Identification and fine mapping of IgG and IgE epitopes in ovomucoid

Exploring the molecular modifications and allergenicity of the egg white protein matrix during boiling

Hen's egg allergy is the second most common food allergy in young children, with the major allergens ovalbumin and ovomucoid found in egg white. While many egg-allergic children can tolerate baked or hard-boiled eggs, there is limited understanding of how heating affects allergen structure and allergenicity within the egg white protein matrix. This study investigated the impact of egg white boiling for 10 or 45 min on the structure and allergenicity of the main egg white allergens. Our results showed that 45 min of boiling led to significant structural changes and a strong reduction in egg white allergenicity, while 10 min of boiling had a minor effect. Gastric digestion further reduced allergenicity, especially in 45 min boiled eggs. These findings highlight how increasing the boiling time of egg white can reduce allergenicity through structural changes in the main egg white allergens.

Molecular Allergology: Epitope Discovery and Its Application for Allergen-Specific Immunotherapy of Food Allergy

The prevalence of food allergy continues to rise, posing a significant burden on health and quality of life. Research on antigenic epitope identification and hypoallergenic agent design is advancing allergen-specific immunotherapy (AIT). This review focuses on food allergens from the perspective of molecular allergology, provides an overview of integration of bioinformatics and experimental validation for epitope identification, highlights hypoallergenic agents designed based on epitope information, and offers a valuable guidance to the application of hypoallergenic agents in AIT. With the development of molecular allergology, the characterization of the amino acid sequence and structure of the allergen at the molecular level facilitates T-/B-cell epitope identification. Alignment of the identified epitopes in food allergens revealed that the amino acid sequence of T-/B-cell epitopes barely overlapped, providing crucial data to design allergen molecules as a promising form for treating (FA) food allergy. Manipulating antigenic epitopes can reduce the allergenicity of allergens to obtain hypoallergenic agents, thereby minimizing the severe side effects associated with AIT. Currently, hypoallergenic agents are mainly developed through synthetic epitope peptides, genetic engineering, or food processing methods based on the identified epitope. New strategies such as DNA vaccines, signaling molecules coupling, and nanoparticles are emerging to improve efficiency. Although significant progress has been made in designing hypoallergenic agents for AIT, the challenge in clinical translation is to determine the appropriate dose and duration of treatment to induce long-term immune tolerance.

Practical experience of allergy to egg proteins clinical manifestation

Food allergy occupies a significant place among disorders that impair the quality of patients’ lives, bringing a large number of restrictions to their diet and lifestyle. Therefore, the purpose of this study is to examine the clinical features of allergy to chicken eggs with the determination of key trends in diagnosis and treatment. A descriptive and comparative analysis of three cases was carried out with a large-scale assessment of specific Immunoglobulins E (IgE), determined by the enzyme-linked immunosorbent assay. It becomes clear, that due to the high prevalence of allergy to white and yolk of chicken eggs in the general population (among the Polish population including), chicken eggs have severe allergenic characteristics and may display various symptoms that may be problematic to differentiate. The patients from the presented cases were characterized by a severe course of the disease – minimal consumption of chicken eggs led to the development of urticaria, swelling of the eyelids, and bronchospasm, which required urgent administration of adrenaline and hospitalization. For the purpose of diagnosis, patients with anaphylactic reactions are highly restricted, because methods of skin prick testing, and provocation tests (oral and nasal) are contraindicated. In this regard, molecular diagnostics and the determination of specific immunoglobulins E for ovalbumin, ovomucoid, and other glycoproteins are recommended. This research can lead to the creation of purified recombinant allergens for use in the process of diagnosis and treatment, as well as in the food industry, also, it emphasizes the introduction of preventive measures for the development of anaphylaxis.

Effects of unfolding treatment assisted glycation on the IgE/IgG binding capacity and antioxidant activity of ovomucoid

Ovomucoid is the immune-dominant allergen in the egg white of hens. Due to its structure based on nine disulfide bonds as well as its resistance to heat and enzymatic hydrolysis, the allergenicity of this food protein is difficult to decrease by technological processes. We sought to reduce its allergenicity through the Maillard reaction. The unfolding of ovomucoid with L-cysteine-mediated reduction was used to increase accessibility to conformational and linear epitopes by modifying the secondary and tertiary structures of the allergen. Glycation with different saccharides revealed the beneficial effect of maltose glycation on the IgG-binding capacity reduction. By determining the better glycation conditions of unfolded ovomucoid, we produced ovomucoid with reduced IgE binding capacity due to the glycation sites (K17, K112, K129, and K164) on epitopes. Moreover, after simulated infant and adult gastrointestinal digestion, the unfolded plus glycated ovomucoid showed higher ABTS˙+ scavenging activity, O2˙- scavenging activity, ˙OH scavenging activity, Fe2+ chelating activity, and a FRAP value; in particular, for ˙OH scavenging activity, there was a sharp increase of more than 100%.

Tolerance to heated egg in egg allergy: Explanations and implications for prevention and treatment

Hen's egg allergy is the second most frequent food allergy found in children. Allergic symptoms can be caused by raw or heated egg, but a majority of egg-allergic children can tolerate hard-boiled or baked egg. Understanding the reasons for the tolerance towards heated egg provides clues about the molecular mechanisms involved in egg allergy, and the differential allergenicity of heated and baked egg might be exploited to prevent or treat egg allergy. In this review, we therefore discuss (i) why some patients are able to tolerate heated egg; by highlighting the structural changes of egg white (EW) proteins upon heating and their impact on immunoreactivity, as well as patient characteristics, and (ii) to what extent heated or baked EW might be useful for primary prevention strategies or oral immunotherapy. We describe that the level of immunoreactivity towards EW helps to discriminate patients tolerant or reactive to heated or baked egg. Furthermore, the use of heated or baked egg seems effective in primary prevention strategies and might limit adverse reactions. Oral immunotherapy is a promising treatment strategy, but it can sometimes cause significant adverse events. The use of heated or baked egg might limit these, but current literature is insufficient to conclude about its efficacy.

