Characterization of the T-cell epitopes of a major peanut allergen, Ara h 2

T-cell epitope discovery and single-cell technologies to advance food allergy research

There is good evidence for a role of T cells in food allergy, but there is a lack of mechanistic understanding and phenotypic markers of the specific T cells contributing to pathology. Recent technologic advancements have allowed for a new experimental paradigm where we can find and pull out rare antigen-specific T cells and characterize them at the single-cell level. However, studies in infectious disease and broader allergy have shown that these techniques benefit greatly from precisely defined T-cell epitopes. Food allergens have fewer epitopes currently available, but it is growing and promises to overcome this gap. With growing use of this experimental design, it will be important to unbiasedly map T-cell phenotypes across food allergy and look for commonalities and contrasts to other allergic and infectious diseases. Once a pathologic phenotype for T cells has been established, the frequencies of these cells can be monitored with simpler techniques that could be applied to the clinic and used in diagnosis, prediction of treatment responsiveness, and discovery of targets for new treatments.

Use of a Liver-targeting Nanoparticle Platform to Intervene in Peanut-induced anaphylaxis through delivery of an Ara h2 T-cell Epitope

To address the urgent need for safe food allergen immunotherapy, we have developed a liver-targeting nanoparticle platform, capable of intervening in allergic inflammation, mast cell release and anaphylaxis through the generation of regulatory T-cells (Treg). In this communication, we demonstrate the use of a poly (lactide-co-glycolide acid) (PLGA) nanoparticle platform for intervening in peanut anaphylaxis through the encapsulation and delivery of a dominant protein allergen, Ara h 2 and representative T-cell epitopes, to liver sinusoidal endothelial cells (LSECs). These cells have the capacity to act as natural tolerogenic antigen-presenting cells (APC), capable of Treg generation by T-cell epitope presentation by histocompatibility (MHC) type II complexes on the LSEC surface. This allowed us to address the hypothesis that the tolerogenic nanoparticles platform could be used as an effective, safe, and scalable intervention for suppressing anaphylaxis to crude peanut allergen extract. Following the analysis of purified Ara h 2 and representative MHC-II epitopes Treg generation in vivo, a study was carried out to compare the best-performing Ara h 2 T-cell epitope with a purified Ara h 2 allergen, a crude peanut protein extract (CPPE) and a control peptide in an oral sensitization model. Prophylactic as well as post-sensitization administration of the dominant encapsulated Ara h 2 T-cell epitope was more effective than the purified Ara h2 in eliminating anaphylactic manifestations, hypothermia, and mast cell protease release in a frequently used peanut anaphylaxis model. This was accompanied by decreased peanut-specific IgE blood levels and increased TGF-β release in the abdominal cavity. The duration of the prophylactic effect was sustained for two months. These results demonstrate that targeted delivery of carefully selected T-cell epitopes to natural tolerogenic liver APC could serve as an effective platform for the treatment of peanut allergen anaphylaxis.

Prediction and characterization of the T cell epitopes for the major soybean protein allergens using bioinformatics approaches

Protein allergens is a health risk for consumption of soybeans. To understand allerginicity mechanism, T cell epitopes of 7 soybean allergens were predicted and screened by abilities to induce cytokine interleukin (IL) 4. The relationships among amino acid composition, properties, allergenicity, and pepsin hydrolysis sites were analyzed. Among the 138 T cell epitopes identified, YIKDVFRVIPSEVLS, KDVFRVIPSEVLSNS, DVFRVIPSEVLSNSY of Gly m 6.0501 (P04347), and AKADALFKAIEAYLL, ADALFKAIEAYLLAH of Gly m 4.0101 (P26987) were the most possible epitope candidates. In T cell epitopes pattern, the frequencies of amino acids Q, D, E, P, and G decreased, while F, I, N, V, K, H, A, L, and S increased. Hydrophobic residues at positions p1 and p2 and positively charged residues in positions p13 might contribute to allergenicity. Most of epitopes could be hydrolyzed by pepsin into small polypeptides within 12 residues length, and the anti-digestive epitope regions contained I, V, S, N, and Q residues. T cell epitopes EEQRQQEGVIVELSK from Gly m 5.03 (P25974) showed resistance to pepsin hydrolysis and would cause a higher Th2 cell response. This research provides basis for the development of hypoallergenic soybean products in the soybean industry as well as for the immunotherapy design for protein allergy.

Food allergens: Classification, molecular properties, characterization, and detection in food sources

Food allergy is a large and growing public health problem in many areas of the world. The prevalence of food allergy has increased in the last decades in a very significant way in many world regions, particularly in developed countries. In that respect, the research field of food allergy has experienced an extensive growth and very relevant progress has been made in recent years regarding the characterization of food allergens, the study of their immunological properties, and their detection in food sources. Furthermore, food labeling policies have also been improved decidedly in recent years. For that immense progress made, it is about time to review the latest progress in the field of food allergy. In this review, we intend to carry out an extensive and profound overview regarding the latest scientific advances and knowledge in the field of food allergen detection, characterization, and in the study of the effects of food processing on the physico-chemical properties of food allergens. The advances in food labeling policies, and methodologies for the characterization of food allergens are also thoroughly reviewed in the present overview.

Development of a novel Ara h 2 hypoallergen with no IgE binding or anaphylactogenic activity

Background

To date, no safe allergen-specific immunotherapy for patients with peanut allergy is available. Previous trials were associated with severe side effects.

Objective

We sought to determine the relative importance of conformational and linear IgE-binding epitopes of the major peanut allergen Ara h 2 and to produce a hypoallergenic variant with abolished anaphylactogenic activity.

