Molecular diagnosis of peanut and legume allergy. Curr Opin Allergy Clin Immunol. 2011;11:222-228. [PMID: 21464707 DOI: 10.1097/aci.0b013e32834656c2]

Understanding the heterogeneity of childhood allergic sensitization and its relationship with asthma

PURPOSE OF REVIEW

To review the current state of knowledge on the relationship between allergic sensitization and asthma; to lay out a roadmap for the development of IgE biomarkers that differentiate, in individual sensitized patients, whether their sensitization is important for current or future asthma symptoms, or has little or no relevance to the disease.

RECENT FINDINGS

The evidence on the relationship between sensitization and asthma suggests that some subtypes of allergic sensitization are not associated with asthma symptoms, whilst others are pathologic. Interaction patterns between IgE antibodies to individual allergenic molecules on component-resolved diagnostics (CRD) multiplex arrays might be hallmarks by which different sensitization subtypes relevant to asthma can be distinguished. These different subtypes of sensitization are associated amongst sensitized individuals at all ages, with different clinical presentations (no disease, asthma as a single disease, and allergic multimorbidity); amongst sensitized preschool children with and without lower airway symptoms, with different risk of subsequent asthma development; and amongst sensitized patients with asthma, with differing levels of asthma severity.

SUMMARY

The use of machine learning-based methodologies on complex CRD data can help us to design better diagnostic tools to help practising physicians differentiate between benign and clinically important sensitization.

Risk Factors for Anaphylaxis in Children Allergic to Peanuts

Background and Objectives: A peanut allergy is the most common single cause of anaphylaxis in children. The risk factors for anaphylaxis in children with a peanut allergy are not well defined. Therefore, we aimed to identify epidemiological, clinical, and laboratory characteristics of children with a peanut allergy that may predict the severity of the allergic reaction and anaphylaxis. Materials and Methods: We conducted a cross-sectional study and included 94 children with a peanut allergy. Allergy testing was performed, including skin prick testing and the determination of specific IgE levels to peanuts and their Ara h2 component. In case of discordance between patient history and allergy testing, an oral food challenge with peanuts was performed. Results: Anaphylaxis and moderate and mild reactions to peanuts occurred in 33 (35.1%), 30 (31.9%), and 31 (33.0%) patients, respectively. The severity of the allergic reaction was only weakly correlated (p = 0.04) with the amount of peanuts consumed. The median number of allergic reactions to peanuts was 2 in children with anaphylaxis compared to 1 in other patients (p = 0.04). The median level of specific IgE to Ara h2 was 5.3 IU/mL in children with anaphylaxis compared to 0.6 IU/mL and 10.3 IU/mL in children with mild and moderate peanut allergies (p = 0.06). The optimal cutoff for distinguishing between anaphylaxis and a less severe allergic reaction to peanuts was a specific IgE Ara h2 level of 0.92 IU/mL with 90% sensitivity and 47.5% specificity for predicting anaphylaxis (p = 0.04). Conclusions: Epidemiological and clinical characteristics of the patient cannot predict the severity of the allergic reaction to peanuts in children. Even standard allergy testing, including component diagnostics, is a relatively poor predictor of the severity of an allergic reaction to peanuts. Therefore, more accurate predictive models, including new diagnostic tools, are needed to reduce the need for oral food challenge in most patients.

Prevalence of sensitization to molecular food allergens in Europe: A systematic review

Background

Recent reports indicate that the prevalence of food allergy is increasing, but accurate estimates remain a challenge due to cross-reactivity and limited use of precise diagnostic methods. Molecular allergy diagnostics, in which sensitization to individual molecular allergens is measured, is emerging as a promising tool for evaluation of sensitization profiles. In this systematic review, we summarized estimates of prevalence of sensitization to molecular food allergens in the general population in Europe.

Methods

Following a protocol prospectively registered with the International Prospective Register of Systematic Reviews (PROSPERO; reference CRD42021266657), we searched seven databases with no restrictions on publication date or language. Two reviewers independently screened the literature, extracted data, and appraised the risk of bias in the included studies. The findings were synthesized narratively.

Results

From 4776 de-duplicated records, five studies, with low to moderate overall risk of bias, were included. Forty-six molecular allergens from 18 foods were investigated. Overall, the prevalence of sensitization was low, particularly for major allergens, and non-existent for 10 molecular allergens (0% [95% CI 0-0.8]). The highest prevalence was seen for PR-10 proteins, such as Cor a 1.04 (13.6% [95% CI 10.9-16.9]).

Conclusions

Available data, primarily from North-western Europe, indicate that sensitization to molecular food allergens is overall low. The highest estimates were found for cross-reactive PR-10 proteins. There were not enough studies to discern regional differences or perform meta-analysis, highlighting the need for more population-representative studies in order to elucidate patterns of sensitization to molecular food allergens in Europe.

Food Allergy: Catering for the Needs of the Clinician

The practice of food allergy (FA) for clinicians has boomed, with a dramatic rise in the number of patients and families seeking care and with many advances on several fronts. The practice itself sometimes is evidence-based science and sometimes an art of pattern and phenotype recognition. This article examines the tools for diagnosis and management and therapy options available to physicians providing care for patients with FA. The article touches on pressing needs of clinicians and highlights the rapid and important movements in national and international support and advances that will have a positive impact on the field of FA.

Peanut allergy diagnosis: Moving from basic to more elegant testing

Peanut allergy (PNA) is an IgE-mediated immune disorder, which merits particular attention due to its impact on the health and quality of life of millions of patients worldwide. PNA tends to develop in early life and resolves in only 20% of peanut-allergic children. It accounts for the majority of severe food-related allergic reactions. An accurate diagnosis of PNA is vital. In this review, we present the approach to the diagnosis of peanut allergy, starting from the history and proceeding to measures of overall sensitization and then to component-resolved diagnostics and oral food challenges as indicated. Additional testing in development includes basophil activation testing and determination of epitopes for peanut-allergic responses. Based on the literature, stepwise approaches and predictive models for diagnosing PNA are also presented.

