Restraining The Immune System Flashcards
What kind of T cells function to restrain the immune system?
Regulatory T cells (inducible and natural Tregs)
Activated helper T cells secrete what substances to activate the immune system?
TNF and IFN-gamma
Activated regulatory T cells secrete what substances to restrain the immune system?
TGF-beta and IL-10
What is TGF-beta?
Transforming growth factor beta
What is the function of TGF-beta?
Reduces proliferation and CTL killing
To where does TGF-beta bind?
Receptors on T cells
What is the function of IL-10?
Blocks co-stimulatory signals like CD28 making activation more difficult, also reduces proliferation
To where does IL-10 bind?
Receptors on T cells
What is the result of B7 binding to naive T cell’s CD28?
Co-stimulation and activation
What is the result of CTLA-4 binding all the B7 co-stimulatory molecules?
Blockage of co-stimulation and activation
What binded grouping is mostly seen early in an infection?
B7 to CD28 to act as a co-stimulator
What binded grouping is mostly seen after a battle has been going on for a while?
B7 to CTLA-4 makes it harder to reactivate T cells
What kind of T cells live a relatively long time?
Naive ones (spend their whole life looking for cognate antigen)
When does a T cell’s longevity decline?
When activated
Why does a T cell’s longevity decline once activated?
Fas proteins are now more sensitive due to being activated multiple times which leads to cell death
Why do virgin T cells come with increased longevity?
Fas proteins are insensitive to ligation and therefore avoid cell death
Once an invader has been vanquished, around what percentage of T cells die off?
Over 90%!
Why must immune responses be able to be turned off once an invader has been dealt with?
Prevention of autoimmune damage
What mainly controls the activation level of the immune response?
Amount of foreign antigen present
What are the functions of commensal bacteria found in our intestines?
Help digest food
Produce vitamins
Protect us from pathogens by out-competing them
Why is it possible that some bacteria eventually are able to breach the normal barrier into tissue?
Such a large surface area (around 200 square meters)
What makes the macrophages located beneath the intestinal wall special?
They don’t secrete cytokines to avoid signaling a full blown invasion of the GI tract (can lead to inflammation, diarrhea, etc.)
What is the function of macrophages seen beneath the intestinal wall?
Phagocytize invaders that attempt to enter tissue
What is the major type of antibody seen in the intestines and the tissues below?
IgA
What is the specific function of IgA in the GI tract?
Bind and neutralize invaders that attempt to enter the tissues
When IgA finds invaders leaving the GI tract, what is done with them?
Send back to the intestinal tract where they are flushed out in the stool
Can IgA fix complement?
No
Can IgA stimulate inflammation?
No (good for the GI tract then)
What two major things act against the immune system with restraint?
Specialized macrophages and IgA
During non-battle conditions, what are the epithelial cells of the intestine producing to induce regulatory T cells?
TGF-beta
What is the effect of TGF-beta in the intestine?
Causes cells in Peyer’s patches to become regulatory T cells
What is the purpose of the cytokines released by regulatory T cells in the intestines?
Encourage a calmer mucosal immune system
During battle conditions, epithelial cells of the intestine are producing TGF-beta, and what are the dendritic cells producing?
IL-6
During battle conditions, T cells commit to becoming what cells?
Th17
Are iTregs CD4+ or CD8+?
CD4+
iTregs develop from what cells under influence of TGF-beta from the intestine?
Th0 (naive T cells)
What are the two subtypes of iTregs?
Tr1 and Th3
Which has a higher affinity for B7: CD28 or CTLA-4?
CTLA-4 (1000’s X)
What is the function of CD28?
When activated, amplifies the signal and lowers the number of TCR crosslinks needed for activation
Why is it easy to discard of obsolete weapons for the immune system when the invader is dealt with?
Most have short lifespans anyway
Which immune cells live the longest?
Macrophages (for months)
Why do macrophages tend to live longer than other types of immune cells?
NKCs make IFN-gamma which keeps them activated
Which immune cells live the shortest lifespans?
Neutrophils (few days)
When are macrophages able to go back to a resting state?
When NK cells die off and the supply of IFN-gamma decreases
How long do dendritic cells usually live?
About a week once they reach the lymph node
What is the lifespan of a plasma cell?
Five days (of hard labor producing antibodies)
What kind of immune cells are the exception to the “short life” rule?
T cells (or memory cells)
How does the body rid itself of obsolete (experienced) T cells after an attack?
Activation-induced cell death
What death receptor is seen on the surface of cells?
Fas receptor protein
What binds to the Fas receptor protein causes apoptosis?
Fas ligand
Which is found on the natural kill or killer T cell: Fas receptor protein or Fas ligand?
Fas ligand
What type of T cell expresses more Fas protein?
Experienced
