Classification of Hypersensitivity Reactions.

SAQ: Classification of Hypersensitivity Reactions.
Overactivation of the immune system is known as hypersensitivity. Hypersensitivity has tissue-damaging effects and these are referred to as 'immunopathologic'. Coombs and Gell classified hypersensitivity into four types in 1958, based on the immunologic mechanism underlying the tissue damaging reaction.


COOMBS AND GELL CLASSIFICATION OF HYPERSENSITIVITY



Type of Reaction

Clinical Syndrome
Time Required

Mediators
Type I
(IgE type)
Anaphylaxis
Atopy Minutes IgE, mast cells
Type II
(Cytolitic and cytotoxic) Antibody mediated damage: Thrombocytopenia
Agranulocytosis
Haemolytic Anemia Variable: Hours to days IgG
Complement
Cytotoxic cells
Type III
(Immune complex-mediated) Arthus Reaction
Serum Sickness Variable: Hours to days Immune complexes
Complement
PMN
Type IV
(Delayed hypersensitivity/cell mediated) Tuberculin
Contact dermatitis Hours to days T-lymphocytes
Cytokines
Macrophages (and other non-specific cells)