Oesophageal eosinophilia accompanies food allergy to hen egg white protein in young pigs

BACKGROUND

Esophagitis with eosinophilia, inflammation, and fibrosis represent a chronic condition in humans with food allergies.

OBJECTIVE

In this investigation, we asked whether esophagitis with an eosinophilic component is observed in young pigs rendered allergic to hen egg white protein (HEWP).

METHODS

Food allergy was induced in young pigs using two protocols. In one protocol, sensitized pigs were challenged by gavage with a single dose of HEWP. Clinical signs were monitored for 24 hours, and then, gastrointestinal (GI) tissues were collected for histological examination. The phenotype of circulating, ovalbumin (OVA)-specific T cells also was examined in HEWP challenged animals. In the second protocol, sensitized animals were fed HEWP for 28 days. Animals were then examined by endoscopy and gastrointestinal tissues collected for histological examination.

RESULTS

In pigs challenged by gavage with HEWP, clinical signs were noted in 5/6 pigs including diarrhoea, emesis, and skin rash. Clinical signs were not seen in any control group. Histological analysis revealed significant levels of oesophageal eosinophilic infiltration (P < .05) in 4/6 of these animals, with two also displaying eosinophilic infiltration in the stomach. Eosinophils were not increased in ileum or colon samples. Increased numbers of circulating, OVA-specific CD4+ T cells also were observed in pigs that received HEWP by gavage. In the group of animals fed HEWP, endoscopy revealed clinical signs of esophagitis including oedema, granularity, white spots, and furrowing, while histology revealed oedema, immune cell infiltration, and basal zone hyperplasia.

CONCLUSIONS AND CLINICAL RELEVANCE

Food allergy in the pig can be associated with esophagitis based on histological and endoscopic findings, including eosinophilic infiltration. The young pig may, therefore, be a useful large animal model for the study of eosinophilic esophagitis in humans.

Food Allergy Testing

Although the gold standard for diagnosis of immunoglobulin E (IgE)-mediated food allergy is an oral food challenge, clinically relevant biomarkers of IgE sensitization, including serum-specific IgE and skin prick testing, can aid in diagnosis. Clinically useful values have been defined for individual foods. More recently, specific IgE to particular protein components has provided additional diagnostic value. In summary, food allergy diagnostics to evaluate IgE sensitization are clinically useful and continue to evolve to improve evaluation of IgE-mediated food allergies.

Retrospective definition of reaction risk in Italian children with peanut, hazelnut and walnut allergy through component-resolved diagnosis

BACKGROUND

Serum IgE evaluation of peanut, hazelnut and walnut allergens through the use of component-resolved diagnosis (CRD) can be more accurate than IgE against whole food to associate with severe or mild reactions.

OBJECTIVES

The aim of the study was to retrospectively define the level of reaction risk in children with peanut, hazelnut and walnut sensitization through the use of CRD.

METHODS

34 patients [n=22 males, 65%; median age eight years, interquartile range (IQR) 5.0-11.0 years] with a reported history of reactions to peanut and/or hazelnut and/or walnut had their serum analyzed for specific IgE (s-IgE) by ImmunoCAP^® and ISAC^® microarray technique.

RESULTS

In children with previous reactions to peanut, the positivity of Arah1 and Arah2 s-IgE was associated with a history of anaphylaxis to such food, while the positivity of Arah8 s-IgE were associated with mild reactions. Regarding hazelnut, the presence of positive Cora9 and, particularly, Cora14 s-IgE was associated with a history of anaphylaxis, while positive Cora1.0401 s-IgE were associated with mild reactions. Concerning walnut, the presence of positive Jug r 1, Jug r 2, Jug r 3 s-IgE was associated with a history of anaphylaxis to such food. ImmmunoCAP^® proved to be more useful in retrospectively defining the risk of hazelnut anaphylaxis, because of the possibility of measuring Cor a14 s-IgE.

CONCLUSIONS

Our data show that the use of CRD in patients with allergy to peanut, hazelnut and walnut could allow for greater accuracy in retrospectively defining the risk of anaphylactic reaction to such foods.

Ratios of specific IgG4 over IgE antibodies do not improve prediction of peanut allergy nor of its severity compared to specific IgE alone

Background

IgG₄ antibodies have been suggested to play a protective role in the translation of peanut sensitization into peanut allergy. Whether they have added value as diagnostic read‐out has not yet been reported.

Objective

To evaluate whether (a) peanut‐specific IgG, IgG₄ and/or IgA antibodies are associated with tolerance and/or less severe reactions and (b) they can improve IgE‐based diagnostic tests.

Methods

Sera of 137 patients with challenge‐proven peanut allergy and of 25 subjects that tolerated peanut, both with known IgE profiles to peanut extract and five individual peanut allergens, were analyzed for specific IgG and IgG₄. Antibody levels and ratios thereof were associated with challenge outcome including symptom severity grades. For comparison of the discriminative performance, receiver operating characteristic curve (ROC) analysis was used.

Results

IgE against Ara h 2 was significantly higher in allergic than in tolerant patients and associated with severity of reactions (P < 0.001) with substantial diagnostic capability (AUC 0.91, 95%CI 0.87‐0.96 and 0.80, 95%CI 0.73‐0.87, respectively). IgG and IgG₄ were also positively associated albeit significantly weaker (AUCs from 0.65 to 0.72). On the other hand, ratios of IgG and IgG₄ over IgE were greater in patients that were tolerant or had mild symptoms as compared to severe patients but they did not predict challenge outcomes better than IgE alone (AUCs from 0.54 to 0.89).

Conclusion

IgE against Ara h 2 is the best biomarker for predicting peanut challenge outcomes including severity and IgG and IgG₄ antibody ratios over IgE do not improve these outcomes.

Machine learning to identify pairwise interactions between specific IgE antibodies and their association with asthma: A cross-sectional analysis within a population-based birth cohort

BACKGROUND

The relationship between allergic sensitisation and asthma is complex; the data about the strength of this association are conflicting. We propose that the discrepancies arise in part because allergic sensitisation may not be a single entity (as considered conventionally) but a collection of several different classes of sensitisation. We hypothesise that pairings between immunoglobulin E (IgE) antibodies to individual allergenic molecules (components), rather than IgE responses to 'informative' molecules, are associated with increased risk of asthma.

