Type IV hypersensitivity

Type IV hypersensitivity
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MeSH	D006968
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Type 4 hypersensitivity is often called delayed type hypersensitivity as the reaction takes two to three days to develop. Unlike the other types, it is not antibody mediated but rather is a type of cell-mediated response.

CD4+ helper T cells recognize antigen in a complex with MHC II on the surface of antigen-presenting cells. These can be macrophages that secrete IL-12, which stimulates the proliferation of further CD4+ T_h1 cells. CD4+ T cells secrete IL-2 and interferon gamma, inducing the further release of other T_h1 cytokines, thus mediating the immune response. Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.

oak, nickel)

epidermal necrosis, inflammation, skin rash and blisters

Insulitis, beta cell destruction

neuritis, paralysis

hypothyroidism, hard goiter, follicular thymitis

(Mantoux test)

induration and erythema around injection site indicates previous exposure

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