Molecular Diagnosis of Peanut and Legume Allergy

Nicolaos Nicolaou; Adnan Custovic

Disclosures

Curr Opin Allergy Clin Immunol. 2011;11(3):222-228. 

In This Article

Abstract and Introduction

Abstract

Purpose of review To review and discuss recent studies on molecular diagnosis of peanut and other legume allergy.
Recent findings Studies from the UK and France suggest that quantification of Ara h 2-specific IgE may accurately discriminate peanut allergy from tolerance. However, the pattern of allergenic component recognition in peanut-sensitized patients from different populations or geographical areas varies, reflecting different pollen and dietary exposures. In the USA, peanut-allergic patients are commonly sensitized to Ara h 1–3, in Spain to Ara h 9 and in Sweden to Ara h 8. Patients with soybean allergy sensitized to Gly m 5 or Gly m 6 allergens may be at greater risk of experiencing severe allergic reactions.
Summary Accurate diagnosis of peanut and legume allergy is challenging and essential. Measurement of IgE response to specific allergenic molecules may be more useful in predicting the presence and severity of clinical allergy than currently used skin or blood tests based on whole extracts. However, given the heterogeneity in component recognition patterns observed in different geographical areas, further studies are essential to identify and confirm potentially useful molecular diagnostic and prognostic markers. Until such markers are confirmed and replicated in different age groups, oral food challenge (OFC) remains the gold standard for accurate diagnosis.

Introduction

Members of the legume family including peanut, soy, lentils, beans, pea and lupin are a relatively cheap and excellent source of high-biological-value proteins and other nutrients. They are widely used around the world, constitute an important part of healthy and vegan diets, and are common ingredients in many processed food products. For the majority of people legumes represent an excellent food source; however, some individuals may experience allergic reactions even with minimal exposure. Allergy to peanut and other legumes is becoming a significant health problem particularly in westernised countries.[1,2•,3•,4] Legume-induced allergic reactions can be potentially severe and sometimes fatal,[5] and quality of life of patients and their families is highly impaired.[6]

Given the impact of peanut and legume allergy, accurate diagnosis is critically important. The double-blind placebo-controlled food challenge (DBPCFC) is the gold standard for diagnosing food allergy.[7] However, the procedure is time-consuming, expensive and patients may be at risk of severe reaction. In daily clinical practice, diagnosis is usually based on a suggestive clinical history supported by positive skin prick test (SPT) or detection of specific IgE (sIgE) in serum. However, the utility of currently used tests (SPTs and sIgE in-vitro assays) in confirming the diagnosis of food allergy has been questioned.[8] These tests generally have low specificity, and a positive test identifies sensitization, which may suggest, but does not unequivocally confirm clinical reactivity upon exposure (i.e. allergy).

Cut-off points related to the size of skin test responses and sIgE levels which confer high probability of clinical reactivity have been proposed for some allergenic foods, but these decision points may not be applicable to every population or setting.[9] Furthermore, traditional tests do not predict the severity of allergic reactions.

One of the reasons why current tests perform relatively poorly in differentiating asymptomatic sensitization from true allergic reactions may be consequent to the fact that they are mostly based on crude natural extracts which contain both allergenic and nonallergenic molecules, with some of these molecules crossreacting with homologous proteins from other sources (e.g. pollen).[10] A classical example of crossreactive structures with limited clinical relevance is that of crossreactive carbohydrate determinants (CCDs) which have been implicated in clinically irrelevant 'sensitization' to peanut among grass pollen-sensitized patients.[11•,12]

Recent advances in molecular biology and biochemistry have led to isolation, characterization and recombinant production of many allergenic proteins, as well as the synthesis of IgE epitope-emulating peptides for individual food allergens, including members of the legume family.[13•,14•,15••,16–20] These molecules are increasingly used within the context of molecular diagnosis[21•] or component-resolved diagnosis (CRD)[10] to facilitate more accurate diagnosis of food allergy. This has been aided by the advances in microarray technology, which have allowed simultaneous measurement of IgE antibodies to a large number of allergenic components using minute amounts of sera and antigens.[22]

Using allergenic components or synthetic epitopes in diagnostic tests, a detailed analysis of a patient's sensitization profile can be determined and association between the pattern of such sIgE responses and clinically relevant aspects of the allergic disease investigated.[10,21•] This may help identification of disease-eliciting molecules, components implicated in crossreactivity, and molecules associated with disease severity. Immunotherapy with the clinically relevant specific components to which a patient is sensitized could then be undertaken.

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