hypersensitivity and the lung

Question 1

Gell and Coombs classification

Answer 1

• Recognition of foreign antigen can cause collateral tissue damage
• 1960s
• Imperfect classification, but still holds as description of pathology
• Does not hold well for complex immune reactions

Question 2

Type 1

Answer 2

• Antigen interacts with IgE bound to mast cells or basophils
• Degranulation of mediators lead to local effects
• Histamine the predominant mediator
e.g. anaphylaxis to peanuts

Question 3

type 2

Answer 3

• Antibodies reacting with antigenic determinants on the host cell membrane
• Usually igG or IgM
• Outcome depends on whether complement is activated and if metabolism of cell is affected
e.g. anti Glomerular basement membrane disease

Question 4

type 3

Answer 4

• Antigen-immunoglobulin complexes are formed on exposure to the allergen
• These are deposited in tissues and cause local activation of complement and neutrophil attraction
e.g. hypersensitivity pneumonitis

Question 5

type 4

Answer 5

• T-cell mediated, releasing IL2, ILy and other cytokines
• Requires primary sensitisation
• Secondary reaction takes 2-3 days to develop
• May result from normal immune reaction – if macrophages cannot destroy pathogen, they become giant cells and form granuloma
e.g. Sarcoidosis