Allergenicity and antigenicity of wild-type and mutant, monomeric, and dimeric carrot major allergen Dau c 1: destruction of conformation, not oligomerization, is the roadmap to save allergen vaccines

Cross-protection of allergen immunotherapy-induced antibodies to related allergens requires a high degree of structural identity

BACKGROUND

In contrast to sublingual immunotherapy (SLIT) with recombinant Mal d 1 (rMal d 1-SLIT), SLIT with rBet v 1 (rBet v 1-SLIT) induced Mal d 1-cross-reactive antibodies without IgE-blocking activity. To elucidate whether the development of cross-protective IgG responses depends on the degree of molecular identity of allergens we compared the cross-reactivity, cross-blocking activity, and affinity of SLIT-induced antibodies with allergens of varying amino acid sequence identities to Bet v 1 and Mal d 1, namely Cor a 1.04 (hazelnut), Pru av 1 (cherry), and Dau c 1 (carrot).

METHODS

Allergen-specific antibodies were quantified by ELISA. IgE blocking was analyzed by inhibition of allergen-induced basophil activation and IgE-facilitated allergen-presentation to T cells. The affinity of SLIT-induced antibodies was studied by acidic dissociation ELISA and competition ELISA. Identical surface areas on allergens were predicted using an in-house designed script based on structural alignments.

RESULTS

rBet v 1-SLIT-induced IgG antibodies cross-reacted with all allergens except Dau c 1. rMal d 1-SLIT-induced antibodies predominantly cross-reacted with Pru av 1 and displayed significantly higher IgE blocking to Pru av 1 than rBet v 1-SLIT-induced antibodies. rMal d 1-SLIT-induced IgG1 showed higher affinity to Mal d 1 and Pru av 1. Surface analysis revealed 84% identical area on Mal d 1 and Pru av 1. Furthermore, we identified two surface areas potentially containing epitopes present on these allergens and absent on Bet v 1.

CONCLUSION

In summary, our findings suggest that a relatively high threshold of similarity is required to establish effective cross-blocking antibodies to related allergens. Apparently, the structural identity between Bet v 1 and Mal d 1 is below this threshold. Therefore, this study may explain why immunotherapy with birch pollen allergen often fails to reduce birch pollen-related apple allergy.

Low-pH induced structural changes, allergenicity and in vitro digestibility of lectin from black turtle bean (Phaseolus vulgaris L.)

Lectin was incubated in corresponding acidic buffers (pH 1.0-3.5) for a certain period (0.5, 1, 2, 4, 8, 12 and 24 h) at 25 °C. Low-pH induced changes in structure, allergenicity and in vitro digestibility of lectin from black turtle bean (Phaseolus vulgaris L.) were investigated in the present study. Results indicated that the alteration in structure was a progressive unfolding process mainly depending on pH environment, and the treated lectin attained a stable state at 8 h. Electrophoretic, dynamic light scattering (DLS) and size exclusion chromatography (SEC) analyses suggested that lectin monomers appeared in the solutions of pH < 2.0. Differential scanning calorimetry (DSC) confirmed that thermal stability of lectin weakened in low pH environments. Furthermore, ELISA and in vitro digestion assay showed allergenicity and digestibility significantly decreased with the structural alterations. These results showed low-pH treatments have great potential to reduce the damage of legumes protein consumption.

A robust method for the estimation and visualization of IgE cross-reactivity likelihood between allergens belonging to the same protein family

