Hypersensitivity Type 3

Question 1

What is type 3 hypersensitivity?

Answer 1

Immune complex mediated. Where antibodies bind to soluble antigens

Question 2

What is the pathophysiology of type 3 hypersensitivity?

Answer 2

1) In the presence of excess antigen, antibody binds forming small immune complexes which increase in size
2) These become too large to be phagocytosed and get deposited in small blood vessels, joints and glomeruli
3) The complement system is activated and attracts inflammatory cells like neutrophils
4) Neutrophils release enzymes causing damage to cells => more inflammation and chronic inflammatory disease.

Question 3

What are the clinical examples of hypersensitivity type 3 reactions?

Answer 3

Hypersensitivity pneumonitis eg. Farmer’s lung, cheese workers lung etc.

Question 4

Describe how hypersensitivity pneumonitis causes a type 3 reaction?

Answer 4

1) Mould spores and fungal particles are soluble and are inhaled and deposited in the lung
2) Antibody formation => immune complexes =>complement activation

Question 5

What are the symptoms of hypersensitivity pneumonitis?

Answer 5

Wheezing and malaise 4-8 hours after antigen exposure.
May have a dry cough, shortness of breath and pyrexia
Examination often normal

Question 6

How is hypersensitivity pneumonitis managed?

Answer 6

1) Antigen avoidance
2) Corticosteriods to decrease inflammation and production of IgG
3) Immunosupression to decrease antibody production