T-Cell Activation, T-Cell Cytokines

Question 1

What are the 4 conditions for T-cell activation?

Answer 1

1. antigen is membrane-bound
2. antigen is processed (occurs in APCs)
3. processed antigen must associate with MHC class I or II molecules
4. the APC secretes IL-1 or IL-2

Question 2

Key differences between CD4 and CD8 T cells?

Answer 2

CD4: on Th cells, is receptor for Class II MHC, presents exogenous antigens
CD8: on Tc cells, is receptor for Class I MHC, presents endogenous antigens

Question 3

Why can’t antibodies penetrate hepatic or epithelial cells?

Answer 3

They do not express MHC Class II molecules

Question 4

What are the 2 signals required for T-cell activation?

Answer 4

1. Primary signal: antigen-specific (delivered thru TCR/CD complex)
2. Secondary signal: co-stimulatory (membrane interactions of CD28 on T cells with B7 on APC)

Question 5

Helper T cells can differentiate into three subtypes (once primary and secondary signals have occurred): Th-1, Th-2, and Th-17. What cytokine(s) must be present for this differentiation to occur for each?

Answer 5

Th-1 clonal expansion: IL-12

Th-2 clonal expansion: IL-10 & IL-4

Th-17 clonal expansion: as long as IFN-gamma and IL-4 cytokines are not present

Question 6

What derived cytokine does the clonal expansion of Th-1 secrete/what are its effects?

Answer 6

IFN-gamma –> binds to its corresponding receptor on a macrophage –> ACTIVATED MACROPHAGE (MØ) –> binds to pathogen & eliminates it. Also inhibits Th-2 growth.

Question 7

What derived cytokine does the clonal expansion of Th-2 secrete/what are its effects?

Answer 7

IL-4 –> stimulates B cells (IgE // allergies and helminths) –> B cell binds to pathogen and eliminates it. Also inhibits Th-1 growth.

Question 8

What derived cytokine does the clonal expansion of Th-17 secrete/what are its effects?

Answer 8

IL-17 –> recruits monocytes and neutrophils; up-regulates pro-inflammatory chemokines and cytokines

Question 9

What is the importance of regulatory T cells in suppressing immune responses in a newborns?

Answer 9

Prevention of excess I.R.s while the infant adjusts to changing environments (e.g., out of mom and into world)

Question 10

What are three mechanisms of how cytotoxic T cells induce apoptosis of target cells?

Answer 10

1. granzymes/perforins (enter through hole in MAC and polymerize within target cell)
2. TNF-beta
3. Fas-fas ligand pathway