Charakterisierung Hymenopterengift-spezifischer Antikörper mit dem EliFAB Assay

Stings by insects of the order Hymenoptera represent a common and often underestimated event in every day life. Epidemiological studies reveal that 0,3-3,4 % of people being stung by Hymenoptera develop a systemic reaction and thereby a potentially lifethreatening incident. In case of the diagnosis of a Hymenoptera venom allergy the allergen-specific immunotherapy (AIT) offers a safe and effective treatment. While numerous studies have proven the success of this therapy, underlying immunological mechanisms are not yet completely understood. The importance of understanding these mechanisms becomes evident since no parameter exists to measure the efficacy of AIT so far. At this point IgG antibodies and its subclass IgG4 have gained high attention. Concentrations of these so-called blocking antibodies rise during therapy and are considered as indicators of an effective treatment. In theory, allergen-specific IgG antibodies compete with mast cell-bound IgE antibodies for binding allergen and thus inhibit the activation of effector cells. Nevertheless, studies could not show a correlation between allergenspecific IgG antibody concentrations and clinical success of AIT. Of more clinical relevance are methods which detect qualitative changes of the blocking effect of these antibodies. Studies on pollen-allergic patients show a significant higher correlation between clinical improvement and the results of measuring blocking activity. These data were obtained using the so-called IgE facilitated antigen binding assay which determines the influence of blocking antibodies on the binding of allergen- IgE-complexes by B cells. Recently, a cell-free modification of this assay was published. The so-called enzyme-linked immunosorbent facilitated antigen binding (EliFAB) assay is based on the ELISA method and therefore less expensive, time-consuming and prone to errors. In this study the assay was established for the most frequent major allergens of bee and wasp venom in order to assess the blocking effects of IgG antibodies induced during AIT. Subsequently, serum samples could be measured which had been drawn within the ultra-rush initiation phase of AIT with Hymenoptera venom. Furthermore, blocking activity in patients sera was quantified before, under and up to 12 years after the end of therapy. These data could be compared to the results of sting challenges during therapy and field stings after finishing AIT. Within the initiation phase blocking activity rose in parallel to the concentration of IgG4 antibodies and was observed earliest after 8 days. All patients tolerated a sting challenge during therapy accompanied by an increase of blocking activity in nearly all sera. These data imply a high correlation of clinical success of AIT and blocking activity in patients‘ sera. Future studies need to focus on the question whether the detection of blocking activity during therapy may replace a sting challenge. In contrast to the observations under therapy serum samples taken from patients an average of nine years after AIT did not show an increased blocking activity. Even though the median blocking activity was still higher than in untreated patients, no statistical significant change could be observed. In contrast clinical studies collecting data on field stings up to 12 years after the end of therapy reveal a high protection against a systemic reaction of more than 80 %. Thus, for the majority of the patients the expression of blocking activity seems to be an important, but not an indispensable immunological mechanism of prolonged tolerance to stings. However, those clinical data reveal that individual patients loose the therapy-induced protection shortly after the end of AIT. Since the continuation of AIT is associated with long-lasting clinical efficacy and moreover the elongation of injection intervals for probably up to six months shows an equal safety and efficacy, the concept of booster injections in terms of a prolonged maintenance therapy for high-risk patients should be brought back into discussion. Besides known risk factors the assessment of serum blocking activity could represent a tool for the identification of those patients.