T Cell Development

Question 1

Where does T cell development take place?

Answer 1

Thymus

Question 2

What are the phases of T cell development that take place in the thymus?

Answer 2

Maturation
Cell proliferation
TCR gene rearrangements
Cell apoptosis

Question 3

What are the two methods of T cell selection?

Answer 3

Positive and negative

Question 4

What is DeGeorge’s syndrome?

Answer 4

Chromosomal disorder leading to decreased T cells

Question 5

What pharyngeal pouches does the thymus come from?

Answer 5

3rd pair

Question 6

What are the pouches made out of?

Answer 6

endoderm

Question 7

What are the clefts made out of?

Answer 7

exoderm

Question 8

What forms the capsule around the thymus?

Answer 8

Mesenchyme

Question 9

What is the cellular organization of the thymus?

Answer 9

1- subcapsular region
2- cortex
3- corticomedullary junction
4- medulla

Question 10

Where are hassall’s corpuscles located?

Answer 10

in the medulla of the thymus

Question 11

Is the cortex or the medulla more dense?

Answer 11

the cortex

Question 12

What type of cells travel to the thymus?

Answer 12

T cell precursors (prothyrocytes)

Question 13

Where do prothyrocytes come from?

Answer 13

Fetal lever and bone marrow

Question 14

Where do prothyrocytes enter the thymus?

Answer 14

at the cortico-meduallary junction

Question 15

How do the prothyrocytes enter the thymus?

Answer 15

blood vessels

Question 16

What signals are used to get the prothyrocytes to the thymus?

Answer 16

chemotactic substances control prothyrocyte travel

Question 17

What are the most immature T cells? What do they express?

Answer 17

The least mature are double negative t cells that have just migrated from the bone marrow

Question 18

Do double negative’s express the TCR?

Answer 18

Some do, but about 2/4 are triple negative

Question 19

What type of somatic rearrangement occurs at the DN stage?

Answer 19

gamma, beta and delta. NOT alpha

Question 20

What does gamma pair with? What does alpha pair with?

Answer 20

gamma pairs with delta and alpha pairs with beta

Question 21

What are double positive T cells?

Answer 21

express both CD4 and CD8

Question 22

when does alpha somatic rearrangment occur?

Answer 22

at the DP stage

Question 23

When does the most apoptosis of T cells occur?

Answer 23

At the DP stage because dp’s are bery sensitive to anything that can cause apoptosis

Question 24

What are single positives?

Answer 24

DP’s that have down regulated one of the two co-receptors

Question 25

Which is more prevalent, CD4+ or CD8+?

Answer 25

CD4+

Question 26

What gets turned on first, CD4 or CD8?

Answer 26

CD4

Question 27

What is it easier to become? AB or DG?

Answer 27

Alpha beta

Question 28

A precursor cell that comes to the thymus is destined to become what?

Answer 28

dendritic cell, B cell or T cell. The cell needs to chhose the T cell lineage

Question 29

SInce beta and alpha rearrangements occur at different times, what does beta pair with?

Answer 29

a surrogate alpha chain so some rounds of proliferation can occur before teh alpha chain is rearranged

Question 30

Where does DP selection happen?

Answer 30

inner corted

Question 31

When a cell has committed to either CD4 or CD8 where does it go within the thymus?

Answer 31

The medulla

Question 32

What is the first T cell checkpoint?

Answer 32

Beta selection. It is to assess whether TCR beta is functionally rearranged

Question 33

If a cell passes beta selection, what proceeds?

Answer 33

Proliferation and expression of CD4 and CD8 and termination of TCR gamma expression. Alpha rearrangement begins as well

Question 34

What is the second T cell checkpoint?

Answer 34

positive and negative selection

Question 35

what is the purpose of the second t cell checkpoint?

Answer 35

1- assess whether TCR alpha is functional 2- assess whether TCR is self MHC restricted 3- assess whetherTCR is auto-reactive

Question 36

If there is no reaction with the peptide/ MHC?

Answer 36

The cell dies by neglect

Question 37

What is positive selection?

Answer 37

The cell needs to bind MHC and self peptide just enough. I it binds too much or too little is will die via apoptosis

Question 38

What causes peripheral ligands to be expressed in the medullary epithelial cells?

Answer 38

Aire transcription factos

Question 39

What cells mediate positive selection?

Answer 39

cortical epithelial cells

Question 40

What cells mediate negative selection?

Answer 40

any cell can mediate it