t227 Ole e 7

Summary

Ole e 7 is an allergen of olive (Olea europaea) tree pollen, of intermediate prevalence, predominating in areas of high exposure. Ole e 7 belongs to the nonspecific lipid transfer protein (nsLTP) family and displays clinically relevant cross-reactivity with homologues from other allergenic sources, including Pru p 3 from peach. Ole e 7 sensitization is associated with increased prevalence of severe respiratory symptoms in olive pollinosis patients and with nsLTP panallergen sensitization and food-induced reactions with or without olive pollinosis.

Epidemiology

Worldwide distribution

Olea europaea olive trees belong to the cosmopolitan Oleaceae family and are a major cause of pollen sensitization and allergy in the Mediterranean area  [1].

Ole e 7 was described as an O. europaea pollen allergen of intermediate prevalence, binding IgE from 47% of patients allergic to O. europaea [2]. Its prevalence varies according to the study population of olive tree pollinosis, with subsequent studies reporting it from 14.4% [3] to 21.5% [4], peaking at 35% [3] to 47.9%, 51.2% [5, 6] and even 60% [2] of patients with very high exposure to olive tree pollen.

At the low end, in Central Europe, the prevalence of Ole e 7 IgE is low, e.g. 0.9% in a population of pollen-sensitized patients with doctor-diagnosed allergy in the Czech Republic [7].

A significant age effect was reported for Ole e 7 sensitization, with adults affected more frequent than children (24.1% vs. 12.6% respectively) [4].

Monosensitization to Ole e 7 in patients with olive tree pollinosis is infrequent [3].

Environmental Characteristics

Source and tissue

Ole e 7 is mainly present in O. europaea pollen [2].

Risk factors

The main risk factor for developing sensitization to Ole e 7 is exposure to O. europaea pollen [1, 3], notably at very high levels such as those encountered in areas of intensive olive tree culture [6]. Cross-reactivity from other nsLTP is also possible [7, 8].

Clinical Relevance

Detailed information regarding O. europaea pollinosis, which manifests itself mainly as allergic rhinoconjunctivitis and asthma [6], is available in the whole allergen section. 

Disease severity and prediction

In patients with olive tree pollinosis and respiratory symptoms, detection of Ole e 7 sensitization is associated with an increased prevalence of asthma [3] and of concomitant pollinosis to Chenopodiaceae and Poaceae [5]. However, in terms of prevalence, an inverse correlation was reported between Ole e 7 sensitization and exclusively respiratory phenotypes [4].

In patients with olive pollinosis and confirmed plant food allergy, a statistical association between Ole e 7 sensitization and an increased prevalence of fruit-induced reactions, more often severe fruit-induced reactions as opposed to mild symptoms of oral allergy syndrome (OAS), emerged soon after the identification of the Ole e 7 allergen [6]. These findings were confirmed in later cohorts, with odds ratios of 2.4 for severe reactions and 2 for OAS in Ole e 7 sensitized patients [4]. In fact, frequent concomitant sensitization to other nsLTPs (prevalence 80%) was also reported in Ole e 7 sensitized patients [4].

 Conversely, in subjects outside areas of O. europaea exposure, Ole e 7 sensitization was infrequent and not associated to markers of genuine sensitization (i.e., Ole e 1), but concomitant sensitization to one or more other nsLTPs was confirmed [7]. 

Cross-reactive molecules

Ole e 7 shares clinically relevant cross-reactivity with other pollen and food nsLTPs such as Pru p 3 [8], and is now considered as an allergen associated to nsLTP syndrome. ELISA inhibition experiments showed that multiple food extracts induced partial inhibition of Ole e 7 IgE binding, with a maximum at 67% with peach and 52% with pear extracts [8].

Prevention and Therapy

Experimental trials

Not relevant.

Molecular Aspects

Biochemistry

Ole e 7 has a molecular weight of 9.5 kDa [9] and belongs to the nsLTP panallergen family of monomeric, non-glycosylated proteins with a globular conformation comprising four alpha helices stabilized by four disulfide bonds, conferring resistance to heating and acidic pH [1, 10].

Isoforms, epitopes, antibodies

As of December 30th, 2021, two isoallergens of Ole e 7 have been included in the World Health Organization (WHO) and International Union of Immunological Societies (IUIS) Allergen Nomenclature [9].

Cross-reactivity due to structural similarity

Despite low sequence identity between Ole e 7 and the immunodominant food nsLTP Pru p 3 at 20-30%, Ole e 7 shares clinically relevant cross-reactivity with this and other food and pollen nsLTPs [8]. At the molecular level, structural alignment of Ole e 7 and other nsLTPs showed higher similarity than sequence alignment, with similar folding, conserved disulfide bonds and a similar ligand-binding hydrophobic cavity [10]. 

Diagnostic Relevance

Marker allergen for complex sensitization profiles to O. europaea pollen

Patients with olive pollinosis living in areas with high exposure to O. europaea pollen exhibit distinct sensitization profiles, which are more complex and include frequent Ole e 7 sensitization [3].

Marker allergen for nsLTP panallergen sensitization

A statistical association between detectable sensitization to Ole e 7 and to other nsLTPs such as Pru p 3 was reported in some [7] studies but not in others [3, 11]. Studies focusing on the nsLTP syndrome and the place of Ole e 7 showed that Ole e 7 sensitization is present in nsLTP allergic patients with or without olive pollen exposure, e.g. Italy or the United Kingdom (prevalence 30% vs 17%) [12].

Cross-Reactivity

Ole e 7 displays clinically relevant cross-reactivity with other pollen and food nsLTPs [8, 10].

AIT Prescription

Sensitization to Ole e 7 has been associated to an increased prevalence of adverse reactions to AIT for olive tree pollinosis [1, 3]. Conversely, in areas of high exposure to O. europaea pollen, a sensitization profile with Ole e 7 IgE but without Ole e 1 IgE can be found, making up around 2-7% of olive pollinosis patients [5, 6] and indicating different AIT requirements [3].

Exposure

The main route of exposure is through inhalation of O. europaea pollen, usually at high levels of exposure [1]

Compiled By

Author: Joana Vitte

Reviewer: Dr. Christian Fischer

Last reviewed: February  2022