Type:
Whole Allergen
Whole Allergen
t10 Walnut Pollen
t10 Walnut Pollen Scientific Information
Display Name:
Walnut Pollen
Route of Exposure:
Inhalation
Family:
Juglandaceae
Species:
Juglans californica
Latin Name:
Juglans californica
Other Names:
California Black Walnut, California walnut, Jupiter's Nuts, Carya persica (Greek), Carya basilike (Greek)
Summary
Walnut belongs to the Juglandaceae family which consists of 24 different species. Its growth prefers a warm and sheltered site and a long growing season. Soil pH 6 to 7.51 is optimal for growth. The Eastern United States is known as a native place for black walnuts and used for timber. Walnut pollen is moderately allergenic and sensitizes through inhalation. Walnut California, the western species can cause sensitization more than Black walnut. Pollens can cause allergy through inhalation while nuts can cause food. Walnut pollen allergy can induce symptoms such as asthma and rhinitis. Walnut pollens are moderately allergenic and may not lead to severe anaphylaxis. Pollens sensitization was found in young children with rhinitis symptoms. Walnut tree wood has been observed to create dust and can cause occupational allergic contact dermatitis. Prevention measures can be taken by avoiding pollen into the respiratory system during the pollen season. No pollen-related allergens from the Juglans Californica have been determined yet. Walnut pollen has allergen which functions like Bet v 2 (profilin). LTP allergen found in walnut tree pollen is different from the one found in walnut tree nuts. Cross-reactivity is reported between the species from Juglans Carya (Pecan) genus.
Allergen
Nature
Walnut is a large tree that can grow up to a height of 25-35 m and a trunk diameter of 2 m. It can typically live between 100-200 years, but some specimens have been reported to live up to 1000 years. The mature walnut tree has a deep root system while young trees have a tap root system. The bark is a silver-greyish and smooth texture with deep and wide fissures (1).
Walnuts trees are monecious, self-fertile and pollinate by the wind. The heterodichogamy reproductive system is specific to the Juglans family. The species sheds pollen before or after pistillate flowers become receptive (2). Its tree generates pollen from its flower after a period of 20 to 30 years of age between late spring and early summer (3).
Environmental factors, such as climate conditions, temperature, may impact the period of walnut tree flowering. The high temperatures in spring promote the growth of male flowers while this temperature change has no impact on female flowers. (4).
Habitat
Walnut spreads in either pure stands or as individual trees. It prefers a warm and sheltered location and a prolonged growing season. (1) Walnut tree requires moist to dry soil to growth (5). It grows in deep and rich soils, with a pH value of 6-7.51. The tree is photosensitive, highly sensitive to competition, and susceptible to winter and late spring frosts. Germination is improved in mild winters, indicating that a changing climate with warmer winters may prove beneficial to its establishment (1).
Eastern United States is known as a native place for black walnuts where it is used for timber. English walnut grows in the Balkans and China and is widely spread across in many other places for nut production (3).
Taxonomy
Walnut belongs to the botanical family of Juglandaceae with 24 different species (6).
| Taxonomic tree of Walnut (7) | |
|---|---|
| Domain | Eukaryota |
| Kingdom | Plantae |
| Phylum | Spermatophyta |
| Subphylum | Angiospermae |
| Class | Dicotyledonae |
| Order | Juglandales |
| Family | Juglandaceae |
| Genus | Juglans |
| Species | Juglans californica |
| Taxonomic tree of Walnut (7) |
|---|
Tissue
Pollen of walnut are medium to large-sized, with the typical polar axis of 36.84–39.88 μm, and the equatorial axis of 43.12–46.37 μm length. The shape of the pollen grain is circular and oblate in polar and equatorial view respectively (8). Scanning electron microscopy (SEM) assessment showed that walnut genotype pollen grains are isopolar and periporate. During anthesis, dehydrated pollens are depressed at the polar ends (8).
Epidemiology
Worldwide distribution
California walnuts are deemed to be western species and are a major cause of pollen allergic sensitization (3). A significant amount of pollen from trees such as walnut, birch, oak, elm, etc. was observed in a study in Tehran, Iran (1974) which was deemed to induce allergic reactions in sensitized individuals (9). Lewis and Imber suggested that, in the North temperature region, asthma, allergic rhinitis and allergic conjunctivitis are common symptoms following exposure to tree pollen such as from walnut, oak, elm, etc. (10). An aerobiological survey conducted in Bitlis, Turkey reported atmospheric pollens from Juglans spp. and other tree species(11). In some patients, the allergic reaction can be due to pollen rather than the plant’s actual fruit or vegetable (12).
Environmental Characteristics
Worldwide distribution
California is known for Juglans Californica and about 15 associated species of walnut exist in North and South America, and in central/southern parts of Europe and Asia. The Black Walnut considered for pollen allergy is native to the Eastern United States. The English Walnut is native from the Balkans to China and extensively grown in many other temperate areas (3).
Route of Exposure
Main
Airway (Inhalation) is the main route of exposure to pollen allergens (13). Walnut pollens cause inhalant allergies, and the nuts may cause food allergies (3).
Secondary
Food (Ingestion)
A cross-reactivity reaction usually occurs when patients are exposed to pollen grains after eating fruit or vegetables. The digestive system's allergenicity can enhance due to the release of small soluble allergenic fragments from poorly soluble conglomerate (13).
Clinical Relevance
A birth cohort study by Lovasi, O’Neil-Dunne et al, was performed for establishing the relationship of urban tree canopy and asthma, wheeze, rhinitis, and allergic sensitization to tree pollen in New York City. This study was positively correlated with asthma and allergic sensitization at the age of 7 years. A higher prevalence of allergic sensitization was found for tree pollen. The mixed tree pollen used for IgE testing included the walnut with other prevalent pollens. Mixed tree pollen sensitization was found to be 19%. Reported asthma diagnosis at age 7 years was found to be 32% while rhinitis at age 5 years was found in 2% (14).