Among the vast number of identified protein families, allergens emanate from relatively few families which translates to only a small fraction of identified protein families. In allergy diagnostics and immunotherapy, interactions between immunoglobulin E and allergens are crucial because the formation of an allergen-antibody complex is necessary for triggering an allergic reaction. In allergic diseases, there is a phenomenon known as cross-reactivity. Cross-reactivity describes a situation where an individual has produced antibodies against a particular allergenic protein, but said antibodies fail to discriminate between the original sensitizer and other similar proteins that usually belong to the same family. To expound the concept of cross-reactivity, this study examines ten protein families that include allergens selected specifically for the analysis of cross-reactivity. The selected allergen families had at least 13 representative proteins, overall folds that differ significantly between families, and include relevant allergens with various potencies. The selected allergens were analyzed using information on sequence similarities and identities between members of the families as well as reports on clinically relevant cross-reactivities. Based on our analysis, we propose to introduce a new A-RISC index (Allergens’–Relative Identity, Similarity and Cross-reactivity) which describes homology between two allergens belonging to the same protein family and is used to predict the likelihood of cross-reactivity between them. Information on sequence similarities and identities, as well as on the values of the proposed A-RISC index is used to introduce four categories describing a risk of a cross-reactive reaction, namely: high, medium-high, medium-low and low. The proposed approach can facilitate analysis in component-resolved allergy diagnostics, generation of avoidance guidelines for allergic individuals, and help with the design of immunotherapy.

pH and Heat Resistance of the Major Celery Allergen Api g 1

SCOPE

The major celery allergen Api g 1 is a member of the pathogenesis-related 10 class protein family. This study aims to investigate the impact of heat and pH on the native protein conformation required for Immunoglobulin E (IgE) recognition.

METHODS AND RESULTS

Spectroscopic methods, MS and IgE-binding analyses are used to study the effects of pH and thermal treatment on Api g 1.0101. Heat processing results in a loss of the native protein fold via denaturation, oligomerization, and precipitation along with a subsequent reduction of IgE recognition. The induced effects and timescales are strongly pH dependent. While Api g 1 refolds partially into an IgE-binding conformation at physiological pH, acidic pH treatment leads to the formation of structurally heat-resistant, IgE-reactive oligomers. Thermal processing in the presence of a celery matrix or at pH conditions close to the isoelectric point (pI = 4.63) of Api g 1.0101 results in almost instant precipitation.

CONCLUSION

This study demonstrates that Api g 1.0101 is not intrinsically susceptible to heat treatment in vitro. However, the pH and the celery matrix strongly influence the stability of Api g 1.0101 and might be the main reasons for the observed temperature lability of this important food allergen.

IgE Reactivity of the Dog Lipocalin Allergen Can f 4 and the Development of a Sandwich ELISA for Its Quantification

Purpose

Divergent results on the IgE reactivity of dog-allergic subjects to Can f 4 have been reported. The aim of this study was to evaluate the significance of Can f 4 in dog allergy and to develop an immunochemical method for measuring Can f 4 content in environmental samples.

Methods

We purified the natural dog allergen Can f 4 from a dog dander extract by monoclonal antibody-based affinity chromatography and generated its variant in a recombinant form. Sixty-three dog-allergic patients and 12 nonallergic control subjects were recruited in the study. The IgE-binding capacity of natural Can f 4 and its recombinant variant was assessed by ELISA, immunoblotting, and skin prick tests (SPT).

Results

Eighty-one percent of the dog-allergic patients showed a positive result to the immunoaffinity-purified natural Can f 4 in IgE ELISA, but only 46% in IgE immunoblotting. Respective results with the recombinant Can f 4 variant were 54% and 49%. SPT results reflected those obtained in ELISA and immunoblotting. The overall IgE reactivity of the immunoaffinity-purified natural Can f 4 was found to depend strongly on the integrity of the allergen's conformation. A sandwich ELISA based on monoclonal antibodies was found to be functional for measuring Can f 4 in environmental samples.

Conclusions

Can f 4 is a major allergen of dog together with Can f 1 and Can f 5. In combination with other dog allergens, it improves the reliability of allergy tests in dog allergy.

