Improving in-vitro tests for the diagnosis of food hypersensitivity

Optimizing the diagnosis of food allergy

Accurately diagnosing a patient with a possible food allergy is important to avoid unnecessary dietary restrictions and prevent life-threatening reactions. Routine testing modalities have limited accuracy, and an oral food challenge is often required to make a definitive diagnosis. Given that they are labor intensive and risk inducing an allergic reaction, several alternative diagnostic modalities have been investigated. Testing for IgE antibodies to particular protein components in foods has shown promise to improve diagnostics and has entered clinical practice. Additional modalities show potential, including epitope binding, T-cell studies, and basophil activation.

Clinical availability of component-resolved diagnosis using microarray technology in atopic dermatitis

Background

Various allergens play a role in the elicitation or exacerbation of eczematous skin lesions in atopic dermatitis (AD), and much research effort has been focused on improving diagnostic tests to identify causative allergens.

Objective

The purpose of this study was to evaluate the diagnostic effectiveness of a newly introduced microarray-based specific immunoglobulin E detection assay, ImmunoCAP ISAC, for use in AD patients.

Methods

The serum samples of 25 AD patients were tested by using ISAC and a multiple allergen simultaneous test-enzyme immunoassay (MAST-EIA). In addition, 10 of the 25 patients underwent skin prick testing (SPT). The positive reaction rates to allergens in each test and the agreements, sensitivities, and specificities of ISAC and MAST-EIA were evaluated versus the SPT results.

Results

For ISAC versus SPT, the overall results were as follows: sensitivity, 90.0%; specificity, 98.2%; positive predictive value (PPV), 90.0%; and negative predictive value (NPV), 98.2%. The total agreement and κ value for ISAC versus SPT were 96.9% and 0.882, respectively. For MAST-EIA versus SPT, the sensitivity was 80.0%, specificity 92.7%, PPV 66.7%, and NPV 96.2%. The total agreement and κ value for MAST-EIA versus SPT were 90.8% and 0.672, respectively. The overall agreement between the ISAC and MAST-EIA results was 88%.

Conclusion

The ISAC results in AD correlated well with the SPT results, and compared favorably to the MAST-EIA results. This study demonstrates the potential of ISAC as a convenient allergic diagnostic method in AD patients.

High prevalence of food sensitisation in young children with liver disease: a clue to food allergy pathogenesis?

BACKGROUND

The pathogenesis of food allergy is not completely understood - animal models suggest hepatic mechanisms may be important for immune tolerance to orally ingested antigens, but there is little direct evidence for this in humans.

OBJECTIVES

We investigated whether there is an association between liver dysfunction or transplantation in young children and IgE sensitisation to food.

METHODS

We evaluated paired pre- and post- liver transplant sera from children aged 0-36 months treated at a single centre during 2001-2008. Sera were assayed for total IgE and cow's milk, egg and peanut-specific IgE. We quantified hepatic dysfunction pre-transplant using the Paediatric End-stage Liver Disease (PELD) score. We also assessed 70 children after renal transplant to establish whether any association between liver transplant and food sensitisation was organ specific.

RESULTS

Paired sera were available from 50 of 94 children who had a liver transplant during the study period. 35 of 50 (70%) had IgE sensitisation (≥ 0.35 kUa/l) to ≥ 1 food pre-transplant and 18 (36%) post-transplant (p = 0.001). Ten (20%) children had food-specific IgE levels that carry high probability of challenge-confirmed food allergy pre-transplant. Food sensitisation pre-transplant was associated with severity of liver dysfunction [mean (s.d.) pre-transplant PELD score 1.52 (0.13) in food sensitised, 0.77 (0.22) in non-sensitised children p = 0.004]. Total IgE level was raised in 34/42 (81%) pre-transplant and fell significantly post-transplant. Interview assessment of the parents of 40 children revealed that 13 (33%) had a history consistent with food allergy. These findings were not replicated in the renal transplant group.

CONCLUSIONS

Young children with severe liver dysfunction appear to have a high prevalence of food sensitisation. Hepatic mechanisms may therefore be important for establishing immune tolerance to dietary antigens in humans.

