Structural aspects and clinical relevance of Aspergillus fumigatus antigens/allergens.

Robotics-based high throughput screening of Aspergillus fumigatus cDNA libraries displayed on phage surfaces revealed at last 81 different structures able to bind IgE from serum of patients sensitized to this fungus. Among these, species-specific as well as phylogenetically highly conserved structures and such with unknown function have been detected. A subset of cDNAs have been used to produce and characterize the corresponding recombinant allergens which have proven to be useful diagnostic reagents allowing specific detection of A. fumigatus sensitization and differential diagnosis of allergic bronchopulmonary aspergillosis. Phylogenetically highly conserved structures like manganese-dependent superoxide dismutase, P2 acidic ribosomal protein, cyclophilins and thioredoxins induce, beyond sensitization, IgE antibodies able to cross-react with the corresponding homologous self antigens. These reactions, likely to contribute to the exacerbation and perpetuation of allergic bronchopulmonary aspergillosis, can be traced back to shared conformational B-cell epitopes build up from conserved amino acid residues scattered over the surface of the molecules as shown by detailed analyses of the crystal structures.

Cloning of IgE-binding proteins from Simulium vittatum and their potential significance as allergens for equine insect bite hypersensitivity.

Insect bite hypersensitivity (IBH) is an allergic dermatitis of horses caused by bites of Culicoides and sometimes Simulium spp. The aim of this investigation was to identify Simulium allergens associated with IBH. A phage surface display cDNA library expressing recombinant Simulium vittatum salivary gland proteins was screened using sera of IBH-affected horses sensitized to S. vittatum salivary gland proteins as shown in immunoblot, resulting in the identification of seven cDNAs encoding IgE-binding proteins. The deduced amino acid sequences of these proteins showed sequence similarities to antigen 5 like protein (Sim v 1), to a serine protease inhibitor (Sim v 2), to two alpha-amylases (Sim v 3 and Sim v 4), and to three S. vittatum erythema proteins (SVEPs). The cDNA inserts were subcloned and expressed as [His](6)-tagged protein in Escherichia coli and purified using Ni(2+)-chelate affinity chromatography. Mice were immunised with the seven recombinant proteins and the antibodies tested against the recombinant proteins and salivary gland extract (SGE) of S. vittatum and Culicoides nubeculosus in immunoblot analyses. r-Sim v 1 specific mouse Abs recognized a band of about 32 kDa in immunoblots of both S. vittatum and C. nubeculosus SGE, detectable also by serum IgE of IBH-affected horses. Preincubation of horse serum with r-Sim v 1 completely inhibited IgE binding to the 32 kDa band demonstrating the presence of cross-reactive antigen 5 like proteins in both SGE. Determination of IgE levels against the r-Sim v proteins and crude S. vittatum extract by ELISA in sera from 25 IBH-affected and 20 control horses showed that IBH-affected horses had significantly higher IgE levels than controls against r-Sim v 1, 2, 3, 4 and S. vittatum extract, whereas the r-SVEP showed only marginal IgE binding. Further analyses showed that 60% of IBH-affected horses reacted to r-Sim v 1, suggesting that this could be a major allergen for IBH. Forty to twenty percent of the IBH-affected horses reacted with r-Sim v 2, 3 or 4. Combination of the results obtained with the 4 r-Sim v proteins showed that 92% of the IBH-affected but only 15% of the healthy horses had IgE levels against one or more of the 4 r-Sim v proteins. Seventy percent of the healthy horses had detectable IgE against S. vittatum extract, indicating a low specificity of the detection system used. Optimization of the ELISA system will be required to determine reliable cut-off values for the IBH-related allergens. Their in vivo relevance needs to be carefully assessed.

Screening the allergenic repertoires of wheat and maize with sera from double-blind, placebo-controlled food challenge positive patients.

