Ask The Expert
May 11, 2015
Allergen-component Diagnostics Food-pollen Allergy
Allergen-component Diagnostics Food-pollen Allergy
We are encouraged to utilize allergen-component diagnostics for food-pollen allergy in order to guide advice. But these tests are expensive in our country. What is the minimum test profile you would recommend to identify PR-10, profilin, and LTP components. For example, would Pru p 1,3 and 4 be sufficient?
From the Editors: The following discussion addressing allergen component assessment in food-pollen allergy raises several issues: First is the significant worldwide regional differences for pollen sensitization, food cross reactivity and its clinical expression. Second, is the importance of clinical correlation with available and emerging diagnostic testing for allergic diseases, and third is demonstrating the different "styles" physicians have in approaching clinical problems.
By Doctor Robert Wood
It is true that allergen component diagnostics can be very helpful in the management of some patients with food-pollen allergy. However, for the vast majority of patients a careful history supplemented by select skin and / or IgE testing will be completely sufficient to make accurate diagnoses and prescribe effective management. In the United States, the availability of component based testing is relatively limited and most allergists here – including myself – are very comfortable managing most patients with the currently available tools. This is truly an area where a careful history will yield far more clinically relevant information than any laboratory test.
Robert A. Wood, MD
Professor of Pediatrics and International Health
Director, Pediatric Allergy and Immunology
Johns Hopkins University School of Medicine
Baltimore, MD, USA
By Professor Anna Pomes
Patterns of sensitization to PR--‐10, profiling and lipid transfer protein (LTP) allergens show a wide geographical variability, depending on the exposure to pollens and ingested foods in each particular area. The minimum test profile to identify sensitivities to these three groups of proteins in component--‐resolved diagnosis (CRD) should be selected according to the patterns of sensitization to these allergens in that specific country.
Two main patterns of sensitization to PR--‐10, profilins and LTPs have been well described in Europe (1, 2). In northern and central areas, allergies to Rosaceae fruits, Apiaceae vegetables and hazelnut are associated with birch pollinosis, and patients present with mild oropharyngeal symptoms known as oral allergy syndrome (OAS). The allergens responsible for this pollen--‐food cross--‐reactivity are Bet v 1 and pollen profilins, whose sensitivity to pepsin digestion explains the restriction of symptoms to the oral cavity. In contrast, in areas of southern Europe free of birch pollen exposure, peach (Pru p allergens) and certain pollens, such as those from mugwort and plane tree, might contribute to sensitization to LTPs. These are very stable proteins, resistant to digestion, and associated with consequent systemic reactions, that are often severe. One might anticipate that testing for IgE reactivity to only birch and peach allergens would allow distinguishing between both patterns of sensitization. A strong reactivity to Bet v 1 (PR--‐10) could indicate the possibility of mostly mild reactions to cross--‐reacting foods (i.e. apple), but also serious reactions to cross--‐reacting allergens from peanut, hazelnut, celery and soybean (3). On the contrary, a confirmed sensitization to the LTP Pru p 3, considered a primary sensitizer and marker of reactivity to LTPs from the Rosaceae family, combined with a lack of IgE to Bet v 1, would be an indicator of a possible development of systemic reactions to LTPs.
Anna Pomes, PhD, FAAAAI
INDOOR Biotechnologies, Inc.
Charlottesville, VA, USA
By Professor Wayne Thomas
Allergic sensitivity to rosaceous fruits in the Mediterranean region shows an interesting and clinically useful pattern when the IgE binding is measured by component resolved diagnosis (1, 2). Sensitisation to the non-specific lipid transfer protein (LTP) from peach, Pru p 3, is associated with a higher likelihood that subjects will experience systemic symptoms and not just oral allergy symptoms and in addition allergic symptoms from ingesting other fruits and vegetables. These not only include other rosaceous fruits but a long list of genetically disparate plants including celery, carrot, walnut, fennel, peanut, cereals and tomato. The LTP sensitisation is not only best measured with Pru p 3 but it appears that the sensitisation is driven by peach allergen. Sensitisation to the PR-10-like proteins (Bet v 1 homologues) and profilins without LTP is associated with oral allergy syndrome and not systemic reactions and curiously subjects co-sensitised with these specificities and LTP are have fewer symptoms than those sensitised to LTP alone (3). Knowledge that LTP is usually found in the peal of the fruit and vegetable and that profilin sensitisation is associated with melon allergy provides further assistance with the clinical management. There are additional associations of symptoms with sensitisation to the aeroallergen LTPs of the mugwort and plane-tree pollens with the risk of more severe allergy (4) and LTP induced rhinitis (5). This again appears to dependent on the primary peach sensitization because higher IgE titres are found to Pru p 3 (5) and is not found for pollens with the evolutionary more disparate LTP sequences like those found in olive, Parieteria spp. and ragweed pollens. With respect to diagnostic/prognostics tests within the Mediterranean region, Pru p 3 is the LTP of choice. Also within this region profilins from disparate pollen sources have essentially the same IgE binding for subjects sensitised by different species even for subjects selected for peach allergy (6). Grass (Phl p 12), birch (Bet v 2) and date palm (Pho d 2) all appear suitable and a large study of pan allergens (7) showed a good association of titres to diverse pollen profilins. The PR-10 proteins do not exhibit the same concordance of cross reactivity amongst diverse species and allergen source (7) and indeed the food and pollen PR-10 can be divided into food and pollen groups. Mal d 1 from apple detects anti-PR-10 antibodies in fruit allergic subjects better than Bet v 1(8) although in Europe titres of Bet v 1-reactive antibodies are high with pollen sensitisation plus LTP allergy. Sensitisation to Mal d 1 could be used measure PR-10 sensitisation to the food group and Bet v 1 for pollen sensitisation, although they do cross-react. From published reports Pru a 1 and 4 would probably be suitable for PR-10 food markers and profilin but have not been as extensively used.
Wayne Thomas, PhD
Division of Molecular Biotechnology
Telethon Institute for Child Health Research
West Perth, Australia
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