Allergenic characterization of new mutant forms of Pru p 3 as new immunotherapy vaccines

Nowadays, treatment of food allergy only considered the avoidance of the specific food. However, the possibility of cross-reactivity makes this practice not very effective. Immunotherapy may exhibit as a good alternative to food allergy treatment. The use of hypoallergenic molecules with reduced IgE binding capacity but with ability to stimulate the immune system is a promising tool which could be developed for immunotherapy. In this study, three mutants of Pru p 3, the principal allergen of peach, were produced based on the described mimotope and T cell epitopes, by changing the specific residues to alanine, named as Pru p 3.01, Pru p 3.02, and Pru p 3.03. Pru p 3.01 showed very similar allergenic activity as the wild type by in vitro assays. However, Pru p 3.02 and Pru p 3.03 presented reduced IgE binding with respect to the native form, by in vitro, ex vivo, and in vivo assays. In addition, Pru p 3.03 had affected the IgG4 binding capacity and presented a random circular dichroism, which was reflected in the nonrecognition by specific antibodies anti-Pru p 3. Nevertheless, both Pru p 3.02 and Pru p 3.03 maintained the binding to IgG1 and their ability to activate T lymphocytes. Thus, Pru p 3.02 and Pru p 3.03 could be good candidates for potential immunotherapy in peach-allergic patients.

Synthesis of hypoallergenic derivatives of the major allergen Fag t 1 from tartary buckwheat via sequence restructuring

Fag t 1, a legumin-type protein, is the major allergen in tartary buckwheat. In the current study, three recombinant derivatives of Fag t 1, designated as Fag t 1-rs1, Fag t 1-rs2, and Fag t 1-rs3, were constructed via rational design and genetic engineering. However, because of the loss of their native-like folds, the Fag t 1 derivatives failed to bind IgE, and their allergenic activities were reduced. The recombinant hypoallergenic variants are promising vaccine candidates for specific immunotherapy of buckwheat allergy. The unfolding of the Fag t 1 structure reduced its high resistance to gastrointestinal proteolysis and strongly reduced its IgE reactivity. The derivatives showed a more than 90% reduction in allergenic activity compared with rFag t 1. These results suggest that the structure-dependent stability of 11S seed storage proteins is directly related to digestive stability and allergenic potential. Therefore, the destruction of the native conformation is the appropriate strategy to reduce the allergenicity of the cupin family food allergens.

In search of a vaccine for mouse allergy: significant reduction of Mus m 1 allergenicity by structure-guided single-point mutations

BACKGROUND

Mouse urinary proteins are relevant allergens from mice urine. We used the recombinant protein Mus m 1 as an allergen model to identify if, by altering Mus m 1 architecture via single-point mutations, we could effectively modify its allergenicity.

METHODS

Based on structural considerations, we synthesized two single-point mutants, Mus m 1-Y120A and Mus m 1-Y120F, which were expected to harbor large structural alterations. Circular dichroism and fluorescence analysis showed significant conformational rearrangements of the aromatic side chains in the internal cavity of Mus m 1-Y120A when compared to Mus m 1-Y120F and Mus m 1. Evaluation of the allergenic potential of the recombinant molecules was performed in vitro with both immunochemical approaches and assays based on the measurement of basophil degranulation. Moreover, to assess the integrity of the T cell epitopes and as an in vitro measure of immunogenicity, we tested the reactivity of T lymphocytes from subjects allergic to mouse urine against proteins and synthetic peptides encompassing the immunodominant linear epitope containing the mutation.

RESULTS

We found that the selected point mutation was able to modulate the protein allergenicity, and to severely impair the recognition of Mus m 1 by IgE, while T cell reactivity was fully maintained.

CONCLUSIONS

In silico predicted, minimum selected structural modifications allowed to design one protein with reduced allergenicity and preserved immunogenicity. Structurally guided mutations can direct the design of proteins with reduced allergenicity which can be used as vaccines for a safer and more effective immunotherapy of allergic disorders.

Kiwifruit Act d 11 is the first member of the ripening-related protein family identified as an allergen

BACKGROUND

Kiwifruit is an important cause of food allergy. A high amount of a protein with a molecular mass compatible with that of Bet v 1 was observed in the kiwifruit extract.

