Hypersensitivities & Allergic Diseases

Question 1

Define hypersensitivity diseases. Why are they undesirable?

Answer 1

Exaggerated immune response directed against innocuous agents.
* Can result in tissue injury
* Can cause various diseases
* Can be fatal

Question 2

4 types of hypersensitivity diseases (Coombs and Gell classification)

Answer 2

1. Type I: immediate hypersensitivity (IgE)
2. Type II: antibody-dependent cell-mediated cytotoxicity (IgG, IgM)
3. Type III: Immune complex-mediated (IgM, IgG)
4. Type IV: Delayed type (T-cell mediated)

Question 3

4 ways through which an allergen can enter the body

Answer 3

1. Skin contact (e.g. latex)
2. Injection (e.g. bee sting)
3. Ingestion (e.g. nuts)
4. Inhalation (e.g. dust, pollen)

Question 4

How can Type II hypersensitivity cause major hemolytic anemia in response to penicillin?

Answer 4

Penicillin binds to the surface of RBCs, so if it is recognized as an antigen, it will result in RBC destruction and major hemolytic anemia.

Question 4

2 reasons that may lead to IgG or IgM targeting intrinsic antigens

Answer 4

Breakdown of immune tolerance: The immune system fails to recognize self-antigens as “self” and starts attacking the body’s own cells.

Cross-reactivity: Foreign antigens resemble self-molecules, leading to the immune system mistakenly targeting the body’s own tissues.

Question 5

Explain by what processes Type II: ADCC will result in deleterious effects

Answer 5

Binding of antibodies to the surface of host cells will eventually lead to their destruction via…
* opsonization (ABs recruit phagocytes)
* complement activation
* NK cell activation
* activation or blockage of important cell receptors

Question 6

One way in which Type II: ADCC can cause pathology is by activating or blocking important cell receptors.
Name one disease as an example of this process and explain.

Answer 6

Myastenia Gravis:
Autoimmune disease which produces auto-antibodies against the acetylcholine receptors. These ABs block the receptor, so ACh can no longer bind. This causes neuromuscular disease and progressive muscle weakness (including respiratory muscles, leading to respiratory failure).

Question 7

What type of hypersensitivity do transfusion reactions fall under?

Answer 7

AB and Rh blood group incompatibilities are a form of Type II hypersensitivity

Question 8

Mast cells express high affinity receptors for IgE called…

Answer 8

FcεR1

Question 9

During degranulation, mast cells release various pro-inflammatory factors. What chemical mediators are released immediately? (3)

Answer 9

Histamine
TNF-alpha
Heparin

Question 10

During degranulation, mast cells release various pro-inflammatory factors. What chemical mediators are released over the span of a few minutes? (3)

Answer 10

Leukotrienes
Prostaglandins
Lipid mediators

Question 11

During degranulation, mast cells release various pro-inflammatory factors. What chemical mediators are released over the span of a few hours? (2)

Answer 11

Cytokines IL-4 and IL-13

Question 12

Why is antihistamine not useful for treating anaphylaxis?

Answer 12

Antihistamine would only block the action of histamine, which is only one of many chemical mediators responsible for the exaggerated immune response.

Question 13

Epinephrine stimulates 3 receptors…

Answer 13

1. α1 adrenergic receptor
2. β1 adrenergic receptor
3. β2 adrenergic receptor

Question 14

Stimulation of α1 adrenergic receptor by epinephrine results in: (3)

Answer 14

1. Vasoconstriction (increased peripheral vascular resistance)
2. Reduced angioedema
3. Improved coronary perfusion

Question 15

Stimulation of β1 adrenergic receptor by epinephrine results in: (2)

Answer 15

1. Increased chronotropic effect (increased heart rate)
2. Increased inotropic effect (increased heart contractility)

Question 16

Stimulation of β2 adrenergic receptor by epinephrine results in:

Answer 16

1. Bronchodilation
2. Decreased release of inflammatory mediators from mast cells and basophils

Question 17

What is mastocytosis?

Question 18

Eosinophils fight infectious agents and damage tissues though the release of toxic granule proteins such as… (3)

Answer 18

1. major basic protein
2. eosinophil-derived neurotoxin
3. eosinophil cationic protein

Question 19

How do eosinophils fight viruses?

Answer 19

Via RNAses contained in their granules

Question 20

How do eosinophils fight bacteria?

Answer 20

By released mitochondrial DNA sticky networks to capture bacteria