9 T Cell Development Flashcards
name of immature t cells in the thymus?
thymocytes
4 key checkpoints for production of mature Tcells
- Notch Signaling
- Rearrangement of beta then alpha T cell receptor
- Positive and negative selection to identify functional but not self reactive T cells
- Selection of CD4, if it doesn’t match then CD8
What are the most critical T cell maturation markers and what can they identify?
CD4 and CD8
- double negative stage
- double positive stage
- single positive stage
What surface markers of T cells can differentiate 4 distinct double negative stages?
CD44 and CD25
DN1 has what markers?
CD44 +
DN2 has what markers?
CD44+ and CD25+
DN3 has what markers ?
CD44(lower amount) CD 25+
DN4 has what markers?
negative for CD8 and CD4 but has a pre alpha and rearranging beta
negative for CD44 and CD25
Where does DN1 occur?
medulla- 10 days lineage bias
Where does DN2 occur?
Cortex- Commit to tcell, 2 days
Where does DN3 and DN4 occur?
Subcapsular region- TCR express 2 days DN3 2-4 days DN4
Where does immature double positive stage take place?
Cortex–repetoire selection
What determines T or B cell fate?
notch 1 activation —-> Tcell
loss of notch 1 —–> Bcell
The alphbeta TCR contains # proteins from # of genes?
8 proteins from 6 genes
What types of domains does the TCR have?
transmembrane and a constant and variable extracellular domain
deficiencies in TCR or CD3 subunits results in?
decreased surface expression
Cd3 gamma, zeta, and epsilon subunits and the TCR { subunit transmit what types of signals?
intracellular
What type of recombination forms the variable regions of TCR?
somatic recombination that occurs in thymus
TCR alpha gene contains what for recombination?
—TCR alpha chain has multiple copies of V and J and single copy of the constant. 1 V 1 J and constant are selected for final TCR alpha gene
TCR beta gene contains what for recombination?
Multiple copies of V, D and J, and 2 copies of the constant region. 1 of each is selected for final TCR beta gene
How many TCR alphas and betas on a mature T cell?
single alpha and single beta gene
TCR recombination is controlled by what?
recombination signal sequences spaced be 23 bp on the 3’end and 12 base pairs on the 5’end
What 2 proteins recognize the RSS sequences and facilitate alignment?
Rag 1 and Rag 2- catalyze cleavage of the RSS and formation of closed hairpin loops
What encompasses the region of DNA that will encode for a functional TCR gene?
coding joints
What are the intervening DNA sequences that are removed by recombination?
signal joints
What binds to the coding joint and signal joint?
Ku70/Ku80- the recruit several proteins to ligate and create hairpin loops etcs.
The diversity of TCR is driven by what?
combinatorial diversity and junctional diversity
random selection of VDJ regions?
combinatorial diversity
random addition of P and N nucleotides?
junctional diversity
why is actual TCR diversity much smaller?
non-productive or self reactives are eliminated
Is TCR alpha or beta rearranged first?
beta during the DN3 stage- formation required for further differentiation the alpha is also required for further differentiation but it comes second during the double positive stage
Can T cells express TCR alpha chains from both genes?
yes, but only one is expressed on the surface
Which chain has an intracellular tail for mediation of intracellular signaling pathways that tests the TCR beta chain?
pre-TCR alpha chain- only expressed during late double negative stage and early double positive stage—induces proliferation of immature thymocytes
The inappropriate expression of TCR alpha chain is linked to what disease?
immature T cell leukemia
What is the second type of TCR?
gamma/delta T cells.– replaces alpha beta TCR chain and eliminates CD3 delta chain and replaces with a second copy of the CD3 gamma chain
What happens to the alpha chain if it rearranges through all of the V and J regions before producing a functional chain?
apoptosis
What must happen due to the fact that the TCR delta gene is in the TCR alpha gene?
rearrangement of the TCR alpha or delta is mutually exclusive—production of both is impossible in the same cell
Once the t cell produces a TCR alpha and beta and expresses it on a surface what takes place?
testing for functionality and self reactivity
fail function-death by neglect
fail self reactivity- negative selection
ONLY 2% are positively selected!!!!!!!
what expresses self peptides to test TCR expression?
medulla epithelial cells
What is down regulated in selected double positive T cells?
CD8
CD4 expressing T cells with competent signaling differentiate into? incompetent?
CD4, incompetent leads to CD8
What can cause immature T cell leukemia?
Non appropriate expression of the pre alpha chain on T cells during differentiation.
