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Whole Allergen

t7 Oak Pollen

t7 Oak Pollen Scientific Information

Type:

Whole Allergen

Display Name:

Oak Pollen

Family:

Fagaceae

Species:

Quercus alba

Latin Name:

Quercus alba

Other Names:

White oak, Forked-leaf white oak, Fork-leaf oak

Summary

Oak (Quercus alba) tree is a wind-pollinated, deciduous, long-lived (up to hundreds of years), and slow-growing tree. The flowering season of this plant falls during spring. It is reported to produce large quantities of pollen. The Oak species are majorly found in deciduous forests of the Northern Hemisphere. The predominant species of the white oak group found in North America is Q. alba which is now also found in Europe, and certain parts of Asia and Africa. Exposure to oak pollen may induce symptoms such as allergic rhinitis, allergic rhino-conjunctivitis, and asthma in sensitive patients. The major allergen listed officially in the database of the World Health Organization/International Union of Immunological Studies Allergen Nomenclature Sub-Committee is Que a 1 (a Bet v 1 homolog, Pathogenesis-related protein). Studies have also identified calcium-binding protein and profilin allergenic molecules from this pollen. Various studies have shown significant cross-reactivity between oak pollen and pollen from other related tree species such as birch, alder, hornbeam, hazel, European chestnut, sawtooth oak, Mongolian oak as well as with pollen from unrelated tree species like ginkgo and grass species like timothy grass.

Allergen

Nature

Oak (Quercus alba) is a common, slow-growing, wind-pollinated, deciduous tree that can attain a height of 18-24 m, and live up to 600 years (1). This tree comprises of green, oval leaves, 4 to 8 inches in length with lobed margins, aligned in an alternate arrangement (2).  It is a monoecious plant with male flowers, appearing earlier than female and in hanging catkins of 2.5 to 8 cm in length. Whereas the female flowers appear either as solitary or in pairs and usually produce acorn as a fruit (1.5 - 2.5 cm long). The flowering season occurs during spring, generally after the lengthening of new leaves. This season usually extends until late March and May (or June), particularly in the Northern hemisphere. Moreover, this period may be affected by the varying altitude, weather conditions, and the genetic composition of the trees. This tree can produce pollens in large quantities than any other plant, but these pollens can travel less than 200 m only. Shedding of pollens (occurs within 3 days) is affected by light winds (increased shedding) or long rainy days (delayed shedding) (1).

Oak is cultivated as an ornamental tree due to its fall colors of purple reddish to violet-purplish, dense leaf arrangement, and wide crown. The acorns from the trees are a natural food source for animals like squirrels, chipmunks, deer, etc. This tree’s wood is long-lasting and robust, thus used as timber for producing interior woodwork, flooring, lumber, and barrels (2).

Habitat

Oaks are naturally reproduced in regions comprising of clay and loamy soil. This tree usually grows well on slopes facing north and east direction with dense soil. Deep, well-drained, damp, rough soil with slight acidity and mid-level nutrient composition is preferred for its growth. The tree is moderately tolerant to drought, salty soil and water spray and submersion, frost cracking and sensitive to flood (2). 

Taxonomy

The genus Quercus is a diverse keystone taxon which is further divided into subgenus Cyclobalanopsis (mostly Asian) and subgenus Quercus. The Quercus subgenus is further classified into distinct taxonomic sections: Quercus (white oaks having about 200 species), Lobatae (red oaks), Protobalanus (golden cup oaks), Virentes (live oaks), and Cerris (black oaks). Several species of Quercus section are found in North America with Q. alba being predominant (3, 4). These North American oaks are distributed in five subgroups. They are white oaks, red oaks, chestnut oaks, willow oaks, and live oaks (4).  

Taxonomic tree of White Oak (5)
Domain Eukaryota
Kingdom Plantae
Phylum Spermatophyta
Subphylum Angiospermae
Class Dicotyledonae 
Order Fagales
Family Fagaceae
Genus Quercus
Species Quercus alba
Taxonomic tree of White Oak (5)

Tissue

Oak pollens are 40 µm in size, with an irregular outer layer (exine) and three tapered apertures (furrows). These pollens are tricolpate comprising of three grooves with verrucate (wart-like) or scabrate (isodiametric rough structure) on the exterior surface (1). Que a 1 is identified as the most potential allergen from the pollens of this oak species (6).

Epidemiology

Worldwide distribution

The oak and beech species from the Fagaceae family are known to be of allergenic significance, among others. Oak is capable of causing tree pollinosis, especially in areas with numerous oak tree population (1). The oak pollen allergy is of particular significance in Europe and North America (7). The prevalence of tree pollen allergy, due to species from the Fagales order (oak, hornbeam, hazel, alder, and birch), is determined to be 20% amongst the European allergic population (8).

