Ara h 9
Summary
Ara h 9 is non-specific lipid-transfer protein (nsLTP) peanut allergen component. Regional variation has been reported for IgE sensitization to Ara h 9 and therefore it is considered to be a predictor of clinical peanut allergy in Spanish and Asian populations. LTPs are stable and able to withstand thermal and protease treatment. Patients who are LTP-sensitized can display systemic clinical signs in addition to symptoms associated with oral allergy syndrome. A study found that patients who were monosensitized to Ara h 9 were more likely to experience symptoms of bronchospasm compared to patients who were not sensitized. Ara h 9 IgE has limited diagnostic accuracy for peanut allergy because of cross-reactivity between LTPs however, it can be valuable when diagnosing allergy symptoms due to cross-reactions with other LTPs found in pollen and fruit. Cosensitization with peach Pru p 3 and mugwort Art v 3 LTPs have been observed.
Epidemiology
Worldwide distribution
Studies have typically reported peanut allergy prevalence rates between 1–2% in Western nations. Peanut allergy appears to be less common in Asia and other global areas, although epidemiological studies in non-Western regions have been sparse. Peanut allergy usually begins in childhood and persists throughout the affected individual’s lifetime however, approximately 20% of young children develop tolerance.
IgE sensitization to Ara h 9 is estimated to affect 10–20% of the population in the USA, with Ara h 9 sensitization identified in 11% and 22% of peanut-allergic patients in Sweden and Austria, respectively. Similarly, Ara h 9 sensitization was detected in 20% of 192 peanut-allergic patients in the UK. Regional differences have been identified with 90% (29/32) prevalence in peanut-allergic Spanish patients (Mediterranean group) whereas four out of six USA patients and two of 35 German patients were sensitized to Ara h 9 in the non-Mediterranean peanut-allergic group. Over 80% of peanut-sensitized patients recruited for a study in China were sensitized to Ara h 9 and 12 out of 18 peanut-allergic patients were monosensitized to this allergen component. In summary, Ara h 9 is considered to be a predictor of clinical peanut allergy in Spanish and Asian populations.
Clinical Relevance
Patients who are LTP-sensitized can display systemic clinical signs in addition to symptoms associated with oral allergy syndrome, commonly experienced with birch pollen-related food allergies. With LTPs being resistant to both heat and proteases, they are able to trigger systemic reactions as well as local symptoms.
Patients monosensitized to Ara h 9 were more likely to experience symptoms of bronchospasm compared to patients who were not sensitized (26% versus 9%; P = 0.05). Ara h 9-sensitized patients were older however, the association between bronchospasm and Ara h 9 sensitization remained significant even after adjusting for age.
Cross-reactive Molecules
Thirteen patients who were allergic to peanuts were also allergic to peaches (Pru p 3) and presented with the same clinical symptoms. However, two of these patients experienced more severe symptoms to peanuts compared to peaches.
Diagnostics
Cross-reactivity
The results of a meta-analysis study found that Ara h 9 sIgE has limited diagnostic accuracy because of cross-reactivity between LTPs. However, IgE to Ara h 9 can be valuable to use when diagnosing allergy symptoms due to cross-reactions with other LTPs found in pollen and fruit.
Cross-Reactivity
The two isoforms of Ara h 9 share 60–70% identical amino acid sequence with LTPs from other plant produce.
Peach LTP, Pru p 3 could be a sensitizing allergen in people with peanut allergy for whom the major peanut allergens did not contribute to primary sensitization. Ma et al. (2016) reported cosensitization of Ara h 9 with Pru p 3 and also the mugwort nsLTP, Art v 3. Art v 3 has an important role in peach sensitization, but currently the relationship between Ara h 9 and Art v 3 is yet to be fully explored.
References
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