OBJECTIVE

To identify and characterize kirola, the 17-kDa protein of green kiwifruit (Act d 11).

METHODS

Act d 11 was purified from green kiwifruit. Its primary structure was obtained by direct protein sequencing. The IgE binding was investigated by skin testing, immunoblotting, inhibition tests, and detection by the ISAC microarray in an Italian cohort and in selected Bet v 1-sensitized Austrian patients. A clinical evaluation of kiwi allergy was carried out.

RESULTS

Act d 11 was identified as a member of the major latex protein/ripening-related protein (MLP/RRP) family. IgE binding to Act d 11 was shown by all the applied testing. Patients tested positive for Act d 11 and reporting symptoms on kiwifruit exposure were found within the Bet v 1-positive subset rather than within the population selected for highly reliable history of allergic reactions to kiwifruit. Epidemiology of Act d 11 IgE reactivity was documented in the two cohorts. IgE co-recognition of Act d 11 within the Bet v 1-like molecules is documented using the microarray IgE inhibition assay.

CONCLUSIONS

Act d 11 is the first member of the MLP/RRP protein family to be described as an allergen. It displays IgE co-recognition with allergens belonging to the PR-10 family, including Bet v 1.

Reshaping the Bet v 1 fold modulates T(H) polarization

BACKGROUND

Several alternative mechanisms have been proposed to explain why some proteins are able to induce a T(H)2-biased and IgE-mediated immune response. These include specific interactions with receptors of the innate immune system, proteolytic activities, allergen-associated carbohydrate structures, and intrinsic structural determinants.

OBJECTIVES

Available data suggest that a fold-dependent allergy-promoting mechanism could be a driving force for the T(H)2-polarization activity of Bet v 1, the major birch pollen allergen.

METHODS

Computer-aided sequence and fold analysis of the Bet v 1 family identified a short stretch susceptible for mutations inducing an altered fold of the entire molecule. With this knowledge, 7 consecutive amino acids of Bet v 1 were replaced with the homologous Mal d 1 sequence, creating the derivative BM4.

RESULTS

The minimal changes of the sequence led to a loss of the Bet v 1-like fold and influenced the immunologic behavior. Compared to wild-type Bet v 1, BM4 induced elevated T-cell proliferation of human PBMCs. In the mouse model, immunization with Bet v 1 absorbed to aluminum hydroxide triggered strong T(H)2 polarization, whereas BM4 immunization additionally recruited T(H)1 cells. Furthermore, the fold variant BM4 showed enhanced uptake by dendritic cells and a decreased susceptibility to endo-/lysosomal proteolysis.

CONCLUSION

Modifications in the 3-dimensional structure of Bet v 1.0101 resulted in a change of its immunologic properties. We observed that the fold alteration led to a modified crosstalk with dendritic cells and a shift of the immune response polarization toward a mixed T(H)1/T(H)2 cytokine production.

Development and in-house validation of allergen-specific ELISA tests for the quantification of Dau c 1.01, Dau c 1.02 and Dau c 4 in carrot extracts (Daucus carota)

Even though carrot allergy is common in Europe, the amount of different allergens in carrots is still unknown due to a lack of methods for quantitative allergen measurements. The current study aimed at the development of quantitative ELISA tests for the known carrot allergens, namely Dau c 1.01, Dau c 1.02, and Dau c 4 in pure carrot extracts. Monoclonal antibodies targeting the major carrot allergen isoforms Dau c 1.01 and Dau c 1.02 were generated and combined in sandwich ELISA with rabbit antisera against Api g 1, the celery homologue of Dau c 1. A competitive ELISA for the carrot profilin Dau c 4 was based on a polyclonal rabbit antiserum. The three ELISA tests were allergen-specific and displayed detection limits between 0.4 and 6 ng allergen/ml of carrot extract. The mean coefficient of variation (CV) as a means of intraassay variability of the Dau c 1.01, Dau c 1.02 and Dau c 4 ELISA tests was 8.1%, 6.9%, and 11.9%, and the mean interassay CV 13.3%, 37.1% and 15.6%, respectively. Target recovery ranged between 93 and 113%. In conclusion, the specific, accurate and reproducible quantification of three important carrot allergens may help to identify less allergenic carrot varieties, as well as to standardize the amount of allergens in extracts used for carrot allergy diagnosis.