Methods

Wild-type Ara h 2 and a mutant lacking the loops containing linear IgE epitopes were produced in insect cells. Conformational IgE epitopes were removed by unfolding these proteins through reduction and alkylation. IgE binding was tested by means of ELISA with sera from 48 Ara h 2–sensitized patients with peanut allergy. Basophil activation and T-cell proliferation were tested with blood samples from selected patients. Anaphylactogenic potency was tested by using intraperitoneal challenge of mice sensitized intragastrically to peanut extract.

Results

Patients’ IgE recognized conformational and linear epitopes in a patient-specific manner. The unfolded mutant lacking both types of epitopes displayed significantly lower IgE binding (median ELISA OD, 0.03; interquartile range, 0.01-0.06) than natural Ara h 2 (median ELISA OD, 0.99; interquartile range, 0.90-1.03; P < .01). Basophil activation by unfolded mutant Ara h 2 was low (median area under the curve, 72 vs 138 for native wild-type Ara h 2; P < .05), but its ability to induce T-cell proliferation was retained. Unfolded mutants without conformational epitopes did not induce anaphylaxis in peanut-sensitized mice.

Conclusions

By removing conformational and linear IgE epitopes, a hypoallergenic Ara h 2 mutant with abolished IgE binding and anaphylactogenic potency but retained T-cell activation was generated.

Peanut-specific T cell responses in patients with different clinical reactivity

Whole extract or allergen-specific IgE testing has become increasingly popular in the diagnosis of peanut allergy. However, much less is known about T cell responses in peanut allergy and how it relates to different clinical phenotypes. CD4+ T cells play a major role in the pathophysiology of peanut allergy as well as tolerance induction during oral desensitization regimens. We set out to characterize and phenotype the T cell responses and their targets in peanut sensitized patients. Using PBMC from peanut-allergic and non-allergic patients, we mapped T cell epitopes for three major peanut allergens, Ara h 1, 2 and 3 (27 from Ara h 1, 4 from Ara h 2 and 43 from Ara h 3) associated with release of IFNγ (representative Th1 cytokine) and IL5 (representative Th2 cytokine). A pool containing 19 immunodominant peptides, selected to account for 60% of the total Ara h 1-3-specific T cell response in allergics, but only 20% in non-allergics, was shown to discriminate T cell responses in peanut-sensitized, symptomatic vs non-symptomatic individuals more effectively than peanut extract. This pool elicited positive T cell responses above a defined threshold in 12/15 sensitized, symptomatic patients, whereas in the sensitized but non-symptomatic cohort only, 4/14 reacted. The reactivity against this peptide pool in symptomatic patients was dominated by IL-10, IL-17 and to a lesser extend IL-5. For four distinct epitopes, HLA class II restrictions were determined, enabling production of tetrameric reagents. Tetramer staining in four donors (2 symptomatic, 2 non-symptomatic) revealed a trend for increased numbers of peanut epitope-specific T cells in symptomatic patients compared to non-symptomatic patients, which was associated with elevated CRTh2 expression whereas cells from non-symptomatic patients exhibited higher levels of Integrin β7 expression. Our results demonstrate differences in T cell response magnitude, epitope specificity and phenotype between symptomatic and non-symptomatic peanut-sensitized patients. In addition to IgE reactivity, analysis of peanut-specific T cells may be useful to improve our understanding of different clinical manifestations in peanut allergy.

Heterogeneity of Ara h Component-Specific CD4 T Cell Responses in Peanut-Allergic Subjects

Understanding the peanut-specific CD4 T cell responses in peanut-allergic (PA) subjects should provide new insights into the development of innovative immunotherapies for the treatment of peanut allergy. Although peanut-specific CD4 T cells have a TH2 profile in PA subjects, the immunogenicity of different Ara h components in eliciting specific CD4 T cell responses and the heterogeneity of these Ara h-reactive TH2 cells remains unclear. In this study, we investigated Ara h 1, 2, 3, 6, and 8-specific T cell responses in PA and sensitized non-peanut-allergic (sNPA) subjects, using the CD154 upregulation assay and the class II tetramer technology. In the PA group, T cells directed against Ara h 1, 2, 3, and 6 have a heterogeneous TH2 phenotype characterized by differential expression of CRTH2, CD27, and CCR6. Reactivity toward these different components was also distinct for each PA subject. Two dominant Ara h 2 epitopes associated with DR1501 and DR0901 were also identified. Frequencies of Ara h-specific T cell responses were also linked to the peanut specific-IgE level. Conversely, low peanut-IgE level in sNPA subjects was associated with a weak or an absence of the allergen-specific T cell reactivity. Ara h 8-specific T cell reactivity was weak in both PA and sNPA subjects. Thus, peanut-IgE level was associated with a heterogeneous Ara h (but not Ara h 8)-specific T cell reactivity only in PA patients. This suggests an important immunogenicity of each Ara h 1, 2, 3, and 6 in inducing peanut allergy. Targeting Ara h 1-, 2-, 3-, and 6-specific effector-TH2 cells can be the future way to treat peanut allergy.

Lactobacillus buchneri S-layer as carrier for an Ara h 2-derived peptide for peanut allergen-specific immunotherapy

