IMMUNOLOGY - Roitt I. - Mir 2000

Chapter 23. Hypersensitivity - Type I

THE ALLERGIC BREAKTHROUGH HYPOTHESIS

The Development of allergy is undoubtedly determined by multiple factors. According to the allergic breakthrough hypothesis, Clinical symptoms of allergy appear only when immunological activity exceeds a certain threshold (Fig. 23.27). This threshold depends on a variety of conditions, including the level of allergen exposure, genetic predisposition, the propensity for IgE production, as well as other factors such as upper respiratory viral infection, the relative participation of Th1/Th2 Cells in the Immune Response, and transient IgA deficiency. Another factor contributing to the allergic breakthrough is the increasing level of environmental pollution.

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Fig. 23.27. Upon allergen exposure, individuals with a low IgE response may develop a transient IgE response that subsequently disappears As a result of regulation by T-Cell suppressive activity and/or Changes in the Th1/Th2 ratio. In high-responder individuals, the IgE response to the allergen is much higher, but overt clinical symptoms appear only at the point of allergic breakthrough. This breakthrough may depend on concomitant factors (X), such as an upper respiratory viral infection, transient IgA deficiency, or reduced T-cell suppressive activity. All these factors enhance the IgE response and trigger the onset of clinical symptoms. In the absence of factor X and upon short-term allergen exposure, clinical symptoms do not always develop even in high IgE responders, whereas prolonged allergen exposure combined with factor X can lead to The Emergence of such symptoms.