In a study on sera from 102 individuals allergic to Fagales tree pollens, oak tree pollen sensitization was found to be 72% across different areas of Europe based on positive SPT. It was found to be 69% (n=38) in Austria, 76% (n=27) in France, 60% (n=19) in Sweden and 84% (n=18) in Switzerland (8). Also, the prevalence of sensitization to oak tree pollen was reported to be 14% among pollen-allergic patients in Spain while in Sweden, it was 70-80% among pollen-allergic patients especially in the spring season (7).

Allergy due to pollens from the oak species is also found to be of significance in Switzerland (Zurich), the Iberian peninsula, Turkey, South Africa (Cape Town), Florida (Tampa), Mexico city, Japan, and Korea (1).

A United States (US) based study identified oak as one of the heaviest pollinators along with maple, hemlock, birch, juniper, and pine species. In the same study, the most common skin prick test (SPT) reactions were found positive to oak along with other tree pollens like willow, ash, maple, beech, and birch (9).

A study was conducted on 371 allergic patients in New York City to analyze the sensitization rate to tree pollen. The results showed the highest prevalence (34.3%) of hypersensitivity towards oak tree pollens (10).

In Korea, in a study, the sensitization to white oak along with birch pollens among respiratory allergic patients was found to have increased from 6.7% in 1999 to 9.6% in 2008 owing to widespread oak trees in Korean forests (11, 12). Further, another study’s evaluation on 12 allergic Korean patients found white oak sensitization in 83% based on measurement of serum specific immunoglobulin E (IgE) (11).

Environmental Characteristics

Worldwide distribution

The Quercus genus, commonly known as oaks are majorly found in deciduous forests of the Northern Hemisphere but lately have been found in Southern Hemisphere as well. They are majorly distributed in the Western Hemisphere (250 species) in addition to Mexico (> 150 species) the US (60 species) and Canada (11 species) (4). The predominant species of white oak group (Q. alba) is widely found in North America (3). It was native to the eastern US ranging from the Atlantic sea in the east, Missouri river in the west, Gulf coast in the south to the Great Lakes in the north of US. It further extended to Ontario and Quebec in Canada. Oak tree is now also been settled commonly in European countries (13, 14). It is found to be growing in Maine, Minnesota, Florida, and Texas states of the US (2). It is also found as a common deciduous tree along with beech in certain parts of Asia and Africa (13). 

Route of Exposure

Main

A significant route of exposure for oak pollen is through inhalation (11).

Clinical Relevance

Oak allergy may induce respiratory symptoms such as asthma, allergic rhinitis, and conjunctivitis in sensitive individuals (11).  

Allergic Rhinitis (AR) and Allergic Rhino-conjunctivitis (ARC)

A US-based study conducted on 562 military children (≤18 years) with rhinitis underwent SPT with an 8-test screening panel (various allergen mixes) (n=209) or a 51-aeroallergen standard panel (n=345). 8 patients were excluded from the study based on positive diluent or negative histamine control. 80.3% (277/345) of the patients showed positive SPT towards at least 1 aeroallergen. Out of these, 31% were reported to show positive SPT towards oak tree (mix of red, white, and Virginia live) extract allergen (15).

A study on 12 allergic Korean patients found white oak tree pollen sensitization in 10 of them in addition to sensitization to other allergens. Allergic conjunctivitis and allergic rhinitis were observed in 30% and 90% respectively of allergic patients having sensitization to white oak pollens (11).

Another study was conducted in Korea on 976 children from an urban and suburban region with or without ARC. Out of these, overall 19.3% (53/274) of children with allergic conjunctivitis reported positive SPT towards oak allergen (16).

Asthma

A study was conducted in 10 Canadian cities to examine the role of different tree pollen allergies and its association with increased risk of hospitalization due to aggravation from severe asthma. The results showed an increased risk of hospitalization (2.3%) for asthma due to Quercus (oak) tree pollen along with Castanea (chestnut) and Fagus (beech) tree pollen (17).

In another study conducted on woodworkers from a furniture factory, the results showed the occurrence of bronchial hyperresponsiveness as well as sore throat in these workers due to occupational exposure to oak (Quercus spp.) and beech (Fagus spp.) wood dust (18).

A study on 12 allergic Korean patients found white oak tree pollen sensitization in 10 of them in addition to sensitization to other allergens. Asthma was observed in 40% of allergic patients having sensitization to white oak pollens (11).

Other topics

Oak processionary caterpillar and moth are prevalent in many European countries. Their larvae contain toxic hairs (setae) which may induce serious reactions like lepidopterism (lesions, toxic dermatitis, itchy papules), urticaria, conjunctivitis, respiratory (upper tract) symptoms, pharyngitis, anaphylaxis, and malaise after its contact. In the study, 42 people were observed to develop such symptoms as severe pruritus, Quincke edema, dyspnea, bronchoconstriction, etc. due to contact with an infested oak tree. However, very few of them were reported to have contact with caterpillars (19).