Peanut allergy is an IgE-mediated severe hypersensitivity disorder. The lack of a treatment of this potentially fatal allergy has led to intensive research on vaccine development. Here, we describe the design and initial characterization of a carrier-bound peptide derived from the most potent peanut allergen, Ara h 2, as a candidate vaccine. Based on the adjuvant capability of bacterial surface (S-) layers, a fusion protein of the S-layer protein SlpB from Lactobacillus buchneri CD034 and the Ara h 2-derived peptide AH3a42 was produced. This peptide comprised immunodominant B-cell epitopes as well as one T cell epitope. The fusion protein SlpB-AH3a42 was expressed in E. coli, purified, and tested for its IgE binding capacity as well as for its ability to activate sensitized rat basophil leukemia (RBL) cells. The capacity of Ara h 2-specific IgG rabbit-antibodies raised against SlpB-AH3a42 or Ara h 2 to inhibit IgE-binding was determined by ELISA inhibition assays using sera of peanut allergic patients sensitized to Ara h 2. IgE specific to the SlpB-AH3a42 fusion protein was detected in 69% (25 of 36) of the sera. Despite the recognition by IgE, the SlpB-AH3a42 fusion protein was unable to induce β-hexosaminidase release from sensitized RBL cells at concentrations up to 100ng per ml. The inhibition of IgE-binding to the natural allergen observed after pre-incubation of the 20 sera with rabbit anti-SlpB-AH3a42 IgG was more than 30% for four sera, more than 20% for eight sera, and below 10% for eight sera. In comparison, anti-Ara h 2 rabbit IgG antibodies inhibited binding to Ara h 2 by 48% ±13.5%. Our data provide evidence for the feasibility of this novel approach towards the development of a peanut allergen peptide-based carrier-bound vaccine. Our experiments further indicate that more than one allergen-peptide will be needed to induce a broader protection of patients allergic to Ara h 2.

Developing therapies for peanut allergy

Peanut allergy is an IgE-mediated, persisting immune disorder that is of major concern worldwide. Currently, no routine immunotherapy is available to treat this often severe and sometimes fatal food allergy. Traditional subcutaneous allergen immunotherapy with crude peanut extracts has proven not feasible due to the high risk of severe systemic side effects. The allergen-specific approaches under preclinical and clinical investigation comprise subcutaneous, oral, sublingual and epicutaneous immunotherapy with whole-peanut extracts as well as applications of hypoallergenic peanut allergens or T cell epitope peptides. Allergen-nonspecific approaches include monoclonal anti-IgE antibodies, TCM herbal formulations and Toll-like receptor 9-based immunotherapy. The potential of genetically engineered plants with reduced allergen levels is being explored as well as the beneficial influence of lactic acid bacteria and soybean isoflavones on peanut allergen-induced symptoms. Although the underlying mechanisms still need to be elucidated, several of these strategies hold great promise. It can be estimated that individual strategies or a combination thereof will result in a successful immunotherapy regime for peanut-allergic individuals within the next decade.

In silico prediction of Ara h 2 T cell epitopes in peanut-allergic children

BACKGROUND

Despite the frequency and severity of peanut allergy, the only approved treatment is strict avoidance. Different types of immunotherapy with crude peanut extract are not universally effective and have been associated with relatively high adverse reaction rates.

OBJECTIVE

We sought to determine whether in silico predictive algorithms were useful in identifying candidate peptides for an Ara h 2 peptide-based vaccine using peanut-allergic patients' peripheral blood mononuclear cells (PBMCs) in vitro. A human leucocyte antigen (HLA) distribution analysis was also performed.

METHODS

Major histocompatibility complex (MHC)-class II-binding peptides were predicted using NetMHCIIpan-2.0 and NetMHCII-2.2 algorithms. PBMCs from 80 peanut-allergic patients were stimulated with overlapping 20-mer Ara h 2 peptides. Cell supernatant cytokine profiles were evaluated by multiplex assays. HLA-DRB1* and HLA-DQB1* typing were performed.

RESULTS

Four regions of overlapping sequences induced PBMC proliferation and predominant Th2 cytokine production. HLA genotyping showed 30 different DRB1* allele specificities and eight DQ serological specificities. The in silico analysis revealed similar relevant regions and predicted identical or similar core 9-mer epitopes to those identified in vitro. If relevant peptides, as determined by either in vitro or in silico analysis (15 peptides and 9 core epitopes respectively), were used in a peptide-based vaccine, they would cover virtually all subjects in the cohort studied.

CONCLUSIONS AND CLINICAL RELEVANCE

Four dominant regions in Ara h 2 have been identified, containing sequences that could serve as potential candidates for peptide-based immunotherapy. MHC-class II-based T cell epitope prediction algorithms for HLA-DR and -DQ loci accurately predicted Ara h 2 T cell epitopes in peanut-allergic subjects, suggesting their potential utility in a peptide-based vaccine design for food allergy.

Vaccines and immunomodulatory therapies for food allergy

The apparent increase in food allergy prevalence has led to a surge in the amount of clinical and basic science research dedicated to the field. At the current time, allergen avoidance remains the cornerstone of treatment; however, recent clinical trials investigating various forms of immunotherapy have opened doors to the possible future application of an active treatment strategy in everyday practice. In addition, improvements in molecular biology have allowed researchers to purify, clone, and modify allergens, thus laying the groundwork for research on vaccines using modified proteins of decreased allergenicity. Finally, various allergen-nonspecific immunomodulatory therapies are also being investigated as a means to alter the immune response to food allergens. With these emerging therapeutic strategies, it is hoped that practitioners will have options in caring for their food-allergic patients in the near future.

Treatments for food allergy: how close are we?

Food allergy continues to be a challenging health problem, with prevalence continuing to increase and anaphylaxis still an unpredictable possibility. While improvements in diagnosis are more accurately identifying affected individuals, treatment options remain limited. The cornerstone of treatment relies on strict avoidance of the offending allergens and education regarding management of allergic reactions. Despite vigilance in avoidance, accidental ingestions and reactions continue to occur. With recent advances in the understanding of humoral and cellular immune responses in food allergy and mechanisms of tolerance, several therapeutic strategies for food allergies are currently being investigated with the hopes of providing a cure or long-term remission from food allergy.

Ara h 2: crystal structure and IgE binding distinguish two subpopulations of peanut allergic patients by epitope diversity

BACKGROUND

Peanut allergy affects 1% of the population and causes the most fatal food-related anaphylactic reactions. The protein Ara h 2 is the most potent peanut allergen recognized by 80-90% of peanut allergic patients.

