Table of Contents

Whole Allergen

t8 Elm

t8 Elm Scientific Information

Type:

Whole Allergen

Display Name:

Elm

Allergen code:

Family:

Ulmaceae

Species:

Ulmus americana

Route of Exposure:

Inhalation

Source Material:

Pollen

Latin Name:

Ulmus americana

Other Names:

American elm, white elm

Summary

Elm is a member of the Ulmaceae family. It is a wind-pollinated deciduous tree found in countries like the US, Canada, Europe, and middle eastern countries. Exposure to elm pollen may induce allergic reactions like allergic rhinitis and bronchial asthma in allergic individuals. A Canadian study reported elm as the prime contributor (ranked first) for an increase in the number of hospitalized patients, based on its pollen concentration potency. No allergens have been identified for elm tree pollen yet. Elm pollen may cross-react with pollen from other species of its own order Urticales such as Morus (mulberry trees) and Urtica (nettle trees). Moreover, elm pollen has exhibited cross-reactivity with melon, peach and pollens originating from birch.

Allergen

Nature

Elm, also known as white elm or American elm, belongs to the Ulmaceae family. Elm is a wind-pollinated, deciduous tree that can grow up to 30-38m with a life span of 175-200 years (1). The tree possesses large, oval-shaped leaves with serrated edges. It produces abundant pollen quantities and has a brief pollination season, generally ranging from late January to early March (2). This tree is extensively utilized either for shading or as an ornamental tree in various US regions (3).

Habitat

The favorable climate for elm varies from warm-humid in the southeast to cold-dry in the northwest of the US. They can grow in low-temperature areas such as -18° C in Canada to comparatively warmer temperatures like 41° C in southern and western parts of the US. It is commonly found on plains, low-lying land, and sometimes near swamps and streams. It prefers rich, well-drained sandy soil with clay and slit clay, organic content, and pH of 5.5 to 8.0 (1).

Taxonomy

Elm belongs to the genus Ulmus, and there are about 45 species of elm trees; 6 of these, including American elm, are native to North America. Some of the other species belonging to the same genus are Chinese elm (U. parvifolia), Siberian elm (U. pumila), red or slippery elm (U. rubra), September elm (U. serotinai), and cedar elm (U. crassifolia) (2).

Taxonomic tree of Elm
Domain	Eukaryota
Kingdom	Plantae
Phylum	Spermatophyta
Subphylum	Angiospermae
Class	Dicotyledonae
Order	Urticales
Family	Ulmaceae
Genus	Ulmus
Species	Ulmus americana

Tissue

Elm pollen grains are stephanoporate (a ring of pores around the grain's equatorial circumference) (2), and their diameter ranges in-between 23 to 38 µ (5). The grain surface pores are ovoid, ranging from 3 - 7 in number (5) and around 4 µm in diameter (2).

Epidemiology

Worldwide distribution

Tree pollen allergens are one of the critical causes of aggravated asthma, leading to further hospitalization. This fact was confirmed by a study conducted in Canada, which associated the surge in hospitalization with an increase in tree pollen concentration from outdoor trees like maple, alder birch, elm, etc. Elm is a significant contributor to the increase in hospitalization due to severe asthma caused by a daily rise in pollen concentration in the cities’ atmosphere (6).

According to a pollen-count study conducted in Spain between 1979-1983, pollen from species of the Ulmaceae family and Ulmus sp. genus accounted for 1.66% of the total airborne pollens (7).

As per a comparative study conducted in the US on 371 allergy patients, elm pollen hypersensitivity was prevalent among 24.6% (8). Graphical information from a study conducted in the US stated approximately 6%-7% of individuals suffering from allergic rhinitis (n=100) showed positive skin prick test (SPT) against elm tree antigen (9).

A study conducted in Buenos Aires (Argentina) on 439 bronchial asthma and/or allergic rhinitis patients analyzed the prevalence of sensitivity to tree pollen. From 401 atopic patients, 309 (77.1%) exhibited positive skin-prick test for at least one of the 12 investigated tree species pollen. Among these, 37.4% showed a positive skin prick test to Ulmus sp., which was highly prevalent, but in correlation, had a lesser percentage of tree population within the study area. Therefore, as per the study, this could be caused by the cross-reactivity with other trees, like Morus (mulberry trees) and Urtica (nettle trees), for which pollination was reported higher than Ulmus (elm) (10).

A Turkish study evaluated pollen sensitization on 54 patients suffering from seasonal allergic rhinitis. Trees were regarded as the most common pollen source, accounting for 95% of pollen's total amount in the atmosphere. Among the subjects, 10 (18.2%) individuals showed positive SPT to elm pollen (Ulmus)(11).

Environmental Characteristics

Worldwide distribution

Elm is found in eastern parts of the United States and Canada (3). Elm pollen is abundantly found from January to April in Spain (Europe) (7). Its pollen is also seen in middle eastern countries like Turkey between March and early May (11).

Route of Exposure

Main

The main route of exposure for elm tree pollen is through inhalation (airway) (12).

Secondary

Contact urticaria (allergic reaction) was reported in one of the case studies after exposure to the elm tree (13).