Relevant B cell epitopes in allergic disease

The 3-dimensional structure of an allergen defines the accessible parts on the surface of the molecule or epitopes that interact with antibodies. Mapping the antigenic determinants for IgE antibody binding has been pursued through strategies based on the use of overlapping synthetic peptides, recombinant allergenic fragments or unfolded allergens. These approaches led to the identification of mostly linear epitopes and are useful for food allergens that undergo digestion or food processing. For inhaled allergens, conformational epitopes appear to be the primary targets of IgE responses. Knowledge of the molecular structure of allergens alone and in complex with antibodies that interfere with IgE antibody binding is important to understand the immune recognition of B cell-antigenic determinants on allergens and the design of recombinant allergens for immunotherapy. Starting with the molecular cloning and expression of allergens, and with the advent of X-ray crystallography and nuclear magnetic resonance techniques, we have been able to visualize conformational epitopes on allergens.

Relevance of IgE binding to short peptides for the allergenic activity of food allergens

BACKGROUND

Analysis of IgE antibody binding to epitopes provides information for food allergy diagnosis and management and construction of hypoallergenic candidate vaccines, but the contribution of sequential epitopes to functionally relevant IgE binding is not fully understood.

OBJECTIVES

We sought to study the impact of IgE-binding peptides described as major sequence epitopes in the literature on IgE-binding capacity of 2 selected food allergens.

METHODS

IgE-binding peptides of the food allergens Ara h 2 (peanut) and Pen a 1 (shrimp) were identified. Synthetic soluble peptides representing the identified sequences were assessed for their capacity to inhibit IgE binding to the parent allergens by means of ELISA and in mediator release assay. The IgE-binding capacity of unfolded recombinant (r) Ara h 2 was analyzed. A hybrid tropomyosin carrying the IgE-binding regions of Pen a 1 grafted into the structural context of the nonallergenic mouse tropomyosin was applied in ELISA inhibition experiments and ImmunoCAP analysis.

RESULTS

Although IgE-binding peptides representing sections of the allergen sequences were detected, no relevant capacity to inhibit the IgE binding to the parent allergen in ELISA or basophil activation test was observed. Unfolded rAra h 2 showed reduced IgE-binding capacity compared with folded rAra h 2 and failed to elicit mediator release. Hybrid tropomyosin bound less IgE than rPen a 1 in ImmunoCAP analysis and revealed marginal inhibitory capacity.

CONCLUSION

Peptides identified as major sequence epitopes on Pen a 1 and Ara h 2 show little contribution to the IgE binding of the allergens studied.

Coordinated and standardized production, purification and characterization of natural and recombinant food allergens to establish a food allergen library

Reliable diagnosis of food allergy is dependent on the analytes used. Approaches based on well-defined individual molecules of either natural or recombinant origin are likely to replace those based on food extracts in the future. Therefore, a library comprising well-characterized authentic natural and recombinant allergens was formed within the EC funded IP EuroPrevall. The advantages and disadvantages of including either natural or recombinant proteins are summarized, together with inclusion criteria such as purity and the implications of both allergenic and nonallergenic impurities for the performance of diagnostic assays. In order to harmonize quality criteria of the individual food allergens included in the library, as suite of characteristics and associated methodologies used to define them, was agreed. The application of these methods and impact on the quality and performance of the final purified food allergens included in the EuroPrevall allergen library is discussed.