METHODS

The crystal structure of the major peanut allergen Ara h 2 was determined for the first time at 2.7 Å resolution using a customized maltose-binding protein (MBP)-fusion system. IgE antibody binding to the MBP fusion construct vs the natural allergen was compared by ELISA using sera from peanut allergic patients.

RESULTS

The structure of Ara h 2 is a five-helix bundle held together by four disulfide bonds and related to the prolamin protein superfamily. The fold is most similar to other amylase and trypsin inhibitors. The MBP--Ara h 2 fusion construct was positively recognized by IgE from 76% of allergic patients (25/33). Two populations of patients could be identified. Subpopulation 1 (n = 14) showed an excellent correlation of IgE antibody binding to natural vs recombinant Ara h 2. Subpopulation 2 (n = 15) showed significantly reduced IgE binding to the MBP fusion protein. Interestingly, about 20% of the IgE binding in subpopulation 2 could be recovered by increasing the distance between MBP and Ara h 2 in a second construct.

DISCUSSION

The reduced IgE binding to the MBP--Ara h 2 of subpopulation 2 indicates that the MBP molecule protects an immunodominant epitope region near the first helix of Ara h 2. Residues involved in the epitope(s) are suggested by the crystal structure. The MBP--Ara h 2 fusion constructs will be useful to further elucidate the relevance of certain epitopes to peanut allergy.

Interaction of allergens, major histocompatibility complex molecules, and T cell receptors: a 'ménage à trois' that opens new avenues for therapeutic intervention in type I allergy

T cells are major players in the initiation and perpetuation of the allergic immune response. In this review, we summarize the current knowledge on allergen recognition by T lymphocytes and address the components of the trimeric recognition complex: T cell receptors, major histocompatibility complex molecules, and allergen-derived peptides. Furthermore, possible implications of this scientific background for future therapeutic developments are discussed.

Clinical allergy to hazelnut and peanut: identification of T cell cross-reactive allergens

BACKGROUND

Peanut and tree nut allergies are life-threatening conditions for many affected individuals worldwide. Currently there is no cure. While co-allergy to peanut and tree nuts is a common clinical observation, and IgE cross-reactivity between peanut and tree nuts is reported, T cell cross-reactivity is poorly defined.

METHODS

Hazelnut-specific T cell lines were established using peripheral blood mononuclear cells from 5 subjects with co-allergy to hazelnut and peanut. These lines were stimulated with hazelnut and peanut extracts and purified major peanut allergens, Ara h 1 and Ara h 2. Proliferation was determined by (3)H-thymidine incorporation and secretion of key Th1 (IFN-γ) and Th2 (IL-5) cytokines analysed by ELISA.

RESULTS

Hazelnut-specific T cell lines from all 5 subjects proliferated upon stimulation with both hazelnut and peanut extracts and for 4 subjects, to Ara h 1 and/or Ara h 2. Proliferating cells were mainly CD4+ T cells and produced both IL-5 and IFN-γ in response to hazelnut and peanut stimulation. Mitogenicity of extracts and allergens was excluded by their lack of stimulation of house dust mite-specific T cells.

CONCLUSION

Our finding that hazelnut and peanut co-allergy is associated with cross-reactive T cell responses, driven partly by cross-reactivity to the major peanut allergens Ara h 1 and Ara h 2, points to future development of allergen immunotherapy by targeting cross-reactive T cells.

Ara h 2 peptides containing dominant CD4+ T-cell epitopes: candidates for a peanut allergy therapeutic

BACKGROUND

Peanut allergy is a life-threatening condition; there is currently no cure. Although whole allergen extracts are used for specific immunotherapy for many allergies, they can cause severe reactions, and even fatalities, in peanut allergy.

OBJECTIVE

This study aimed to identify short, T-cell epitope-based peptides that target allergen-specific CD4(+) T cells but do not bind IgE as candidates for safe peanut-specific immunotherapy.

METHODS

Multiple CD4(+) T-cell lines specific for the major peanut allergen Ara h 2 were generated from PBMCs of 16 HLA-diverse subjects with peanut allergy by using 5,6-carboxyfluorescein diacetate succinimidylester-based methodology. Proliferation and ELISPOT assays were used to identify dominant epitopes recognized by T-cell lines and to confirm recognition by peripheral blood T cells of epitope-based peptides modified for therapeutic production. HLA restriction of core epitope recognition was investigated by using anti-HLA blocking antibodies and HLA genotyping. Serum-IgE peptide-binding was assessed by dot-blot.

RESULTS

Five dominant CD4(+) T-cell epitopes were identified in Ara h 2. In combination, these were presented by HLA-DR, HLA-DP, and HLA-DQ molecules and recognized by T cells from all 16 subjects. Three short peptide variants containing these T-cell epitopes were designed with cysteine-to-serine substitutions to facilitate stability and therapeutic production. Variant peptides showed HLA-binding degeneracy, did not bind peanut-specific serum IgE, and could directly target T(H)2-type T cells in peripheral blood of subjects with allergy.

CONCLUSION

Short CD4(+) T-cell epitope-based Ara h 2 peptides were identified as novel candidates for a T-cell-targeted peanut-specific immunotherapy for an HLA-diverse population.

Potential therapies for peanut allergy

OBJECTIVE

To review the investigated therapies for peanut allergy beyond avoidance measures and self-injectable epinephrine.

DATA SOURCES

A PubMed search was performed using the Keywords peanut allergy and therapy. Additional citations were generated by surveying the reference lists of the pulled articles

STUDY SELECTION

More than 120 articles were reviewed and references were selected based on their relevance to the subject matter.

