Type IV hypersensitivity

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Type IV hypersensitivity' is often called delayed type 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.

CD8+ cytotoxic T cells and CD4+ helper T cells recognize antigen in a complex with either type 1 or 2 major histocompatibility complex. The antigen-presenting cells in this case are macrophages which secrete IL-12, which stimulates the proliferation of further CD4+ T cells. CD4+ T cells secrete IL-2 and interferon gamma, further inducing the release of other Type 1 cytokines, thus mediating the immune response. Activated CD8+ T cells destroy target cells on contact while activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.

Some clinical examples:

• Contact dermatitis (poison ivy rash, for example)
• Atopic dermatitis (eczema)
• Temporal arteritis
• Hashimoto's thyroiditis
• Symptoms of leprosy
• Symptoms of tuberculosis
• Mantoux test
• Coeliac disease
• Chronic transplant rejection

v • d • e Pathology: Immune disorders (primarily D80-D89, 273, 279) Immunodeficiency/ primary Antibody/humoral (B) Hypogammaglobulinemia/agammaglobulinemia (X-linked, Transient of infancy) - Dysgammaglobulinemia (IgA, IgG) - Common variable immunodeficiency - WHIM syndrome Cell-mediated (T) DiGeorge syndrome - Nezelof syndrome - Purine nucleoside phosphorylase deficiency Combined (B+T) Severe combined immunodeficiency (Adenosine deaminase deficiency, Omenn syndrome, X-SCID, ZAP70 deficiency) - Bare lymphocyte syndrome - Wiskott-Aldrich syndrome Complement deficiency Angioedema PBD chemotaxis/degranulation (Leukocyte adhesion deficiency, Chédiak-Higashi syndrome, Hyper-IgE syndrome) respiratory burst (Chronic granulomatous disease, Myeloperoxidase deficiency) Other ICF syndrome Immunoproliferative Hypergammaglobulinemia Paraproteinemia (Cryoglobulinemia, Heavy chain disease, POEMS syndrome, Monoclonal gammopathy of undetermined significance) Lymphoproliferative disorders (Sarcoidosis) Hypersensitivity Type I (Allergy) - Type II - Type III (Serum sickness) - Type IV (Contact dermatitis) Autoimmunity/Autoimmune disease See also hematological malignancy and hematology