| Type I hypersensitivity | |
|---|---|
| Classification and external resources | |
 SEM of miscellaneous plant pollens. Pollens are very common allergens. |
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| 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 I hypersensitivity (or immediate hypersensitivity) is an allergic reaction provoked by reexposure to a specific type of
Exposure may be by ingestion, inhalation, injection, or direct contact.
Contents |
Pathophysiology
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.
| Vasodilation and increased permeability | ||
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| Smooth muscle spasm |
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| Leukocyte extravasation |
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| 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.
Examples
Some examples:
- Allergic asthma
- Allergic conjunctivitis
- Allergic rhinitis ("hay fever")
- Anaphylaxis
- Angioedema
- Urticaria (hives)
- Eosinophilia
- Penicillin allergy
- Cephalosporin allergy
- Food allergy
References
- ^ med/1101 at eMedicine
- ^ "The Adaptive Immune System: Type I Immediate Hypersensitivity". http://student.ccbcmd.edu/courses/bio141/lecguide/unit5/hypersensitivity/type1/type1.html. Retrieved 2008-09-22.
- ^ 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
- Type I hypersensitivity (Flash Animation)
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