Role of food allergy in childhood atopic dermatitis

The interplay between atopic dermatitis (AD) and food allergy is complex and subject to significant misconceptions both by the general public and the medical community. Childhood AD is a very prevalent disorder. In its moderate and severe forms, AD is a challenging disorder to manage from the perspective of the child, parent and treating doctor. As AD is one of the disease manifestations of atopy, it is unsurprising that many children with AD also have a coexisting IgE-mediated food allergy. It is a common misconception that food allergy is causal in the setting of AD. However, in a proportion of sufferers, food allergy does play a role in triggering or exacerbating pre-existing AD by immune-mediated mechanisms and potentially by non-immune mechanisms. It is, therefore, important to differentiate causality, co-existent disease and disease modifiers in this context. This paper seeks to clarify the role of food allergy in childhood AD, and to outline a rational framework for the diagnosis and approach to food allergy in the context of the management of a child with problematic AD.

Beyond skin testing: state of the art and new horizons in food allergy diagnostic testing

Food allergy affects approximately 1% to 10.8% of the general population, and its prevalence seems to be increasing. An accurate diagnosis is particularly important because a misdiagnosis could lead to life-threatening reactions or to unnecessary restrictive diets. However, allergy tests currently used in clinical practice have limited accuracy, and an oral food challenge, considered as the gold standard, is often required to confirm or exclude a food allergy. This article reviews several promising novel approaches for the diagnosis of food allergy, such as new molecular diagnostic technologies and functional assays, along with their potential clinical applications.

Microarray based IgE detection in poly-sensitized allergic patients with suspected food allergy - an approach in four clinical cases

BACKGROUND

Component-resolved diagnosis and microarray technology have been recently introduced into clinical allergy practice, and may be particularly useful in poly-sensitized allergic patients.

METHODS

We compare the clinical usefulness of a microarray-based IgE detection assay (ISAC(®)) with skin tests and specific IgE with standard allergens (sIgE) or their monocomponents in four case reports of patients poly-sensitized to aeroallergens and food.

RESULTS

Case 1: a woman with rhinitis, oral allergy syndrome to several fruits and anaphylaxis to cherry. Diagnostic tests supported non-specific lipid transfer proteins (nsLTPs) primary sensitization. Case 2: a woman with exercise-induced asthma, rhino-conjunctivitis and oral allergy syndrome to fresh fruits of different families. A diagnosis of primary grass and weed pollen allergy with profilin and pathogenesis-related protein family 10 (PR-10) cross-reactive food allergy was proposed. Case 3: a man with atopic eczema, asthma, rhinitis, and multiple anaphylactic episodes with cashew nuts and oral allergy syndrome to fruits. The diagnostic workup supported a primary birch pollen allergy with PR-10 and nsLTPs cross-reactive food allergy. Case 4: a woman with rhino-conjunctivitis, per-operative anaphylaxis due to latex and recent pharyngeal angio-oedema episodes. The diagnosis was a primary grass and weed pollen allergy with equivocal profilin sensitization and no obvious cross-reactivity mediated by nsLTPs sensitization.

CONCLUSIONS

The possibility to carry out multiple sIgE measurements with single protein allergens, in particular with the microarray technique, is a useful, simple and non-invasive diagnostic tool in complex poly-sensitized allergic patients.

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.

In vitro model for IgE mediated food allergy

BACKGROUND

In intestinal food allergy, the non-specificity of gastrointestinal symptoms and the limited access to the reacting organ are the reasons for the limited understanding of the pathophysiology of this disease and the difficulties in establishing an appropriate diagnosis in the individual patient.

OBJECTIVE

To develop an in vitro model reproducing pathophysiological mechanisms of IgE mediated food allergy.

METHODS

Distal duodenum biopsies of nine patients with food allergy and 10 control subjects were cultured for 3 h with medium alone and with 1 mg/ml of peptic-tryptic digest of wheat gliadin, wheat albumins, and apple proteins. Each biopsy was used for conventional histological examination and for immunohistochemical detection of IgE-positive cells. We have also analyzed the expression of tight junction proteins, occludin, claudin-1, and ZO-1 by immunoconfocal microscopy. Histamine and tryptase release were measured in the culture medium and collected at 0, 30 min, and 3 h of culture using an enzyme and radio immunoassay, respectively.

RESULTS

Exposure of small intestinal biopsy specimens of patients with food allergy to food allergens led to a significative increase of IgE-positive cells with a significative increase of histamine and tryptase release and an altered expression of tight junction proteins. No differences were found in intestinal biopsies of controls, cultured with or without food antigens.