METHODS AND FINDINGS

In a cross-sectional analysis among 461 children aged 11 years participating in a population-based birth cohort, we measured serum-specific IgE responses to 112 allergen components using a multiplex array (ImmunoCAP Immuno‑Solid phase Allergy Chip [ISAC]). We characterised sensitivity to 44 active components (specific immunoglobulin E [sIgE] > 0.30 units in at least 5% of children) among the 213 (46.2%) participants sensitised to at least one of these 44 components. We adopted several machine learning methodologies that offer a powerful framework to investigate the highly complex sIgE-asthma relationship. Firstly, we applied network analysis and hierarchical clustering (HC) to explore the connectivity structure of component-specific IgEs and identify clusters of component-specific sensitisation ('component clusters'). Of the 44 components included in the model, 33 grouped in seven clusters (C.sIgE-1-7), and the remaining 11 formed singleton clusters. Cluster membership mapped closely to the structural homology of proteins and/or their biological source. Components in the pathogenesis-related (PR)-10 proteins cluster (C.sIgE-5) were central to the network and mediated connections between components from grass (C.sIgE-4), trees (C.sIgE-6), and profilin clusters (C.sIgE-7) with those in mite (C.sIgE-1), lipocalins (C.sIgE-3), and peanut clusters (C.sIgE-2). We then used HC to identify four common 'sensitisation clusters' among study participants: (1) multiple sensitisation (sIgE to multiple components across all seven component clusters and singleton components), (2) predominantly dust mite sensitisation (IgE responses mainly to components from C.sIgE-1), (3) predominantly grass and tree sensitisation (sIgE to multiple components across C.sIgE-4-7), and (4) lower-grade sensitisation. We used a bipartite network to explore the relationship between component clusters, sensitisation clusters, and asthma, and the joint density-based nonparametric differential interaction network analysis and classification (JDINAC) to test whether pairwise interactions of component-specific IgEs are associated with asthma. JDINAC with pairwise interactions provided a good balance between sensitivity (0.84) and specificity (0.87), and outperformed penalised logistic regression with individual sIgE components in predicting asthma, with an area under the curve (AUC) of 0.94, compared with 0.73. We then inferred the differential network of pairwise component-specific IgE interactions, which demonstrated that 18 pairs of components predicted asthma. These findings were confirmed in an independent sample of children aged 8 years who participated in the same birth cohort but did not have component-resolved diagnostics (CRD) data at age 11 years. The main limitation of our study was the exclusion of potentially important allergens caused by both the ISAC chip resolution as well as the filtering step. Clustering and the network analyses might have provided different solutions if additional components had been available.

CONCLUSIONS

Interactions between pairs of sIgE components are associated with increased risk of asthma and may provide the basis for designing diagnostic tools for asthma.

Evolution of IgE responses to multiple allergen components throughout childhood

BACKGROUND

There is a paucity of information about longitudinal patterns of IgE responses to allergenic proteins (components) from multiple sources.

OBJECTIVES

This study sought to investigate temporal patterns of component-specific IgE responses from infancy to adolescence, and their relationship with allergic diseases.

METHODS

In a population-based birth cohort, we measured IgE to 112 components at 6 follow-ups during childhood. We used a Bayesian method to discover cross-sectional sensitization patterns and their longitudinal trajectories, and we related these patterns to asthma and rhinitis in adolescence.

RESULTS

We identified 1 sensitization cluster at age 1, 3 at age 3, 4 at ages 5 and 8, 5 at age 11, and 6 at age 16 years. "Broad" cluster was the only cluster present at every follow-up, comprising components from multiple sources. "Dust mite" cluster formed at age 3 years and remained unchanged to adolescence. At age 3 years, a single-component "Grass" cluster emerged, which at age 5 years absorbed additional grass components and Fel d 1 to form the "Grass/cat" cluster. Two new clusters formed at age 11 years: "Cat" cluster and "PR-10/profilin" (which divided at age 16 years into "PR-10" and "Profilin"). The strongest contemporaneous associate of asthma at age 16 years was sensitization to dust mite cluster (odds ratio: 2.6; 95% CI: 1.2-6.1; P < .05), but the strongest early life predictor of subsequent asthma was sensitization to grass/cat cluster (odds ratio: 3.5; 95% CI: 1.6-7.4; P < .01).

CONCLUSIONS

We describe the architecture of the evolution of IgE responses to multiple allergen components throughout childhood, which may facilitate development of better diagnostic and prognostic biomarkers for allergic diseases.

Mast cell activation test in the diagnosis of allergic disease and anaphylaxis

Background

Food allergy is an increasing public health issue and the most common cause of life-threatening anaphylactic reactions. Conventional allergy tests assess for the presence of allergen-specific IgE, significantly overestimating the rate of true clinical allergy and resulting in overdiagnosis and adverse effect on health-related quality of life.

Objective

To undertake initial validation and assessment of a novel diagnostic tool, we used the mast cell activation test (MAT).

Methods

Primary human blood-derived mast cells (MCs) were generated from peripheral blood precursors, sensitized with patients' sera, and then incubated with allergen. MC degranulation was assessed by means of flow cytometry and mediator release. We compared the diagnostic performance of MATs with that of existing diagnostic tools to assess in a cohort of peanut-sensitized subjects undergoing double-blind, placebo-controlled challenge.

Results

Human blood-derived MCs sensitized with sera from patients with peanut, grass pollen, and Hymenoptera (wasp venom) allergy demonstrated allergen-specific and dose-dependent degranulation, as determined based on both expression of surface activation markers (CD63 and CD107a) and functional assays (prostaglandin D₂ and β-hexosaminidase release). In this cohort of peanut-sensitized subjects, the MAT was found to have superior discrimination performance compared with other testing modalities, including component-resolved diagnostics and basophil activation tests. Using functional principle component analysis, we identified 5 clusters or patterns of reactivity in the resulting dose-response curves, which at preliminary analysis corresponded to the reaction phenotypes seen at challenge.

