Type I Hypersensitivity: Pathogenesis and clinical findings

Definition: Production of lgE Antibodies that bind to harmless allergens and induce mast cell degranulation, leading to an allergic reaction.

"Sensitization" to Allergen:

Initial exposure to allergen (ex. dust, pollen, foods, drugs) -> Patient's immune system mistakenly recognizes allergen as potentially harmful -> Formation of allergen-specific plasma cells that secrete lgE-antibodies -> Allergen-specific lgE Abs persist in body after clearance of allergen

Second Exposure to Allergen:

Pre-formed lgE binds allergen, creating an allergen-antibody complex -> 

Allergen-antibody complexes bind to mast cells, causing them to "degranulate": release the pro-inflammatory molecules within them (i.e. histamine) into the blood

=> 

 • Increased Vascular permeability

 • Smooth muscle contraction in airways

 • Mucus secretion 

 • Inflammatory cells recruited

Complications:

 • Acute Asthma

 • Antibiotic Allergies (ex. penicillin & cephalosporin)

 • Food Allergies (ex. peanuts)

 • Hay fever (allergic rhinitis to airborne particles like pollen & dust)

 • Urticaria (hives)

 • Allergic conjunctivitis

 • Anaphylaxis



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