Type I Hypersensitivity (Allergy and Anaphylaxis

Type I Hypersensitivity (Allergy and Anaphylaxis)

• IgE-mediated hypersensitivity• Time: 2-30 mins• Mechanism: results from IgE antibodies bound to

mast cells, when these IgE molecules bind their specific antigen (allergen), they are triggered to release vasoactive mediators that in turn affect vascular permeability and smooth muscle contraction in various organs.

• Examples: 1-Local reaction: (e.g., seasonal rhinitis, or hay fever) and asthma)

• 2-Systemic disorder (anaphylaxis).

Type I Hypersensitivity

Chemical mediators of type I Hypersensitivity

Clinical Manifestations of Type I Hypersensitivity

Systemic anaphylaxis results from systemic (parenteral) administration of protein antigens or drugs (e.g., bee venom or penicillin).

• Within minutes of an exposure in a sensitized host, itching, urticaria , skin erythema, followed by bronchoconstriction and Laryngeal edema that cause respiratory obstruction.

• In addition, vomiting, abdominal cramps, and diarrhea.• Without immediate intervention, there may be systemic

vasodilation (anaphylactic shock), and the patient may die within minutes.

Local reactions occur when the antigen is confined to a particular site by the route of exposure, such as

• Skin (contact), causing urticaria & eczema • GIT (ingestion), causing diarrhea in food allergy • Lung (inhalation), causing bronchoconstriction as in asthma

and hay fever.