Conclusion

The MAT is a robust tool that can confer superior diagnostic performance compared with existing allergy diagnostics and might be useful to explore differences in effector cell function between basophils and MCs during allergic reactions.

Allergy to Peanut, Soybean, and Other Legumes: Recent Advances in Allergen Characterization, Stability to Processing and IgE Cross-Reactivity

Peanut and soybean are members of the Leguminosae family. They are two of the eight foods that account for the most significant food allergies in the United States and Europe. Allergic reactions to other legume species can be of importance in other regions of the world. The major allergens from peanut and soybean have been extensively analyzed and members of new protein families identified as potential marker allergens for symptom severity. Important recent advances concerning their molecular properties or clinical relevance have been made. Therefore, there is increasing interest in the characterization of allergens from other legume species such as lupine, lentil, chickpea, green bean, or pea. As legumes are mainly consumed after thermal processing, knowledge about the effect of such processing on the allergenicity of legumes has increased during the last years. In the present review, recent advances in the identification of allergens from peanut, soybean, lupine, and other legume species are summarized and discussed. An overview of the most recently described effects of thermal processing on the allergenic properties of legumes is provided and the potential IgE cross-reactivity among members of the Leguminosae family is discussed.

Sensitization profiles to peanut allergens across the United States

BACKGROUND

Measurement of IgE antibody to peanut components can aid in the prediction of allergic responses the food.

OBJECTIVE

To investigate the association between patient demographics (age, location) and allergic sensitization to peanut components across the United States.

METHODS

Serum samples from 12,155 individuals with peanut extract specific IgE levels of 0.35 kUA/L or higher were analyzed for IgE antibodies to Ara h 1, 2, 3, 8, and 9 by ImmunoCAP.

RESULTS

Among this population of peanut sensitized individuals, 79.1% of children (<3 years old) were sensitized to one or more peanut storage proteins (Ara h 1, 2, and/or 3), in contrast to 64.2% of adolescents (12-15 years old) and 22.1% of adults (>20 years old). Although sensitization was more prevalent to Ara h 2 than to the other storage proteins, a sizable fraction of patients were sensitized to Ara h 1 and/or 3 but not to Ara h 2 (eg, 13% of children <3 years old). Moreover, 9.6% of children, 10.2% of adolescents, and 10.5% of adults were sensitized to Ara h 9, whereas 2.4% of children, 49.4% of adolescents, and 42.9% of adults produced IgE to Ara h 8 (pathogenesis-related protein 10). Sensitization to Ara h 8 alone was markedly higher in the Northeastern United States relative to other regions of the country.

CONCLUSION

We conclude that sensitization to individual peanut components is highly dependent on age and geographic location. Given that a severe allergic reaction to peanut is unlikely in individuals with isolated sensitization to Ara h 8, a sizable fraction of patients, in particular adolescents and adults, may be at lower risk than anticipated based only on demonstration of sensitization to whole peanut extract.

Dietary patterns and the risk of rhinitis in primary school children: a prospective cohort study

This study was to investigate the association between dietary patterns and rhinitis in primary school children. 1,599 students without rhinitis at baseline survey were selected from a primary school children cohort. Information on food consumption, respiratory symptoms, and confounders was collected using questionnaires. Dietary patterns were defined using principal component analysis. Logistic regression was performed to calculate odds ratio (OR) with 95% confidence intervals (95% CI). The incidence of rhinitis during 12 months follow-up was 21.2%. Three patterns were extracted and labeled as pattern I, II and III. Dietary pattern II which had higher factor loadings of legumes, butter, nuts and potatoes was associated with an increased risk of rhinitis (OR: 1.34, 95% CI: 1.01-1.87) when the highest tertile of pattern score was compared to the lowest tertile, after adjusted for confounders. Besides, every 1-unit increase of score of pattern II was also associated with an increased risk of rhinitis (OR: 1.19, 95% CI: 1.05-1.35). Neither pattern I nor Pattern III was observed to be associated with risk of rhinitis. A diet with higher levels of consumption of legumes, butter, nuts and potatoes may increase the risk of allergic rhinitis in primary school children.

Evidence in immunotherapy for paediatric respiratory allergy: Advances and recommendations

Allergic respiratory diseases are major health problems in paediatric population due their high level of prevalence and chronicity, and to their relevance in the costs and quality of life. One of the most important risk factors for the development of airway diseases in children and adolescents is atopy. The mainstays for the treatment of these diseases are avoiding allergens, controlling symptoms, and preventing them through sustained desensitization by allergen immunotherapy (AIT). AIT is a treatment option that consists in the administration of increasing amounts of allergens to modify the biological response to them, inducing long-term tolerance even after treatment has ended. This treatment approach has shown to decrease symptoms and improve quality of life, becoming cost effective for a large number of patients. In addition, it is considered the only treatment that can influence the natural course of the disease by targeting the cause of the allergic inflammatory response. The aim of this publication is to reflect the advances of AIT in the diagnosis and treatment of allergic respiratory diseases in children and adolescents reviewing articles published since 2000, establishing evidence categories to support the strength of the recommendations based on evidence. The first part of the article covers the prerequisite issues to understand how AIT is effective, such as the correct etiologic and clinical diagnosis of allergic respiratory diseases. Following this, the article outlines the advancements in understanding the mechanisms by which AIT achieve immune tolerance to allergens. Administration routes, treatment regimens, dose and duration, efficacy, safety, and factors associated with adherence are also reviewed. Finally, the article reviews future advances in the research of AIT.

Particularities of allergy in the Tropics

Allergic diseases are distributed worldwide and their risk factors and triggers vary according to geographical and socioeconomic conditions. Allergies are frequent in the Tropics but aspects of their prevalence, natural history, risk factors, sensitizers and triggers are not well defined and some are expected to be different from those in temperate zone countries. The aim of this review is to investigate if allergic diseases in the Tropics have particularities that deserve special attention for research and clinical practice. Such information will help to form a better understanding of the pathogenesis, diagnosis and management of allergic diseases in the Tropics. As expected, we found particularities in the Tropics that merit further study because they strongly affect the natural history of common allergic diseases; most of them related to climate conditions that favor permanent exposure to mite allergens, helminth infections and stinging insects. In addition, we detected several unmet needs in important areas which should be investigated and solved by collaborative efforts led by the emergent research groups on allergy from tropical countries.