RESULTS

Peanut allergy affects more than 1% of the US population and is increasing in prevalence. During the past 15 years multiple therapies have been researched and many have provided promising results. Sustained oral tolerance over desensitization is the goal, and most therapies are unable to demonstrate this because they are currently in their relative infancy. Therapeutic options should be safe, easily administered, and relatively inexpensive. To minimize risk, many therapies will require investigation of combined modalities.

CONCLUSIONS

Peanut allergy is a challenging diagnosis for physicians because few treatment options are available. However, it seems plausible that new offerings may become accepted therapy within the next decade. The ability of a patient to tolerate amounts of peanut in an unintentional ingestion without experiencing anaphylaxis would offer peace of mind to patients and families living with peanut allergy.

Immunologic therapeutic approaches in the management of food allergy

Food allergy affects up to 6% of children and 3-4% of adults in Westernized countries, and is the most common cause of outpatient anaphylaxis in most studies. The mainstay of treatment is strict avoidance of the offending allergens and education regarding the use of emergency medication in cases of accidental ingestions or exposures. While these approaches are generally effective, there are no definitive treatments that cure or provide long-term remission from food allergy. However, with recent advances in characterizing food allergens and understanding humoral and cellular immune responses in food allergy, several therapeutic strategies are being investigated. Potential treatments include allergen-specific immunotherapy as well as allergen-nonspecific approaches to downregulate the overall allergic response in food-allergic individuals.

T-cell epitopes of aeroallergens

OBJECTIVE

To describe the current knowledge of the T-cell epitopes of common aeroallergens, how they were discovered, and implications for future therapy.

DATA SOURCES

PubMed search of English-language articles without date limits pertaining to T-cell epitopes of aeroallergens included on a standard skin test panel.

STUDY SELECTION

A total of 127 articles were screened based on the results of the PubMed search and cross-indexed as needed. The highest quality and most clinically relevant articles were included for discussion.

RESULTS

Of the 47 allergen extracts included on the standard skin test panel at our instittition, T-cell epitopes have been described for 13. Immunodominant epitopes have been used for peptide immunotherapy trials.

CONCLUSIONS

T-cell epitopes have been characterized for a minority of common aeroallergens. However, knowledge is rapidly expanding and can lay the groundwork for therapies that specifically target T cells.

Identification and characterization of a hypoallergenic ortholog of Ara h 2.01

Peanut (Arachis hypogaea L.), can elicit type I allergy becoming the most common cause of fatal food-induced anaphylactic reactions. Strict avoidance is the only effective means of dealing with this allergy. Ara h 2, a peanut seed storage protein, has been identified as the most potent peanut allergen and is recognized by approximately 90% of peanut hypersensitive individuals in the US. Because peanut has limited genetic variation, wild relatives are a good source of genetic diversity. After screening 30 Arachis duranensis accessions by EcoTILLing, we characterized five different missense mutations in ara d 2.01. None of these polymorphisms induced major conformational modifications. Nevertheless, a polymorphism in the immunodominant epitope #7 (S73T) showed a 56-99% reduction in IgE-binding activity and did not affect T cell epitopes, which must be retained for effective immunotherapy. The identification of natural hypoallergenic isoforms positively contributes to future immunological and therapeutic studies and peanut cultivar development.

T-cell epitopes of the major peach allergen, Pru p 3: Identification and differential T-cell response of peach-allergic and non-allergic subjects

Lipid transfer proteins (LTPs), particularly peach Pru p 3, are the most relevant plant food allergens in the South of Europe, and, therefore, their allergic properties have been extensively studied. However, neither T-cell epitopes nor their effect on the patients' T-cell response has been investigated in any member of the LTP panallergen family. The objective of the present study was to map the major T-cell epitopes of Pru p 3, as well as to evaluate their induced T-cell response in peach-allergic versus control subjects. Thus, peripheral blood mononuclear cells (PBMCs) from 18 peach-allergic patients and Pru p 3-specific T-cell lines (TCLs) from 9 of them were cultured with Pru p 3 and with a panel of 17 derived peptides (10-mer overlapping in 5 amino acids representing the full sequence of Pru p 3). Proliferation in 5-day assays was carried out via tritiated-thymidine incorporation, while IL4 and IFNgamma production was assessed via sandwich enzyme-linked immunosorbent tests (ELISA) of TCL culture supernatants. The results were compared to those obtained from 10 non-peach allergic control volunteers. Two consecutive peptides showed the highest activation capacity. About 74% of PBMCs and TCLs recognized them, forming a single T-epitope: Pru p 3(65-80). Additionally, other specific T-cell epitopes were observed. Pru p 3(25-35) was detected by more than 60% of TCLs from peach-allergic patients, and Pru p 3(45-55) only activated PBMCs from control subjects. Interestingly, TCLs from patients were associated with a Th2-type, whereas control TCLs presented a Th1-type cytokine response. The major immunogenic T-cell epitope identified in Pru p 3, Pru p 3(65-80), is a good candidate to develop new vaccines for hypersensitivity reactions associated with LTP allergens from Rosaceae fruits.

Novel T-cell epitopes of ovalbumin in BALB/c mouse: potential for peptide-immunotherapy

The identification of food allergen T-cell epitopes provides a platform for the development of novel immunotherapies. Despite extensive knowledge of the physicochemical properties of hen ovalbumin (OVA), a major egg allergen, the complete T-cell epitope map of OVA has surprisingly not been defined in the commonly used BALB/c mouse model. In this study, spleen cells obtained from OVA-sensitized mice were incubated in the presence of 12-mer overlapping synthetic peptides, constructed using the SPOTS((R)) synthesis method. Proliferative activity was assessed by 72-h in vitro assays with use of the tetrazolium salt WST-1 and led to identification of four mitogenic sequences, i.e., A39R50, S147R158, K263E274, and A329E340. ELISA analyses of interferon (IFN)-gamma and interleukin (IL)-4 productions in cell culture supernatants upon stimulation with increasing concentrations of peptides confirmed their immunogenicity. Knowledge of the complete T-cell epitope map of OVA opens the way to a number of experimental investigations, including the exploration of peptide-based immunotherapy.

