Type:
Whole Allergen
Allergen Encyclopedia
Table of Contents
Whole Allergen
t70 Mulberry Pollen
t70 Mulberry Pollen Scientific Information
Display Name:
Mulberry Pollen
Route of Exposure:
Inhalation
Family:
Moraceae
Species:
Morus alba
Latin Name:
Morus alba
Other Names:
White mulberry, Silkworm mulberry
Summary
Mulberry (Morus alba) is a small to mid-sized tree belonging to the genus Morus of the family Moraceae. It is generally found in areas with a subtropical or mild temperate climate and primarily cultivated worldwide to raise silkworms. The pollination period for this tree ranges typically from April to May. According to some studies, mulberry pollen is considered a significant contributor to allergic pollen in the atmosphere. Exposure to its pollen may trigger symptoms like allergic rhinitis, allergic rhino-conjunctivitis, asthma, and, in some rare instances, contact dermatitis in sensitive patients. A cobalamin-independent methionine synthase protein, Mor a 2, has been detected as a significant novel allergen from mulberry pollen. Studies have also detected other allergenic proteins such as profilin, nsLTP (non-specific lipid transfer protein), a ubiquitin-like protein, and a cystatin-like protein from mulberry pollen extract. Significant cross-reactivity between mulberry pollen and other members of the Moraceae family, such as paper mulberry, breadfruit, fig-trees, and jackfruit, has been demonstrated. Cross-reactivity has also been reported with grass pollen and other tree pollens such as olive and alder.
Allergen
Nature
Mulberry tree (Morus alba) is generally small to a medium-sized, rapidly growing tree, reaching up to a height of 10 to 20 meters (1). The leaves of the tree are quite variable, with an oval shape and serrated margins. The flowers are generally bisexual but can also be unisexual and are present on different branches of the same plant (2). The bark possesses a rough surface with greyish brown color and longitudinal fissures (2). The pollination generally occurs from April to May (3). The sericulture industry widely utilizes its leaves as a food source for rearing silkworms (1). These leaves are also used to treat sore throats, eye infections, and nose bleeds (4). Its wood is often used for making paper, sports equipment (like rackets and sticks), building material, boats, houses, flooring, and furniture items (2, 4).
Habitat
White mulberry thrives in areas with subtropical or mild temperate climatic conditions and can grow at an altitude ranging between 0-3300 meters. It is found in areas with mean annual temperatures ranging between 0° to 43° Celsius. It is a shade-tolerant tree and, therefore, can grow in areas with less sunlight (2). A combination of warm, moist, and well-drained loamy soil is preferable to achieve optimal plant growth. Moreover, white mulberry is also claimed to be wind resistant and salt-tolerant (tolerates high soil salinity) (4).
Taxonomy
Mulberry tree (M. alba), belonging to the Moraceae family and genus Morus, is also known as white mulberry. Morus genus consists of more than 15 species overall. Some of the major species of this genus other than white mulberry (M. alba) are black mulberry (M. nigra), M. atropurpurea, African Mulberry (M. mesozygia), red mulberry (M. rubra), Hua Sang (M. cathayana), Korean mulberry (M. australis), and M. notabilis (1).
| Taxonomic tree of White Mulberry (5) | |
|---|---|
| Domain | Eukaryota |
| Kingdom | Plantae |
| Phylum | Spermatophyta |
| Subphylum | Angiospermae |
| Class | Dicotyledonae |
| Order | Urticales |
| Family | Moraceae |
| Genus | Morus |
| Species | Morus alba |
Tissue
The mulberry pollen grain size ranges between 14 to 20 µm in diameter (6). Though studies have determined sensitization to its pollen extract through skin prick test (SPT) or specific-IgE testing but relevant patient sensitivity to its different allergens is yet to be characterized (7). Mor a 2, a cobalamin-independent methionine synthase protein, has been identified as one of the potentially allergenic mulberry pollen proteins listed in the IUIS database (8).
Epidemiology
Worldwide distribution
Pollen grains are considered as one of the causes of allergic reactions in vulnerable populations around the world (9). Among the Moraceae family, mulberry pollen is considered one of the significant contributors to allergic pollen in Spain (7). According to a study conducted in Delhi, to determine the prevalence of airborne pollen concentration, the atmosphere's annual average mulberry pollen concentration was reported highest (34.2%) compared to other pollens (10).
An aeropalynological survey-based study of pollen grains and spores (palynomorphs) in the atmosphere was conducted in Argentina. According to the result, 12 tree pollens like Morus (mulberry), Platanus, Urticaceae, and others contributed more than 1% of the total annual aeroallergen concentration. The arboreal pollen grains from trees such as Morus (mulberry) were reported to contribute more than 68% relative to the total yearly pollen amount of each year (11). Studies have reported tree pollen from mulberry to be one of the inducers for naso-bronchial allergy in allergic patients (12).
In a non-randomized cross-sectional Spanish study among 30 patients with allergic rhino-conjunctivitis (ARC), 13 % confirmed positive SPT to mulberry pollen (13).
A study conducted in Arizona (US) among children with allergic rhinitis exhibited independent association with Bermuda grass and mulberry tree pollen sensitization among subjects of age 11 years. Among the children from the same age group, 23.6% of children with asthma and 18.2% of children with rhinitis reported positive SPT to mulberry pollen (14).