Generation of an Ovomucoid-Immune scFv Library for the Development of Novel Immunoassays in Hen's Egg Detection

Hen's egg allergy is the second most common food allergy among infants and young children. The possible presence of undeclared eggs in foods poses a significant risk to sensitized individuals. Therefore, reliable egg allergen detection methods are needed to ensure compliance with food labeling and improve consumer protection. This work describes for the first time the application of phage display technology for the generation of a recombinant antibody aimed at the specific detection of hen's ovomucoid. First, a single-chain variable fragment (scFv) library was constructed from mRNA isolated from the spleen of a rabbit immunized with ovomucoid. After rounds of biopanning, four binding clones were isolated and characterized. Based on the best ovomucoid-binding candidate SR-G1, an indirect phage enzyme-linked immunosorbent assay (phage-ELISA) was developed, reaching limits of detection and quantitation of 43 and 79 ng/mL of ovomucoid, respectively. The developed ELISA was applied to the analysis of a wide variety of food products, obtaining a good correlation with a commercial egg detection assay used as a reference. Finally, in silico modeling of the antigen-antibody complex revealed that the main interactions most likely occur between the scFv heavy chain and the ovomucoid domain-III, the most immunogenic region of this allergen.

Pulsed Electric Field-Assisted Alcalase Treatment Reduces the Allergenicity and Eliminates the Antigenic Epitopes of Ovomucoid

Physically assisted chemical modifications can effectively reduce the allergenicity of ovomucoid (OVM). However, only a few studies have used pulsed electric field (PEF)-assisted alcalase hydrolysis to reduce the allergenicity of OVM. Herein, we investigated the effect of PEF-assisted alcalase treatment on the spatial conformation, allergenicity, and antigenic epitopes of OVM based on multispectroscopic analyses, bioinformatics, and mass spectrometry. The results showed that PEF-assisted alcalase treatment promoted the hydrolysis of OVM; moreover, the α-helix content and surface hydrophobicity of OVM significantly decreased, which disordered its spatial conformation and weakened its intermolecular interactions. Additionally, enzyme-linked immunosorbent assay (ELISA) results showed that the PEF-assisted alcalase treatment significantly reduced the binding levels of IgE and IgG1, which were 47.66 and 36.41%, respectively. Finally, eight epitopes of OVM were obtained by immunoinformatic tools. Nano-high performance liquid chromatography coupled to tandem mass spectrometry (nano-HPLC MS/MS) results showed that the hydrolysate of OVM and alcalase (HOVM) had nine more peptide-containing epitopes than the hydrolysate of PEF-treated OVM and PEF-treated alcalase (HOVM-PP'), indicating that PEF could promote the elimination of linear epitopes in OVM, thereby reducing OVM allergenicity.

The Heterogeneity of Ovomucoid-Specific IgE Idiotype Is Associated With Egg Allergy Symptom Severity

Immunoglobulin E (IgE)-mediated egg allergy presents as one of the most common food allergies. The level of specific IgE (sIgE) antibody is widely used as an important in vitro diagnostic indicator. However, sIgE antibody levels are often inconsistent with the clinical manifestations of patients. The heterogeneity of egg-specific IgE idiotypes (sIgE-IDs) may help reflect clinical egg allergy severity. Eight peptides were synthesized, corresponding to the linear epitopes of ovomucoid (OVM). The sIgE-IDs of egg-allergic patients were detected by enzyme-linked immunosorbent assay. Fresh peripheral blood was collected from patients with different heterogeneity strength of sIgE-ID, and egg extract was used as a stimulus to the basophil activation test (BAT). RBL-2H3 cells were sensitized with serum with different strength of sIgE-ID heterogeneity and the release rate of β-hexosaminidase was calculated. Among 75 patients with egg allergy, 24% had sIgE for all epitopes and 85% had sIgE for at least one epitope. Analysis of individual patients revealed differences in epitope recognition patterns among the patients, that is, heterogeneity in sIgE-ID. More importantly, the number of IgE-positive peptides had a strong correlation with allergic symptoms in egg-allergic patients (r = 0.706). BAT and RBL-2H3 cell degranulation confirmed that higher sIgE-ID heterogeneity strength was more effective in inducing effector cell responses. Our results suggest that the greater the heterogeneity strength of OVM-sIgE-ID, the more severe the allergic symptoms.

Epitope mapping and the effects of various factors on the immunoreactivity of main allergens in egg white

Egg white has high protein content and numerous biological/functional properties. However, reported allergenicity for some of the proteins in egg white is an issue that needs to be paid exclusive attention. A consideration of the structure of IgE epitopes and their sequences, as well as a comprehensive understanding of the effects of various processes on epitopes and the impact of the gastrointestinal tract on them, can help target such issues. The current study focuses on the identified IgE epitopes in egg white proteins and evaluation of the effects of the gastrointestinal digestion, carbohydrate moiety, food matrix, microbial fermentation, recombinant allergen, heat treatment, Maillard reaction and combination of various processes and gastrointestinal digestion on egg white allergenicity. Although the gastrointestinal tract reduces the immunoreactivity of native egg white proteins, some of the IgE epitope-containing fragments remain intact during the digestion process. It has been found that the gastrointestinal tract can have both positive and negative impacts on the IgE binding activities of egg white proteins. Elimination of the carbohydrate moiety leads to a reduction in the immunoreactivity of ovalbumin. But, such effects from the carbohydrate parts in the IgE binding activity need to be explored further. In addition, the interaction between the egg white proteins and the food matrix leads to various effects from the gastrointestinal tract on the digestion of egg white proteins and their subsequent immunoreactivity. Further on this matter, studies have shown that both microbial fermentation and Maillard reaction can reduce the IgE binding activities of egg white proteins. Also, as an alternate approach, the thermal process can be used to treat the egg white proteins, which may result in the reduction or increase in their IgE binding activities depending on the conditions used in the process. Overall, based on the reported data, the allergenicity levels of egg white proteins can be mitigated or escalated depending on the conditions applied in the processing of the food products containing egg white. So far, no practical solutions have been reported to eliminate such allergenicity.

Production and characterization of eggs from hens with ovomucoid gene mutation

Ovomucoid is a major egg white protein which is considered as the most dominant allergen in chicken eggs. Owing to the difficulty of separating ovomucoid from egg whites, researchers have adopted genetic deletion for development of hypoallergenic eggs. Previously, we used CRISPR/Cas9 to establish chickens with ovomucoid gene (OVM) mutations, but it remained unknown whether such hens could produce eggs at maturity. Here, we have reported on eggs laid by OVM-targeted hens. Except for watery egg whites, the eggs had no evident abnormalities. Real-time PCR revealed alternative splicing of OVM mRNA in hens, but their expression was limited. Immunoblotting detected neither mature ovomucoid nor ovomucoid-truncated splicing variants in egg whites. Sixteen chicks hatched from 28 fertilized eggs laid by OVM-targeted hens, and fourteen of the sixteen chicks demonstrated healthy growth. Taken together, our results demonstrated that OVM knockout could almost completely eliminate ovomucoid from eggs, without abolishing fertility. Thus, the eggs developed in this study have potential as a hypoallergenic food source for most patients with egg allergies.

