t224 Ole e 1

Summary

Ole e 1, a group I allergen, is the most abundant in olive pollen. Olive pollen allergy is the most frequent allergy affecting people in the Mediterranean region. Ole e 1 has a sensitization frequency of 70% to more than 80% in patients allergic to Olive pollens. Exposure to Olive pollens triggers conjunctival and nasal symptoms in sensitized individuals. It may also exacerbate asthma in these patients, particularly when the olive pollen counts are high. The pollination season for olive ranges from mid-April to June end.

Ole e 1 is a glycoprotein composed of 145 amino acids. It shows widespread cross-reactivity with the main allergens of other genera from the Oleaceae family, including ash, privet, and lilac, due to the high degree of sequence homology between them. The cross-reactivity between Ole e 1 and ash is so high that Ole e 1 has been established to be a marker allergen for diagnosing allergy against the European ash pollen.

Allergen-specific immunotherapy (AIT) has been proved to be the only treatment that can effectively alter the disease course in pollen allergic patients. IgE testing for Ole e 1 has proved to be useful in the diagnostic workup for olive AIT. Since the period of pollination of Olive differs according to climate and geography, changes in the climate and sensitization spectrum of an individual must be recognized so that the exposure to pollens can be prevented as the patient may avoid visiting areas with Olive trees. 

Epidemiology

Worldwide distribution

Pollen from an Olive tree is the most significant allergy-causing pollen in the region of the Mediterranean basin (1-5). The prevalence of sensitization to Ole e 1 is very high, nearly 80% in Olive-pollen allergic individuals since it is the major protein in the Olive pollen (6, 7). Out of 891 pollen-sensitized patients in areas with high exposure to olive pollens in Spain, 75.3% were found to be sensitized to Ole e 1 (8). In Zurich (Switzerland), 181 out of 183 pollen-allergic patients in the age range of 7-76 years exhibiting typical allergic symptoms (rhinitis, conjunctivitis, and/or asthma) were found to be sensitized to Ole e 1 (9). Among 35 summer or spring pollinosis patients (sera samples) in Strasbourg, France, 60% of the patients were found to be sensitized to Ole e 1 (10).

Environmental Characteristics

Source and tissue

Ole e 1 is an allergen derived from pollens of the olive tree (0. europaea). It is the major allergen out of all the allergenic molecules of olive (11, 12), with a prevalence of 55-90 % (13).

Ole e 1 is explicitly found in the cisternae of the rough endoplasmic reticulum (RER) (14). It is synthesized and stored in the endoplasmic reticulum of the pollen grain (15).

The recombinant olive pollen allergens have been expressed using two different heterologous systems, Escherichia coli (prokaryotic host) and Pichia pastoris (P. pastoris), the methylotrophic yeast (as a eukaryotic system) (13).

Initially, Ole e 1 was expressed in E. coli in the form of a fusion protein associated with the glutathione S-transferase (13,21).  Ole e 1 has also been produced in P. pastoris, as well-folded cys-containing proteins (17).

Risk factors

Ole e 1 has a sensitization prevalence ranging from 70% to more than 80% amongst patients sensitive to olive pollen (7, 13). There is a great variation in the pollination period of Olea, depending on the geographical location. The pollination period for Olive pollens is between Mid-April and June-end in Spain and Italy, respectively (6). During the pollination period, there is an increase in the number of allergic individuals and individuals with severe symptoms due to the rise in pollen production (6).

Clinical Relevance

Specific molecules

Ole e 1, a group 1 allergen, is a part of the protein family associated with pollen germination, tube growth, and/or pollen hydration (13).

Ole e 1 is a polymorphic protein, representing nearly 20% of the entire protein content in Olive pollen extracts (13, 16). Ole e 1 has a major impact on the total allergenicity of the olive pollen (17).

The recombinant form of Ole e 1 (r Ole e 1) is as efficient as the natural Ole e 1 (n ole e 1) allergen molecule in diagnosing olive pollinosis (13).

Cross-reactive molecules

The comparable folding and/or glycosylation patterns account for the cross-reactivity of Ole e 1, not only with Ole e 1-like protein from allergenic species of Oleaceae, but also with other members of the Caryophyllales (i.e., Chenopodium album), Lamiales (i.e., Plantago lanceolata), or Poales (i.e., Lollium perenne or Phleum pratense) although to a lesser extent (7). Other genera of the Oleaceae family such as Lig v 1 (privet), Fra e 1 (ash), and Syr v 1(lilac) possess several Ole e 1 homologs. These are accountable for the high degree of IgE cross-reactivity among different species of Oleaceae plants (18-20).  Ole e 1-specific IgE in the serum of patients sensitized to Olive pollens inhibits cross-reactivity of pollens from Oleaceae family with non-Oleaceae families (21). Also, the similarity in the sequence of amino acids is very low (30–44%) between Ole e 1 and non-Oleaceae homologs. Thus, the cross-reactivity appears to be very low despite the presence of Ole e 1-homologous proteins in non-Oleaceae plants (e.g., grasses, plantain, and Chenopodium) pollens (20).

