Regulation of the Immune Response

Question 1

One of the cardinal features of all immune responses is their _____-_____.

Answer 1

Self-limitation.

Question 2

T or F?

The main reasons for self-limitation of the immune response is that each immune response eliminates the antigen that initiated the response and thus eliminates the necessary first signal for lymphocyte activation.

Answer 2

TRUE.

Question 3

T or F?

The initial response will not result in memory for the antigen; only the second exposure will establish memory for more vigorous immune responses for subsequent exposures.

Answer 3

FALSE.

The initial response establishes memory for the antigen, so that subsequent exposure to the same antigen triggers a more vigorous immune response.

Question 4

What is the ‘engine’ that drives the immune response?

Answer 4

The antigen.

Question 5

What are the two possible outcomes when the immune system encounters an antigen?

Answer 5

1 - Immunity.

2 - A state of immunologic unresponsiveness called: “tolerance”

Question 6

What is immune tolerance?

Answer 6

A state of immunologic unresponsiveness.

Question 7

What is the primary regulator of the intensity of an immune response?

Answer 7

The antigen concentration.

Question 8

T or F?

Optimal antigenic doses for maximal immune response intensity will vary for different antigens.

Answer 8

TRUE.

Question 9

T or F?

Excessively large doses of antigen often result in tolerance and inhibition of the immune response (immune paralysis).

Answer 9

TRUE.

Question 10

Which immune responses do protein antigens (T-dep antigens) induce? More specifically, what do these protein antigens stimulate?

Answer 10

A) Protein antigens (T-dep antigens) will induce BOTH humoral and cell-mediated immune responses.

B) Proteins will stimulate isotype switching, affinity maturation, and the generation of memory B cells.

Question 11

The immune response will mostly use which antibodies in response to non-protein antigens (T-ind antigens).

Answer 11

The immune response to T-ind antigens consists largely of IgM antibodies.

Question 12

What cells will endocytose protein antigens administered subcutaneously (SC), or, intradermally (ID) and carry them to regional lymph nodes where immune responses are initiated?

Answer 12

Langerhans cells.

Question 13

T or F?

Antigen given intravenously (IV), or, orally will never cause tolerance.

Answer 13

FALSE.

Antigen given IV, or, orally may cause tolerance; possibly due to the rapid elimination of the antigen.

Question 14

Antibody exerts feedback _______ (stimulation/inhibition?) on its own further production.

Answer 14

Inhibition.

Question 15

T or F?

If an animal is immunized with a specific antigen and is injected with preformed antibody to that same antigen just before or within 5 days after antigen priming, the immune response to the antigen is increased up to 100-fold.

Answer 15

FALSE.

If an animal is immunized with a specific antigen and is injected with preformed antibody to that same antigen just before or within 5 days after antigen priming, the immune response to the antigen is REDUCED up to 100-fold.

Question 16

How does antibody exert negative feedback on its own further production?

Answer 16

Antibodies will help eliminate the antigens they were produced against, thereby removing the initiating stimulus for antigen-reactive B cell clonal expansion.

Question 17

T or F?

Circulating antigen-antibody complexes (immune complexes) can either enhance or suppress specific immune responses.

Answer 17

TRUE.

Question 18

Antigen-antibody complexes can simultaneously bind to BCR (via antigen) and the CD32 (FcyRIIB) via the Fc portion of the antibody (IgG)… What will this result in? How?

Answer 18

INHIBITION; The Fc receptor-associated phosphotase will remove phosphates in the B cell-receptor complex, which will subsequently block B cell receptor signaling –> This blocks naive B cell activation (receptor cross-linking does not appear to affect memory B cells).

Question 19

What kind of cells will “trap” immune complexes, which is crucial for the selection of B cells that express high-affinity BCRs during the process of affinity maturation in antibody responses to T-dep antigens.

Answer 19

Follicular dendritic cells (FDCs via FcyRs).

Question 20

T or F?

FDCs are capable of retaining Ag-Ab complexes for long periods, thereby prolonging and enhancing the antibody response.

Answer 20

TRUE.

Question 21

T cells responding to antigens will proliferate and differentiate into ______ and ______ cells.

Answer 21

Effector and memory cells.

Question 22

What is T cell survival dependent on?

Answer 22

T cell survival is dependent upon antigens, costimulators, and cytokines produced during the immune response.

Question 23

What will survival stimuli for lymphocytes induce the formation of?

Answer 23

Antiapoptotic proteins.

Question 24

T or F?

As the effector response leads to the elimination of the antigen, effector T cells will be exposed to increased survival stimuli.

Answer 24

FALSE.

As the effector response leads to the elimination of the antigen, effector T cells are DEPRIVED OF SURVIVAL STIMULI and thus, will die by apoptosis.

Question 25

Effector T cells have ____ (short/long?) tissue half-lives _____ (days/weeks/months/years?).

Answer 25

Effector T cells have short tissue half-lives (days).

Question 26

What are the only cells that survive following an immune response?

Answer 26

Long-lived, functionally quiescent memory T cells.

Question 27

What is CTLA-4? What does it do? What is it expressed by? What does it bind?

Answer 27

CTLA-4 (cytolytic T lymphocyte-associated protein 4; CD152) is a physiologic terminator of T cell activation that is expressed ONLY BY ACTIVATED T CELLS. It is a high affinity receptor for B7-1 and B7-2 (the same proteins also bind CD28).

Question 28

What happens when CTLA-4 interacts with B7 proteins?

Answer 28

When CTLA-4 interacts with B7 proteins, it sends an inhibitory signal to the T cell.

Question 29

What is the physiologic significance of CD28 in relation to B7 proteins? What is it expressed by/how often?

Answer 29

CD28 is the ACTIVATING RECEPTOR FOR B7 PROTEINS and is constitutively expressed on resting T cells, where it is needed to initiate the immune response.

Question 30

What do mutations in CTLA-4 genes result in?

Answer 30

Mutations in CTLA-4 genes results in uncontrolled T cell proliferation and autoimmunity.

Question 31

What is TGF-B? What does it do?

Answer 31

TGF-B is transforming growth factor-B; a potent inhibitor of T cell and B cell proliferation.

Question 32

What does IL-10, IL-4 and IL-3 inhibit? How? What kind of reactions will these inhibit as a result?

Answer 32

They inhibit macrophage activation.

IL-3 and IL-4 are antagonists of IFN-y, the most potent activator of macrophages; therefore, these cytokines may suppress cell-mediated immunity and delayed hypersensitivity reactions.

Question 33

T or F?

Stress will reduce immune functions of an animal.

Answer 33

TRUE.

Question 34

How does stress reduce immune functions?

Answer 34

Stress will affect the hypothalamus to release corticotropin-releasing factor, which causes the anterior pituitary: to release endorphins+enkephalins; and ACTH, which causes the adrenal glands to release more glucocorticoids…

The endorphins, enkephalins and glucocorticoids will suppress the immune system.

Question 35

How does glucocorticoids affect immune cells?

Answer 35

The glucocorticoids will act directly on immune cells to suppress their activity.

Question 36

T or F?

If stress occurs BEFORE an immune response, antigen will still be able to activate immune cells that have been suppressed by corticosteroids.

Answer 36

FALSE.

If stress occurs BEFORE an immune response, antigen may NOT be able to activate immune cells that have been suppressed by corticosteroids.

Question 37

T or F?

If stress occurs DURING an immune response, the level of corticosteroids may be higher and remain elevated for a longer period of time, resulting in prolonged immune suppression of effector functions.

Answer 37

TRUE.