Ovomucoid epitope-specific repertoire of IgE, IgG4 , IgG1 , IgA1 , and IgD antibodies in egg-allergic children

BACKGROUND

Egg-white ovomucoid, that is, Gal d 1, is associated with IgE-mediated allergic reactions in most egg-allergic children. Epitope-specific IgE levels have been correlated with the severity of egg allergy, while emerging evidence suggests that other antibody isotypes (IgG₁ , IgG₄ , IgA, and IgD) may have a protective function; yet, their epitope-specific repertoires and associations with atopic comorbidities have not been studied.

METHODS

Bead-based epitope assay (BBEA) was used to quantitate the levels of epitope-specific (es)IgA, esIgE, esIgD, esIgG₁ , and esIgG₄ antibodies directed at 58 (15-mer) overlapping peptides, covering the entire sequence of ovomucoid, in plasma of 38 egg-allergic and 6 atopic children. Intraclass correlation (ICC) and coefficient of variation (CV) were used for the reliability assessment. The relationships across esIgs were evaluated using network analysis; linear and logistic regressions were used to compare groups based on egg allergy status and comorbidities.

RESULTS

BBEA had high reliability (ICC >0.75) and low variability (CV <20%) and could detect known IgE-binding epitopes. Egg-allergic children had lower esIgA₁ (P = .010) and esIgG₁ (P = .016) and higher esIgE (P < .001) and esIgD (P = .015) levels compared to the atopic controls. Interestingly, within the allergic group, children with higher esIgD had decreased odds of anaphylactic reactions (OR =0.48, P = .038). Network analysis identified most associations between esIgE with either esIgG₄ or esIgD; indicating that IgE-secreting plasma cells could originate from either sequential isotype switch from antigen-experienced intermediate isotypes or directly from the IgD⁺ B cells.

CONCLUSIONS

Collectively, these data point toward a contribution of epitope-specific antibody repertoires to the pathogenesis of egg allergy.

Detection of specific IgE against linear epitopes from Gal d 1 has additional value in diagnosing hen's egg allergy in adults

Background

Although hen's egg allergy is more prevalent in children, up to 0.6% of adults from different European countries suffer from a persistent or newly onset hen's egg allergy, making accurate diagnosis in adults necessary. However, sensitization to hen's egg extracts, components and linear epitopes is solely studied in children.

Methods

Hen's egg allergic (n = 16) and tolerant (n = 19) adults were selected by sensitization towards recombinant components rGal d 1 and/or 3. Sensitization profiles towards egg white and yolk extract and the native components Gal d 1, 2, 3 and 4 were respectively evaluated with the ImmunoCAP or the EUROLINE system. Characterization of linear epitopes was performed with a peptide microarray containing 15mer peptides representing the entire sequence of mature Gal d 1 and 3.

Results

Overall, sIgE titres against hen's egg extracts and single components overlapped largely between allergic and tolerant adults. Although the median sIgE/sIgG4 ratio to Gal d 1 was increased in allergic adults, the range was comparable between both groups. Clinically relevant sensitization to Gal d 1 was confirmed by sIgE‐binding to the linear epitopes aa30‐41, aa39‐50 or aa84‐95 in 6/13 allergic adults, mainly suffering from objective symptoms. In comparison, these epitopes were recognized by 1/15 tolerant patient. Only a few linear epitopes were detected for Gal d 3, suggesting a greater importance of conformational epitopes for the recognition of Gal d 3.

Conclusion and Clinical Relevance

Specific IgE‐binding to linear epitopes of Gal d 1 is highly specific in identifying hen's egg allergic adults with objective symptoms.

IgE and IgG4 responses to shrimp allergen tropomyosin and its epitopes in patients from coastal areas of northern China

Sensitization to allergens and their peptides varies among patients due to geographical or ethnic differences. The present study aimed to investigate immunoglobulin (Ig)E and IgG₄ responses to tropomyosin and its peptides in shrimp allergic patients from northern China. A total of 92 subjects were studied, including 35 shrimp allergic patients, 29 patients with house dust mite (HDM) and/or cockroach allergic patients and 28 healthy volunteers. Serum IgE and IgG₄ antibodies to recombinant shrimp tropomyosin (rPen a 1) and its peptides were measured by means of a light-initiated chemiluminescent assay. A total of 9 major sequential epitopes of Pen a 1 reported in the literature were synthesized. Of 35 shrimp allergic patients, 25 (71.4%) had positive Pen 1-specific IgE (sIgE) antibodies and 22 (62.9%) contained measurable rPen a 1-specific IgG₄ (sIgG₄) antibodies. A strong IgG₄ response accompanied the presence of IgE to Pen a 1. None of the patients with HDM and/or cockroach allergy demonstrated IgE reactivity to rPen a 1. The reaction frequency of IgE binding epitope was 20–48%, while that of IgG₄ binding epitope was 63.6–3.9%. The IgE and IgG₄ recognition patterns of the tropomyosin peptides demonstrated high interpatient heterogeneity. Diversity of IgE binding epitopes was positively correlated with Pen a 1 sIgE levels. In the study population, tropomyosin was a major allergen recognized by the majority of shrimp allergic patients, which is consistent with previous reports. However, none of the 9 epitopes are major (reaction frequency >50%) IgE-binding regions, indicating the epitopes profile may be different in other regions.

Effect of enzyme immobilization and in vitro digestion on the immune-reactivity and sequence of IgE epitopes in egg white proteins

Immune-reactivity reduction of egg white proteins by free and immobilized enzymes and determination of degraded IgE epitopes.

Bioactive Egg Proteins

The nutritional excellence of chicken egg is derived from its task as a life-giving medium, supplying the necessary nutrients to the hen's embryo while protecting it from external threats. Additionally, egg proteins possess unique biological activities above and beyond their known functional and nutritional roles. In the last few decades, extensive research has been done to evaluate the various biological activities of egg proteins and protein-derived peptides. Egg proteins and protein-derived peptides have been attributed to diverse biological activities, the most well-known being their antimicrobial properties. However, egg proteins and peptides have been shown to have other biological activities, such as antihypertensive, antioxidant, anticancer, immunomodulatory, and protease inhibitory activity. Egg-derived bioactive proteins have had a relevant scientific impact and exhibit promising applicability as an ingredient for the development of functional foods and nutraceuticals. However, it is critical to understand the effects of these proteins in signaling pathways to delineate their molecular mechanisms of action. Further studies are required to fill the current knowledge gaps. Therefore, the purpose of the chapter is to illustrate the present knowledge of the bioactivity of different egg proteins and their physiological effects.

