Grass allergen-specific T-cells of atopic patients

IgE recognition of chimeric isoforms of the honeybee (Apis mellifera) venom allergen Api m 10 evaluated by protein array technology

Api m 10 has recently been established as novel major allergen that is recognized by more than 60% of honeybee venom (HBV) allergic patients. Previous studies suggest Api m 10 protein heterogeneity which may have implications for diagnosis and immunotherapy of HBV allergy. In the present study, RT-PCR revealed the expression of at least nine additional Api m 10 transcript isoforms by the venom glands. Two distinct mechanisms are responsible for the generation of these isoforms: while the previously known variant 2 is produced by an alternative splicing event, novel identified isoforms are intragenic chimeric transcripts. To the best of our knowledge, this is the first report of the identification of chimeric transcripts generated by the honeybee. By a retrospective proteomic analysis we found evidence for the presence of several of these isoforms in the venom proteome. Additionally, we analyzed IgE reactivity to different isoforms by protein array technology using sera from HBV allergic patients, which revealed that IgE recognition of Api m 10 is both isoform- and patient-specific. While it was previously demonstrated that the majority of HBV allergic patients display IgE reactivity to variant 2, our study also shows that some patients lacking IgE antibodies for variant 2 display IgE reactivity to two of the novel identified Api m 10 variants, i.e. variants 3 and 4.

[From the allergen-recognition by antibodies to new therapeutic concepts]

Cross-linking of IgE antibodies through allergens is a basic event in type I allergy and leads to the immediate release of mediators like histamine, responsible for allergic symptoms like rhino-conjunctivitis or asthma. Critical for the binding of allergens to IgE are the IgE-epitopes, which represent a congregation of several amino acid residues often derived from different regions of the allergen. By means of the mimotope-technology, we isolated peptides from phage libraries, which were able to structurally mimic IgE-epitopes of the plant allergens Bet v 1 (birch) and Phl p 5a (timothy grass). Hence, these are candidates for an epitope-specific immunotherapy. In this mode of immunotherapy, it is the aim to induce IgG antibodies directed exclusively against the IgE-epitopes of allergens without induction of anaphylactogenic IgG species, and without the risk of anaphylaxis through cross-linking of IgE. Immunizing mice, we applied the mimotopes displayed on bacteriophages as well as on alternative carrier systems to enhance their antigenicity. With these systems it was possible to elicit an allergen-specific immune response, which was also accompanied by the appropriate T-cell help. Mimotopes resemble a promising concept for an epitope-tailored immunotherapy of allergic patients.