T cell Activation

Question 1

What are the three phases of gene activation in T cells?

Answer 1

1. immediate genes (30 min): transcription factors
2. early genes (1-2 hours): various cytokines/receptors. ie. growth factors like IL-2R, IL-3, IL-6
3. late genes (2 days): mostly adhesion molecules

Question 2

What is required for T cell activation?

Answer 2

formation of the tri-molecular complex (TMC) and THEN interactions with APC cells (B7-CD28)

Question 3

Which cells constitutively express class II MHC and B7?

Answer 3

dendritic cells

Question 4

Which cells needs to be activated to express MHC II and B7?

Answer 4

macrophages

Question 5

Which cells constitutively express MHC II but need to be activated to express B7?

Answer 5

B cells

Question 6

Where is CD28 found?

Answer 6

on resting and active T cells

Question 7

Where is CTLA-4 found and how does it function?

Answer 7

on activated T cells. it binds to B7 with a higher affinity than CD28 (an antagonist to CD28)

Question 8

What does the Fab fragment do?

Answer 8

blocks CD28 from binding to B7

Question 9

How can an antibody promote T cell activation?

Answer 9

In the absence of B7, the antibody can cross-link CD28 so that the T cell is ‘tricked’ into being activated

Question 10

What is another way to bypass a missing B7 on an APC?

Answer 10

a seconds APC with a functional B7 can bind to the CD28 and activate the T cell

Question 11

Under what conditions do T and B cells undergo apoptosis?

Answer 11

if they do not rearrange productively, when they are not stimulated by the proper signals, and when activated cells do not receive activation signals

Question 12

List the events in T cell development

Answer 12

1. T cells form in the bone marrow and differentiate in the thymus
2. mature T cells leave the thymus via blood and get into lymph nodes (LN)
3. they leave the LN via lymphatic vessels, go to the thoracic duct, to the heart, then repeat the migration cycle
4. when the T cell encounters antigen in the LN, they divide rapidly over the next 48 hours
5. T cells produce large amounts of IL-2
6. stimulated T cells divide 2-3 times per day, some becoming effector cells and some memory cells