Characteristic motifs for families of allergenic proteins

The identification of potential allergenic proteins is usually done by scanning a database of allergenic proteins and locating known allergens with a high sequence similarity. However, there is no universally accepted cut-off value for sequence similarity to indicate potential IgE cross-reactivity. Further, overall sequence similarity may be less important than discrete areas of similarity in proteins with homologous structure. To identify such areas, we first classified all allergens and their subdomains in the Structural Database of Allergenic Proteins (SDAP, http://fermi.utmb.edu/SDAP/) to their closest protein families as defined in Pfam, and identified conserved physicochemical property motifs characteristic of each group of sequences. Allergens populate only a small subset of all known Pfam families, as all allergenic proteins in SDAP could be grouped to only 130 (of 9318 total) Pfams, and 31 families contain more than four allergens. Conserved physicochemical property motifs for the aligned sequences of the most populated Pfam families were identified with the PCPMer program suite and catalogued in the webserver MotifMate (http://born.utmb.edu/motifmate/summary.php). We also determined specific motifs for allergenic members of a family that could distinguish them from non-allergenic ones. These allergen specific motifs should be most useful in database searches for potential allergens. We found that sequence motifs unique to the allergens in three families (seed storage proteins, Bet v 1, and tropomyosin) overlap with known IgE epitopes, thus providing evidence that our motif based approach can be used to assess the potential allergenicity of novel proteins.

Peanut allergy

Peanut allergy has become a major health concern worldwide, especially in developed countries. However, the reasons for this increasing prevalence over the past several decades are not well understood. Because of the potentially severe health consequences of peanut allergy, those suspected of having had an allergic reaction to peanuts deserve a thorough evaluation. All patients with peanut allergy should be given an emergency management plan, as well as epinephrine and antihistamines to have on hand at all times. Patients and families should be taught to recognise early allergic reactions to peanuts and how to implement appropriate peanut-avoidance strategies. It is imperative that severe, or potentially severe, reactions be treated promptly with intramuscular epinephrine and oral antihistamines. Patients who have had such a reaction should be kept under observation in a hospital emergency department or equivalent for up to 4 h because of the possible development of the late-phase allergic response. This Seminar looks at the changing epidemiology of this allergy--and theories as to the rise in prevalence, diagnosis, and management of the allergy, and potential new treatments and prevention strategies under development.

Homology modelling and conformational analysis of IgE-binding epitopes of Ara h 3 and other legumin allergens with a cupin fold from tree nuts

Linear IgE-binding epitopes identified in legumin allergens of peanut (Ara h 3) and other allergenic tree nuts (Jug r 4 of walnut, Cor a 9 of hazelnut, Ana o 2 cashew nut) were mapped on three-dimensional models of the proteins built up by homology modelling. A conformational analysis revealed that consensual surface-exposed IgE-binding epitopes exhibited some structural homology susceptible to account for the IgE-binding cross-reactivity observed among peanut and tree nut allergens. This structurally related cross-reactivity seems irrespective of the botanical origin of the allergens and thus demands that persons allergic to peanut avoid other three nuts to prevent possible allergic reactions. IgE-binding epitopes similar to those found in 11S globulin allergens do not apparently occur in other vicilin allergens with the cupin fold from peanut (Ara h 1) or tree nuts (Jug r 2 of walnut, Cor a 1 of hazel nut, Ana o 3 of cashew nut).

Fasciola hepatica: identification of CD4+ T-helper epitopes from the 11.5 kDa saposin-like protein SAP-2 using synthetic peptides

Fasciola hepatica saposin-like protein (FhSAP-2) is a novel antigen expressed at an early stage of infection and has been shown to induce in rabbits a significant protection to infection with F. hepatica. There are no studies to identify the immunologically relevant regions of FhSAP-2. In this work the amino acid sequence of FhSAP-2 was analyzed to identify potential T-cell epitopes. A predictive algorithm identified four possible sites. Experimental determination of the T-cell epitopes was achieved using a panel of overlapping peptides spanning the entire sequence of FhSAP-2, which was evaluated for their ability to induce lymphoproliferative responses of spleen cells from 8 immunized BALB/c (H-2d) mice. Five different epitopes were identified. There was minimal agreement between theoretical and experimental approaches. It was found that peptides containing amino acid residues AVTFA and IDIDLCDICT as part of their structure induce high levels of IL-2 and IFNgammain vitro and was classified as Th1 epitopes. Peptides that contain the residues ADQTV, CIEFVQQEVD and YIIDHVDQHN induced significant amount of IL-4 and IL-2 were considered as containers of Th0 epitopes. Identification of prominent T-cell epitopes from FhSAP-2 offers the possibility of understanding how the CD4+ T-cell response is involved in protection against fasciolosis and how it is implicated in susceptibility to infection.

Bioinformatics approaches to classifying allergens and predicting cross-reactivity

Allergenic proteins from very different environmental sources have similar sequences and structures. This fact may account for multiple allergen syndromes, whereby a myriad of diverse plants and foods may induce a similar IgE-based reaction in certain patients. Identifying the common triggering protein in these sources, in silico, can aid designing individualized therapy for allergen sufferers. This article provides an overview of databases on allergenic proteins, and ways to identify common proteins that may be the cause of multiple allergy syndromes. The major emphasis is on the relational Structural Database of Allergenic Proteins (SDAP []), which includes cross-referenced data on the sequence, structure, and IgE epitopes of over 800 allergenic proteins, coupled with specially developed bioinformatics tools to group all allergens and identify discrete areas that may account for cross-reactivity. SDAP is freely available on the Web to clinicians and patients.

