The application of phage display in allergy research: characterization of IgE, identification of allergens and development of novel therapeutics

Display of wasp venom allergens on the cell surface of Saccharomyces cerevisiae

BACKGROUND

Yeast surface display is a technique, where the proteins of interest are expressed as fusions with yeast surface proteins and thus remain attached to the yeast cell wall after expression. Our purpose was to study whether allergens expressed on the cell surface of baker's yeast Saccharomyces cerevisiae preserve their native allergenic properties and whether the yeast native surface glycoproteins interfere with IgE binding. We chose to use the major allergens from the common wasp Vespula vulgaris venom: phospholipase A1, hyaluronidase and antigen 5 as the model.

RESULTS

The proteins were expressed on the surface as fusions with a-agglutinin complex protein AGA2. The expression was confirmed by fluorescent cytometry (FACS) after staining the cells with antibody against a C-tag attached to the C-terminal end of the allergens. Phospholipase A1 and hyaluronidase retained their enzymatic activities. Phospholipase A1 severely inhibited the growth of the yeast cells. Antigen 5 - expressing yeast cells bound IgE antibodies from wasp venom allergic patient sera but not from control sera as demonstrated by FACS. Moreover, antigen 5 - expressing yeast cells were capable of mediating allergen-specific histamine release from human basophils.

CONCLUSIONS

All the three major wasp venom allergens were expressed on the yeast surface. A high-level expression, which was observed only for antigen 5, was needed for detection of IgE binding by FACS and for induction of histamine release. The non-modified S. cerevisiae cells did not cause any unspecific reaction in FACS or histamine release assay despite the expression of high-mannose oligosaccharides.In perspective the yeast surface display may be used for allergen discovery from cDNA libraries and possibly for sublingual immunotherapy as the cells can serve as good adjuvant and can be produced in large amounts at a low price.

Analysis of B-cell epitopes from the allergen Hev b 6.02 revealed by using blocking antibodies

Hev b 6.02 (hevein), identified as a major allergen from natural rubber latex (NRL), is involved in the latex-fruit syndrome and also acts as a pathogenesis defense-related protein. Its 3D structure has been solved at high resolution, and its linear epitopes have already been reported. However, information about conformational epitopes is still controversial, even though it is relevant for an accurate diagnosis and treatment, as well as for the study of allergen-antibody molecular interactions. We sought to analyze the B-cell epitopes of Hev b 6.02 at a molecular and structural level, using specific recombinant antibodies. We obtained a murine monoclonal antibody (mAb 6E7) and three human single chain fragments (scFvs A6, H8, and G7) anti-Hev b 6.02 that were able to compete for hevein binding with serum IgEs from latex allergic patients. In vitro assays showed that the mAb 6E7 and scFv H8 recognized the area of Hev b 6.02 where the aromatic residues are exposed; while the scFv G7 defined the amino and carboxy-terminal regions that lie close to each other, as a different epitope. The structural modeling of the Hev b 6.02-scFv H8 and Hev b 6.02-scFv G7 complexes revealed the putative regions of two conformational epitopes. In one of these, the aromatic residues, as well as polar side chains are important for the interaction, suggesting that they are part of a dominant conformational epitope also presented on the Hev b 6.02-IgE interactions. Antibodies recognizing this important allergen have potential to be used to diagnose and ultimately treat latex allergy.

Genomic analysis of allergen genes inAspergillusspp.: the relevance of genomics to everyday research

Full genomic sequencing of Aspergillus fumigatus and other genomes has allowed correction of Aspergillus allergen gene sequences and requires revision of Genbank and IUIS sequences of allergens. In addition allergens in other fungal species may be found in the aspergilli. We compared the published sequences of numerous allergens with recently available genome sequences. This analysis suggests that Aspf 56KD, Asp f 15 and Asp f 16 should be removed from the approved allergen list and that Asp f 17 is a larger protein than published. Additionally we propose likely gene candidates for Asp f GST (Afu6g09690) and Asp o lipase (AO090701000644). We suggest that the heat shock allergens should be re-classified: Asp f 12 should be classified as HSP90 (Asp f 12), HSP88 (Mala s 10) and HSP70 (Alt a 3, Cla h 4 and Pen c 19) according to human gene nomenclature. Comparison of fungal allergen databases with genome sequences suggests the presence of a core set of allergen - like proteins in all fungi. We also analysed allergens in the 3 sequenced aspergilli to look for internal homologies and this suggests that multi gene families may produce numerous cross-reactive allergens.

Exploiting the avian immunoglobulin system to simplify the generation of recombinant antibodies to allergenic proteins

BACKGROUND

Monoclonal antibodies are a valuable tool in the study of allergens, but the technology used in their generation can be slow and labour-intensive. Therefore, we have examined recombinant antibody development by phage-display against single allergens and protein mixtures.

OBJECTIVE

We used the avian immunoglobulin system (generated from single V(H) and V(L) genes) to provide a rapid method for generating highly specific recombinant antibody fragments from a minimal number of animals.

METHODS

A single-chain antibody fragment (scFv) library was generated from a single chicken immunized with model allergens. ScFvs were isolated by phage-display and their properties investigated by ELISA and Western blot.

RESULTS

Mono-specific scFvs were generated against recombinant Fel d 1 and native Amb a 1. Pannings against yellow jacket venom extracts only yielded clones that reacted with multiple proteins in the venom extract. The scFvs from each panning type were effectively expressed in Escherichia coli and readily purified. Highly specific and sensitive recognition of Fel d 1 and Amb a 1 was demonstrated in ELISA, with scFvs displaying antibody-concentration-dependent absorbance curves down to picogram levels of antibody. The specificity of selected antibodies for their cognate antigen was further confirmed in Western blot analysis, with scFvs directed to either Fel d 1 or Amb a 1 showing no reactivity for the other antigens used in immunization. Anti-Amb a 1 scFvs also mapped Amb a 1-isoform location in Western blot of ragweed extracts separated by 2D SDS-PAGE. DNA sequence analysis of scFvs showed that multiple different clones had been generated against Fel d 1 and Amb a 1. Using two anti-Fel d 1 scFv for ELISA analysis of Fel d 1 content in crude cat pelt extracts, we could produce data which were highly similar (P=0.33 and 0.89 by paired t-test analysis) to those obtained using conventional assays (radial immunodiffusion).

CONCLUSION

Phage-display technology may generate multiple allergen-specific recombinant antibody fragments from a single chicken, to allergens from mammalian, plant and insect sources. The resulting antibody fragments are of demonstrable use in allergen identification and quantification, in comparison with standard immunoassays.

Designing scaffolds of peptides for phage display libraries

Phage display is a powerful method for the discovery of peptide ligands that are used for analytical tools, drug discovery, and target validations. Phage display technology can produce a huge number of peptides and generate novel peptide ligands. Recently, phage display technology has successfully managed to create peptide ligands that bind to pharmaceutically difficult targets such as the erythropoietin receptor. As a result of the structural analysis of their ligands, we found that the conformational design of peptides in library is important for selecting high-affinity ligands that bind to every target from a phage peptide library. Key issues concern constraints on the conformation of peptides on the phage and the development of chemically synthesized peptides derived from peptides on phage. This review discusses studies related to the conformation of peptides selected from phage display peptide libraries in addition to the conversion from peptides to non-peptides.