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HTHSCI 3I03 Lecture Notes - Cd86, Cd80, Ctla-4

Health Sciences
Course Code
Jonathan Bramson

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Lecture: CD8+ T-cells- The Third signal
Naïve T-cell activation
During activation, you cannot just be activated by MHC peptide
Signal 1= MHC peptide complex (signal 1 not alone enough)
Signal 2= costimulation= happens mostly through CD28 (on T-cell) and B7-
1(CD80) and B7-2(CD86) (APC Ligand)
Only signal 1= anergy (tolerant T-cells that can give rise to regulatory T-cells)
o Deals with a lot of the autoreactive T-cells
Only signal 2= no response
Up until here= primed
Known as the expansion phase
Need rapid activation of the cells
T-cells go into effector function
o By this point, they will only need signal 1 to function
Contraction phase= 70-90% of cells die through apoptosis
Not all die= will have some memory T-cells
No infection= DCs will only provide signal 1 (no co-stimulatory molecule)
Will only generate anergic T-cells
Will undergo weak proliferation (not enough energy/signal)
Presence of PAMPS
Bound to by DCs
Get costimilation (i.e. licensed)
Presence of signal 1 and signal 2= STRONG proliferation
Yields effector T-cells
Coinhibitory Receptor
Yields CTLA-4 production
o Decreases IL-2, anergy occurs, apoptosis
Naïve T-cells= only express CD28
Once activated= T-cells start to express CTLA-4 = susceptible to being primed
Lecture: The Third Signal and CD4+ T-cells
The third signal= cytokines= controls differentiation
Eg. Interleukin= between leukocytes
How do CD4+ Helper T-cells help with T-cell activation?
CD4+ T-cell help is required
APCs will FIRST activate your CD4+ t-cells
CD4+ t-cells in response to APCs will increase their CD40-L (ligand) and
increase IL-2 = will then gen binding to APC CD40 on APC
Increase co-stimulatory molecules
APCs go onto activate more CD8+ T-cells
IL-2= very important for sustaining proliferation for CD4+ T-cells
How do CD4+ Helper Cells Act?
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