Molecular Aspects

Biochemistry

Ole e 1 is a glycoprotein made up of 145 amino acids (7). It occurs in glycosylated and nonglycosylated forms. Based on the carbohydrates present, the apparent molecular weight of Ole e 1 ranges between 18 kDa (nonglycosylated) and 20 kDa (glycosylated) (16, 19). Other forms, such as 22-kDa (hyperglycosylated) and 40-kDa (dimers of the glycosylated forms), also appear in the protein preparations occasionally (13, 15).

rOle e 1 exhibits differing degrees of glycosylation (12). The site for N-glycosylation is positioned at residue Asn111. As per the circular dichroism analyses, Ole e 1 comprises 22% a-helices, 38% β-structures, and 40% turns or random conformations. Antibody recognition requires both, glycosylation and an intact structure (7).

The spectroscopic properties (fluorescence and CD) and immunological reactivities (binding of IgG to the monoclonal antibodies that are sensitive to denaturation and IgE from sera of allergic patients) of r Ole e 1 are identical to those of the n Ole e 1 (12). 

Isoforms, epitopes, antibodies

Mapping of the B-cell antigenic determinants of Ole e 1 revealed seven overlapping IgG epitopes. Nearly all the epitopes presented a conformational character since the ability to bind to the IgG antibodies is lost after SDS-treatment and/or there is a reduction of the disulfide bridges of the Ole e 1 allergen (13).

At least 4 B-cell epitopes and 2 immunodominant T-cell epitopes in regions, aa 91 to 102, and aa 119 to 130 are found. This region is primarily recognized by patients allergic to olive pollen and induces a T cell-proliferative response lacking IgE-binding capability (22).

An IgE epitope is found in the isolated glycan; it is identified in more than 60% of the sera from Ole e 1 allergic patients (23).

The major binding protein in olive is Ole e 1. Most of the allergenic epitopes of olive pollen are present in Ole e 1 (19). It has an IgE-binding frequency of nearly 80% amongst olive pollinosis patients (7, 16, 17). The disulfide bond integrity determines the IgE recognition of Ole e 1 (20).

Cross-reactivity

The degree of allergenic cross-reactivity essentially depends on the similarity between the structure of the two allergens. Hence, cross-reactivity is frequently seen between homologous proteins  (23). The sequence of amino acids in Ole e 1 exhibits homology (24–34%) to proteins of the pollens from tomato, maize, rice, ryegrass, and birch (15). Similarly, Ole e 1 presents high levels of sequence homology and IgE cross-reactivity to other genera's major allergens from the Oleaceae-family, including ash, lilac, and privet (22, 24).

Widespread cross-reactivity is seen between Olive and ash to the extent that Ole e 1 works as a very good marker allergen for diagnosing allergy against ash pollen (9, 25).

Olive also presents cross-reactivity with Privet pine, Birch, Mugwort, and Cypress (26).

Diagnostic Relevance

Disease Severity

Ole e 1 sensitization signifies primary sensitization to Oleaceae pollens (21). The concentration of Olive allergen and pollen counts in the air is directly proportional to rhinitis and asthma symptoms in patients allergic to olive (27).

Ole e 1 is considered a marker allergen for diagnosing allergy to olive and ash pollen (9, 28).

AIT Prescription

An in vitro analysis conducted on 19 (13 asthmatic and six non-asthmatic) untreated patients who were allergic to olive pollen and ten healthy individuals who were not allergic to olive pollens revealed that Ole e 1 peptides induced an IL-35 and IL-10 mediated regulatory response, thus preventing the proliferation of olive pollens in the allergic patients. This shows that Ole e 1 peptides serve as potential therapeutic tools for preventing respiratory disorders caused by olive pollens (22).

Exposure

A patient’s sensitization profile is affected by the exposure to olive pollen (29). During the pollen season, the prevalence of pollinosis is high. In nearly 80% of olive-allergic patients, Ole e 1 has been identified (22). 

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Magnus Borres

Last reviewed: November 2020