Hypersensitivity

Question 1

Describe the type of hypersensitive reaction that occurs with Farmer’s Lung.

Answer 1

Type III hypersensitivity involves an immune complex and arthus reaction.

Question 2

What are the innate system mediators for Type III hypersensitivity?

Answer 2

Complement and neutrophils are the innate system mediators for Type III.

Question 3

What immunoglobulin (Ig) is the adaptive system mediator for Type III hypersensitivity?

Answer 3

IgG is the adaptive mediator for Type III hypersensitivity.

Question 4

A college student notices that the skin under her favorite ring is red, scaling and itchy. Taking off the ring for the next few weeks relieves the condition, but when it’s worn again for a few days, the itchiness returns. What type of hypersensitivity reaction is this?

Answer 4

Type IV hypersensitivity triggered by contact dermatitis from metal of the ring. This is a delayed type of response (24-72 hours) that involves T-cells, macrophages and neutrophils.

Question 5

A patient comes to the hospital to receive an injection of peniccillin. Within 15 minutes, his skin develops raised, pruritic white wheals on a red, swollen base over most of his body. What type of hypersensitivity is this?

Answer 5

Type I hypersensitivity triggered by an antigen which is the antibiotic. This is a systemic anaphylactic reaction that involves IgE (adaptive), mast cells and neutrophils (innate mediators).

Question 6

The recipient of a kidney transplant experiences a fever, tenderness over the site of the transplant and decreased urine output (indicative of kidney dysfunction). What type of hypersensitivity is occurring here?

Answer 6

Type IV hypersensitivity occurs with an organ transplant rejection. This involves T-cells, macrophages and neutrophils.

Question 7

A farmer notices chills, fever and SOB when he works in his barn, especially when he is moving hay bales. He doesn’t experience these issues on the days he’s off the barn. Which type of reaction is this and what’s the hypersensitivity associated?

Answer 7

Farmer’s lung is an immune-complex condition triggered by the allergens or fungal spores from work in agriculture. This is part of Type III hypersensitivity that involves IgG, complement and neutrophils.

Question 8

A patient who has a bad reaction from a blood transfusion experiences chills, fever and light-headedness. The next day, the patient has back pain and passes dark urine. Which type of reaction is this?

Answer 8

Antigen-antibody reaction (IgG and IgM) from Type II Cytotoxic hypersensitivity from the blood transfusion. The dark urine is indicative of extravascular hemolysis (from incompatible blood). This process involves IgG, complement and phagocytes.

Question 9

What is the onset (time from event to symptom presentation) for each of the hypersensitivities (1-4)?

Answer 9

1. 2-30 minutes
2. 5-8 hours
3. 4-12 hours
4. 24-72 hours

Question 10

Describe what occurs in an Arthus reaction.

Answer 10

An intra-dermal injection can result in a wheal and flare symptom within 1-12 hours after the event. This is a type III hypersensitivity reaction.

Question 11

Describe the purpose of the radioallergosorbent test (RAST).

Answer 11

RAST is used to detect pre-formed IgE levels in serum. The process involves allergens being coupled to beads, serum being added to said beads and labeled anti-IgE being added thereafter. The radio-label present can quantify the amount of IgE.

Question 12

Describe what occurs in a “wheal and flare” reaction.

Answer 12

An insect bite or allergy skin test can trigger local edema (wheal) and vasodilation (flare).

Question 13

What is the purpose of desensitization when it comes to relieving chronic allergies?

Answer 13

Desensitization involves micro-dosing the allergen into a person with allergies. The small amount of antigen applied over time will decrease TH2 and induce T-regs to secrete IL-10. This will inhibit IgE and suppress mast cells/ inflammation.

Question 14

What innate system mediators work in Type II hypersensitivity?

Answer 14

Complement and phagocytes (such as NK cells, monocytes and eosinophils) play a major role in Type II hypersensitivity.

Question 15

Which hypersensitivity condition results in necrosis and lodging of immunoglobulins at filtering organs?

Answer 15

Type III hypersensitivity is immune-complex mediated (IgG) and involves antibodies making complexes to clear out antigens in the blood or affected organs. Type III reaction also binds complement.

Question 16

For type IV hypersensitivity, what is the antibody and what are the effector cells involved?

Answer 16

Type IV hypersensitivity does not involve an antibody and includes CTL, Th1 and macrophages as effector cells.

Question 17

Which Type Hypersensitivity Reaction activates complement? What antibodies are involved and what effector cells are recruited?

Answer 17

Type II cytotoxic (ADCC) reaction activates complement. IgG and IgM are the autoantibodies made. This calls upon NK cells, eosinophils, neutrophils and macrophages as effector cells.

Question 18

What types of cells are expected to be at a site of infection that appears 48 hours later? What type of Hypersensitivity is this?

Answer 18

Type IV (DTH) is mediated by TH1 cells, so T-lymphocytes would be expected at a site of infection that manifests 48 hours later.

Question 19

Desensitization by a series of injections is less effective for ragweed allergic rhinitis than for bee sting allergy because… Why?

Answer 19

…the blocking antibody is less likely to bind the allergen in ragweed allergic rhinitis, compared to bee sting allergy. Bee venom must travel via the blood from the site of the sting to the target tissue and combines with serum IgG blocking antibody in the blood. Whereas, ragweed allergen can get to mast cells in the nasal mucosa with less exposure to IgG blocking antibody.

Question 20

What is the blocking antibody? How does it work?

Answer 20

The blocking antibody is IgG which binds the allergen to prevent it from causing an allergic reaction.

Question 21

What is the treatment of choice in severe, allergic respiratory distress? Why?

Answer 21

Epinephrine is the mainstay for anaphylaxis!! Remember this! This blocks severe bronchoconstriction and can be life-saving.

Question 22

Describe the events that initiates degranulation from mast cells.

Answer 22

2 IgE molecules close to each other on the surface of the mast cell must bind the same antigen to perturb the cell to initiate degranulation.

Question 23

What is the function of Cromolyn sodium as a drug for allergies?

Answer 23

Cromolyn sodium stabilizes the mast cell membrane and therefore makes it more difficult for degranulation to occur.