Bioinformatics analysis of aflatoxins produced by Aspregillus sp. in basic consumer grain (corn and rice) in Saudi Arabia

The food contaminants by aflatoxins are inevitable even when all precautions and good agricultural practices are applied. Samples of white rice and corn (yellow, red) grains were collected from different local markets and houses. Three Aspergillus flavus strain isolated were identified using molecular characterization of AFLR (aflR) toxin gene. DNA genome of the three A. flavus isolates (namely A. flavus _ YC; A. flavus _ RC; A. flavus _ Rice) which corresponds to isolates from, yellow corn, red corn and white rice respectively were used as a template for PCR to amplify Aspergillus flavus AFLR (aflR) toxin gene. Partially sequenced was amplified using a specific primer set to confirm its identity, phylogenetic relationships between the three isolates as well as determination of the corresponding antigenic determinants. The epitope prediction analysis demonstrated that there were 1, 2, 3 and 4 epitopes whose score were equal 1 in A. flavus _ YC; A. flavus _ RC; A. flavus _ Rice, respectively. Interestingly, there were great dissimilarity in the epitope sequences among the three isolates except in RLQEGGDDAAGIPA, SPPPPVETQGLGGD, RPSESLPSARSEQG and PAHNTYSTPHAHTQ were found to be similar between all isolates. This work articulates that the molecular identification and characterization of three A. flavus using Aspergillus flavus AFLR (aflR) toxin gene and the unique antigenic determinants that could be used for design of a broad-spectrum antibody for rapid detection of A. flavus in foods and support quality system of food safety.

Advances on the impact of thermal processing on structure and antigenicity of chicken ovomucoid

BACKGROUND

Ovomucoid (OVM) is the dominant allergen found in egg white. The heat-induced changes on chicken OVM structure and antigenic properties were assessed at acidic, neutral and alkaline pH values.

RESULTS

The fluorescence spectroscopy measurements indicated changes in the conformation of OVM caused by both pH and thermal treatment. The OVM molecule exhibited higher exposure of hydrophobic residues at 7.0, as indicated by the synchronous spectra, intrinsic fluorescence and quenching experiments. When heating the protein at pH 9.5, the molecular structure appeared more compact. The antigenic properties of OVM, estimated through the enzyme-linked immunosorbent assay, appeared not to be sensitive to heat at pH 7.0 and 4.5. Single molecule level investigations indicated that the secondary and tertiary structure of OVM was affected by the thermal treatment.

CONCLUSIONS

Experimental results indicated over 90% reduction of the antigenicity at pH 9.5 and temperature of 100 °C. Significant changes of the linear epitopes exposure and location of the conformational epitopes were highlighted after performing heating molecular dynamics simulations of OVM from 25 °C to 100 °C. © 2017 Society of Chemical Industry.

Effect of acid treatment on allergenicity of peanut and egg

BACKGROUND

Many food experts have studied various treatments or processing techniques in order to develop hypoallergenic foods. In a previous study, acid treatment dramatically mitigated the allergenicity of peanut, especially Ara h 2.

RESULTS

Gel electrophoresis showed that most protein bands of acid-treated peanut were not detected, but protein bands of egg white became weaker and broader by acid treatment. In immunoblotting using a rabbit antibody, the antigenicity against ovalbumin or ovomucoid in acid-treated egg white was decreased but the antigenicity against Ara h 1 or Ara h 2 in peanut treated with pH 2 acetic acid was completely undetected. The allergenicity of ovalbumin and peanut fell significantly to 1/10²² and 1/5380, respectively, when measured as IC₅₀ in the sample treated with pH 2.0 acetic acid.

CONCLUSION

This study showed that acid treatment was more effective in peanut and barely effective in ovomucoid. This may contribute to the development of hypoallergenic food and clinical management of food allergy. © 2016 Society of Chemical Industry.

Hypoallergenic Variant of the Major Egg White Allergen Gal d 1 Produced by Disruption of Cysteine Bridges

BACKGROUND

Gal d 1 (ovomucoid) is the dominant allergen in the chicken egg white. Hypoallergenic variants of this allergen can be used in immunotherapy as an egg allergy treatment approach. We hypothesised that disruption of two of the nine cysteine-cysteine bridges by site-directed mutagenesis will allow the production of a hypoallergenic variant of the protein; Methods: Two cysteine residues at C192 and C210 in domain III of the protein were mutated to alanine using site-directed mutagenesis, to disrupt two separate cysteine-cysteine bridges. The mutated and non-mutated proteins were expressed in Escherichia coli (E. coli) by induction with isopropyl β-d-1-thiogalactopyranoside (IPTG). The expressed proteins were analysed using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting to confirm expression. Immunoglobulin E (IgE) reactivity of the two proteins was analysed, by immunoblotting, against a pool of egg-allergic patients' sera. A pool of non-allergic patients' sera was also used in a separate blot as a negative control; Results: Mutant Gal d 1 showed diminished IgE reactivity in the immunoblot by showing lighter bands when compared to the non-mutated version, although there was more of the mutant protein immobilised on the membrane when compared to the wild-type protein. The non-allergic negative control showed no bands, indicating an absence of non-specific binding of secondary antibody to the proteins; Conclusion: Disruption of two cysteine bridges in domain III of Gal d 1 reduces IgE reactivity. Following downstream laboratory and clinical testing, this mutant protein can be used in immunotherapy to induce tolerance to Gal d 1 and in egg allergy diagnosis.

Common food allergens and their IgE-binding epitopes

Food allergy is an adverse immune response to certain kinds of food. Although any food can cause allergic reactions, chicken egg, cow's milk, wheat, shellfish, fruit, and buckwheat account for 75% of food allergies in Japan. Allergen-specific immunoglobulin E (IgE) antibodies play a pivotal role in the development of food allergy. Recent advances in molecular biological techniques have enabled the efficient analysis of food allergens. As a result, many food allergens have been identified, and their molecular structure and IgE-binding epitopes have also been identified. Studies of allergens have demonstrated that IgE antibodies specific to allergen components and/or the peptide epitopes are good indicators for the identification of patients with food allergy, prediction of clinical severity and development of tolerance. In this review, we summarize our current knowledge regarding the allergens and IgE epitopes in the well-researched allergies to chicken egg, cow's milk, wheat, shrimp, and peanut.