BACKGROUND: Food allergy to wheat and maize is an increasing factor of deterioration of life quality, especially childhood and can, in rare cases, even induce anaphylaxis. Although omega-5 gliadin from wheat and maize lipid transfer protein have been characterized as major cereal allergens on the molecular level, the list of food allergens is far to be complete. METHODS: To identify the IgE-binding repertoires of wheat and maize we screened respective cDNA libraries displayed on phage surface with sera from patients with a confirmed food allergy. The study included six patients with a positive double-blind, placebo-controlled food challenge (DBPCFC) to wheat, nine patients with a positive DBPCFC to maize, and six patients with anaphylactic reactions after ingestion of wheat. RESULTS: The enriched sequences encoding IgE-binding proteins showed heterogeneous repertoires for both, wheat and maize. The selected wheat repertoire yielded 12, the maize repertoire 11 open reading frames. Among these we identified allergens belonging to already characterized allergens families, such as gliadin, profilin and beta-expansin. Besides, we found novel proteins with high cross-reactive potential, such as thioredoxins, as well as sequences that had so far not been related to cereal allergy at all. The IgE-binding capacity of some selected proteins was evaluated in vitro and cross-reactivity was demonstrated by competition ELISA. CONCLUSION: With regard to the heterogeneity of the characterized sequences as well as to the biochemical nature of the new allergens detected we conclude that wheat and maize-related food allergy is more complex than so far anticipated.

Nuclear transport factor 2 represents a novel cross-reactive fungal allergen.

BACKGROUND: Ubiquitously occuring moulds are important allergenic sources known to elicit IgE-mediated allergic diseases and to share cross-reactive allergens. Limited information is available about the molecular structures involved in cross-reactivity. We aimed to clone and characterize cross-reactive mould allergens. METHODS: Phage surface-displayed Alternaria alternata and Cladosporium herbarum cDNA libraries were screened using sera from Aspergillus fumigatus-sensitized patients. Inserts encoding putative allergens were sequenced, and recombinant proteins used to demonstrate cross-reactivity by inhibition experiments and skin test. Three-dimensional homology models of cloned putative nuclear transport factor 2 (NTF2) were constructed based on known NTF2 structure to corroborate the functional and structural properties of the novel allergens. RESULTS: After six rounds of affinity selection, the libraries were enriched for clones displaying allergens. Sequencing of inserts showed that some clones derived from Alternaria alternata and Cladosporium herbarum contain open reading frames predicting proteins of 124 and 125 amino acids corresponding to NTF2. The recombinant proteins were able to bind and cross-inhibit IgE binding and to elicit type I skin reactions in mould-sensitized individuals, demonstrating the allergenicity of the proteins. CONCLUSIONS: NTF2 represents a novel cross-reactive fungal allergen as demonstrated by sequence homology, three-dimensional modelling, inhibition experiments and skin test reactivity.

Immunoglobulin E-binding and skin test reactivity to hydrophobin HCh-1 from Cladosporium herbarum, the first allergenic cell wall component of fungi.

BACKGROUND: For many years, fungal spores have been recognized as potential causes of respiratory allergies. All fungal allergens cloned so far represent either secreted or cytoplasmatic proteins, but nothing is known about the involvement of fungal surface proteins in allergic diseases. METHODS: A phage surface displayed cDNA-library from the mould Cladosporium herbarum was constructed and phage displaying IgE-binding proteins were selectively enriched with immobilized serum IgE from C. herbarum-sensitized individuals. Inserts encoding putative allergens were sequenced, subcloned and used to produce recombinant proteins. Allergenicity of the proteins was evaluated by IgE binding in Western blots, enzyme-linked immunosorbent assay (ELISA) and skin prick test in a total of 84 patients sensitized to either C. herbarum or Aspergillus fumigatus and three healthy controls. RESULTS: After four rounds of affinity selection, the cDNA-library was enriched for clones displaying IgE-binding molecules. Sequencing of inserts showed that one clone contained an open reading frame predicting a protein of 105 amino acids and a calculated molecular weight of 10.5 kDa showing the classical signature of members of the hydrophobin family. The recombinant protein, termed HCh-1, was able to bind IgE from six patients sensitized to fungi in vitro. Two of those patients were also included in a skin prick test survey and showed strong type I skin reactions to HCh-1, demonstrating the allergenic nature of C. herbarum hydrophobin and indicating a prevalence of sensitization in the range of 8-9%. In contrast, the hydrophobin HYP1 from Aspergillus fumigatus was not recognized by the sera of the same patients and controls investigated with HCh-1. CONCLUSION: C. herbarum hydrophobin represents the first component of the cell wall of fungi demonstrated to act as a rare but clinically relevant allergen in vitro and in vivo.