Unit 9

Question 1

When the wasps stung Sally, the injection of venom initiated a type I hypersensitivity reaction called anaphylaxis. Which of the following best describes a hypersensitivity reaction?

Answer 1

a reaction that occurs in a sensitized individual resulting in tissue damage rather than immunity;

Sally didn’t realize it, but the stings that she received prior to today were actually sensitizing events.

Her body generated antibodies against wasp venom (because she got stung before), including the antibodies that are going to be involved in mediating the hypersensitivity reaction. When the venom entered her body this time, the antibodies initiated a series of events that are going to result in a harmful, not protective, outcome.

Question 2

What type of reaction is an anaphylactic reaction?

Answer 2

A type I hypersensitivity reaction;

This occurs when the immune system overreacts to a substance (in this case, the wasp venom) that it has been previously sensitized to (she got stung before);

The anaphylactic reaction that Sally is experiencing differs from a normal immune response not only in its outcome but also in some of the specific molecules and mediators that are involved.

Question 3

What mediators are involved in anaphylactic reactions?

IgM
basophils
mast cells
B cells
T cells
IgE

Answer 3

1. basophils
2. mast cells
3. IgE

During anaphylaxis, mast cells, basophils, and IgE molecules initiate a response in the body that has negative effects for the host.

Although all of these are parts of the immune system and are designed to protect the host, in anaphylaxis their activation doesn’t help to protect the host.

Question 4

What can be a side effect of an anaphylactic reaction?

Answer 4

Hives;

This is a multistep reaction resulting from the interaction of the wasp venom and Sally’s immune system.

Question 5

Arrange the following statements in the order that best represents the chronological order of events in generating an anaphylactic reaction:

1. neutrophils and eosinophils move to the site
2. IgE molecules bind to mast cells and basophils
3. degranulation occurs
4. antigen molecules cross link adjacent IgE molecules
5. chemical mediators such as histamine are released
6. capillary permeability and smooth muscle contractions increase

Answer 5

1. IgE molecules bind to mast cells and basophils
2. Antigen molecules cross-link adjacent IgE molecules
3. Degranulation occurs
4. Chemical mediators such as histamine are released
5. Capillary permeability and smooth muscle contractions increase

Question 6

What is Degranulation?

Answer 6

A cellular process that releases granules, which are packets of chemicals, from cells involved in the immune system:

mast cells
basophils
neutrophils
eosinophils
natural killer (NK) cells
and cytotoxic T cells

Question 7

Which of the following is true regarding systemic anaphylactic reactions?
Select all that apply.

Systemic reactions are commonly associated with antigens that are ingested or inhaled.

Systemic reactions always involve the respiratory system.

Systemic reactions can result in a dramatic decrease in blood pressure.

Systemic reactions are commonly associated with injected antigens.

A systemic reaction can be fatal in only a few minutes.

Systemic reactions can be treated only with an injection of epinephrine.

Answer 7

Systemic reactions can result in a dramatic decrease in blood pressure.

Systemic reactions are commonly associated with injected antigens.

A systemic reaction can be fatal in only a few minutes.

The injection of venom into Sally’s body provides a rapid route for distribution throughout her system. The effects can be seen all over her body, hence the appearance of hives.

Sally is lucky that her symptoms are limited to the hives and itching—many cases of systemic anaphylaxis involve significant changes in blood pressure (which can lead to shock) and respiration.

Question 8

Predict which of the following outcomes would result from taking an antihistamine.
Select all that apply.

increased breakdown of the histamine molecule

decreased contraction of respiratory smooth muscles

decreased mucus secretions

decreased permeability of blood vessels

decreased histamine-based stimulation of cells

decreased stimulation of mast cells

Answer 8

1. decreased mucus secretions
2. decreased permeability of blood vessels
3. decreased histamine-based stimulation of cells
4. The antihistamines that Sally took actually work as a receptor antagonist. This means that the antihistamine blocks the ability of histamine to bind to its targets, thereby blocking the cellular effects of histamine.
5. By this action, the physiological impact of histamine should begin to decrease, and Sally’s symptoms should begin to subside.

Question 9

Sally decides to go through the desensitization program recommended by her doctor. What is the overall purpose/goal of this process?

Answer 9

Repeated exposure to wasp venom antigen will increase the amount of IgG produced by Sally’s immune system;

which can block the allergens from interacting with IgE which causes allergy response

Question 10

The IgG molecules that are produced during desensitization function as blocking antibodies. These antibodies are extremely effective in providing protection from a hypersensitivity reaction. Why are blocking IgG antibodies so effective at protecting Sally from another anaphylactic response to wasp venom?

Answer 10

The blocking IgG antibodies “outnumber” the IgE antibodies and bind to wasp venom before the IgE antibodies can bind;

During a desensitization program, Sally will be injected with increasing doses of wasp venom. The goal is to build the level of wasp venom-specific IgG circulating in Sally’s system.

If successful, the next time that Sally is stung by a wasp, the IgG molecules will bind to the venom, thereby preventing (or limiting) the amount of venom antigen that binds to IgE present on mast cells and basophils.