes?
Double-negative CD3- thymocytes in the subcapsular zone
Describe thymocyte location and characteristics at the time of positive selection
Double-positive CD3+ thymocytes in the thymic cortex
Describe Thymocyte location and characteristics during negative selection
Double-positive CD3+ thymocytes throughout cortex and especially at the cortico-medullary junction
Describe thymocyte location and characteristics as they enter the circulation
Mature self-restricted, self-tolerant, single-positive CD4 or CD8 T cells leave the thymus in blood venules
Positive selection ensures _____ is bound
MHC
Positive Selection of alpha:beta T cells is done by _______ in the ________-
- Corical epithelial cells
2. Thymus
How do epithelial cells conduct positive selection?
- Epithelial cells present MHC I/II self-peptide complexes
- If the TCR binds moderately or strong it lives
- If the TCR has weak or no binding, it dies
In positive selection, TCR must bind MHC within ________
3 to 4 days
What effect does binding of TCR to MHC have on the RAG 1/2 complex?
It turns it off
T/F in the 3 to 4 days that TCR has to bind MHC, alpha chain rearrangement can occur
True,
I think this would be to modify it to bind with more affinity to MHC
T/F Positive selection is the second checkpoint in T cell development
True
What determines CD4 vs CD8 expression?
Positive Selection
How Does Positive selection determine CD4 or CD8 expression?
Basically, the T cell is presented with MHC 1 and 2 and whichever one it interacts with the best determines whether it is CD8 or CD4 lineage
During Positive Selection what would a Double positive thymocyte become if it interacted with MHC1?
A CD8 T cell
During Positive selection, what would a double positive thymocyte become if it interacted with a MHC II?
A CD4 T cell
What is required in positive selection to determin CD4 vs. CD8 expression?
Co-signaling
T/F There are different models of selection for CD4 or CD8 expression
True
What cells perform negative selection of alpha:beta T cells?
- Dendritic cells
- Macrophages
- Other cells in the thymus
How is negative selection performed?
- Dendritic cells and macrophages present self-peptides
- Excessively binding induces apoptosis
- Moderate binding allows the cell to live
T/F Central Tolerance is a result of Negative selection
True
What other type of tolerance may also occur other than central?
Peripheral
T/F Following Selection, Naive Mature T cells are done differentiating
False, They can still undergo differentiation
Naive T cells can enter a draining lymph node by two routes. What are they?
- In the blood
2. In the afferent lymph coming from an upstream lymph node
In the life of a T cell, what happens as T cell progenitors develop in the bone marrow and migrate to the thymus?
T-cell precursor rearranges its T-cell receptor genes in the thymus
In the life of a T cell, what happens during positive and negative selection? (in a general sense)
Immature T cells that recognize self MHC receive signals for survival. Those that interact strongly with self-antigen are removed from the repertoire
In the life of a T cell, what happens as Mature T cells migrate to the peripheral lymphoid organs?
Mature T cells encounter foreign antigens in the peripheral lymphoid organs and are activated
In the life of a T cells what happens as Activated T cells migrate to the sites of infection?
Activated T cells Proliferate and eliminate infection
Beta chain rearrangement forms ___________
Pre-T cell Receptors
During the first Checkpoint of T cell development, the beta chain binds a ________
Surrogate alpha-chain analogue (pTa)
T/F a CD3 complex is assembled during the first checkpoint in T cell development
True
What happens if signaling occurs during the first checkpoint of T cell development?
- Signaling drives further development
- RAG function halts
- Proliferation
T/F Pre-T cell receptor formation and the first checkpoint involves the formation of a superdimer
True