Hypersensitivity Disease

Question 1

What kind of response is a type I hypersensitivity reaction?
What can it be triggered by ?

Answer 1

IgE mediated antibody response to external antigen

- triggered by allergens like pollen, dust, latex, bee/wasp venom

Question 2

How does an allergic encounter become more amplified for the second encounter?

Answer 2

After the first encounter IgE will bind to the mast cell using the Fc receptor so when the second attack comes the allergen binds to the bound IgE molecule to cause calcium influx causing release of the mast cells vasoactive mediators e.g histamine and leukotrienes

Question 3

What is the treatment for type I hypersensitivity reactions?

Answer 3

• avoidance of allergen
• block mast cell activation by using a sodium cromoglycate which acts on the H1 receptor of a mast cell
• anti-inflammatory agent (corticosteroid like predinisolone)

Question 4

How does an allergic reaction present?

Answer 4

Tissue swelling
Low blood pressure
Rash
Dysphagia
Abdominal pain
Vomiting
Wheeze
Stridor
Itchiness

Question 5

What kind of response is a type II hypersensitivity reaction?
What can it activate/cause?

Answer 5

Direct killing of an antigen through antibodies binding to the antigen’s cell membrane.

Can result in the activation of the complement system causing cell lysis, chemotaxis, opsonisation.

Question 6

What are two clinical example of type II hypersensitivity reaction?

What does it present as? What is treatment?

Answer 6

Acute haemolytic transfusion reaction (blood transfusion)- presenting as tachycardia, increased resp rate, kidney failure

Drug induced haemolysis- commonly occuring with penicillin as it binds with rbcs to mimic a pathogen causing the immune response to be stimulated. Presenting as lower back pain (spleen working hard), decreased BP, increased resp rate. Treated with plasmapheresis or immunosuppression.

Question 7

What kind of response is a type III hypersensitivity reaction?
What is a clinical example of this?
What does it present as/ how can it be treated?

Answer 7

Immune complex mediated where the antigen invading is in excess so antibodies bind with it and to vessel walls and then stimulate neutrophil to degranulate

• occurs in hypersensitivity pneumonitis
• presents as rashes, wheeze (due to bronchoconstriction), breathlessness (due to alveolities), malaise/pyrexia (result of inflammation)
• treated with corticosteroids (decreased inflammation), immunosuppresents (decrease antibody production)

Question 8

What kind of response is a type IV hypersensitivity reaction?
What cells are involved?
Give a clinical examples of the two types

If response cant clear an antigen waht occurs?

Answer 8

Driven by CD4t cells

• Th1 cells (activate macrophages by expressing IFNgamma) and memory T cells are involved
• automimmune= type 1 diabetes, psoriasis, and rhymatoid arthritis
• non-autoimmune= TB, sarcoidosis, dermatitis
• granulomas are formed