Einfluss einer Helminthen-Infektion auf die allergische Sensibilisierung und das IgE-Repertoire im murinen Asthma-Modell

Twenty years ago the hygiene hypothesis was introduced identifying pathogenic helminths as potential protectors against allergic disease. Epidemiologic studies showed an inverse relationship between helminth infection and the prevalence of allergic disease such as allergic bronchial asthma. During the last few years the intention was to identify key players responsible for immunomodulation and antiallergic potential during helminth infection. The immune response induced by chronic helminth infection has been proposed as alternative TH2-response which is characterized by high systemic levels of IgE antibodies yet without pathology and symptoms (Yazdanbakhsh et al., 2002). This “helminth paradoxon” (Smits et al., 2010) remains to be solved. Especially the role of IgE is uncertain. For this reason BALB/c mice were infected with L3 larvae of the nematode L.sigmodontis by bite of the natural vector O. barcoti. The phenotype of infected mice was then being investigated in a well established model of acute allergic airway inflammation. The first question was whether infection with L. sigmodontis would protect against allergic asthma. Secondly the effect of infection on the process of allergic sensitization and the character of the IgE repertoire was to be determined. This study is the first to describe the IgE repertoire of helminth infected animals in a murine model of allergic asthma. For this reason splenic RNA was extracted, transcribed and amplified using RT-PCR for a defined area of murine IgE including the variable region of the H-chain. The amplification product was further ligated into a plasmid which was transferred to fully competent E. coli cells and being cloned later on. The monoclonal IgE amplificats were sequenced by a commercial provider and analyzed by an established algorithm. Furthermore serum antibody levels were measured by means of ELISA, splenic b cells were counted and characterized by means of FACS and allergic influx of eosinophils was measured by automatic cell counting and microscopic differentiation of BALF. Non-infected animals showed a strong influx of eosinophils indicating allergic airway inflammation. L. sigmodontis infection however – as predicted by the hygiene hypothesis – protected against airway inflammation. These animals showed a much stronger TH2 response than non-infected OVA-sensitized animals. The immune response to OVA was overshadowed by helminth infection. The IgE repertoire of infected animals differed with respect to CDR-H3 composition, longer CDR-H3, enhanced use of extended CDR-H3 base structures and higher variability. There were also higher rates of somatic mutation and signs of antigen selection indicating an oligoclonal immune response driven by classic affinity maturation. One can conclude that an infection with L. sigmodontis protected against allergic asthma in this specific mouse model influencing the IgE repertoire in structure and function. The results support the “IgE blocking hypothesis” which postulates that helminth specific IgE antibodies act as competitor for FcɛR1 with allergen specific IgE thereby prohibiting effector cell degranulation.