Allergische Soforttypreaktionen und kreuzreaktive Kohlenhydratepitope (CCD)*

[Food sensitivities of the digestive tract-Part 1: Food allergies]

Adverse reactions to food affect approximately one third of the population. They are based on very different mechanisms and are divided into food intolerances, which manifest mainly in the gastrointestinal tract, and food allergies, which can also cause extraintestinal symptoms and have an immunological genesis. The most common food allergies in adults are pollen-associated allergies to cereals or pome and stone fruits, while allergies to peanut, milk and egg are particularly common in children. The diagnostics of food allergies are complex and therapy is primarily based on targeted elimination diets. This advanced education article focuses on food allergies with gastrointestinal symptoms.

[Molecular-allergological aspects of allergen-specific immunotherapy]

Allergen-specific immunotherapy (SIT) does not achieve 100% efficacy, nor is there a reliable marker for therapy failure. However, advances in molecular allergology over the past few years have allowed a significantly improved characterization of the patients using molecular-allergological analysis methods (molecular phenotyping). Thus, major and minor allergens can be identified. In addition, the marker allergens for the severity of an allergic reaction, the pathological and therapeutic predictive marker allergens, and sensitization patterns are identified.

Glycans and glycan-specific IgE in clinical and molecular allergology: Sensitization, diagnostics, and clinical symptoms

Glycan-specific IgE antibodies cross-react with highly similar or even identical carbohydrate structures on a variety of different natural allergens, the so-called cross-reactive carbohydrate determinants (CCDs). In clinical practice CCDs often interfere with the specificity of in vitro allergy diagnostics, thus impairing allergy therapy decisions for individual patients. Strikingly, these IgE antibodies directed against CCDs often do not cause clinically relevant allergy symptoms. On the other hand, the IgE-binding glycan allergen galactose-α-(1,3)-galactose (α-Gal) is associated with IgE-mediated delayed anaphylaxis in meat allergy. The reason for this discrepancy is not known. The discovery of α-Gal stimulated new discussions and investigations regarding the relevance of anti-glycan IgE for allergic diseases. In this review the effect of glycans and glycan-specific IgE on sensitization to allergens and allergy diagnosis is described. Because parasite infections elicit a similar immunologic environment as allergic diseases, the association of glycan-specific antibodies against parasite glycoproteins with glycan structures on allergens is discussed.

Food allergies resulting from immunological cross-reactivity with inhalant allergens: Guidelines from the German Society for Allergology and Clinical Immunology (DGAKI), the German Dermatology Society (DDG), the Association of German Allergologists (AeDA) and the Society for Pediatric Allergology and Environmental Medicine (GPA)

A large proportion of immunoglobulin E (IgE)-mediated food allergies in older children, adolescents and adults are caused by cross-reactive allergenic structures. Primary sensitization is most commonly to inhalant allergens (e.g. Bet v 1, the major birch pollen allergen). IgE can be activated by various cross-reactive allergens and lead to a variety of clinical manifestations. In general, local and mild — in rare cases also severe and systemic — reactions occur directly after consumption of the food containing the cross-reactive allergen (e. g. plant-derived foods containing proteins of the Bet v 1 family). In clinical practice, sensitization to the primary responsible inhalant and/or food allergen can be detected by skin prick tests and/or in vitro detection of specific IgE. Component-based diagnostic methods can support clinical diagnosis. For individual allergens, these methods may be helpful to estimate the risk of systemic reactions. Confirmation of sensitization by oral provocation testing is important particulary in the case of unclear case history. New, as yet unrecognized allergens can also cause cross-reactions.

The therapeutic potential of specific immunotherapy (SIT) with inhalant allergens and their effect on pollen-associated food allergies is currently unclear: results vary and placebo-controlled trials will be necessary in the future. Pollen allergies are very common. Altogether allergic sensitization to pollen and cross-reactive food allergens are very common in our latitudes. The actual relevance has to be assessed on an individual basis using the clinical information.

Cite this as Worm M, Jappe U, Kleine-Tebbe J, Schäfer C, Reese I, Saloga J, Treudler R, Zuberbier T, Wassmann A, Fuchs T, Dölle S, Raithel M, Ballmer-Weber B, Niggemann B, Werfel T. Food allergies resulting from immunological cross-reactivity with inhalant allergens. Allergo J Int 2014; 23: 1–16 DOI 10.1007/s40629-014-0004-6

Inhibition of IgE binding to cross-reactive carbohydrate determinants enhances diagnostic selectivity

Background

Allergy diagnosis by determination of allergen-specific IgE is complicated by clinically irrelevant IgE, of which the most prominent example is IgE against cross-reactive carbohydrate determinants (CCDs) that occur on allergens from plants and insects. Therefore, CCDs cause numerous false-positive results. Inhibition of CCDs has been proposed as a remedy, but has not yet found its way into the routine diagnostic laboratory. We sought to provide a simple and affordable procedure to overcome the CCD problem.

Methods

Serum samples from allergic patients were analysed for allergen-specific IgEs by different commercial tests (from Mediwiss, Phadia and Siemens) with and without a semisynthetic CCD blocker with minimized potential for nonspecific interactions that was prepared from purified bromelain glycopeptides and human serum albumin.

Results

Twenty two per cent of about 6000 serum samples reacted with CCD reporter proteins. The incidence of anti-CCD IgE reached 35% in the teenage group. In patients with anti-CCD IgE, application of the CCD blocker led to a clear reduction in read-out values, often below the threshold level. A much better correlation between laboratory results and anamnesis and skin tests was achieved in many cases. The CCD blocker did not affect test results where CCDs were not involved.

Conclusion

Eliminating the effect of IgEs directed against CCDs by inhibition leads to a significant reduction in false-positive in vitro test results without lowering sensitivity towards relevant sensitizations. Application of the CCD blocker may be worthwhile wherever natural allergen extracts or components are used.