Type:
Whole Allergen
Whole Allergen
t14 Cottonwood Pollen
t14 Cottonwood Pollen Scientific Information
Display Name:
Cottonwood Pollen
Route of Exposure:
Inhalation
Family:
Salicaceae
Species:
Populus deltoides
Latin Name:
Populus deltoides
Other Names:
Eastern cottonwood, Poplar tree, plains cottonwood, black poplar of eastern North America, necklace poplar, eastern poplar, Carolina poplar
Summary
Cottonwood is a deciduous, fast-growing tree that can attain a height of around 175 to 190 feet. This tree is claimed to possess an average life-span of 55 to 65 years. The tree originated from North America and is prevalent in countries like the US, Canada, Sweden, United Kingdom, Netherlands, India, China, Nepal, Australia, Pakistan, and New Zealand. This tree can release pollens in abundance, which might be responsible for the manifestation of allergic reactions. Exposure to cottonwood pollen can elicit allergic rhinitis and asthma among allergic individuals. To date, no cottonwood allergens have been identified in the IUIS database. Cross-reactivity has been reported between tree species from Salicaceae and Fagales order. Species from the Populus (cottonwood) and Salix (willow) genus are also reported to exhibit strong cross-reactivity.
Allergen
Nature
Cottonwood tree, also known as eastern cottonwood, is a rapidly growing tree that originated from North America. On fertile land, this tree can attain a height of around 175 to 190 feet and a diameter of 4 to 6 feet. The tree can survive up to 55 – 65 years of age under optimal growth conditions (1). The leaves from this tree are broad, 3 – 5 inches in length and width, and triangle-shaped with oval lining. The leaves are dark green with a glossy upper surface and light green with a smooth underneath surface. The bark of this tree is smooth and greenish-grey initially, and later with aging, it turns into ash-grey with rough (deep, elongated furrows) texture (2). The flowering season commonly starts during early spring before the emergence of leaves (3). However, the flowering period may differ as per the altitude and location of the tree. The wood from this tree is used for producing high-grade pulp, containers, furniture (internal parts), and plywood (core stock) (2).
Habitat
Cottonwood can survive in various soil conditions, including infertile sand, fairly stiff clays, and fine sandy loams. The preferred soil type for cottonwood tree is claimed to be moist, well-drained, near to stream with a pH of 4.5 - 8.0. This tree requires an average yearly rainfall of around 600-1500 mm and an annual average temperature of 8-14 ºC (4).
Taxonomy
The genus Populus possesses a total of 22 to 75 species based on various taxonomic classifications. However, based on morphological characteristics, around 30 species are considered part of this genus (5).
| Taxonomic tree of Cottonwood (6) | |
|---|---|
| Domain | Eukaryota |
| Kingdom | Plantae |
| Phylum | Spermatophyta |
| Subphylum | Angiospermae |
| Class | Dicotyledonae |
| Order | Salicales |
| Family | Salicaceae |
| Genus | Populus |
| Species | Pupolus deltoides |
| Taxonomic tree of Cottonwood (6) |
|---|
Tissue
The cottonwood pollen grains are spheroidal (24 to 37 µ in diameter) and acolpate ( absence of germinal furrows). These grains possess a thick intine (internal layer) and a very delicate outer layer (exine), which at times is found to be grainy, webbed, and fragmented (7). To date, no allergenic protein has been identified from cottonwood tree pollen in the IUIS database (8).
Epidemiology
Worldwide distribution
Aeroallergens (like cottonwood pollens) are regarded as one of the potential contributors of allergic diseases (allergic rhinitis, atopic dermatitis, and asthma) in sensitized individuals upon exposure (acute or chronic) (9).
Cottonwood pollen has been reported to be one of the crucial pollens prevalent in the atmosphere during the tree pollen season in Tehran (Iran) (10).
A study was conducted in the United Arabic Emirates (UAE) on 327 patients (with ophthalmologic, dermatologic, and respiratory diseases) to find the correlation between allergen-specific IgE and skin test reactivity in asthmatic patients. 244 patients responded positively towards the skin prick test (SPT) for the investigated aeroallergens. 33.1% of 244 patients were reported to exhibit positive SPT towards cottonwood pollen (11).
A United States (US) based study was conducted on 345 military children with rhinitis to analyze the aeroallergen mediated sensitization rates. The study confirmed cottonwood tree allergen to be responsible for sensitization in 32.8% of this study population through SPT (12).
Environmental Characteristics
Worldwide distribution
The species from the genus Populus are usually prevalent around the Northern Hemisphere (floodplain forests in several ecoregions) (13). Populus Deltoides (Cottonwood) originated from the US and Canada. It is considered an exotic species in countries like Sweden, the United Kingdom, Netherlands, India, China, Nepal, Australia, Pakistan, and New Zealand (4).
Route of Exposure
Main
The route of exposure for cottonwood pollen allergen is through inhalation (14).
Clinical Relevance
Cottonwood tree pollen might induce symptoms like allergic rhinitis and asthma in allergic patients (15).
Allergic rhinitis (AR)
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 one aeroallergen. 32.8% of the 345 patients exhibited positive SPT towards cottonwood tree allergen (12).
