f430 Act d 8, PR-10 protein, Actinidia deliciosa fruit

Summary

Act d 8, an allergen from kiwifruit (Actinidia deliciosa), is a member of the Pathogenesis Related (PR)-10 family, cross-reactive with Bet v 1, the major allergen of birch pollen. Act d 8 is a major kiwifruit allergen in geographical areas subject to birch pollinosis. In patients reacting upon kiwifruit ingestion, Act d 8 sensitization is not associated with severity of the reaction but is inversely correlated to kiwifruit monosensitization. Using Act d 8 specific IgE determination increases the sensitivity of kiwifruit diagnosis compared to skin prick tests or specific IgE to kiwifruit whole allergen extract.

Epidemiology

Worldwide distribution

During the 40 years since the description of the first case, allergy to kiwifruit, usually Actinidia (A.) deliciosa has become a major cause of food and fruit allergy worldwide [1, 2]. In Europe, data collected from 2005 through 2009 as part of the EuroPrevall study placed kiwifruit allergy at the 4th place of most prevalent food allergies in adults from Zurich (Switzerland) and Utrecht (the Netherlands) with a prevalence of 1.34% and 0.57% respectively [2]. In children, the EuroPrevall study found similar prevalence figures, with a maximum of 1.06% in Madrid (Spain) [3]. The prevalence of sensitization to A. deliciosa ranged from 1.8% to 9.4% in both adults and children [2-4]. Kiwifruit was also reported as the most frequent culprit food for pollen-food syndrome in Turkey, reported by 39% of patients [5] and the 3rd most frequent in Korea (30%) [6].

Act d 8 sensitization is part of PR-10 cross-reactivity and therefore displays considerable variation depending on the geographic and climate area considered. In Europe, Act d 8 sensitization was demonstrated in 58% of kiwifruit-allergic patients from Central and Western Europe and in 44% of those from Eastern Europe, but only in 11% of those from birch-free Southern Europe [7].

Environmental Characteristics

Source and tissue

Act d 8 is present in the peripheral pulp of mature green kiwifruit [8].

Risk factors

The main risk factor for developing sensitization to Act d 8 is exposure to birch pollen [9].

Detection methods

Similar to other PR-10 proteins, Act d 8 is a low-abundant, relatively unstable protein which may not be sufficiently represented in whole allergen extracts and therefore lead to insufficient detection sensitivity. Using Act d 8 or a representative allergen such as Bet v 1 in addition to the whole allergen extract improves the diagnostic performance [9].

Clinical Relevance

Act d 8 sensitization is associated with pollen-kiwifruit cross-reactivity and therefore usually manifests itself as an oral allergy syndrome [9]. However, Act d 8 sensitization often occurs in polysensitized patients [7].

Disease severity and prediction

Act d 8 sensitization can coexist with sensitization to other kiwifruit allergens, explaining the lack of a statistically significant association with increased or decreased severity of kiwifruit allergy [7, 10].

Cross-reactive molecules

Act d 8, a member of the PR-10 family of proteins, exhibits cross-reactivity with Bet v 1 and Bet v 1-related allergens [8, 11]. Another kiwifruit allergen, Act d 11, cross-reacts with PR-10 proteins despite low sequence identity and its inclusion in the distinct family of Ripening-Related Proteins /Major Latex Proteins [9, 12].

Prevention and Therapy

Experimental trials

Not relevant.

Molecular Aspects

Biochemistry

Act d 8 is a 157-aminoacid protein displaying the typical PR-10 sequence and structure [8, 13]. It is present in low amounts in the pulp of green kiwifruit [8]. Similar to other PR-10 proteins, Act d 8 is thermolabile, degraded by thermal processing, and relatively unstable, explaining its under-representation in allergenic extracts [9]. 

Isoforms, epitopes, antibodies

As of April 26, 2022, only one isoallergen of Act d 8 has been included in the World Health Organization (WHO) and International Union of Immunological Societies (IUIS) Allergen Nomenclature [14].

Cross-reactivity due to structural similarity

Act d 8 displays moderate sequence identity with other allergenic PR-10 proteins, ranging from 50% to 57% for the main pollen homologues (Bet v 1 53%, Cor a 1 55%, Aln g 1 50%) and from 54% to 61% for the main fruit homologues (Pru p 1 54%, Mal d 1 57%, Pru ar 1 61%). [8]. Studies addressing Act d 8 sensitization in the context of other PR-10 allergens show that Act d 8 is one of the most infrequent PR-10 sensitizations, both in birch-pollen areas and in those without birch pollen [11, 15].

Diagnostic Relevance

Cross-Reactivity

Act d 8 sensitization in kiwifruit-allergic patients is mainly associated with Bet v 1-related cross-reactivity in birch pollen-sensitized patients [9]. Of note, Act d 8-related kiwifruit allergy was reported in patients with birch pollen sensitization but lacking birch pollen-induced symptoms [7].

Exposure

The main route of exposure is through consumption of kiwifruit [9]. 

Compiled By

Author: Joana Vitte

Reviewer: Dr.Christian Fischer

Last reviewed: June 2022