Hypersensitivity
The Gell and Coombs classification divides hypersensitivity traditionally divides reactions into 4 types:
In recent times a further category has been added:
| Type | Mechanism | Examples |
|---|---|---|
| Type I - Anaphylactic | Antigen reacts with IgE bound to mast cells | • Anaphylaxis • Atopy (e.g. asthma, eczema and hayfever) |
| Type II - Cell bound | IgG or IgM binds to antigen on cell surface | • Autoimmune haemolytic anaemia • ITP • Goodpasture's syndrome • Pernicious anaemia • Acute haemolytic transfusion reactions • Rheumatic fever • Pemphigus vulgaris / bullous pemphigoid |
| Type III - Immune complex | Free antigen and antibody (IgG, IgA) combine | • Serum sickness • Systemic lupus erythematosus • Post-streptococcal glomerulonephritis • Extrinsic allergic alveolitis (especially acute phase) |
| Type IV - Delayed hypersensitivity | T-cell mediated | • Tuberculosis / tuberculin skin reaction • Graft versus host disease • Allergic contact dermatitis • Scabies • Extrinsic allergic alveolitis (especially chronic phase) • Multiple sclerosis • Guillain-Barre syndrome |
In recent times a further category has been added:
| Type | Mechanism | Examples |
|---|---|---|
| Type V | Antibodies that recognise and bind to the cell surface receptors. This either stimulating them or blocking ligand binding | • Graves' disease • Myasthenia gravis |