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The pathomechanism of type I reactions is very complex
The pathomechanism of type I reactions is presented below in a schematically condensed form (Allergopharma graphic).
In IgE-mediated immediate reactions, there is an imbalance between T-helper cell (TH) subpopulations TH1 and TH2 cells with a preponderance of TH2 cells and a simultaneously attenuated TH1 reaction.
These two cell types secrete different cytokines that are important to the course of antibody production and hence to antibody class lineage choice.
Following specific stimulation by an antigen/allergen, TH1 cells release interferon-γ and interleukin-2 (IL-2), which cause B-cells to predominantly produce IgG antibodies.
TH2 cells, on the other hand, produce IL-4 and IL-13, which lead to increased IgE synthesis by B-cells. TH2 cells also secrete IL-5, which has a stimulatory effect on eosinophils. Moreover, recent studies have shown that allergic patients also have a relative deficiency of regulatory T-cells (T-regs) and the cytokines formed by T-regs including TGF-β and IL-10. This may cause suppression of immunomodulatory allergen tolerance induction.
IL-10 induces the synthesis of IgG4, for example, and TGF-β induces the synthesis of IgA. Increased production of IgG4 during high-dose specific immunotherapy (SIT), for example, has been suggested as an immunologic marker of allergen tolerance induction as a result of treatment .
Read more on the next page: "Allergy - Clinical conditions"
 Akdis CA, Akdis M. Mechanisms of allergen-specific immunotherapy. J Allergy Clin Immunol 2011;127:18-27.