The diagnostic value of component-resolved diagnostics in peanut allergy in children attending a Regional Paediatric Allergology Clinic

BACKGROUND

To date, diagnosing food allergies in children still presents a diagnostic dilemma, leading to uncertainty concerning the definite diagnosis of peanut allergy, as well as to the need for strict diets and the potential need for adrenalin auto-injectors. This uncertainty in particular is thought to contribute to a lower quality of life. In the diagnostic process double-blind food challenges are considered the gold standard, but they are time-consuming as well as potentially hazardous. Other diagnostic tests have been extensively studied and among these component-resolved diagnostics appeared to present a promising alternative: Ara h2, a peanut storage protein in previous studies showed to have a significant predictive value.

METHODS

Sixty-two out of 72 children, with suspected peanut allergy were analyzed using serum specific IgE and/or skin prick tests and specific IgE to several components of peanut (Ara h 1, 2, 3, 6, 8, 9). Subsequently, double-blind food challenges were performed. The correlation between the various diagnostic tests and the overall outcome of the double-blind food challenges were studied, in particular the severity of the reaction and the eliciting dose.

RESULTS

The double-blind provocation with peanut was positive in 33 children (53 %). There was no relationship between the eliciting dose and the severity of the reaction. A statistically significant relationship was found between the skin prick test, specific IgE directed to peanut, Ara h 1, Ara h 2 or Ara h 6, and the outcome of the food challenge test, in terms of positive or negative (P < .001). However, we did not find any relationship between sensitisation to peanut extract or the different allergen components and the severity of the reaction or the eliciting dose. There was no correlation between IgE directed to Ara h 3, Ara h 8, Ara h 9 and the clinical outcome of the food challenge.

CONCLUSIONS

This study shows that component-resolved diagnostics is not superior to specific IgE to peanut extract or to skin prick testing. At present, it cannot replace double-blind placebo-controlled food challenges for determination of the eliciting dose or the severity of the peanut allergy in our patient group.

Clinical management of food allergy

Food allergies are commonly seen by the practitioner, and managing these patients is often challenging. Recent epidemiologic studies report that as many as 1 in 13 children in the United States may have a food allergy, which makes this an important disease process to appropriately diagnose and manage for primary care physicians and specialists alike. Having a understanding of the basic immunologic processes that underlie varying presentations of food-induced allergic diseases will guide the clinician in the initial workup. This review will cover the basic approach to understanding the immune response of an individual with food allergy after ingestion and will guide the clinician in applying appropriate testing modalities when needed by conducting food challenges if indicated and by educating the patient and his or her guardian to minimize the risk of accidental ingestion.

Overview of food allergy diagnosis

Food allergy is a condition with significant social and economic impact and a topic of intense concern for scientists and clinicians alike. Worldwide, over 220 million people suffer from some form of food allergy, but the number reported is just the tip of the iceberg. Recent years have brought new perspectives in diagnosing food allergy. Elucidating incriminated immunological mechanisms, along with drawing the clinical phenotype of food hypersensitivity reactions ensures an accurate diagnosis of food allergy. Moreover, molecular based allergy diagnosis, which is increasingly used in routine care, is a stepping-stone to improved management of food allergy patients. The aim of this review is to summarize the topic of IgE-mediated food allergy from the perspective of current diagnostic methods.

The effect of thermal processing on the behaviour of peanut allergen peptide targets used in multiple reaction monitoring mass spectrometry experiments

Identification of processing-stable targets provides important validation when developing targeted mass spectrometry methods for quantifying peanut allergens.

Utility of Component-Resolved Diagnostics in Food Allergy

Allergen component-resolved diagnostic testing (CRD) is a new methodology in clinical food allergy diagnosis, improving the ability to identify specific clinical phenotypes. Instead of relying on the crude allergen extracts used in standard allergy diagnostics, CRD utilizes purified or recombinant allergens for identification of specific molecules causing sensitization or allergy. This method is able to determine risk of the severity of allergic reactions in specific cases, like soy, peanut, and hazelnut allergy. The severity of allergic reaction can be predicted in peanut allergy with Ara h 2, and clinically relevant disease in pollen-allergic patients can be identified. However, age and geographic differences affect CRD results and it should always be utilized in the context of a clinical history. In the future, clinical phenotypes may be differentiated with larger prospective studies utilizing food challenges.

Component-resolved allergen testing: The new frontier

The discovery that allergen specific IgE (sIgE) identified individuals who were allergic to specific allergens, revolutionized allergy and immunology. Recently, component-resolved allergen testing (CRD) has shown promise in improving the field yet again. Prior to development of CRD immunoassays, whole allergen extracts were used to detect IgE mediated allergic disease either by oral, cutaneous, or conjunctival provocation. The most widely used immunoassays detect sIgE to either whole allergen sources or individual allergic components. The use of CRD micro-assay technology (not Food and Drug Administration approved in the United States) has been used to evaluate multiple allergens in parallel. This technique allows for determination of primary vs secondary sensitizations from either close sequence homology or cross-reactive carbohydrate determinants. Published studies have shown beneficial uses in hymenoptera venom immunotherapy, anaphylaxis, and food allergy. The use of component testing for aeroallergen immunotherapy has been studied, however clinical use is hampered by lack of allergen components approved for injection. Therefore, although promising in many respects, the frontier of CRD testing requires more data before it can be widely used in clinical practice.

Evolution pathways of IgE responses to grass and mite allergens throughout childhood

BACKGROUND

Little is known about longitudinal patterns of the development of IgE to distinct allergen components.

OBJECTIVE

We sought to investigate the evolution of IgE responses to allergenic components of timothy grass and dust mite during childhood.

METHODS

In a population-based birth cohort (n = 1184) we measured IgE responses to 15 components from timothy grass and dust mite in children with available samples at 3 time points (ages 5, 8, and 11 years; n = 235). We designed a nested, 2-stage latent class analysis to identify cross-sectional sensitization patterns at each follow-up and their longitudinal trajectories. We then ascertained the association of longitudinal trajectories with asthma, rhinitis, eczema, and lung function in children with component data for at least 2 time points (n = 534).

