Allergy diagnosis based on purified allergen molecules provides detailed information regarding the individual sensitization profile of allergic patients, allows monitoring of the development of allergic disease and of the effect of therapies on the immune response to individual allergen molecules. Allergen microarrays contain a large variety of allergen molecules and thus allow the simultaneous detection of allergic patients' antibody reactivity profiles towards each of the MeDALL is a European research program in which allergen microarray technology is used for the monitoring of the development of allergic disease in childhood, to draw a geographic map of the recognition of clinically relevant allergens in different populations and to establish reactivity profiles which are associated with and predict certain disease manifestations. We describe technical advances of the MeDALL allergen-chip regarding specificity, sensitivity and its ability to deliver test results which are close to in vivo reactivity. In addition, the usefulness and numerous advantages of allergen microarrays for allergy research, refined allergy diagnosis, monitoring of disease, of the effects of therapies, for improving the prescription of specific immunotherapy and for prevention are discussed. Europe PMC Funders Group

We report the three-dimensional structure of the complex between the major respiratory grass pollen allergen Phl p 2 and its specific human IgE-derived Fab. The Phl p 2-specific human IgE Fab has been isolated from a combinatorial library constructed from lymphocytes of a pollen allergic patient. When the variable domains of the IgE Fab were grafted onto human IgG1, the resulting Ab (huMab2) inhibited strongly the binding of allergic patients’ IgE to Phl p 2 as well as allergen-induced basophil degranulation. Analysis of the binding of the allergen to the Ab by surface plasmon resonance yielded a very low dissociation constant (KD = 1.1 × 10−10 M), which is similar to that between IgE and Fcε;RI. The structure of the Phl p 2/IgE Fab complex was determined by x-ray crystallography to 1.9 Å resolution revealing a conformational epitope (876 Å2) comprised of the planar surface of the four-stranded anti-parallel β-sheet of Phl p 2. The IgE-defined dominant epitope is discontinuous and formed by 21 residues located mostly within the β strands. Of the 21 residues, 9 interact directly with 5 of the 6 CDRs (L1, L3, H1, H2, H3) of the IgE Fab predominantly by hydrogen bonding and van der Waals interactions. Our results indicate that IgE Abs recognize conformational epitopes with high affinity and provide a structural basis for the highly efficient effector cell activation by allergen/IgE immune complexes.

Formation of IgE antibodies against per se harmless antigens (i.e. allergens) is the hallmark and key pathomechanism of type I allergy, a hypersensitivity disease affecting more than 25% of the population. Classical experiments performed more than 65 years ago demonstrated that allergen-specific IgG antibodies, termed blocking antibodies, can antagonize the cascade of allergic inflammation resulting from allergen recognition by IgE antibodies. However, controversial results have questioned the protective role of IgG antibodies in allergic diseases. Here, we review recent data demonstrating that blocking antibodies inhibit allergen-induced release of inflammatory mediators from basophils and mast cells as well as IgE-facilitated allergen presentation to T cells, thus leading to suppression of T cell activation. Furthermore, it has been reported that the development of blocking antibodies is associated with reduced boosts of allergen-specific IgE production in patients receiving allergen-specific immunotherapy. These findings suggest that blocking antibodies have protective activity by inhibiting immediate as well as late inflammatory responses and long-term ameliorating activity on the allergic immune response by antagonizing the underlying IgE production. Induction of blocking antibodies is thus an important mechanism underlying allergen-specific immunotherapy. In addition, passive administration of blocking antibodies may be considered as a potential therapeutic strategy for allergic diseases.

Timothy grass pollen extracts from different manufacturers exhibit a considerable heterogeneity regarding the presence of individual allergens and hence yield varying in vivo test results. Problems related to the use of natural grass pollen allergen extracts may be circumvented by using defined recombinant grass pollen allergens.