Pru p 1
Summary
The peach allergen, Pru p 1, is a pathogenesis-related (PR)-10 protein family member and shares a structure homology to the major birch pollen, Bet v 1. Thus, Pru p 1 sensitization is quite prevalent in areas with high exposure to birch pollen and typically results in oral allergy syndrome (oral itching, oral mucosa irritation, or angioedema of lips, tongue, or throat) symptoms. It is found to be sensitive to heat and gastrointestinal digestion. Pru p 1 can also cross-react with pollens such as grass or alder members and result in pollen-food allergy syndrome (PFAS). It can also cross-react with other members of Rosaceae family (apple, apricot, pear, cherry). Pru p 1 is one of the diagnostic indicators to detect allergy to Rosaceae family fruits.
Epidemiology
Worldwide distribution
Pru p 1 sensitivity is commonly found in parts of Northern and Central Europe which has high birch pollinosis due to the presence of cross-reactive IgE antibodies against Bet v 1 (major birch pollen allergen). A study by Gaier et al. (2009) conducted on Austrian patients showed that 87% (47/54) patients had Pru p 1 sensitivity and 75.9% (41/54) patients were having birch pollen allergy. Besides, 6 of 47 Pru p 1 positive peach allergic patients were not having birch pollen allergy. On the contrary, a prospective cross-sectional study among 57 children showed that sensitization to Pru p 1 is quite low (11% of 53) in Spain (part of Southern Europe) where birch pollen sensitized patients were less. Thus, Pru p 1 was found to be an important allergen in patients sensitized to birch pollen. Further, another study in Italy (part of Southern Europe) supported this sensitization pattern and found Pru p 1 sensitization in only 4 of 244 patients sensitized to peach.
Furthermore, another study evaluated the difference in sensitization pattern of Pru p 1 among 133 Pru p 3 positive patients from Northeast Italy and South Italy having a birch sensitization pattern like Northern Europe. Northeast patients sensitized to Pru p 1 were found to be 42.8% while none of the South Italy patients were sensitized towards Pru p 1.
The prevalence of Pru p 1 sensitization was also found prevalent in Japanese peach allergic patients. It was found to be 91.7% among 12 patients showing oral or mucosal symptoms while 80% among 15 patients showing systemic symptoms including anaphylaxis. Another study in Japan among 50 patients also reported Pru p 1 sensitization to be 66% and mainly associated with oral and mucosal symptoms.
Pru p 1 sensitization was found to be 82.4% among the 51-birch pollen-sensitive patients in a study in Korea. The sensitization was found higher among the patients with OAS.
Clinical Relevance
Cross-reactive Molecules
Strong cross-reactivity exists between PR-10 allergens of peach (Pru p 1) and birch pollen (Bet v 1). Also, the prevalence of peach allergy is associated with birch pollinosis. The major symptoms manifested due to birch sensitivity include OAS. In a study in Austria on 35 Bet v 1-sensitized birch pollen allergic patients, peach allergy was found in 100% due to cross-sensitization to Pru p 1.
Further, co-sensitization of peach allergy with alder or grass pollens allergy is also found and is related to PFAS. Further, alder pollen was proposed to be a primary sensitizer in peach allergic patients for their Pru p 1 and Pru p 4 sensitizations.
Disease severity
Clinical symptoms associated with Pru p 1 sensitivity usually affect the oral cavity and are often mild to moderate. These can be referred to as OAS.
A study in Japan showed that 94.2% of peach allergic patients (31/33) with Pru p 1 sensitivity developed oropharyngeal symptoms (p<0.005).
A study conducted on 54 Austrian patients found that sensitization to Pru p 1 was significantly associated with reduced occurrence of urticaria (p<0.001) and systemic reactions (p=0.003). Further, a cross-sectional study in 526 PR-10 sensitized individuals in Italy showed that specific Immunoglobulin E (sIgE) reactivity to Pru p 1 was linked with symptoms of OAS (63% of 270) like oral itching, oral mucosa irritation, or angioedema of lips, tongue, or throat. This was significant when compared to respiratory symptoms (53% of 405) (p<0.05). Another study also reported that co-sensitization of Pru p 3, Pru p 1, and/or Pru p 4 among peach allergic patients may provide a shield against severe symptoms due to Pru p 3.
Diagnostics
Disease Severity
Pru p 1 is a heat-labile protein and thus easily destroyed by cooking making cooked peach tolerable in aspects of allergenicity. Thus, only the unprocessed form of the fruit leads to the usual symptoms such as local oropharyngeal symptoms. A study conducted on 27 peach allergic patients has shown that serum specific IgE of Pru p 1 was found to be higher in patients experiencing local symptoms (91.7%) as compared to patients experiencing systemic symptoms including anaphylaxis (80%).
Exposure
The main exposure route for this allergen is through ingestion.
Cross-Reactivity
Pru p 1 can cross-react with other PR-10 protein families that are homologous to Bet v 1 protein such as Rosaceae fruits, hazelnut, carrot, and celery. Besides, PR-10 proteins are also found in plants of the Fagales order (birch, hazel, beech) and also in distantly related food sources like peach, peanut, strawberry, and cherry.
Pru p 1.01 in peach consists of a proline residue in the p-loop which is like the structure in Bet v 1 isoforms (birch pollen) and Mal d 1.01 (apple). IgE cross-reactivity was found to be highest (88%) between Pru p 1 and Mal d 1 (apple) in a cross-sectional study. Thus, showing that a resembling protein structure can also result in cross-reactivity. Moreover, Pru p 1 has 59% and 86% identical amino acid sequence with Bet v 1 and Mal d 1 respectively.
Further, amino acid sequence homology of Pru p 1 is also observed with other fruits such as cherry (98%), apricot (76%), and pear (83%).
References
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