T Lymphocyte Development

Question 1

where does T lymphocyte development occur?

Answer 1

in the thymus of all species

Question 2

wheere do T cell precursors develop (generally)

Answer 2

in the bone marrow

Question 3

after maturing in the bone marrow, what do T cell precursors do?

Answer 3

migrate to the thymus

Question 4

what does the thymus have for T cell development?

Answer 4

distinct microenvironments that provide signals for maturation and development of T cells

Question 5

what 2 things happen in the first phase of T cell development?

Answer 5

1. committment to T cell lineage

2. recombination of TCRs

Question 6

what 2 things happen in the second phase of T cell development?

Answer 6

1. selection: MHC recognition and non-self

2. committment to CD4 or CD8

Question 7

what are DN cells?

Answer 7

double negative T cell precursors that are negative for both CD4 and CD8

Question 8

what kind of T cell precursors enter stage one? what are they positive for?

Answer 8

DN cells that are negative for CD4 and CD8 but positive for CD44 and CD25

Question 9

what is stage 1 of the DN stage of development and what happens there? (3)

Answer 9

DN1 stage

1. T cell precursors enter the thymus and express CD44
2. proliferation occurs
3. T cell precursors start to express CD25

Question 10

what is stage 2 of DN phase of development and what happens there? (4)

Answer 10

DN2

1. T cell precursors express CD44 and CD25
2. recombination of TCR Beta chain
3. cells now committed to T cell lineage
4. lose expression of CD44

Question 11

what is stage 3 of DN phase of development and what happens there? (3)

Answer 11

DN3

1. T cell precursors express only CD25
2. Beta selection occurs, inidicates successful recombination of Beta chain and signals for alpha chain recombination
3. lose expression of CD25

Question 12

what is stage 4 of DN phase of development and what happens there?

Answer 12

DN4; cell begins to express CD4 and CD8, now as double positive (DP) cells!

Question 13

what 3 things happen in the second phase of T lymphocyte development?

Answer 13

1. positive selection
2. negative selection
3. lineage committment

Question 14

what happens in positive selection of the second phase of T cell development?

Answer 14

select for cells that bind to self-MHC (which is needed to activate T cells), and cells that do not bind self-MHC die

Question 15

what happens in negative selection of the second phase of T cell development?

Answer 15

select against cells that have a high affinity for self-MHC/self-antigen complexes to establish self tolerance; cells that have this high affinity will die

Question 16

what happens in lineage committment of the second phase of T cell development?

Answer 16

cells lose expression of either CD4 or CD8; commit to being either CD4+ or CD8+ cells

Question 17

what happens to T lymphocytes after the second stage of development?

Answer 17

mature T cells leave the thymus and begin to circulate through the body

Question 18

what are regulatory T cells? (Tregs)

Answer 18

some self-reactive cells survive selection and become Tregs

Question 19

what is the role of Tregs?

Answer 19

to suppress the immune response

Question 20

what are the 4 mechanisms by which Tregs suppress the immune response?

Answer 20

1. compete for cytokines that activate T cells need to survive (cytokine depravation)
2. secrete cytokines that inhibit activity of other T cells
3. inhibit antigen-presenting cells, which inhibits activation of T cells
4. kill other cells by secreting perforin and granzyme