Allergen structures and biologic functions: the cutting edge of allergy research

Studies of structure and function of allergens using state-of-the-art technologies have led to a better understanding of allergenicity, including aspects related to cross-reactivity, allergen nomenclature, and the identification of antigenic determinants. This information is being applied to the design and production of allergy vaccines, some of which already have proven efficacy and safety in clinical trials.

Allergy vaccines: dreams and reality

Allergy, extrinsic asthma and atopic eczema derive from deregulated immune responses against innocuous antigens. The incidence of atopic diseases is actually affecting approximately 30% of the population in industrialized countries. Although much progress has been achieved in the development of efficient symptomatic treatments for allergic diseases, the only curative treatment remains allergen-specific immunotherapy. In contrast to classical vaccines, which elicit strong host immune responses after one or a few injections, allergen-specific immunotherapy might require a long treatment time of 3-5 years with up to 80 injections to confer some protection. The reality is that 'allergy vaccines' achieve beneficial effects through immunomodulation, which takes a long time to establish. The dream would be to develop highly efficient allergy vaccines able to cure the disease with a few injections.

Crystal structure of a dimerized cockroach allergen Bla g 2 complexed with a monoclonal antibody

The crystal structure of a 1:1 complex between the German cockroach allergen Bla g 2 and the Fab' fragment of a monoclonal antibody 7C11 was solved at 2.8-angstroms resolution. Bla g 2 binds to the antibody through four loops that include residues 60-70, 83-86, 98-100, and 129-132. Cation-pi interactions exist between Lys-65, Arg-83, and Lys-132 in Bla g 2 and several tyrosines in 7C11. In the complex with Fab', Bla g 2 forms a dimer, which is stabilized by a quasi-four-helix bundle comprised of an alpha-helix and a helical turn from each allergen monomer, exhibiting a novel dimerization mode for an aspartic protease. A disulfide bridge between C51a and C113, unique to the aspartic protease family, connects the two helical elements within each Bla g 2 monomer, thus facilitating formation of the bundle. Mutation of these cysteines, as well as the residues Asn-52, Gln-110, and Ile-114, involved in hydrophobic interactions within the bundle, resulted in a protein that did not dimerize. The mutant proteins induced less beta-hexosaminidase release from mast cells than the wild-type Bla g 2, suggesting a functional role of dimerization in allergenicity. Because 7C11 shares a binding epitope with IgE, the information gained by analysis of the crystal structure of its complex provided guidance for site-directed mutagenesis of the allergen epitope. We have now identified key residues involved in IgE antibody binding; this information will be useful for the design of vaccines for immunotherapy.

A structural basis for food allergy: the role of cross-reactivity

PURPOSE OF REVIEW

Immunologic cross-reactivity, which is important in many aspects of host defense and immune-mediated diseases, is a prominent feature of allergic disorders. The goal of this article is to define allergenic cross-reactivity and its role in food allergy, review current understanding of mechanisms of cross-reactivity, and consider how advances in our ability to predict cross-reactivity can impact diagnosis and treatment of food allergy.

RECENT FINDINGS

Recent evidence suggests that specific T cells, in addition to IgE, developed in response to inhaled allergens can cross-react with related food allergens, leading to distinct clinical reactions. Several new cross-reactivities have been identified, including food-food, pollen-food, and latex-venom associations. Debate continues regarding prediction of allergenicity based on protein structure, and clinical relevance of in-vitro testing. Cross-reactivity is also being used to develop specific immunotherapy for treatment of food allergy.

SUMMARY

A thorough understanding of immunologic cross-reactivity is essential to advancing our knowledge about food allergy. This knowledge will help elucidate the pathogenesis of the disorder and prevent exposures to allergenic, genetically engineered foods. New insight will allow for better utilization of current diagnostic tools and the development of more accurate tests and therapies for food allergy.

