Type iv reaction

Type IV reaction: Type IV allergy is the most common form of allergy after Type I allergy. Local inflammatory reaction that starts within 24 hours by infiltration of the epidermis with basophilic granulocytes. Effector cells are allergen-specific inflammatory and cytotoxic T cells.

The clinical prototype of the type IV reaction is allergic contact dermatitis. Here, an incipient reaction to allergen contact occurs within 48-72 hours, in which the allergen (contact allergen) penetrates the epidermis. The contact with specific T-cells leads to an alteration of the epidermis by releasing lymphokines. Depending on the lymphocyte population significantly involved, an immunological subdivision of the reactions into classes IVa-IVd has been proposed.

• Type IVa: INF-gamma and/or TNF-alpha secreting CD4+ T-helper cells (Th1-type)
• Type IVb: IL-5 (and IL-4, IL-13) secreting CD4+-T-helper cells (Th2-type) are mainly responsible for the mobilization and activation of eosinophilic granulocytes .
• Type IVc: Perforin- and granzyme-B-producingCD8+ cytotoxic T cells are the essential effector cells of many drug reactions. Depending on the extent of T-cell activation and the release of perforin and granzyme B, reversible keratinocyte damage of varying degrees(dyskeratosis cell necrosis) occurs
• Type IVd: Indicators are CXCL8 and GM-CSF producing T cells (CXCL8 stands for CXC motif chemokine 8). They are mainly responsible for the recruitment of neutrophilic granulocytes. This mechanism plays a role in acute generalized exanthematic pustulose(AGEP).

1. Biedermann T (2018) Basic principles of allergy and intolerance reactions. In: Braun-Falco`s Dermatology, Venerology Allergology G. Plewig et al. (Hrsg) Springer Verlag S 450-451