Cracking the egg: An insight into egg hypersensitivity

Hypersensitivity to the chicken egg is a widespread disorder mainly affecting 1-2% of children worldwide. It is the second most common food allergy in children, next to cow's milk allergy. Egg allergy is mainly caused by hypersensitivity to four allergens found in the egg white; ovomucoid, ovalbumin, ovotransferrin and lysozyme. However, some research suggests the involvement of allergens exclusively found in the egg yolk such as chicken serum albumin and YGP42, which may play a crucial role in the overall reaction. In egg allergic individuals, these allergens cause conditions such as itching, atopic dermatitis, bronchial asthma, vomiting, rhinitis, conjunctivitis, laryngeal oedema and chronic urticaria, and anaphylaxis. Currently there is no permanent cure for egg allergy. Upon positive diagnosis for egg allergy, strict dietary avoidance of eggs and products containing traces of eggs is the most effective way of avoiding future hypersensitivity reactions. However, it is difficult to fully avoid eggs since they are found in a range of processed food products. An understanding of the mechanisms of allergic reactions, egg allergens and their prevalence, egg allergy diagnosis and current treatment strategies are important for future studies. This review addresses these topics and discusses both egg white and egg yolk allergy as a whole.

Influence of the carbohydrate moieties on the immunoreactivity and digestibility of the egg allergen ovomucoid

BACKGROUND

Ovomucoid (OM) has two carbohydrate chains on each of the first and second domains and one in the third. The contribution of the covalently bound carbohydrate chains to the overall OM allergenicity is controversial. Another aspect directly related with the immunological properties of OM that has not been studied in depth is the importance of the carbohydrate chains on its digestibility.

OBJECTIVE

The aim of the study was to assess the involvement of the carbohydrate moieties of OM in its digestibility and allergenic properties.

METHODS

IgE-binding and basophil activation by glycosylated and enzymatically deglycosylated OM (dOM) were compared using blood from egg-allergic patients. The peptides obtained after digestion using a physiologically relevant model were identified by RP-HPLC-MS/MS and the IgE-binding of the resulting fragments was evaluated by DOT-Blot.

RESULTS

No structural changes were observed after deglycosylation of OM. 80% of the patients showed lower IgE binding to dOM as compared with OM and, in some patients, IgE reactivity could not be inhibited by pre-incubation with dOM. A subtle reduction in the percentage of activated basophils was observed when incubated with dOM as compared to OM. Following simulated digestion, dOM was more extensively degraded than OM, particularly during the gastric phase and both, OM and dOM, yielded, after the duodenal phase, immunoreactive fragments that were totally or partially coincident with previously described epitopes.

CONCLUSION & CLINICAL RELEVANCE

this work demonstrated an enhanced IgE reactivity towards carbohydrate containing OM in some egg-allergic patients that could be attributed to cross-sensitization or sensitization to the glycosylated components. The carbohydrate chains contributed to an increased resistance to proteolysis, and thus, to its allergenic potency. Evaluation of the products of digestion of OM and dOM revealed the presence of high-frequency IgE-binding epitopes that could remain linked by disulphide bonds.

Mapping of the IgE and IgG4 sequential epitopes of ovomucoid with a peptide microarray immunoassay

BACKGROUND

Ovomucoid (Gal d 1) has been demonstrated to be the most important allergen in IgE-mediated egg allergy. Peptide microarray analysis is a novel method that can provide useful information on the nature of specific allergens.

METHODS

A peptide microarray immunoassay was performed using a 15- and 20-amino acid (aa) library of overlapping peptides (3-offset) of the primary sequence of ovomucoid. Sera from 50 patients with IgE-mediated egg allergy and reactivity to ovomucoid, with more than 1 year of follow-up, and sera from 10 controls were tested. Peptides were considered major epitopes when the average weighted Z-score was greater than 3 and recognized by at least 20% of the patient's sera. Specific IgE epitopes were established on the basis of the IgE/IgG4 Z-score ratio.

RESULTS

The IgE and IgG4 recognition pattern was similar in both sets of peptides, but the signal intensity was generally higher in the 20-aa set. Thirty-four percent of the patients did not recognize any IgE sequential peptide and 20% of the patients recognized more than 10 sequential peptides. We identified 3 major IgE B-cell epitopes in domains I and II of ovomucoid. IgE/IgG4 ratio analysis showed that peptides 1-2 (aa 4-20) and peptides 29-31 (aa 91-104) were specific IgE epitopes.

CONCLUSION

By using peptide microarray immunoassay in egg-allergic patients, we established that 34% of the patients do not have any linear epitope recognized by IgE. Further studies are needed to determine the clinical relevance of this finding.

Molecular diagnosis of egg allergy

PURPOSE OF REVIEW

Allergy to hen's egg is common in infancy and childhood. Oral food challenges are often required to diagnose egg allergy, because of the limitation in the diagnostic accuracy of skin test and specific IgE to egg white. New molecular diagnostic technologies have been recently introduced into allergological research. In this article, we will review the recent literature regarding the potential value of these tests for the clinical management of egg-allergic patients.

RECENT FINDINGS

Component-resolved diagnosis that can be combined with the microarray technology is promising as measurement of specific IgE antibodies to individual egg white components has been shown to predict different clinical patterns of egg allergy. Specific IgE to ovomucoid has been identified as a risk factor for persistent allergy and could indicate reactivity to heated egg. Ovomucoid and ovalbumin IgE and IgG4-binding epitope profiling could also help distinguish different clinical phenotypes of egg allergy. Particularly, egg-allergic patients with IgE antibodies reacting against sequential epitopes tend to have more persistent allergy.

SUMMARY

Using recombinant allergens, IgE-binding epitopes, and microarrays, molecular-based technologies show promising results. However, none of these tests is ready to be used in clinical practice and oral food challenge remains the standard for the diagnosis of egg allergy.

Novel immunogenic peptides elicit systemic anaphylaxis in mice: implications for peptide vaccines

Peptide-based therapies are showing increasing potential for the development of vaccines and in the treatment of many important diseases. We previously reported two peptide conjugate vaccines that protected mice against pneumococcal disease. During this study, we observed an unexpected phenomenon; several vaccine candidates induced a rapid, fatal anaphylaxis after booster injection of the peptide conjugate. Further investigation indicated the reaction was mediated by the production of peptide-specific IgE and the release of histamine. Notably, among seven peptides tested, all of which bound the same mAb that selected them from a phage library, only four elicited this severe reaction. Sequence alignment analysis of all peptides revealed unique clusters of acidic amino acid residues in the allergenic peptides. Substitution of the acidic amino acid residues, ED, of peptide MP2 with their amine equivalents, QN, eliminated the anaphylactic effects but did not affect the production of peptide-specific IgG. These results have important implications for both the study of allergens and the development of future peptide-based therapies.

