Delayed hypersensitivity or Type IV reactions (Table 11) are T-cell-mediated, i.e., specifically sensitised CD4+ T-lymphocytes initiate the reactions. Sensitisation develops slowly requiring repeated exposures to a specific allergen. Once sensitised, upon reexposure immunologically committed lymphocytes react with the allergen (antigen) and damage tissue by direct toxic effects or through the release of cytokines, which activate eosinophils, monocytes, neutrophils, and macrophages and killer cells.
Table 11. Delayed Hypersensitivity Reaction.
|Signs and symptoms:
| Nota bene: