T-Cell Activation, T-Cell Cytokines Flashcards
What are the 4 conditions for T-cell activation?
- antigen is membrane-bound
- antigen is processed (occurs in APCs)
- processed antigen must associate with MHC class I or II molecules
- the APC secretes IL-1 or IL-2
Key differences between CD4 and CD8 T cells?
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
Why can’t antibodies penetrate hepatic or epithelial cells?
They do not express MHC Class II molecules
What are the 2 signals required for T-cell activation?
- Primary signal: antigen-specific (delivered thru TCR/CD complex)
- Secondary signal: co-stimulatory (membrane interactions of CD28 on T cells with B7 on APC)
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?
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
What derived cytokine does the clonal expansion of Th-1 secrete/what are its effects?
IFN-gamma –> binds to its corresponding receptor on a macrophage –> ACTIVATED MACROPHAGE (MØ) –> binds to pathogen & eliminates it. Also inhibits Th-2 growth.
What derived cytokine does the clonal expansion of Th-2 secrete/what are its effects?
IL-4 –> stimulates B cells (IgE // allergies and helminths) –> B cell binds to pathogen and eliminates it. Also inhibits Th-1 growth.
What derived cytokine does the clonal expansion of Th-17 secrete/what are its effects?
IL-17 –> recruits monocytes and neutrophils; up-regulates pro-inflammatory chemokines and cytokines
What is the importance of regulatory T cells in suppressing immune responses in a newborns?
Prevention of excess I.R.s while the infant adjusts to changing environments (e.g., out of mom and into world)
What are three mechanisms of how cytotoxic T cells induce apoptosis of target cells?
- granzymes/perforins (enter through hole in MAC and polymerize within target cell)
- TNF-beta
- Fas-fas ligand pathway