CONCLUSIONS

Small intestinal organ culture is a functional model of food allergy and could be considered as an in vitro oral food challenge, with evident reduction of costs and risks for the patients.

The multinational birth cohort of EuroPrevall: background, aims and methods

BACKGROUND/AIM

The true prevalence and risk factors of food allergies in children are not known because estimates were based predominantly on subjective assessments and skin or serum tests of allergic sensitization to food. The diagnostic gold standard, a double-blind placebo-controlled food provocation test, was not performed consistently to confirm suspected allergic reactions in previous population studies in children. This protocol describes the specific aims and diagnostic protocol of a birth cohort study examining prevalence patterns and influential factors of confirmed food allergies in European children from different regions.

METHODS

Within the collaborative translational research project EuroPrevall, we started a multi-center birth cohort study, recruiting a total of over 12 000 newborns in nine countries across Europe in 2005-2009. In addition to three telephone interviews during the first 30 months, parents were asked to immediately inform the centers about possible allergic reactions to food at any time during the follow-up period.

RESULTS

All children with suspected food allergy symptoms were clinically evaluated including double-blind placebo-controlled food challenge tests. We assessed sensitization to different food allergens by measurements of specific serum immunoglobulin E and skin prick tests, collect blood, saliva or buccal swabs for genetic tests, breast milk for measurement of food proteins/cytokines, and evaluate quality-of-life and economic burden of families with food allergic children.

CONCLUSIONS

This birth cohort provides unique data on prevalence, risk factors, quality-of-life, and costs of food allergies in Europe, leading to the development of more informed and integrated preventative and treatment strategies for children with food allergies.

Clinical usefulness of microarray-based IgE detection in children with suspected food allergy

BACKGROUND

Component-resolved diagnostics using microarray technology has recently been introduced into clinical allergology, but its applicability in children with food allergy has hardly been investigated so far. The aim of this study was to evaluate the utility of microarray-based IgE detection in the diagnostic workup of food allergy and to compare this new diagnostic tool with established methods of allergen-specific IgE detection.

METHODS

We investigated 130 infants and children with suspected allergy to cow's milk (CM) or hen's egg (HE). Serum IgE measurements, skin prick tests, allergen microarray assays and controlled oral food challenges with HE and CM were performed.

RESULTS

We analyzed 145 oral challenges that served as reference parameters for assay performance assessment. On this basis, the panel of microarrayed allergen components was shown to represent a comprehensive repertoire of clinically relevant CM and HE proteins. Additionally, the implemented CM and HE components respectively sufficed for equivalent test performance as compared to the corresponding fluorescence enzyme immunoassay extract and skin testing. However, component-resolved diagnostics for HE and CM allergy did not make oral food challenges superfluous. Clinical IgE decision points predicting positive oral food challenges could be calculated for both in vitro test methods.

CONCLUSIONS

Allergen microarrays provide a new tool to diagnose symptomatic CM and HE allergy. They show performance characteristics comparable to the current diagnostic tests and may be indicated in small children in whom only small blood volumes are obtainable. However, they are not capable of replacing double-blind, placebo-controlled food challenges in most cases.

Anaphylaxis to foods

Three crucial areas of the management of anaphylaxis due to food allergy are discussed: making a diagnosis, deciding who needs a self-injectable adrenaline device and spotting the novel allergen. Managing children and teenagers with anaphylaxis is challenging due to the lack of available evidence that specific addresses these issue. The available evidence is presented and discussed.