Allergic rhinitis
The nuts from walnut trees consist of lipid transfer protein (LTP) allergen but to date similar, LTP allergen has not been found in pollen from walnut trees. Cross-reactivity of LTP appears only in food through ingestion, but not through pollens inhalation. Walnut pollens can cause inhalant allergy. Dermatitis, asthma, and rhinitis were found in Central American walnut (Juglans olanchana) due to dust but not through pollen. This pollen inhalation resulted in immediate bronchospasm (3).
Wong, Wilson et al. conducted a study in children to detect pollens that trigger early sensitization in young children suffering from symptoms such as allergic rhinitis. The study included 123 pediatric cases (age ≤ 8years). It was observed that more than 50% were sensitized to at least one aeroallergen like walnut. Among 2 to 3-year-old children, 75% (16 children) were sensitized to walnut. In the contrast, walnut didn't sensitize children from the age group of 4 to 7 years (15).
Asthma
A case report of asthma and rhinitis induced due to Central American walnut dust is reported in a 48-year-old man with disease severity. The intradermal test showed a negative result, but dust inhalation induced immediate bronchospasm response (3, 16). De Roos et al conducted a retrospective study for tree and grass pollen sensitization which includes walnut species as one of the pollen allergen. The most prevalent exposure-response trend was observed for walnut, ornamental, ash, oak and sweetgum trees with asthma exacerbation (17).
Atopic dermatitis
Walnut tree wood has been observed to create dust and may cause occupational allergic contact dermatitis (3, 16).
Prevention and Therapy
Prevention strategies
Prevention measures can be taken by avoiding pollen into the respiratory system during the pollen season. Allergic patients should stay indoors or wear masks outdoors to avoid exposure. Patients should move to live in a pollen-restricted area (18).
Molecular Aspects
Allergenic molecules
No pollen-related allergens from the Juglandaceae family have been determined yet.
Cross-reactivity
Cross-reactivity is reported between the species from genus Juglans and on a moderate level was observed with the genus Carya (Pecan) (19, 20). The walnut tree nut consists of a lipid transfer protein allergen (LTP) (21).
But similar LTP allergen is present in walnut tree pollen has not been found yet. Cross-reactivity due to LTP allergens appears to be relevant only in foods ingested, not in inhaled pollens.
Compiled By
Author: Turacoz Healthcare Solutions
Reviewer: Dr. Magnus Borres
Last reviewed: December 2020
References
- de Rigo D, Enescu CM, Houston Durrant T, Tinner W, Caudullo G. Juglans regia in Europe: distribution, habitat, usage and threats. 2016.
- Ebrahimi A, Lawson SS, Frank GS, Coggeshall MV, Woeste KE, McKenna JR. Pollen flow and paternity in an isolated and non-isolated black walnut (Juglans nigra L.) timber seed orchard. PLoS One. 2018;13(12):e0207861.
- Harris Steinman. Tree pollens - ImmunoCAP Explorer. 2008.
- Mariana BI, Sina Niculina C. Effect of climatic conditions on flowering of walnut genotypes in Romania. Journal of Nuts. 2017;8(02):161-7.
- UFEI UFEI-. SOUTHERN CALIFORNIA BLACK WALNUT: Juglans californica 2020 [15-10-2020]. Available from: https://selectree.calpoly.edu/tree-detail/juglans-californica#content.
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- CABI.org. Juglans californica 2020 [01-12-2020]. Available from: https://www.cabi.org/isc/datasheet/29046.
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- Shafiee A. Atmospheric pollen counts in Tehran, Iran, 1974. Pahlavi medical journal. 1976;7(3):344.
- Lewis W, Imber W. Allergy epidemiology in the St. Louis, Missouri, area. III. Trees. Annals of allergy. 1975;35(2):113-9.
- Celenk S, Bicakci A. Aerobiological investigation in Bitlis, Turkey. Annals of Agricultural and Environmental Medicine. 2005;12(1):87-93.
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- Lovasi GS, O’Neil-Dunne JP, Lu JW, Sheehan D, Perzanowski MS, MacFaden SW, et al. Urban tree canopy and asthma, wheeze, rhinitis, and allergic sensitization to tree pollen in a New York City birth cohort. Environmental health perspectives. 2013;121(4):494-500.
- Wong V, Wilson NW, Peele K, Hogan MB. Early pollen sensitization in children is dependent upon regional aeroallergen exposure. Journal of allergy. 2012;2012.
- Bush R, Clayton D. Asthma due to Central American walnut (Juglans olanchand) dust. Clinical & Experimental Allergy. 1983;13(4):389-94.
- De Roos AJ, Kenyon CC, Zhao Y, Moore K, Melly S, Hubbard RA, et al. Ambient daily pollen levels in association with asthma exacerbation among children in Philadelphia, Pennsylvania. Environment International. 2020;145:106138.
- Xie Z-J, Guan K, Yin J. Advances in the clinical and mechanism research of pollen induced seasonal allergic Asthma. American journal of clinical and experimental immunology. 2019;8(1):1.
- Weber RW. Patterns of pollen cross-allergenicity. Journal of Allergy and Clinical Immunology. 2003;112(2):229-39.
- White JF, Bernstein DI. Key pollen allergens in North America. Annals of Allergy, Asthma & Immunology. 2003;91(5):425-35.
- Asero R, Mistrello G, Roncarolo D, Amato S, van Ree R. A case of allergy to beer showing cross-reactivity between lipid transfer proteins. Annals of Allergy, Asthma & Immunology. 2001;87(1):65-7.
