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Type I hypersensitivity
Classification and external resources

SEM of miscellaneous plant pollens. Pollens are very common allergens.
MeSH D006969
Hypersensitivity types
Type I - Allergy (immediate)
Type II - Cytotoxic, antibody-dependent
Type III - Immune complex disease
Type IV - Delayed-type hypersensitivity
(Antibody Independant)
Type V - Autoimmune disease

Type I hypersensitivity (or immediate 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 in the latter plasma cells secrete IgE. This class of antibodies binds to Fc receptors on the surface of tissue mast cells and blood basophils. [2] 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 (LTC4 and LTD4), and prostaglandin that act on the surrounding tissues. The principal effects of these products are vasodilation and smooth-muscle contraction.

Overview of mediators released by mast cells in type 1 hypersensitivity, and their actions:
Vasodilation and increased permeability
Smooth muscle spasm
  • Histamine
  • PAF
  • Leukotriene C4, D4 and E4
  • Prostaglandin
Leukocyte extravasation
Unless else specified in boxes, then ref is: [3]

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.


Some examples:


  1. ^ med/1101 at eMedicine
  2. ^ "The Adaptive Immune System: Type I Immediate Hypersensitivity". Retrieved 2008-09-22.  
  3. ^ 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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