- Type I hypersensitivity
Name = Type I hypersensitivity
Caption = SEM of miscellaneous plant pollens. Pollens are very common allergens.
MeshID = D006969
Type I hypersensitivity (or immediate hypersensitivity) is an allergic reaction provoked by reexposure to a specific type of
antigenreferred to as an allergen. [eMedicine|med|1101]
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.cite web |url=http://student.ccbcmd.edu/courses/bio141/lecguide/unit5/hypersensitivity/type1/type1.html |title=The Adaptive Immune System: Type I Immediate Hypersensitivity |format= |work= |accessdate=2008-09-22] 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 degranulationand the secretion of pharmacologically active mediators such as histamine, leukotriene, and prostaglandinthat act on the surrounding tissues. The principal effects of these products are vasodilationand smooth-muscle contraction.
The reaction may be either local or systemic. Symptoms vary from mild irritation to sudden death from anaphylactic shock.
Treatment and prognosis
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.
Allergic rhinitis("hay fever")
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