RESULTS

Longitudinal latent class analysis revealed 3 grass sensitization trajectories: (1) no/low sensitization; (2) early onset; and (3) late onset. The early-onset trajectory was associated with asthma and diminished lung function, and the late-onset trajectory was associated with rhinitis. Four longitudinal trajectories emerged for mite: (1) no/low sensitization; (2) group 1 allergens; (3) group 2 allergens; and (3) complete mite sensitization. Children in the complete mite sensitization trajectory had the highest odds ratios (ORs) for asthma (OR, 7.15; 95% CI, 3.80-13.44) and were the only group significantly associated with comorbid asthma, rhinitis, and eczema (OR, 5.91; 95% CI, 2.01-17.37). Among children with wheezing, those in the complete mite sensitization trajectory (but not other longitudinal mite trajectories) had significantly higher risk of severe exacerbations (OR, 3.39; 95% CI, 1.62-6.67).

CONCLUSIONS

The nature of developmental longitudinal trajectories of IgE responses differed between grass and mite allergen components, with temporal differences (early vs late onset) dominant in grass and diverging patterns of IgE responses (group 1 allergens, group 2 allergens, or both) in mite. Different longitudinal patterns bear different associations with clinical outcomes, which varied by allergen.

Evaluation of basophil allergen threshold sensitivity (CD-sens) to peanut and Ara h 8 in children IgE-sensitized to Ara h 8

Background

Diagnosing peanut allergy properly is important and can be achieved by combining clinical history with various diagnostic methods such as IgE-antibody (IgE-ab) measurements, skin-prick test, basophil allergen threshold sensitivity (CD-sens) and food challenge. We aimed to evaluate CD-sens to peanut, Ara h 8 and Gly m 4 in relation to an oral peanut challenge in children IgE-sensitized to birch, peanut and Ara h 8 avoiding peanuts.

Methods

Twenty children IgE-sensitized to birch pollen and Ara h 8, but not to Ara h 1, Ara h 2 or Ara h 3 were challenged orally with roasted peanuts. Blood samples were drawn for IgE-ab and CD-sens analysis. To measure CD-sens, basophils were stimulated in vitro with decreasing doses of allergens until threshold sensitivity was reached.

Results

All children passed challenge without objective symptoms, but mild oral allergy syndrome (OAS) symptoms were reported in 6/20 children. Nineteen of twenty children were negative in CD-sens to peanut but 17/20 were positive to rAra h 8. Eleven of twenty children were positive in CD-sens to rGly m 4.

Conclusion

Positive CD-sens to rAra h 8 show that the Ara h 8 IgE-ab sensitized basophils can be activated by a rAra h 8 allergen and initiate an allergic inflammation despite a negative challenge. Hence, children sensitized to Ara h 8 but not to peanut storage proteins may be at risk for systemic allergic reaction when eating larger amounts of peanuts but most likely don’t have to fear smaller amounts.

Electronic supplementary material

The online version of this article (doi:10.1186/s12948-014-0007-3) contains supplementary material, which is available to authorized users.

Allergy to cooked, but not raw, peas: a case series and review

Allergic reactions to legumes are common.Food allergy to cooked, but not raw, pea has been rarely reported in the literature. This case series describes five children who had various IgE-mediated symptoms upon consumption of cooked pea, but tolerated raw pea. Skin testing then confirmed positive responses to cooked, but not raw, peas. It is important to consider allergy to cooked legumes, even in the context of raw legume tolerance.

Ara h 2 and Ara h 6 sensitization predicts peanut allergy in Mediterranean pediatric patients

BACKGROUND

Peanut allergy (PA) management was improved by the introduction of molecular allergology, but guidelines for Mediterranean patients are lacking. We aimed at evaluating peanut component-resolved diagnosis as a diagnostic and prognostic tool in children from Southern France.

METHODS

In 181 pediatric patients, PA diagnosis was founded on medical history, skin prick testing, serum-specific IgE to Arachis hypogea extract and components, Pru p 4, and plant carbohydrates, and oral food challenge. Allergen microarray was also performed in 68 of these patients.

RESULTS

In peanut-allergic children (n = 117), IgE to Ara h 6 were most prevalent (64%), followed by Ara h 2 (63%), Ara h 1 (60%), and Ara h 9 (52%). Ara h 6 was the best predictor of PA. The second best predictor was the ratio of Ara h 2 IgE to peanut IgE (cutoff 0.113). Persistent childhood PA was associated with complex molecular profiles. Comparison of singleplex and microarray results showed poor concordance for Ara h 2 and Ara h 9.

CONCLUSION

Ara h 6 and Ara h 2 are the best predictors of PA at diagnosis in Mediterranean pediatric patients. Ara h 1, Ara h 8, and molecular complexity are associated with PA persistence.

Component resolved diagnosis: when should it be used?

The knowledge on molecular allergy diagnosis is continuously evolving. It is now time for the clinician to integrate this knowledge and use it when needed to improve the accuracy of diagnosis and thus provide more precise therapeutic and avoidance measures. This review does not intend to comprehensively analyze all the available allergen molecules, but to provide some practical clues on use and interpretation of molecular allergy diagnosis. The potential role of component resolved diagnosis in circumstances such as the indication of allergen immunotherapy, pollen polysensitization, food allergy, latex allergy or anaphylaxis, is assessed. Interpreting the information provided by molecular allergy diagnosis needs a structured approach. It is necessary to evaluate single positivities and negativities, but also to appraise "the big picture" with perspective.

Food allergy: a practice parameter update-2014

This parameter was developed by the Joint Task Force on Practice Parameters, representing the American Academy of Allergy, Asthma & Immunology (AAAAI); the American College of Allergy, Asthma & Immunology (ACAAI); and the Joint Council of Allergy, Asthma & Immunology (JCAAI). The AAAAI and the ACAAI have jointly accepted responsibility for establishing "Food Allergy: A practice parameter update-2014." This is a complete and comprehensive document at the current time. The medical environment is a changing one, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, ACAAI, and JCAAI. These parameters are not designed for use by pharmaceutical companies in drug promotion.

