Type I hypersensitivity

Hypersensitivity

Also known as immediate hypersensitivity or allergy

 

Examples 

• Allergic rhinitis 
• Allergic sinusitis
• Anaphylaxis
• Asthma 
• Atopy
• Eosinophilic granulomatosis with polyangiitis (Churg-Strauss Syndrome)  
• Food allergies

Mechanism

1. Immunoglobulin E (IgE) molecules bind to an antigen called an allergen. 
2. IgE molecules on the surface of mast cells and basophils become cross-linked by allergens. 
3. Mast cells and basophils degranulate, releasing various vasodilators such as histamine and inflammatory mediators such as prostaglandins. 
4. Local blood vessels dilate and become more permeable. 
5. Fluid leaves the circulation into the tissue spaces. The tissues swell.