Prevention and Therapy

Allergen immunotherapy

A randomized, double-blind, placebo-controlled trial was conducted in 219 birch allergic patients (aged 18-65 years) with moderate to severe ARC with or without asthma. Oak sensitization was found in 75% of the patients based on positive SPT. The sublingual allergen immunotherapy induced IgG4 antibodies in patients who reacted to birch as well as oak showing a high correlation (r = 0.78) between them. The immunotherapy tablet was able to significantly (p=0.03) reduce ARC symptoms induced by birch or oak tree pollen in birch allergic patients. The significant reduction of ARC symptoms due to exposure to oak confirms the clinical relevance of cross-reactivity between birch and oak (21).

Prevention strategies

Avoidance

One of the preventive measures to be taken is to cut down the amounts of pollen entering the respiratory system. During pollen season, allergic patients are suggested to stay indoors or wear masks outdoors to keep away from pollen allergens. In worse situations, patients may be suggested to move to a non-pollen area (20).

Molecular Aspects

Allergenic molecules

Oak tree pollen allergens have been reported to be homologous to birch pollen allergens: Bet v 1 (PR-10 protein) and Bet v 2 (profilin) (8). Besides, calcium-binding allergenic protein (polcalcin) has also been characterized from oak tree pollens (22).

A study on 23 tree pollen-allergic patients from Switzerland and 26 birch pollen-allergic patients from Austria has identified Bet v 1 (PR-10), Bet v 2 (profilin), and Bet v 4 (polcalcin) related allergens in oak pollens. However, they have shown weak IgE reactivity and recognized by fewer patients than the birch pollens. They have also found a 60 kDa allergen to be the most prominent IgE-reactive allergen in oak pollen (13).

However, currently, only one protein has been listed officially in the database of the World Health Organization/International Union of Immunological Studies (WHO/IUIS) Allergen Nomenclature Sub-Committee (6).

The table below provides detailed information on the allergenic protein identified by WHO/IUIS:

Allergen Biochemical name Molecular Weight (kDa) Allergenicity
Que a 1 Pathogenesis-related protein, PR-10,  17
  • Major Allergen (23)
  • Bet v 1 family member
  • IgE reactivity was observed in 7 of 11 sera from birch tree pollen allergic patients as seen on immunoblots performed with oak pollen extract (8)
  • In immunoblot analysis performed in 16 patients with oak pollen allergy, 100% were sensitized to Que a 1 (7).
Allergen Biochemical name Molecular Weight (kDa) Allergenicity

Biomarkers of severity

Bet v 1 (major allergen from birch) is recognized as a marker allergen for sensitization to pollen from species of order Fagales (birch, alder, hornbeam, hazelnut, common beech, oak, chestnut). This allergen is also revealed to show high cross-reactivity and sequence similarity with other Fagales species (23).

Cross-reactivity

The studies have demonstrated significant cross-reactivity between oak pollen and birch pollen (13). Members of the birch family (Betulaceae) has been shown to have strong cross-reactivity with oak (24). It has demonstrated that Bet v 1 and Bet v 2 of birch pollens possess most of the IgE epitopes of Fagales pollens including oak pollen allergen Que a. Sera from European patients (Austria, Switzerland, France, and Sweden) displayed similar IgE reactivity to birch, beech, and oak pollens (8, 13). Cross-reactivity is also shown between oak pollen allergen and timothy grass pollen allergen Phl p 4 in IgE-inhibition experiments (13).

Amino acid sequence homology has been shown among Fagales allergens like Que a 1 (oak), Bet v 1 (birch), Aln g 1 (alder) and Car b 1 (hornbeam) (24). Further, a study reported amino acid sequence identity of Que a 1 with other PR-10 allergens like Bet v 1 (68%), Aln g 1 (60%), Car b 1 (58%), Cor a 1 of hazel (74%), Fag s 1 of beech (74%) Mal d 1 of apple (69%), Pru av 1 of cherry (66%) and highest similarity of 88% with Cas s 1 of sweet chestnut (7).

Studies have also shown sequence homology and cross-reactivity between oak pollen and alder, hornbeam, hazel, and European chestnut pollen (23).

Significant cross-reactivity was shown between oak pollen and sawtooth oak, Mongolian oak as well as common silver birch pollen in a Korean study (11). Furthermore, 86% IgE-binding to ginkgo pollen proteins were inhibited oak pollens in an immunoblot analysis (25). 

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Fabio Iachetti

 

Last reviewed: January 2021

References
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  3. Aldrich PR, Cavender-Bares J. Quercus. In: (eds) KC, editor. Wild Crop Relatives: Genomic and Breeding Resources. Berlin, Heidelberg: Springer; 2011. p. 89-129.
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  5. CABI. Invasive Species Compendium 2020 [04-01-2021]. Available from: https://www.cabi.org/isc/datasheet/4652.
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