Figure 3.

The early and late phase of allergic reaction. The key elements for the course of the early phase of an allergic reaction are basophils and mastocytes. These cells express large amounts of FcεRI on their surface that bind IgE molecules through the mediation of their Cε3 domains. In the case interaction of the variable part of IgE with a soluble allergen occurs, as well as the so-called bridging of two adjacent IgE molecules, it is triggered the activation cascade inside the cells via intracellular ITAM domains and tyrosine kinases. Activated basophils and mastocytes then rapidly release large amounts of preformed, biologically highly active mediators, such as histamine, heparin and prostaglandins. This reaction usually lasts about 2–3 h. In addition to above-mentioned early phase of an allergic reaction, mastocytes, basophils and other cells (such as eosinophils) can infiltrate the inflamed tissue and produce a number of other substances (the synthesis of which occurs only after their activation, with their levels increasing within minutes to hours after the insult). These other substances include lipid mediators such as cysteine leukotrienes (CysLT) or prostaglandin D₂ (PgD₂), or large amounts of cytokines (e.g. IL-4, IL-5, IL-13 and IL-9), all contributing to the overall modulating of the immune system towards Th2 reactivity and subsequently to remodelling. The classical late phase of allergic reaction begins within 4–6 hours and lasts 18–24 hours.