Type I hypersensitivity (or immediate hypersensitivity) is an allergic reaction provoked by reexposure to a specific type of antigen referred to as an allergen. Type I is not to be confused with type II, type III, or type IV hypersensitivities, nor is it to be confused with Type I Diabetes or Type I of any other disease or reaction.
Exposure may be by ingestion, inhalation, injection, or direct contact.
Video Type I hypersensitivity
Pathophysiology
In type 1 hypersensitivity, B-cells are stimulated (by CD4+TH2 cells) to produce IgE antibodies specific to an antigen. The difference between a normal infectious immune response and a type 1 hypersensitivity response is that in type 1 hypersensitivity, the antibody is IgE instead of IgA, IgG, or IgM. During sensitisation, the IgE antibodies bind to Fc?RI receptors on the surface of tissue mast cells and blood basophils. Mast cells and basophils coated by IgE antibodies are "sensitized". Later exposure to the same allergen cross-links the bound IgE on sensitized cells, resulting in anaphylactic degranulation, which is the immediate and explosive release of pharmacologically active pre-formed mediators from storage granules and concurrent synthesis of inflammatory lipid mediators from arachidonic acid; some of these mediators include histamine, leukotriene (LTC4 and LTD4), and prostaglandin, which act on proteins (e.g., G-protein coupled receptors) located on surrounding tissues. The principal effects of these products are vasodilation and smooth-muscle contraction.
Type 1 hypersensitivity can be further classified into immediate and late-phase reactions. The immediate hypersensitivity reaction occurs minutes after exposure and includes release of vasoactive amines and lipid mediators, whereas the late-phase reaction occurs 2-4 hours after exposure and includes the release of cytokines.
The reaction may be either local or systemic. Symptoms vary from mild irritation to sudden death from anaphylactic shock.
Maps Type I hypersensitivity
Treatment and prognosis
Treatment usually involves adrenaline (epinephrine), antihistamines, and corticosteroids.
If the entire body is involved, then anaphylaxis can take place, which is 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
- Sweet itch
See also
- Type V hypersensitivity
References
Source of the article : Wikipedia
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