Abordagem laboratorial no diagnóstico da alergia alimentar

OBJETIVO: Revisar os exames laboratoriais disponíveis utilizados no diagnóstico da alergia alimentar mediada ou não por IgE. FONTES DE DADOS: Artigos publicados em base de dados PubMed e Embase (língua inglesa e portuguesa) nos últimos dez anos. As palavras-chave utilizadas como fonte de busca foram "alergia alimentar", "diagnóstico" e "laboratório", isolados e/ou associados. SÍNTESE DOS DADOS: A abordagem diagnóstica das reações alérgicas a alimentos inclui história clínica completa, estudos laboratoriais, dietas de eliminação e desencadeamentos cegos com alimentos. Recentemente, a medida quantitativa de anticorpos IgE específicos a alimentos tem mostrado ser mais preditiva de alergia alimentar sintomática mediada por IgE. Níveis séricos de IgE específica a alimento que excedam os valores diagnósticos indicam que o paciente tem chance maior que 95% de apresentar uma reação alérgica se ingerir o alimento em questão. Estes "valores de decisão" foram definidos para alguns alimentos e resultados inconsistentes são obtidos ao se estudar diferentes populações. Os desencadeamentos com alimento, especialmente o duplo-cego controlado por placebo (DADCCP), representa a maneira mais confiável de estabelecer ou descartar o diagnóstico de hipersensibilidade alimentar. CONCLUSÕES: Número crescente de aquisições tem melhorado o valor preditivo de alguns testes laboratoriais empregados no diagnóstico de alergias alimentares. Entretanto, até hoje, não há teste in vitro ou in vivo que mostre correlação completa com a clínica da alergia alimentar. O DADCCP continua sendo o padrão-ouro no diagnóstico definitivo de alergia alimentar específica. São necessárias, urgentemente, novas abordagens diagnósticas válidadas em pacientes com alergia alimentar confirmada por DADCCP positivo.

Pathophysiology, diagnosis and treatment of food protein-induced gastrointestinal diseases

PURPOSE OF REVIEW

Although our general understanding of food hypersensitivity has improved in recent years, gastrointestinal food protein-induced diseases still pose diagnostic and therapeutic dilemmas.

RECENT FINDINGS

Food allergy in children and adults may involve any part of the gastrointestinal tract. Clinical presentations include protein-induced enterocolitis syndrome, enteropathy and proctocolitis, as well as eosinophilic gastroenteritis and related disorders. For many of these conditions, our understanding of the pathophysiology is incomplete. Manifestations are mostly non-IgE mediated, and skin prick testing and measurement of food-specific IgE antibody levels are of limited diagnostic value. Atopy patch testing may be of benefit in identifying food items associated with late-onset gastrointestinal reactions. A definitive diagnosis of gastrointestinal food allergy, however, still relies on formal food challenges. Depending on the clinical presentation, gastrointestinal biopsies may be required. In infancy, hypoallergenic formula or maternal elimination diets have been shown to effectively control the gastrointestinal manifestations of food allergies. Growth parameters and micronutrient levels need to be carefully monitored while on elimination diets for prolonged periods. In older children and adults with eosinophilic gastrointestinal disorders, the response to dietary restriction is variable. Corticosteroids may be required to control symptoms in those who failed to respond to hypoallergenic diets. In eosinophilic esophagitis, steroids can be administered topically in the form of swallowed aerosols. Leukotriene receptor antagonists and other novel therapies may be useful as steroid-sparing agents.

SUMMARY

Early diagnosis and treatment of food protein-induced gastrointestinal diseases may prevent significant nutritional complications. Further research is needed to develop diagnostic tools for these mainly cell-mediated disorders.

Characterization of allergenic food proteins for improved diagnostic methods

PURPOSE OF REVIEW

Diagnostic decision points for food allergen-specific serum IgE concentration and for skin prick test results have been established for several foods, reducing the requirement for food challenges in a number of patients. Many patients, however, still need to undergo oral food challenges because their food-specific IgE level is in the undefined range. In addition, diagnostic decision points could not be established for several foods. It appears that measurement of serum specific IgE concentrations to individual allergens is superior to determination of specific IgE to the crude food extract containing allergenic and nonallergenic proteins. This review will outline recent advantages in characterization of food allergens as well as the relevance of this knowledge for use in recently developed protein microarray technology.

RECENT FINDINGS

Protein microarrays have been developed to profile allergen-specific IgE antibodies from human serum with the advantage of screening hundreds of allergens in parallel using minute amounts of blood. This technology, however, requires prior knowledge of the proteins to be studied. The identification and characterization of clinically relevant allergens have increased dramatically within the last several years. Relevant new allergens have been identified, especially in tree nuts and seeds. Interestingly, most of these allergens belong to the same family of seed storage proteins. In addition, known food allergens have been further characterized and IgE-binding sites have been determined. Moreover, 'informative' peptides shown to be predictive for the persistence of food allergy have been identified.

SUMMARY

The combination of food allergen characterization and protein or peptide microarray technology will enable us to develop improved diagnostic tools in food allergy.