Ask The Expert
April 12, 2022
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 p1,3 and 4 be sufficient?
By Dra. Iris E. Hidalgo Nicho
Pollen Food Allergy Syndrome (PFAS) is a hypersensitivity reaction in patients with seasonal allergic rhinitis (SAR) caused by cross-reaction among pollens and homologous epitopes in plant-derived food allergens. The prevalence of PFAS varies from 9.6% to 55% worldwide according to geographic location, local diet, and the regional prevalence of atopic diseases. PFAS is the most frequent food allergy in adults and the typical comorbidity of pollinosis. The frequency of PFAS in childhood is higher than previously recognized, including those who suffer from pollen-induced seasonal allergic rhinoconjunctivitis.
PFAS is much higher in northern Europe because of birch pollen allergy. Osterballe et al. estimated that 40–50% of birch-allergic patients also had PFAS. Dreborg and Erikson showed in large adult and pediatric studies that over 70% of patients with birch allergy had symptoms of PFAS, and 20% of those were allergic to grass and mugwort.
Plant–food allergens share similarities with pollen allergens in their sequence, structure, and function, triggering the symptoms. Due to their widespread nature, these are known as panallergens. The principal pan-allergens comprise three protein families: profilins, pathogenesis-related protein type 10 (PR-10), and non-specific lipid transfer proteins (nsLTPs, PR-14). In Northern and Central Europe, where pollen allergy is mainly related to birch and alder pollen, the symptoms are triggered mainly by PR-10-containing Rosaceae. The Rosaceae family includes many edible fruits, where apple, cherry, and peach are the best-known species. People's reactions to certain foods will depend on the birch component they are sensitized to; for example, Bet v1 has been associated with Mal d 1 (apple), while Pru p 4 (peach) with Bet v 2.
PFAS is typically characterized by isolated oral and pharyngeal symptoms of immediate onset following food intake, clinically known as oral allergy syndrome (OAS). Symptoms typically last for a few minutes to half an hour. Systemic reactions occur in 2–10% of PFAS cases, including nausea, abdominal discomfort, diarrhea, rhinitis, difficulty breathing, skin rash, urticaria-angioedema, hypotension, and anaphylaxis (1–2% of reactions). Clinical history is fundamental for diagnosis, combined with skin prick tests and open/blind oral food challenges (OFC), which can identify the syndrome with high sensitivity and specificity. OFC is mandatory when history is unclear and systemic reactions occur. It is essential to mention that it has been extensively documented that the sensitivity and specificity of SPTs with fresh fruit using the prick-by-prick technique are higher than those of SPTs using commercial extract. This is very useful if specific IgE cannot be measured or molecular tests cannot be performed.
Component-resolved diagnostics (CRD) represents a reliable instrument in diagnosing PFAS, as it offers the opportunity to establish and compare individual sensitization profiles based on the cross-reactive proteins. High cost is the major limitation to use CRD worldwide. Due to high cross-reactivity between PR-10 proteins, profilins, and nsLTPs, the corresponding allergens derived from peach are usually applied for diagnostic approaches in all Rosaceae fruit allergies. So, it would be possible that allergens like Pru p1, Pru p3, and Pru p4 are enough. Furthermore, it would be necessary to consider allergens such as Mal d1, Mal d3, and Mal d4 from apples due to several studies showing that 70% of patients with birch pollinosis develop an allergy to apples or other foods, taking into consideration the different geographical scenarios.
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Iris E. Hidalgo Nicho
Allergy and Immunology
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