Primary structure of potential allergenic proteins in emu (Dromaius novaehollandiae) egg white

The emu (Dromaius novaehollandiae) egg is considered promising as an alternative egg product. To obtain basic biochemical information on emu egg white, the major protein compositions in emu and chicken egg whites and the primary structures of potential allergenic proteins were compared. The dominant protein in emu egg white was ovotransferrin (OVT), followed by ovalbumin (OVA) and TENP protein. The OVA and ovomucoid (OVM) levels in emu egg white were estimated as significantly lower than those in chicken egg white by Western blotting and enzyme-linked immunosorbent assays using anti-chicken OVA or OVM antibodies. Lysozyme and its enzymatic activity were not detected in emu egg white. OVT, OVA, and OVM genes were also cloned, and their nucleotide and amino acid sequences were determined. The protein sequences of OVT, OVA, and OVM from emu showed lower similarities to those of chicken than other avian species, such as quail and turkey. These results emphasize the low allergenicity of emu egg white and its potential as an alternative to chicken egg white.

Potential, pitfalls, and prospects of food allergy diagnostics with recombinant allergens or synthetic sequential epitopes

This article aims to critically review developments in food allergy diagnostics with regard to the verification of specific IgE antibodies and the identification of the responsible allergens. Results of IgE-binding tests with food extracts are hampered by cross-reactive proteins, low-quality test agents, or both. Specificity can be increased by defining adequate cutoff values, whereas sensitivity can be improved by using high-quality test agents. IgE-binding tests with purified allergens enabled reliable quantification of allergen-specific IgE titers, with higher levels found in individuals with food allergy compared with individuals without food allergy. However, the overlap in individual test reactivity between allergic and nonallergic subjects complicates interpretation. Recombinant allergens and synthetic sequential epitopes enabled detection of sensitization profiles, with IgE specific to several allergens and substructures now being suggested as markers of severity, persistence, or both. However, high-power quantitative studies with larger numbers of patients are required to confirm these markers. IgE-binding tests merely indicate sensitization, whereas the final proof of clinical relevance still relies on family/case history, physical examinations, and provocation tests. Novel technologies promise superior diagnostics. Microarray technology permits simultaneous measurement of multiple IgE reactivities regarding specificity, abundance, reactivity, or interaction. Improved functional tests might enable reliable estimation of the clinical relevance of IgE sensitizations at justifiable expenses.

T cell proliferation and cytokine responses to ovalbumin and ovomucoid detected in children with and without egg allergy

BACKGROUND

The specific T cell responses in egg allergy and resolution have not been fully elucidated.

OBJECTIVE

To characterize egg allergen-specific T cells of children with active and resolved egg allergy, in comparison with non-allergic controls.

METHOD

We studied children with active (n=35) or resolved (n=20) egg allergy determined by oral challenge, and non-allergic controls (n=15). Peripheral blood mononuclear cells were labelled with carboxyfluorescein succinimidyl ester (CFSE) and stimulated with ovalbumin (OVA), ovomucoid (OM) or tetanus toxoid. Flow cytometry was used to detect divided CD3+ CFSE(lo) cells that expressed intra-cytoplasmic IL-4 or IFN-gamma. The cell division index (CDI) was calculated as a measure of allergen-specific proliferation. Peanut-specific T cells of a subgroup of children who also had peanut allergy were also studied.

RESULTS

OVA-specific T cells were found in subjects with active (87%) or resolved (75%) egg allergy and in controls (67%), with a trend towards increased T cell proliferation in allergy. OM-induced weaker T cell responses than OVA, stimulating fewer responders (46% allergic, 50% resolved, 60% controls) and 10-fold less proliferation [CDI(OVA) 2.0 (median), 25.6 (maximum) vs. CDI(OM) 0.2 (median), 15.1 (maximum); P<0.01]. Both egg allergens induced significant IL-4+ (median 10%, range 1.4-58%) and IFN-gamma+ (median 28%, range 4.5-63%) cells in responders, including non-allergics. There were no significant differences in IFN-gamma+ or IL-4+ cells or in IFN-gamma/IL-4 ratios between groups. Peanut-specific T cell proliferation was significantly higher in peanut allergy [CDI(CPE) 16.5 (median), 24.8 (maximum)] compared with controls [CDI(CPE) 2.1 (median), 16.1 (maximum)] but cytokine profiles were not different. Tetanus-specific T cells were seen in 90% of the subjects, with no significant inter-group differences in responses.

CONCLUSION

Egg allergen-specific T cells are readily detected in all groups and not restricted to egg allergy. In contrast, peanut-specific proliferation was significantly higher in peanut allergy. This suggests that T cell responses in peanut and egg allergy may differ. We did not find T helper type 2-deviated cytokine responses in egg or peanut allergy.

Genetically glycosylated ovomucoid third domain can modulate Immunoglobulin E antibody production and cytokine response in BALB/c mice

BACKGROUND

Food allergies are on the rise and it is estimated that in North America, 8% of the children and 4% of the adults have food allergies. Food allergies tend to occur more often in children than in adults due to their immature digestive and immune systems. Hen's egg is among the most common cause of food-induced allergic reactions in North America.

OBJECTIVE

The present study was undertaken to investigate the role of N-glycans of the third domain of ovomucoid in IgE binding and modulation of allergen-specific immune response in BALB/c mice.

METHODS

The cDNA encoding the third domain of ovomucoid was inserted into the yeast genome and expressed in Pichia pastoris X-33 cells, under the control of the glyceraldehyde-3-phosphate (GAP) dehydrogenase promoter for constitutive expression to obtain a post-translationally modified and functionally active ovomucoid third domain. Upon expression, the protein was secreted into the extracellular medium and was purified by size exclusion chromatography. The recombinant protein was produced at 10 mg/L of the culture supernatant. BALB/c mice were sensitized with the recombinant and native forms of glycosylated ovomucoid third domain antigen. The allergic response of the native and the recombinant glycosylated forms of ovomucoid third domain antigens were compared using antibody and cytokine measurements.

RESULTS

ELISA tests indicated a significant decrease in specific IgE antibodies to the recombinant N-linked glycosylated form (P-Gly), when compared with the native glycosylated form (DIII+) using mice sera. Immunization with P-Gly induced the production of IFN-gamma [T-helper type 1 (Th1) response] and lowered the production of IL-4 (Th2 response), and a skewed balance towards the Th1 cytokine demonstrated that P-Gly has a modulating ability on Th1/Th2 balance to down-regulate Th2 response. Furthermore, N-linked glycan (N28) in the third domain of ovomucoid was shown to be associated with suppression of the allergic response.