Clinical Relevance

Exposure to elm pollen may induce allergic reactions like allergic rhinitis, asthma, and in rare instances, contact urticaria. More than half are allergic to pollens in a population suffering from persistent rhinitis (9). Elm is known to be one of the prime contributors of allergenic pollen in the atmosphere. Some studies reported severe asthma induced by common tree pollens such as elm pollen, which might further increase the patient's hospitalization risk (6). According to studies, allergic rhinitis mediated complications induced by aeroallergens such as tree pollen may lead to a learning disability, cognitive impairment, sleep deprivation, and diminished quality of life (9).

Allergic rhinitis

A cross-sectional epidemiological survey was performed on asthmatic and/or allergic rhinitis patients (n=6304) in 17 cities of China. The result revealed elm tree pollen sensitivity in 4.5% of the total patients with moderate-severe persistent rhinitis (n=339) and 9.1% of 281 patients with moderate-severe intermittent rhinitis (14).

Asthma

In a daily time-series experimental study conducted in Canada, elm tree pollen was responsible for a 2.63% increase in the risk of asthma-mediated hospitalization. The study concluded that the disease burden (such as asthma) is correlated to the tree pollen potency and its variation in the atmospheric concentration (6). Another cross-sectional study in China on patients (n=6304) with asthma and/or allergic rhinitis reported a 4% prevalence of IgE-positivity to elm allergen among 628 patients with severe persistent asthma (14).

Contact Urticaria

In a case study report of a 39-years old male patient without any history of contact dermatitis, contact urticaria occurred after exposure to elm tree (13).

Prevention and Therapy

Prevention strategies

Avoidance

One of the main measures to be taken is to cut down the pollen amount in the respiratory system. During pollen season, allergic patients are suggested to stay indoors or wear a face mask outdoors to keep away the pollen allergens. As per the severity of the condition, patients might be advised to move to a non-pollen area (15).

Molecular Aspects

Allergenic molecules

No allergens have been identified for elm tree pollen to date.

Cross-reactivity

Elm pollen is speculated to cross-react with Morus and Urtica pollen, which are species belonging to the same Urticales order as elm (10). Studies have demonstrated cross-reactivity of elm pollen with peach and birch pollen (16).

According to a study, allergy to melon was associated with pollen allergy, as co-sensitization to pollen is usually seen in melon-allergic patients. A significant sensitization to tree pollen like Ulmus (elm) and weed pollen was observed in melon allergic patients (17).

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr. Fabio Iachetti

Last reviewed: December 2020

References

Bey CF. USDA 2020 [11-12-2020]. Available from: https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/ulmus/americana.htm.
Weber RW. American elm (Ulmus americana) is a native tree that has had a wide range from the entire eastern states through the Central Plains. Ann Allergy Asthma Immunol. 2001;86(2):A7.
Whittemore AT, Olsen RT. Ulmus americana (Ulmaceae) is a polyploid complex. Am J Bot. 2011;98(4):754-60.
CABI. Invasive Species Compendium 2019 [11-12-2020]. Available from: https://www.cabi.org/isc/datasheet/4652.
Wodehouse RP. Pollen Grains. McGraw-Hill Book Company, New York. 1935:384-5.
Dales RE, Cakmak S, Judek S, Coates F. Tree pollen and hospitalization for asthma in urban Canada. Int Arch Allergy Immunol. 2008;146(3):241-7.
Subiza J, Jerez M, Jiménez JA, Narganes MJ, Cabrera M, Varela S, et al. Allergenic pollen pollinosis in Madrid. J Allergy Clin Immunol. 1995;96(1):15-23.
Lin RY, Clauss AE, Bennett ES. Hypersensitivity to common tree pollens in New York City patients. Allergy Asthma Proc. 2002;23(4):253-8.
Basak P, Arayata R, Brensilver J. Prevalence of specific aeroallergen sensitivity on skin prick test in patients with allergic rhinitis in Westchester County. The Internet Journal of Asthma, Allergy and Immunology. 2008;6(2).
Ardusso E, Rosso J, Herrero T, Isorna M, Jares E, Grillo M. Prevalencia de sensibilidad cutánea a 12 especies de pólenes de árboles aerotransportados en pacientes con asma y/o rinitis residentes en el área de la Ciudad Autónoma de la Ciudad de Buenos Aires. Archivos de Alergia e Inmunología Clínica. 2010;41(2):54-60.
Dursun AB, Celik G, Alan S, Pinar NM, Mungan D, Misirligil Z. Regional pollen load: effect on sensitisation and clinical presentation of seasonal allergic rhinitis in patients living in Ankara, Turkey. Allergologia et immunopathologia. 2008;36(6):371-8.
Weryszko-Chmielewska E, Piotrowska-Weryszko K. Airborne pollen calendar of Lublin, Poland. Annals of agricultural and environmental medicine : AAEM. 2004;11:91-7.
Czarnecki D, Nixon R, Bekhor P, Mason G. Delayed prolonged contact urticaria from the elm tree. Contact Dermatitis. 1993;28(3):196-7.
Li J, Huang Y, Lin X, Zhao D, Tan G, Wu J, et al. Influence of degree of specific allergic sensitivity on severity of rhinitis and asthma in Chinese allergic patients. Respir Res. 2011;12(1):95-.
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. Cross-reactivity of plant and animal allergens. Clin Rev Allergy Immunol. 2001;21(2-3):153-202.
Figueredo E, Cuesta-Herranz J, De-Miguel J, Lázaro M, Sastre J, Quirce S, et al. Clinical characteristics of melon (Cucumis melo) allergy. Annals of Allergy, Asthma & Immunology. 2003;91(3):303-8.