Gell and Coombs classification of hypersensitivity reactions
| Type | Hypersensitivity reaction | Immune mechanism | Description |
|---|---|---|---|
| I | Immediate hypersensitivity | Immunoglobulin E–mediated reaction driven by immunoglobulin E bound to mast cells or basophils or both | Engagement of immunoglobulin E with its appropriate antigen leads to degranulation and release of histamine, leukotrienes, and other inflammatory mediators (eg, anaphylaxis) |
| II | Cytotoxic antibody | Antigen-antibody interaction | Local production of anaphylatoxin (C5a) and recruitment of polymorphonuclear leukocytes lead to release of hydrolytic neutrophil enzymes and subsequent tissue injury (eg, immune cytopenia) |
| III | Immune complex | Immunoglobulin G and M antibodies bind to antigen | Antigen-antibody complexes deposit in the glomerular basement membrane, pulmonary basement membrane, or both, leading to tissue injury and organ damage (eg, serum sickness reaction) |
| IV | Delayed hypersensitivity | Cell-mediated immune response | T cells are activated by an antigen-presenting cell; when antigen is presented again, memory T cells activate leukocytes (macrophages, neutrophils, eosinophils), leading to an inflammatory response with possible tissue injury via reactive oxygen species, lysosomal enzymes, and inflammatory cytokines (eg, tuberculin skin test, Rhus dermatitis, Stevens-Johnson syndrome or toxic epidermal necrolysis) |