The peanut allergy epidemic: allergen molecular characterisation and prospects for specific therapy

Peanut (Arachis hypogaea) allergy is a major cause of food-induced anaphylaxis, with increasing prevalence worldwide. To date, there is no cure for peanut allergy, and, unlike many other food allergies, it usually persists through to adulthood. Prevention of exposure to peanuts is managed through strict avoidance, which can be compromised by the frequent use of peanuts and peanut products in food preparations. Conventional subcutaneous-injection allergen immunotherapy using crude peanut extract is not a recommended treatment because of the risk of severe side effects, largely as a result of specific IgE antibodies. Consequently, there is an urgent need to develop a suitable peanut allergen preparation that can induce specific clinical and immunological tolerance to peanuts in allergic individuals without adverse side effects. This requires detailed molecular and immunological characterisation of the allergenic components of peanut. This article reviews current knowledge on clinically relevant peanut allergens, in particular Ara h 1, Ara h 2 and Ara h 3, together with options for T-cell-reactive but non-IgE-binding allergen variants for specific immunotherapeutic strategies. These include T-cell-epitope peptide and hypoallergenic mutant vaccines. Alternative routes of administration such as sublingual are also considered, and appropriate adjuvants for delivering effective treatments at these sites examined.

Lack of association of HLA class II alleles with peanut allergy

BACKGROUND

Peanut allergy is a common and severe phenotype of food allergy with a strong genetic component; HLA class II polymorphisms are attractive candidate genes for this disorder.

OBJECTIVE

To determine possible genotypic associations of HLA class II with peanut allergy and attempt replication of previously reported associations.

METHODS

Sibling pairs discordant for peanut allergy were genotyped (low resolution) by polymerase chain reaction-based methods to 7 DQ and 18 DR allele groups. A chi2 analysis was undertaken against sibling controls with statistical adjustment for multiple analyses.

RESULTS

Seventy-three children with confirmed peanut allergy (mean age, 6.5 years; male, 72%; asthma, 58%; atopic dermatitis, 62%; allergic rhinitis, 67%; other food allergies, 41%) and 75 of their siblings who eat peanut (mean age, 8 years; male, 52%; asthma, 12%; atopic dermatitis, 22%; allergic rhinitis, 37%; other food allergy, 7%) were genotyped. Distribution of DQ7 (29% of children with peanut allergy vs 47% sibling controls) was statistically significantly different (P = .04) before statistical correction for multiple comparisons was made by multiplying them by the number of alleles tested (and not statistically significant after correction; P = .30). Distribution of DR11 was nearly statistically significant without statistical adjustment (26% with peanut allergy vs 41% of sibling controls; P = .07; corrected P = 1.3). Alleles that were previously reported to have a weak association with peanut allergy (DRB1 *03, *08; DQB1 *0302, *04) were not verified in this cohort (unadjusted P > .44).

CONCLUSIONS

We could not establish an association between the HLA class II alleles evaluated in this cohort of sibling pairs discordant for peanut allergy.

T-cell epitopes of food allergens

During recent years, a great deal of research has focused on the identification of food allergens, their characterization at the molecular level, and the investigation of immunological mechanisms responsible for food hypersensitivity. Allergen-reactive T-helper 2 cells play a central role in the pathophysiology of allergic diseases. After activation with allergens, this subset of CD4(+) T-lymphocytes produces a spectrum of cytokines that induce high serum levels of immunoglobulin E and eosinophilia, which, in turn, mediate the clinical symptoms. Furthermore, T-helper 2 cells are present in target organs during the late response to allergen exposure. The analysis of the allergic T-cell response, including cytokine production and the identification of T-cell epitopes, provides important information on the characteristics of food allergens. Therefore, in vitro cultures of allergen-specific T-cells derived from peripheral blood or different target organs have been of indispensable help. Results obtained from such studies may not only contribute to the understanding of cellular mechanisms underlying different types of food allergy but also to the development of novel strategies for immunotherapy of food allergy.

Current developments in peanut allergy

PURPOSE OF REVIEW

Peanut allergy is among the most serious, life-threatening food sensitivities, and recent studies indicate increasing prevalence, particularly among children. Our objective is to highlight recent advances in the immunology and treatment of peanut allergy.

RECENT FINDINGS

Peanut sensitization may be both a Th1- and Th2-driven process, and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) may play a role in regulating the response intensity. Preliminary work shows that the food matrix is important in the immune response to peanut and that purified peanut allergens may have little intrinsic stimulatory capacity. Studies characterizing peanut allergens have revealed Ara h 1 and Ara h 2 as the most potent allergens, but Ara h 3 may be more allergenic than previously thought. There appears to be a relationship between the diversity of IgE-binding patterns and the severity of clinical symptoms. Multiple novel approaches to treatment are being investigated, which include traditional Chinese medicine, various forms of modified immunotherapy and the use of adjuvants in modified immunotherapy.

SUMMARY

By understanding the immunologic response to peanut and the roles of the major peanut allergens, it may be possible to predict those at risk for severe reactions, prevent peanut sensitization and effectively treat those already sensitized.

