1. Type I Hypersensitivity (Allergy and Anaphylaxis

2. 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).

4. Type I Hypersensitivity Chemical mediators of type I Hypersensitivity

5. 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.