Benefits and limitations of molecular diagnostics in peanut allergy: Part 14 of the series Molecular Allergology

Allergic reactions to peanut (Arachis hypogaea, Ara h) are caused by immunoglobulin E (IgE)-mediated sensitizations to various proteins. The stability and relative proportion of these proteins in peanut determine the risk of hazardous reactions. Hazardous sensitization to seed storage proteins [S2 albumins (Ara h 2, 6 and 7) > other seed storage proteins (Ara 1 and 3) > oleosins (Ara h 10 and 11)] are distinct from sensitizations to lipid transfer protein (Ara h 9) with moderate risk or cross-sensitizations to Bet v 1-homologous PR-10 protein (Ara h 8) and to profilin (Ara h 5) with low risk. A specific IgE test, e.g. to Ara h 2 in the case of suspected systemic reaction, or where this should be ruled out, can facilitate easier risk assessment. Results, however, are only relevant in the presence of corresponding clinical symptoms. IgE sensitization to peanut extract without hazardous reactions is often caused in this part of the world by Bet v 1-related cross reactions (in birch pollen allergy sufferers), cross-reactive carbohydrate determinants (CCD) or profilin sensitizations. In the case of doubt, clinical relevance can only be established by means of oral challenge, particularly since not all peanut allergens (e. g., oleosins) are available as yet for diagnostic purposes.

Structural functionality, catalytic mechanism modeling and molecular allergenicity of phenylcoumaran benzylic ether reductase, an olive pollen (Ole e 12) allergen

Isoflavone reductase-like proteins (IRLs) are enzymes with key roles in the metabolism of diverse flavonoids. Last identified olive pollen allergen (Ole e 12) is an IRL relevant for allergy amelioration, since it exhibits high prevalence among atopic patients. The goals of this study are the characterization of (A) the structural-functionality of Ole e 12 with a focus in its catalytic mechanism, and (B) its molecular allergenicity by extensive analysis using different molecular computer-aided approaches covering (1) physicochemical properties and functional-regulatory motifs, (2) sequence analysis, 2-D and 3D structural homology modeling comparative study and molecular docking, (3) conservational and evolutionary analysis, (4) catalytic mechanism modeling, and (5) sequence, structure-docking based B-cell epitopes prediction, while T-cell epitopes were predicted by inhibitory concentration and binding score methods. Structural-based detailed features, phylogenetic and sequences analysis have identified Ole e 12 as phenylcoumaran benzylic ether reductase. A catalytic mechanism has been proposed for Ole e 12 which display Lys133 as one of the conserved residues of the IRLs catalytic tetrad (Asn-Ser-Tyr-Lys). Structure characterization revealed a conserved protein folding among plants IRLs. However, sequence polymorphism significantly affected residues involved in the catalytic pocket structure and environment (cofactor and substrate interaction-recognition). It might also be responsible for IRLs isoforms functionality and regulation, since micro-heterogeneities affected physicochemical and posttranslational motifs. This polymorphism might have large implications for molecular differences in B- and T-cells epitopes of Ole e 12, and its identification may help designing strategies to improve the component-resolving diagnosis and immunotherapy of pollen and food allergy through development of molecular tools.

A WAO - ARIA - GA²LEN consensus document on molecular-based allergy diagnostics

Molecular-based allergy (MA) diagnostics is an approach used to map the allergen sensitization of a patient at a molecular level, using purified natural or recombinant allergenic molecules (allergen components) instead of allergen extracts. Since its introduction, MA diagnostics has increasingly entered routine care, with currently more than 130 allergenic molecules commercially available for in vitro specific IgE (sIgE) testing.

MA diagnostics allows for an increased accuracy in allergy diagnosis and prognosis and plays an important role in three key aspects of allergy diagnosis: (1) resolving genuine versus cross-reactive sensitization in poly-sensitized patients, thereby improving the understanding of triggering allergens; (2) assessing, in selected cases, the risk of severe, systemic versus mild, local reactions in food allergy, thereby reducing unnecessary anxiety for the patient and the need for food challenge testing; and (3) identifying patients and triggering allergens for specific immunotherapy (SIT).

Singleplex and multiplex measurement platforms are available for MA diagnostics. The Immuno-Solid phase Allergen Chip (ISAC) is the most comprehensive platform currently available, which involves a biochip technology to measure sIgE antibodies against more than one hundred allergenic molecules in a single assay. As the field of MA diagnostics advances, future work needs to focus on large-scale, population-based studies involving practical applications, elucidation and expansion of additional allergenic molecules, and support for appropriate test interpretation. With the rapidly expanding evidence-base for MA diagnosis, there is a need for allergists to keep abreast of the latest information. The aim of this consensus document is to provide a practical guide for the indications, determination, and interpretation of MA diagnostics for clinicians trained in allergology.

IgE sensitization to the nonspecific lipid-transfer protein Ara h 9 and peanut-associated bronchospasm

Allergen component analysis is now available in many laboratories. The aim of this study was to examine the possible association between peanut allergen IgE components and severity of clinical reactions in patients with a history of peanut allergy. Data and sera collected from 192 patients within the Manchester Allergy Research Database and Serum Bank were used in this retrospective study. Sensitization to peanut specific IgE and Ara h 1, 2, 3, and 8 peanut IgE components, as measured by fluoroenzyme immunoassay, was not associated with anaphylaxis. In contrast, sensitization to the lipid-transfer protein Ara h 9 was significantly more prevalent in patients with peanut-associated bronchospasm (26% versus 9% of patients), even after adjusting for potential confounding effects of age, gender, and severity of concomitant chronic atopic diseases. Patients who were sensitized to Ara h 9 were more likely to have ingested rather than just have had skin contact with peanut and have a more rapid onset of symptoms. These results are consistent with observations that sensitization to heat and protease resistant lipid-transfer protein components of hazelnut, grains, and fruit is predictive of anaphylaxis.

