Type I hypersensitivity - Wikipedia, the free encyclopedia Type I hypersensitivity
(Redirected from Type-I hypersensitivity) Type I hypersensitivity (or immediate
) is an allergic reaction
Type I hypersensitivity
provoked by reexposure to a specific type of Classification and external resources antigen referred to as an allergen.[1] Type I isnot to be confused with Type II, Type III, orType IV hypersensitivities.
Exposure may be by ingestion, inhalation,injection, or direct contact.
SEM of miscellaneous plant pollens. Pollens are very ■ 2 Treatment and prognosis■ 3 Examples MeSH D006969
( Pathophysiology
In type 1 hypersensitivity, an antigen is presented to CD4+ Th2 cells specific to the antigen thatstimulate B cell production of IgE antibodies also specific to the antigen. The difference between anormal infectious immune response and a type 1 hypersensitivity response is that in type 1hypersensitivity the antibody is IgE instead of IgA, IgG, or IgM. During sensitization, the IgE antibodiesbind to Fc receptors on the surface of tissue mast cells and blood basophils.[2] Mast cells and basophilscoated by IgE antibodies are "sensitized." Later exposure to the same allergen cross-links the bound IgEon sensitized cells, resulting in degranulation and the secretion of pharmacologically active mediatorssuch as histamine, leukotriene (LTC4 and LTD4), and prostaglandin that act on the surrounding tissues.
The principal effects of these products are vasodilation and smooth-muscle contraction.
Type 1 hypersensitivity can be further classified into an immediate and late-phase reaction. Theimmediate hypersensitivity reaction occurs minutes after exposure and includes release of vasoactiveamines and lipid mediators, whereas the late-phase reaction occurs 2-4 hours after exposure and includesthe release of cytokines. [3] Type I hypersensitivity - Wikipedia, the free encyclopedia Overview of mediators released by mast cells in type 1 hypersensitivity, and their actions:
Vasodilation and increased
■ Prostaglandin D2■ Neutral proteases Smooth muscle spasm
■ Leukotriene C4, D4 and E4■ Prostaglandin ■ Cytokines (e.g. chemokines and TNF■ Leukotriene B4 Leukocyte extravasation
■ Chemotactic factors for neutrophils and Unless otherwise specified, the reference for this table is:[4] The reaction may be either local or systemic. Symptoms vary from mild irritation to sudden death fromanaphylactic shock.
Treatment and prognosis
Treatment usually involves epinephrine, antihistamines, and corticosteroids. If the entire body getsinvolved, then anaphylaxis can take place, which is an acute, systemic reaction that can prove fatal.
■ Allergic asthma■ Allergic conjunctivitis■ Allergic rhinitis ("hay fever")■ Anaphylaxis■ Angioedema■ Urticaria (hives)■ Eosinophilia■ Penicillin allergy■ Cephalosporin allergy■ Food allergy Type I hypersensitivity - Wikipedia, the free encyclopedia References
1. ^ med/1101 ( at eMedicine
2. ^ "The (
Adaptive Immune System: Type I Immediate Hypersensitivity". Retrieved 2008-09-22.
3. ^ Shiv Pillai MD; Abul K. Abbas MBBS; Andrew Wilson PhD (2011). Cellular and Molecular Immunology:
with STUDENT CONSULT Online Access. Philadelphia: Saunders. ISBN 1-4377-1528-1.
4. ^ Table 5-2 in:Mitchell, Richard Sheppard; Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson. Robbins Basic
Pathology. Philadelphia: Saunders. ISBN 1-4160-2973-7. 8th edition.
External links
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