IgE cross-reactivity between the major peanut allergen Ara h 2 and tree nut allergens

Allergy to peanut and tree nuts is characterised by a high frequency of life-threatening anaphylactic reactions and typically lifelong persistence. Although peanut is the most common cause of nut allergy, peanut allergic patients are frequently also sensitive to tree nuts. It is not known if this is due to cross-reactivity between peanut and tree nut allergens. In this study, the major peanut allergen Ara h 2 was cloned from peanut cDNA, expressed in E. coli cells as a His-tag fusion protein and purified using a Ni-NTA column. Immunoblotting, ELISA and basophil activation indicated by CD63 expression all confirmed the IgE reactivity and biological activity of rAra h 2. To determine whether or not this allergen plays a role in IgE cross-reactivity between peanut and tree nuts, inhibition ELISA was performed. Pre-incubation of serum from peanut allergic patients with increasing concentrations of almond or Brazil nut extract inhibited IgE binding to rAra h 2. Purified rAra h 2-specific serum IgE antibodies also bound to proteins present in almond and Brazil nut extracts by immunoblotting. This indicates that the major peanut allergen, Ara h 2, shares common IgE-binding epitopes with almond and Brazil nut allergens, which may contribute to the high incidence of tree nut sensitisation in peanut allergic individuals.

Towards immunotherapy for peanut allergy

PURPOSE OF REVIEW

Food allergy is a major cause of life-threatening hypersensitivity reactions. Peanut allergy is the most serious of the hypersensitivity reactions to foods due to its persistence and high risk of severe anaphylaxis. Currently, strict avoidance of the allergenic food and ready access to self-injectable epinephrine is the 'standard of care' for food allergy. Based on extensive characterization of food allergens and a better understanding of the immunological mechanisms underlying allergic disease, promising therapeutic modalities for food allergy treatment and prevention are being developed.

RECENT FINDINGS

Immunotherapeutic strategies include peptide immunotherapy, mutated protein immunotherapy and DNA immunization, which all strive to decrease the deleterious Th2 response. Another approach already in clinical trials for peanut allergy is the anti-IgE therapy which prevents circulating IgE from binding to effector cells, consequently decreasing clinical symptoms after peanut ingestion. In order to be applicable, these strategies must be well tolerated, inexpensive and easily administered. Realistic treatment options would likely involve a combination of different approaches.

SUMMARY

Food allergy affects approximately 4-6% of children and 3-4% of adults. Peanut allergy can be devastating as reactions range from urticaria to severe anaphylactic shock and death. The only preventive measure for peanut allergy is strict avoidance of the incriminating food. It is likely immunotherapy will be available in the near future as a well tolerated and effective therapy for treating peanut allergy. The use of the anti-IgE therapy in conjunction with other immunotherapy would possibly be the best treatment option in the future.

Peptide-based vaccination: where do we stand?

PURPOSE OF REVIEW

Allergen-specific immunotherapy represents the only causative approach towards allergy treatment. Specific immunotherapy can, however, include allergic reactions and occasionally life-threatening anaphylaxis. Peptides have been evaluated as a potential therapeutic approach in atopic allergic disease because they have the potential to inhibit T-cell function but not induce anaphylaxis.

RECENT FINDINGS

Data from early clinical trials of peptide vaccination revealed that therapy was associated with a modest improvement in allergic disease, and was accompanied by a high frequency of adverse reactions. More recent studies have demonstrated improved clinical outcomes, improved safety, and have defined the mechanisms of adverse events observed in earlier studies. Mechanisms of peptide vaccination include the hyporesponsiveness of allergen-specific responses and the induction of regulatory T cells and cytokines. Novel peptide design has allowed the generation of fragments that contain T-cell stimulatory epitopes, lack B cell epitopes, and can induce protective IgG responses in both mice and humans. Other approaches have focused on hypoallergenic B-cell epitopes that induce inhibitory IgG antibodies. Peptides that specifically induce regulatory cytokine production would also enhance peptide vaccines. Several recent studies have described immunodominant epitopes from major allergens that may form candidate peptides for use in peptide vaccination.

SUMMARY

The manipulation of peptide epitopes may provide a strategy for the rational design of peptide allergy vaccines further improving safety and efficacy.

Mimotopes identify conformational epitopes on parvalbumin, the major fish allergen

Parvalbumin, the major fish allergen, is recognized by allergen-specific IgE of more than 90% of all fish-allergic patients. A detailed knowledge of allergenic structures is crucial for developing a vaccine inducing blocking antibodies specifically directed towards the IgE binding epitopes. In the present study we aimed to use the phage display technique to generate mimotopes, which mimic epitopes on parvalbumin. Parvalbumin-specific IgE was purified from sera of fish-allergic patients and used for screening of a constrained decamer phage library. After four rounds of biopanning using parvalbumin-specific IgE, five phage clones were selected which were specifically recognized by parvalbumin-specific IgE as well as IgG. DNA sequencing and peptide alignment revealed a high degree of sequence similarities between the mimotopes. Interestingly, on the surface of natural parvalbumin three regions could be defined by computational mimotope matching. In accordance, previously defined allergenic peptides of cod parvalbumin highlighted areas in close proximity or overlapping with the mimotope matching sites. From the presented data we conclude that our approach identified conformational epitopes of parvalbumin relevant for IgE and IgG binding. We suggest that these mimotopes are suitable candidates for an epitope-specific immunotherapy of fish-allergic patients.

Novel treatments for food allergy

Food allergy is a major cause of life-threatening hypersensitivity reactions. Currently, the strict avoidance of the allergenic food and ready access to self-injectable adrenaline is the standard of care for food allergy. Based on extensive characterisation of food allergens and a better understanding of the immunological mechanisms underlying allergic disease, promising therapeutic modalities for the treatment and eventual prevention of food allergy are being developed. Novel immunotherapeutic strategies include peptide immunotherapy, traditional Chinese medicine, mutated or homologous protein immunotherapy, DNA immunisation and immunisation with immunostimulatory sequences, which all strive to elicit a decreased T helper cell type 2-like response or tolerance by the immune system in response to a specific food allergen. Other approaches such as the anti-IgE therapy or the Fcgamma-Fcepsilon fusion protein aim at preventing the release of mediators by mast cells. It is the combination of these different approaches that would probably offer the best treatment option for food-allergic patients in a not too distant future.