Pathogenesis and diagnosis of type I allergy

In type I allergy, allergen-specific IgE antibodies are formed upon initial (symptomless) contact. These bind to the surface of mast cells (histamine-rich cells that are present in all mucous membranes). The reaction occurs on second contact within seconds to a few minutes. In the case of allergies, antigens are free/dissolved molecules that are incorrectly viewed as threatening by the immune system. The binding of the antigen (allergen) leads to the activation of the mast cells and basophils and their degranulation through cross-linking of two or more IgE antibodies. Preformed inflammatory mediators such as histamine are immediately released, and later newly synthesized factors such as leukotrienes and prostaglandins are released. While histamine is primarily responsible for the immediate symptoms (watering of the eyes, runny nose, itching, bronchospasm, anaphylaxis), the leukotrienes and prostaglandins initiate the inflammatory reaction and thus the delayed and often chronic symptoms (eczema, asthma, nasal congestion).