A study conducted serum specific-IgE testing against 16 common aeroallergens among 2268 patients with asthma and/or rhinitis in China. The rhinitis patients were subdivided based on the severity of rhinitis, which included mild intermittent (MII, n = 175), moderate-severe intermittent (MSI, n = 281), mild persistent (MIP, n = 596), and moderate-severe persistent (MSP, n = 339). The rate of prevalence of serum specific-IgE positivity towards cottonwood tree pollen in rhinitis patients was reported as 5% in MII, 6.8% in MSI, 2.7% in MIP, 4.5% in MSP, and with a p-value of 0.050 (15). d
Asthma
In a China-based study, serum specific-IgE testing was conducted on 2268 patients with asthma and/or rhinitis. The asthmatic patients were subdivided based on the severity of asthma, which included mild intermittent (MII, n = 405), mild persistent (MIP, n = 313), moderate persistent (MOP, n = 335), and severe persistent (SEP, n = 628). The rate of prevalence of serum specific-IgE positivity towards cottonwood tree pollen in asthmatic patients was reported as 2.8% in MII, 2.1% in MIP, 3.6% in MOP, and 3.4% in SEP (15).
Prevention and Therapy
Prevention strategies
Avoidance
One of the main measures to be taken is to cut down the pollen amounts in the respiratory system. During the pollen season, allergic patients are suggested to stay indoors or wear a mask when outdoors to keep away from pollen allergens. In worsening conditions, patients may be advised to move to a non-pollen area (16).
Molecular Aspects
Allergenic molecules
To date, no allergens have been identified and listed by the IUIS database (8).
A research study predicted 28 proteins as candidate allergens from mature poplar pollen through proteomic analysis. As per the study, four small heat shock protein (Hsp) and four Hsp70 allergenic molecules were identified from P. deltoides pollen. Similar Hsp allergenic proteins have also been found in soybean, penicillium, cystic echinococcosis, corn dust, and wheat dust. Protein spots similar to Olive (Ole e 1) allergen, thioredoxin proteins, and profilin (similar to allergens in wheat, maize, birch, etc.) have also been identified from P. deltoides pollen (17).
Cross-reactivity
Pollen from cottonwood (P. deltoides) exhibits high cross-reactivity with willow (Salix spp.) (14). Additionally, moderate cross-reactivity has also been observed between the species of order Salicales and Fagales (18).
Compiled By
Author: Turacoz Healthcare Solutions
Reviewer: Dr. Fabio Iachetti
Last reviewed: January 2021
References
- Kennedy HE. Cottonwood: an American wood. Research Paper SHL-RP-231 Stoneville, MS: USDA-Forest Service, Southern Hardwoods Lab 7 p. 1985;231:1-9.
- USDA. Plant Fact sheet - EASTERN COTTONWOOD (Populus deltoides Bartr. ex Marsh.). In: (USDA) USDoA, editor. Washington, DC: USDA NRCS Plant Materials Program; 2002.
- Thapliyal G, Vemanna RS, Pawar PM, Barthwal S, Meena RK, Pandey S, et al. First record of off-season flowering in Populus deltoides from India: paradigm of climate change indicator. International journal of biometeorology. 2020.
- Orwa C AM, Kindt R , Jamnadass R, S Anthony. Populus Deltoides. Agroforestree Database 40. 2009;a tree reference and selection guide version 4.0
- Taylor G. Populus: Arabidopsis for forestry. Do we need a model tree? Annals of Botany. 2002;90(6):681-9.
- CABI. Populus deltoides 2020. Available from: https://www.cabi.org/isc/datasheet/43466.
- Wodehouse RP. Pollen grains. Their structure, identification and significance in science and medicine. 1935.
- WHO/IUIS. Populus deltoides (Cottonwood) 2020 [06.01.2021]. Available from: http://www.allergen.org/search.php?allergenname=&allergensource=Populus+deltoides&TaxSource=&TaxOrder=&foodallerg=all&bioname=.
- Moghtaderi M, Hejrati Z, Kolahi N, Heidari B. Sensitization to aeroallergens in patients with allergic rhinitis, asthma, and atopic dermatitis in Shiraz, Southwestern Iran. Indian Journal of Allergy, Asthma and Immunology. 2015;29(2):79.
- Shafiee A. Atmospheric pollen counts in Tehran, Iran, 1974. Pahlavi medical journal. 1976;7(3):344.
- Bener A, Safa W, Abdulhalik S, Lestringant G. An analysis of skin prick test reactions in asthmatics in a hot climate and desert environment. Allergie et immunologie. 2002;34(8):281.
- Calabria CW, Dice J. Aeroallergen sensitization rates in military children with rhinitis symptoms. Annals of Allergy, Asthma & Immunology. 2007;99(2):161-9.
- Rood SB, Kaluthota S. Cottonwood Seed Dispersal Phenology across North America and Worldwide: Tracking ‘Summer Snow’through an Internet Search. Wetlands. 2020:1-13.
- Chapman JA. Aeroallergens of southeastern Missouri, USA. Grana. 1986;25(3):235-46.
- 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.
- Zhang J, Wu L-S, Fan W, Zhang X-L, Jia H-X, Li Y, et al. Proteomic analysis and candidate allergenic proteins in Populus deltoides CL.“2KEN8” mature pollen. Frontiers in plant science. 2015;6:548.
- Weber RW, Nelson HS. Pollen allergens and their interrelationships. Clinical Reviews in Allergy. 1985;3(3):291-318.