Evaluation of the adult patient with atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with a large impact on quality of life of the patients and their families. In most cases, the diagnosis of AD can easily be made based on (family) history and clinical examination. If necessary, a practical set of diagnostic criteria such as the UK diagnostic criteria can be used. During the diagnostic phase, it is important to pay attention to atopic comorbidity, such as allergic airway disease (allergic asthma and/or rhinitis), allergic eye disease (atopic (kerato) conjunctivitis) and immediate-type food allergy. This will not have direct consequences for the treatment of AD, but may be important for the overall well-being of the patient. Psychological factors, such as family circumstances, work/school performance and lifestyle factors should also be explored. Severity scoring using properly validated scoring lists may not be necessary for the diagnosis, however, is recommended for monitoring therapy. Simple scoring systems, such as TIS and IGA are easy to perform in daily practice. Several flare factors in AD, such as exposure to irritants or UV light, can be identified by history and clinical examination: in individual cases, additional diagnostic tests may sometimes be useful to confirm clinical suspicion. There is only limited evidence that allergen exposure to aeroallergens and/or food allergens influences AD severity. Therefore, routine allergen testing is not necessary for diagnosis and treatment of AD. The decision to perform allergen tests mainly depends on atopic comorbidity.

Molecular diagnosis of peanut allergy

Peanut allergy prevalence has increased in developed countries over the last few decades in the frame of the allergy epidemics, currently affecting 1-2% of children. While less frequent in developing countries, its prevalence is rising as these countries adopt a more westernized lifestyle. There is no curative treatment for peanut allergy at present so patient management relies on peanut avoidance, which requires an accurate diagnosis. Recent progress in peanut allergy diagnosis was made with the introduction of component resolved diagnosis that allows the assessment of IgE specific to individual peanut allergens. Component-resolved diagnosis needs to be interpreted in the context of clinical data but overall increases the diagnostic accuracy, as described in the typical cases that we present. Novel diagnostic tools have been proposed recently, such as the basophil activation test, mRNA expression and resonance magnetic evaluation of biomarkers.

Redefining the major peanut allergens

Food allergy has become a major public health concern in westernized countries, and allergic reactions to peanuts are particularly common and severe. Allergens are defined as antigens that elicit an IgE response, and most allergenic materials (e.g., pollens, danders, and foods) contain multiple allergenic proteins. This has led to the concept that there are "major" allergens and allergens of less importance. "Major allergens" have been defined as allergens that bind a large amount of IgE from the majority of patients and have biologic activity. However, the ability of an allergen to cross-link complexes of IgE and its high-affinity receptor FcεRI (IgE/FcεRI), which we have termed its allergic effector activity, does not correlate well with assays of IgE binding. To identify the proteins that are the most active allergens in peanuts, we and others have employed in vitro model assays of allergen-mediated cross-linking of IgE/FcεRI complexes and have demonstrated that the most potent allergens are not necessarily those that bind the most IgE. The importance of a specific allergen can be determined by measuring the allergic effector activity of that allergen following purification under non-denaturing conditions and by specifically removing the allergen from a complex allergenic extract either by chromatography or by specific immunodepletion. In our studies of peanut allergens, our laboratory has found that two related allergens, Ara h 2 and Ara h 6, together account for the majority of the effector activity in a crude peanut extract. Furthermore, murine studies demonstrated that Ara h 2 and Ara h 6 are not only the major elicitors of anaphylaxis in this system, but also can effectively desensitize peanut-allergic mice. As a result of these observations, we propose that the definition of a major allergen should be based on the potency of that allergen in assays of allergic effector activity and demonstration that removal of that allergen from an extract results in loss of potency. Using these criteria, Ara h 2 and Ara h 6 are the major peanut allergens.

Clinical value of component-resolved diagnostics in peanut-allergic patients

INTRODUCTION

As replacement for the oral food challenge, decision-points for sensitization test have been established, but suboptimal sensitivity and/or specificity, as well as regional differences, have reduced the clinical usability. IgE toward specific peanut protein components has been reported to be of value, but data on correlation with clinical data are sparse. Our aim was to correlate IgE values with the outcome of peanut challenges.

METHOD

Data from 175 positive and 30 negative peanut challenges in patients aged 1-26 years were retrospectively correlated with the levels of specific IgE to peanut and peanut components (Ara h 1-3, h 8, and h 9).

RESULT

The best correlation between IgE and clinical thresholds was found for Ara h 2 (ρ(s) = -0.30, P < 0.01). A cutoff of Ara h 2 > 1.63 kU/l yielded a specificity = 1.00, with a corresponding sensitivity of 0.70. Symptom severity elicited during challenge correlated significantly with the levels of Ara h 2 (ρ(s) = 0.60, P < 0.0001), but large individual variation was found.

CONCLUSION

The level of IgE toward Ara h 2 can improve diagnostic accuracy by introducing a more clear-cut decision-point with an optimal specificity maintaining a high sensitivity. In our study, this would have reduced the necessary number of challenges to be performed from 205 to 92. Extrapolation between centers is difficult and decision-points need to be addressed in relation to settings and population. Further component-resolved diagnostic cannot replace oral challenge neither in determining thresholds nor in the assessment of severity of symptoms elicited during challenge.

Advances in diagnosing peanut allergy

Peanut allergy is often severe, potentially fatal, usually persistent, and appears to have increased in prevalence. An accurate diagnosis is essential because there is a significant burden on quality of life. The tools available for diagnosis include the medical history, skin prick test (SPT), determination of serum peanut-specific IgE antibodies (PN-IgE), and medically supervised oral food challenges. Numerous studies, almost exclusively in children, have correlated clinical outcomes against SPTs and PN-IgE with informative results. The diagnostic utility of SPT and PN-IgE is maximized by considering the degree of positive result and consideration of the medical history (a priori estimation of risk). Emerging tests that evaluate IgE binding to specific proteins in peanut (component testing) add important additional diagnostic information in specific settings. Studies are increasingly focused on how the results of tests considered in combination (or performed serially) may increase diagnostic accuracy. Here, we review the utility of currently available tests and provide suggestions on how to best use them to accurately predict peanut allergy. Still, the physician-supervised oral food challenge remains the most definitive test available.