CONCLUSION

Therefore, we can conclude that P-Gly facilitates and contributes to the discovery of new molecular target for the development of a safe and specific therapeutic vaccine for the treatment of egg allergy, and oligosaccharides do seem to play a major role in the suppression of IgE-binding activity.

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 diagnosis and management of egg allergy

Egg allergy is a common food hypersensitivity in children. Atopic dermatitis represents the main clinical manifestation in infancy. On first exposure, many of these infants present with urticaria, angioedema, or anaphylaxis. The role of egg allergy in gastrointestinal conditions is less well understood. The "gold standard" for the diagnosis of egg allergy is the double-blind, placebo-controlled food challenge. Diagnostic cut-off levels have been defined for food-specific serum immunoglobulin E antibody level and skin prick test wheal diameter that predict an adverse challenge outcome. This has significantly reduced the need for formal food challenges. Atopy patch testing, in conjunction with immunoglobulin E-based tests, may further improve the accuracy of predicting a positive challenge. The treatment of egg allergy consists of dietary elimination, or a maternal elimination diet in breast-fed infants. Approximately two thirds of infants with egg allergy will become tolerant by 7 years of age.

Ablation of ovomucoid-induced allergic response by desensitization with recombinant ovomucoid third domain in a murine model

Attempts to modulate the allergenic response by hypoallergens aimed at eliminating IgE-binding epitopes have been established recently for allergen immunotherapy. Desensitization offers an alternative approach to mounting a protective immune response. We have shown previously that mutation of the decisive amino acids in the B cell epitope of the ovomucoid third domain suppresses IgE binding reactivity against human patient sera and we hypothesize that this hypoallergenic variant could be a potential candidate molecule for specific immunotherapy against an ovomucoid-induced IgE reaction. The aim of this study was to investigate whether hyposensitization with the ovomucoid-modified isoform could desensitize ovomucoid-sensitized mice. We mapped the immunodominant B cell epitopes of ovomucoid in Balb/c mice. A hypoallergenic ovomucoid mutant isoform, having ablated allergenicity against patient sera, was used to desensitize ovomucoid-sensitized Balb/c mice by intraperitoneal injection. Female Balb/c mice were sensitized with intact ovomucoid molecule (Fovm) and desensitized with the modified isoform of the third domain of ovomucoid (GMFA). Intact ovomucoid-sensitized mice desensitized with phosphate-buffered saline (PBS) served as positive controls to maintain hypersensitivity. To gain insight into the efficacy of the modified ovomucoid variant in desensitization, effects on hypersensitivity reactions and histamine levels, followed by its association with antibody levels and cytokine profiles, were measured. Abrogation of the allergic response with complete suppression of anaphylactic symptoms and lower serum histamine levels was observed in the desensitized group by GMFA, accompanied by significantly reduced ovomucoid-specific IgE and IgG1 levels and enhanced specific IgG and IgG2a levels. The sensitized group showed severe anaphylactic symptoms, enhanced serum histamine concentrations and increased levels of specific IgE and IgG1. The level of interleukin (IL)-4 was decreased dramatically in the desensitized group and higher levels of interferon (IFN)-gamma were found, whereas mice sensitized with intact ovomucoid exhibited significantly higher levels of IL-4 favouring a Th2 skewed pathway. We demonstrate clearly that GMFA is able to ablate ovomucoid-induced allergic reactions in sensitized mice. This occurs via a suppression of specific IgE accompanied by an increase in suppressor T cell activity. This approach offers some promise for the development of treatment against ovomucoid-induced allergic response.

Effects of enzymatic deamidation by protein-glutaminase on structure and functional properties of wheat gluten

Protein-glutaminase (PG) purified from Chryseobacterium proteolyticum was used to investigate its deamidation effects on wheat gluten. Water-insoluble gluten was able to be deamidated to the extent of deamidation degree (DD) 72% in 200 mM sodium phosphate buffer (pH 7) at 40 degrees C for 30 h. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis exhibited an upper shift of gluten bands with only deamidation for 1.5-2.0 h (DD 35-45%) compared to the bands of nondeamidated gluten. Results of Fourier transform infrared analysis revealed alterations in secondary structure of gluten by PG deamidation. The assignment within amide I region showed decreases in both inter- (around 1695 cm(-1)) and intramolecular beta-sheets (around 1680 cm(-1)) by deamidation suggesting the deterioration of the aggregation ability of gluten molecules. Solubility and emulsification properties of gluten at pH 7 were improved by deamidation, while both properties at pH 3 were deteriorated by deamidation. Enzyme-linked immunosorbent assay identified that allergenicity of deamidated gluten as compared to the nondeamidated cohorts was decreased remarkably as the deamidation time was prolonged.

Lysine as a Critical Amino Acid for IgE Binding in Phl p 5b C Terminus

BACKGROUND

Allergens induce the formation of specific immunoglobulin (Ig)E and harbor at least two IgE-binding regions (epitopes) to facilitate crosslinking of basophilic or mast-cell-bound specific IgE antibodies. Studies mapping linear epitopes have shown that these regions often contain charged or hydrophobic amino acids. Nevertheless, these studies are hampered by limited significance due to the often conformational nature of IgE epitopes. This prompted us to study the role of lysines in the context of an intact 3-dimensional model.

METHODS

Major allergen Phl p 5b from timothy grass bears 12 lysines in its C-terminal half. Using site-directed mutagenesis, we substituted all 10 surface-exposed lysines by alanines.

RESULTS

Although structural integrity of the lysine-deficient mutant was not altered, IgE-binding capacity measured by ELISA inhibition tests and crosslinking activity in ex vivo basophil stimulation and in vivo skin prick tests were significantly diminished. Interestingly, binding of specific IgG antibodies was considerably less reduced by loss of lysines.

CONCLUSION

Lysine is an important amino acid for IgE binding in more than one epitope of major grass pollen allergen Phl p 5b C terminus. Allergenicity, but not IgG binding of the molecule, is substantially diminished by single amino acid substitutions without structural integrity being hampered.