Biotechnology-based allergy diagnosis and vaccination

The diagnosis and immunotherapy currently applied to allergic diseases involve the use of crude extracts of the allergen source without defining the allergy-eliciting molecule(s). Advances in recombinant DNA technology have made identification, cloning, expression and epitope mapping of clinically significant allergens possible. Recombinant allergens that retain the immunological features of natural allergens form the basis of accurate protein-chip-based methods for diagnosing allergic conditions. The ability to produce rationally designed hypoallergenic forms of allergens is leading to the development of novel and safe forms of allergy vaccines with improved efficacy. The initial clinical tests on recombinant-allergen-based vaccine preparations have provided positive results, and ongoing developments in areas such as alternative routes of vaccine delivery will enhance patient compliance.

Allergological implication of the quaternary hexameric structure of the cockroach allergen Per a 3

BACKGROUND

Cockroach allergens play a very important role in allergic diseases, especially asthma. The major allergen of the American cockroach (Periplaneta americana), Per a 3, naturally occurs as isoforms of hexamers.

OBJECTIVE

The aim of this study was to investigate whether the hexameric structures of Per a 3 influence their allergenicity and immunogenicity.

METHODS

Therefore, we compared the different effects of native hexamers and dissociated monomers of cockroach haemolymph (HL), containing almost only Per a 3 proteins (HL-Per a 3), on proliferation and T-helper type 1 (Th1)/Th2 cytokine production of human CD4(+) T cells in co-culture with allergen-pulsed monocyte-derived autologous dendritic cells (DC) as well as the leukotriene release of basophils.

RESULTS

In P. americana-sensitized and non-sensitized donors the HL-Per a 3 monomers were internalized faster by immature DC and induced higher proliferation and IFN-gamma production than the hexamers. While in non-sensitized donors IL-4 and IL-5 as well as IL-10 production were also increased after stimulation with monomeric HL-Per a 3-pulsed DC, Th2 cytokine and IL-10 production were only enhanced in P. americana-sensitized donors using hexameric HL-Per a 3-pulsed DC. Furthermore, in the leukotriene release assay the monomers were less effective than the hexamers.

CONCLUSION

Our data indicate that the quaternary structure can influence both allergenicity and immunogenicity, also depending on the sensitization status. The monomeric variant of Per a 3 allergens could be a possible candidate for a specific immunotherapy because the IgE-mediated allergic reaction and the Th2-inducing capacity are diminished while the Th1-inducing capacity is retained.

Naturally occurring hypoallergenic Bet v 1 isoforms fail to induce IgE responses in individuals with birch pollen allergy

BACKGROUND

Engineered hypoallergens are currently being investigated for specific immunotherapy of allergic diseases in preclinical and clinical studies. Naturally occurring hypoallergens have by and large not been considered as a source of vaccine candidates.

OBJECTIVE

Evaluation of the antibody response in atopic individuals induced by birch pollen containing isoforms of the major birch pollen allergen Bet v 1.

METHODS

Isoform-specific antibody isotype responses for Bet v 1.0101, Bet v 1.0401, and Bet v 1.1001 were determined for 35 sera of individuals with birch pollen allergy. Isoform structures were compared and related to IgE-binding inhibitory capacities and induction of mediator release in human Fcvarepsilon receptor transformed rat basophilic leukemia cells.

RESULTS

Bet v 1.0101 induced a predominant IgE response, whereas the significant highest levels of IgG(4) antibodies were directed against Bet v 1.0401. Bet v 1.1001 induced only a minimal antibody response. Structural comparisons revealed that most of the amino acid differences between the isoforms were located on the protein surfaces. IgE induced by Bet v 1.0101 only partly cross-reacted with the 2 other isoforms and bound to them with notably lower affinity. Bet v 1.0401 and Bet v 1.1001 also were poor inducers of mediator release.

CONCLUSION

Bet v 1 isoforms possess highly variant immunogenic and allergenic properties. Bet v 1.0101 acts as the sensitizing agent, whereas Bet v 1.0401 and Bet v 1.1001 can induce only a minimal IgE response.