Restraining The Immune System

Question 1

What kind of T cells function to restrain the immune system?

Answer 1

Regulatory T cells (inducible and natural Tregs)

Question 2

Activated helper T cells secrete what substances to activate the immune system?

Answer 2

TNF and IFN-gamma

Question 3

Activated regulatory T cells secrete what substances to restrain the immune system?

Answer 3

TGF-beta and IL-10

Question 4

What is TGF-beta?

Answer 4

Transforming growth factor beta

Question 5

What is the function of TGF-beta?

Answer 5

Reduces proliferation and CTL killing

Question 6

To where does TGF-beta bind?

Answer 6

Receptors on T cells

Question 7

What is the function of IL-10?

Answer 7

Blocks co-stimulatory signals like CD28 making activation more difficult, also reduces proliferation

Question 8

To where does IL-10 bind?

Answer 8

Receptors on T cells

Question 9

What is the result of B7 binding to naive T cell’s CD28?

Answer 9

Co-stimulation and activation

Question 10

What is the result of CTLA-4 binding all the B7 co-stimulatory molecules?

Answer 10

Blockage of co-stimulation and activation

Question 11

What binded grouping is mostly seen early in an infection?

Answer 11

B7 to CD28 to act as a co-stimulator

Question 12

What binded grouping is mostly seen after a battle has been going on for a while?

Answer 12

B7 to CTLA-4 makes it harder to reactivate T cells

Question 13

What kind of T cells live a relatively long time?

Answer 13

Naive ones (spend their whole life looking for cognate antigen)

Question 14

When does a T cell’s longevity decline?

Answer 14

When activated

Question 15

Why does a T cell’s longevity decline once activated?

Answer 15

Fas proteins are now more sensitive due to being activated multiple times which leads to cell death

Question 16

Why do virgin T cells come with increased longevity?

Answer 16

Fas proteins are insensitive to ligation and therefore avoid cell death

Question 17

Once an invader has been vanquished, around what percentage of T cells die off?

Answer 17

Over 90%!

Question 18

Why must immune responses be able to be turned off once an invader has been dealt with?

Answer 18

Prevention of autoimmune damage

Question 19

What mainly controls the activation level of the immune response?

Answer 19

Amount of foreign antigen present

Question 20

What are the functions of commensal bacteria found in our intestines?

Answer 20

Help digest food
Produce vitamins
Protect us from pathogens by out-competing them

Question 21

Why is it possible that some bacteria eventually are able to breach the normal barrier into tissue?

Answer 21

Such a large surface area (around 200 square meters)

Question 22

What makes the macrophages located beneath the intestinal wall special?

Answer 22

They don’t secrete cytokines to avoid signaling a full blown invasion of the GI tract (can lead to inflammation, diarrhea, etc.)

Question 23

What is the function of macrophages seen beneath the intestinal wall?

Answer 23

Phagocytize invaders that attempt to enter tissue

Question 24

What is the major type of antibody seen in the intestines and the tissues below?

Answer 24

IgA

Question 25

What is the specific function of IgA in the GI tract?

Answer 25

Bind and neutralize invaders that attempt to enter the tissues

Question 26

When IgA finds invaders leaving the GI tract, what is done with them?

Answer 26

Send back to the intestinal tract where they are flushed out in the stool

Question 27

Can IgA fix complement?

Answer 27

No

Question 28

Can IgA stimulate inflammation?

Answer 28

No (good for the GI tract then)

Question 29

What two major things act against the immune system with restraint?

Answer 29

Specialized macrophages and IgA

Question 30

During non-battle conditions, what are the epithelial cells of the intestine producing to induce regulatory T cells?

Answer 30

TGF-beta

Question 31

What is the effect of TGF-beta in the intestine?

Answer 31

Causes cells in Peyer's patches to become regulatory T cells

Question 32

What is the purpose of the cytokines released by regulatory T cells in the intestines?

Answer 32

Encourage a calmer mucosal immune system

Question 33

During battle conditions, epithelial cells of the intestine are producing TGF-beta, and what are the dendritic cells producing?

Answer 33

IL-6

Question 34

During battle conditions, T cells commit to becoming what cells?

Answer 34

Th17

Question 35

Are iTregs CD4+ or CD8+?

Answer 35

CD4+

Question 36

iTregs develop from what cells under influence of TGF-beta from the intestine?

Answer 36

Th0 (naive T cells)

Question 37

What are the two subtypes of iTregs?

Answer 37

Tr1 and Th3

Question 38

Which has a higher affinity for B7: CD28 or CTLA-4?

Answer 38

CTLA-4 (1000's X)

Question 39

What is the function of CD28?

Answer 39

When activated, amplifies the signal and lowers the number of TCR crosslinks needed for activation

Question 40

Why is it easy to discard of obsolete weapons for the immune system when the invader is dealt with?

Answer 40

Most have short lifespans anyway

Question 41

Which immune cells live the longest?

Answer 41

Macrophages (for months)

Question 42

Why do macrophages tend to live longer than other types of immune cells?

Answer 42

NKCs make IFN-gamma which keeps them activated

Question 43

Which immune cells live the shortest lifespans?

Answer 43

Neutrophils (few days)

Question 44

When are macrophages able to go back to a resting state?

Answer 44

When NK cells die off and the supply of IFN-gamma decreases

Question 45

How long do dendritic cells usually live?

Answer 45

About a week once they reach the lymph node

Question 46

What is the lifespan of a plasma cell?

Answer 46

Five days (of hard labor producing antibodies)

Question 47

What kind of immune cells are the exception to the "short life" rule?

Answer 47

T cells (or memory cells)

Question 48

How does the body rid itself of obsolete (experienced) T cells after an attack?

Answer 48

Activation-induced cell death

Question 49

What death receptor is seen on the surface of cells?

Answer 49

Fas receptor protein

Question 50

What binds to the Fas receptor protein causes apoptosis?

Answer 50

Fas ligand

Question 51

Which is found on the natural kill or killer T cell: Fas receptor protein or Fas ligand?

Answer 51

Fas ligand

Question 52

What type of T cell expresses more Fas protein?

Answer 52

Experienced