Engineered recombinant ovomucoid third domain can desensitize Balb/c mice of egg allergy

The purpose of this study was to determine the in vivo desensitization efficacy of a hypoallergenic variant of egg white ovomucoid third domain (DIII) in Balb/c mice model. We mapped the immunodominant B-cell epitopes of ovomucoid in Balb/c mice. A hypoallergenic ovomucoid third domain (GMFA) mutant isoform having ablated allergenicity against egg allergic patient's sera was used to desensitize DIII-sensitized Balb/c mice by intraperitoneal injections. Ovomucoid DIII generated high levels of plasma histamine and specific immunoglobulin (Ig)E levels, and increased Th2 type cytokine (IL-4). On the other hand, the allergic response of mice desensitized with the GMFA was found to be significantly inhibited and abrogated by prevention of anaphylaxis reactions, low histamine levels and increased Th1-type cytokine (INF-gamma). It was found that significantly higher levels of IL-10 and IL-12 were secreted in the desensitized group. Desensitization with the GMFA antigen also suppressed synthesis of DIII specific-IgE levels and enhanced specific IgG2a and IgG levels compared with the group treated with the DIII antigen. The present results indicated that hyposensitization with the GMFA can desensitize or down-regulate the allergic response in Balb/c mice and this hypoallergenic variant of ovomucoid DIII can shift an ongoing allergen-specific Th2 response towards a Th1 skewed response.

Engineered recombinant ovomucoid third domain can modulate allergenic response in Balb/c mice model

IgE-mediated allergic reactions to egg white are a serious health problem and ovomucoid being the dominant egg white allergen has been on focus in the past decade. Engineered hypoallergens with reduced reactivity for IgE antibodies are being examined to modulate the allergic response and develop prophylactic allergen vaccines. In this study, we evaluated the immunomodulatory effect of a genetic variant of the third domain of ovomucoid (GMFA) which showed reduced IgE binding with egg allergic patient's sera in comparison to the native form of the third domain of ovomucoid (DIII) in a murine model system. Balb/c mice were injected intraperitoneally with DIII and GMFA antigens. Allergen-specific serum IgG, IgG1, IgG2a, and IgE responses were evaluated using enzyme-linked immunosorbent assay. Splenocyte cytokine levels in the medium of the cultured cells were examined by ELISA and levels of IL-4, INF-gamma, and IL-12 (p70) cytokines were quantified. Neutralization with anti-IL-12 monoclonal antibody was assayed and cytokine levels with respect to GMFA mutant antigen stimulation were measured. GMFA mutant form was found to have significantly reduced levels of specific IgE when compared to the DIII suggesting a mutation-induced abrogation of the IgE binding epitope in mice. The increase in IgG2a levels in GMFA together with the decline of IgE and IgG1 points to a shift from a Th2 response to a Th1 dominated response. The cytokine profile showed a modulation of anti-allergic Th1 phenotype in GMFA from a proallergic Th2 response observed with DIII. Low levels of IL-4 and increased levels of INF-gamma and IL-12 were observed and anti-IL-12 monoclonal antibody restored the levels of IL-4 and suppressed levels of INF-gamma and IL-12 in the GMFA sensitized group. These results indicate that GMFA has a marked suppressive effect on the allergic response of ovomucoid and caused a shift towards a Th1 pathway, thereby modulating the Th1/Th2 cytokine balance and could be used as a potential hypoallergenic candidate for allergen-immunotherapy in the treatment of egg white allergy.

IgE and IgG4 epitope mapping by microarray immunoassay reveals the diversity of immune response to the peanut allergen, Ara h 2

BACKGROUND

Detailed assessment of antibody responses to allergens reveals clinically relevant information about both host response and antigen structure. Microarray technology offers advantages of scale and parallel design over previous methods of epitope mapping.

OBJECTIVE

We designed a redundant peptide microarray for IgE and IgG4 epitope mapping of the previously characterized peanut allergen, Ara h 2.

METHODS

Six complete sets of overlapping peptides were commercially synthesized and site-specifically bound to epoxy-derivatized glass slides in triplicate. Peptides were 10, 15, or 20 amino acids in length with an offset of either 2 or 3 amino acids. A total of 10 control and 45 peanut-allergic sera were assayed. Specific IgE and IgG4 were detected by using fluorochrome-labeled monoclonal secondary antibodies.

RESULTS

By using 15-mer and 20-mer peptides, we could define 11 antigenic regions, whereas only 5 were identifiable using 10-mers. Controls and patients produced IgG4 recognizing a comparable number of Ara h 2 peptides, although the dominant epitopes were distinct. As expected, patient IgE bound a larger number of Ara h 2 peptides (9.4% vs 0.9%). IgE and IgG4 epitopes recognized by patients were largely the same, and there was a positive association between IgE and IgG(4) signal, suggesting coordinate regulation. Cluster analysis of peptide binding patterns confirmed the specificity of antibody-peptide interactions and was used to define 9 core epitopes ranging from 6 to 16 residues in length-7 of which (78%) agreed with previous mapping.

CONCLUSION

Epitope mapping by microarray peptide immunoassay and cluster analysis reveals interpatient heterogeneity and a more detailed map.

Kinetic Analysis of Pepsin Digestion of Chicken Egg White Ovomucoid and Allergenic Potential of Pepsin Fragments

BACKGROUND

The allergenic potential of chicken egg white ovomucoid (OVM) is thought to depend on its stability to heat treatment and digestion. Pepsin-digested fragments have been speculated to continue to exert an allergenic potential. OVM was digested in simulated gastric fluid (SGF) to examine the reactivity of the resulting fragments to IgE in sera from allergic patients.

METHODS

OVM was digested in SGF and subjected to SDS-PAGE. The detected fragments were then subjected to N-terminal sequencing and liquid chromatography/mass spectrometry/mass spectrometry analysis to confirm the cleavage sites and partial amino acid sequences. The reactivity of the fragments to IgE antibodies in serum samples from patients allergic to egg white was then determined using Western blotting (n=24).

RESULTS

The rate of OVM digestion depended on the pepsin/OVM ratio in the SGF. OVM was first cleaved near the end of the first domain, and the resulting fragments were then further digested into smaller fragments. In the Western blot analysis, 93% of the OVM-reactive sera also bound to the 23.5- to 28.5-kDa fragments, and 21% reacted with the smaller 7- and 4.5-kDa fragments.

CONCLUSION

When the digestion of OVM in SGF was kinetically analyzed, 21% of the examined patients retained their IgE-binding capacity to the small 4.5-kDa fragment. Patients with a positive reaction to this small peptide fragment were thought to be unlikely to outgrow their egg white allergy. The combination of SGF-digestibility studies and human IgE-binding experiments seems to be useful for the elucidation and diagnosis of the allergenic potential of OVM.