Type I hypersensitivity

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Type I hypersensitivity is an allergic reaction provoked by reexposure to a specific type of antigen referred to as an allergen.^[1] Exposure may be by ingestion, inhalation, injection, or direct contact. The difference between a normal immune response and a type I hypersensitive response is that plasma cells secrete IgE. This class of antibodies binds to Fc receptors on the surface of tissue mast cells and blood basophils. Mast cells and basophils coated by IgE are "sensitized." Later exposure to the same allergen, cross-links the bound IgE on sensitized cells resulting in degranulation and the secretion of pharmacologically active mediators such as histamine, leukotriene, and prostaglandin that act on the surrounding tissues. The principal effects of these products are vasodilation and smooth-muscle contraction.

The reaction may be either local or systemic. Symptoms vary from mild irritation to sudden death from anaphylactic shock. Treatment usually involves epinephrine, antihistamines, and corticosteroids. If the entire body gets involved, then anaphylaxis can take place; an acute, systemic reaction that can prove fatal.

Some examples:

• Allergic asthma
• Allergic conjunctivitis
• Allergic rhinitis ("hay fever")
• Anaphylaxis
• Angioedema
• Urticaria (hives)
• Eosinophilia
• Penicillin
• Cephalosporin

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