In the middle-east region, among the tree pollens, the allergenicity rate in allergic patients for mulberry pollen was reported as 7% in Pakistan, 1.4% in Qatar, 19.8% in Turkey (15).
Environmental Characteristics
Worldwide distribution
The mulberry tree was introduced into the US for setting up the silkworm industry during the colonial time along the Atlantic coastline (4). It is speculated to have originated from China and then spread in various parts of the world, especially as a food source for raising silkworms (1). It is also cultivated in countries like Japan, Argentina, Europe, Kyrgyzstan, North America, Australia, and Africa (1, 4). Mulberry tree and its pollen is also seen in middle eastern countries like Pakistan, Turkey, Qatar, etc. (15).
Route of Exposure
Main
The main route of exposure for mulberry tree pollen is through inhalation (6). The inhalation of this pollen allergen causes interaction with cellular IgE antibodies present across the respiratory pathway. This further leads to mast cell degranulation and release of other chemical mediators, resulting in upper respiratory tract symptoms like allergic rhinitis and conjunctivitis (16).
Clinical Relevance
Aeroallergen-mediated allergic rhinitis and asthma are primary reasons for increased morbidity, health care expenses, and productivity loss in the sensitive population (17). Such allergic reactions induced by aeroallergens may lead to cognitive impairment, sleep disturbance, and diminished quality of life among impacted children (16). Exposure to mulberry tree pollen may induce allergic reactions such as asthma, rhinitis, and in rare cases, contact dermatitis among allergic individuals (12, 14, 18).
Allergic rhinitis
A study was conducted on 48 patients with naso-bronchial allergy to analyze the sensitization rate to various allergens. In this study, 80% of patients with bronchial asthma also suffered from associated AR, while 25% of the AR subjects suffered from associated bronchial asthma. The SPT results showed 6.25% (3/48) positive SPT for mulberry pollen out of total allergens (12).
Asthma
An aerobiology study was conducted on 1000 patients with asthma or AR in Islamabad (Pakistan). The results revealed positive SPT to various pollens, molds, and house dust in 87.5% of the patients, of which 7% were sensitized to mulberry pollen (19).
Another study conducted in the US exhibited 23.6% positive SPT to mulberry pollen among children (aged 6 to 11 years) with asthma (14).
Contact Dermatitis
According to a case report from Spain, a 12-years old child developed symptoms of contact urticaria (itchy erythema and edema of hands and neck region, angioedema of lips and eyelids) after harvesting mulberry leaves. The symptoms disappeared after 2-3 hours. The child was tested positive for SPT and showed specific-IgE to mulberry pollen (6).
Other topics
Mulberry leaves consumption has demonstrated hypoglycemic and hypolipidemic effects among diabetic patients (20).
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 the pollen season, allergic patients are suggested to stay indoors or wear a mask outdoors to keep away from pollen allergens. In worsening conditions, patients might be advised to move to a pollen-free area (21).
Molecular Aspects
Allergenic molecules
Profilin, an allergenic protein from the mulberry pollen extract, has been detected as a double-band with a molecular weight of 14 to 15 kDa. It has been observed to be present in 21.8% of the sera from allergic patients (n=45). Additionally, three new proteins less than 14 kDa have been identified, which include nsLTP (lipid transfer protein) of 10kDa, a ubiquitin-like protein of 8kDa, and a cystain-like protein of 7kDa (7).
IUIS has listed Mor a 2, a cobalamin-independent methionine synthase protein, as a mulberry pollen allergen (8). A Turkish study has determined methionine synthase protein (molecular weight: 80 to 85 kDa) as a novel allergen from mulberry (M. alba) pollen. According to the study, 5 out of 11 sera showed specific IgE against its pollen peptides and revealed significant action towards this protein of molecular weight 80 kDa (3).
| Allergen | Biochemical Name | Molecular Weight (kDa) | Allergenicity |
|---|---|---|---|
| Mor a 2 | Cobalamin-independent methionine synthase | 84 | 100% (11/11) of the subjects from Turkey with positive SPT to mulberry pollen extract showed positive IgE – reactivity to this protein (8) |
Biomarkers of severity
Mor a 2 has been tested in 45% (5/11) of the patients, sera with specific-IgE to mulberry polypeptides and proposed as a major allergen from mulberry (M. alba) pollen (3).
Significant sensitization to mulberry pollen extract profilin in sera of 21.8% of the 45 mulberry allergic patients and its cross-reactivity with profilin from other plant pollens have been observed (7).
Cross-reactivity
Some studies have demonstrated significant cross-reactivity between mulberry pollen and other members of the Moraceae family, such as paper mulberry (Broussonetia papyrifera), fig-trees (Ficus species), jackfruit (Artocarpus heterophyllus), and breadfruit (Artocarpus altilis) (7). Mulberry pollen cross-reactivity has also been reported with olive and alder tree pollen (18).
A study showed IgE-binding inhibition of mulberry pollen extract profilin (14-15 kDa) and nsLTP-10 protein by grass and olive pollen, demonstrating cross-reactivity of profilins with other plant pollens of unrelated family. The study also reported similar inhibition of IgE-binding from Parietaria judaica allergen towards mulberry pollen nsLTP-10 protein. (7).
Compiled By
Author: Turacoz Healthcare Solutions
Reviewer: Dr. Fabio Iachetti
Last reviewed: December 2020
References
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- Orwa AM, R Kindt, R Jamnadass, A Simons. Agroforestree Database:a tree reference and selection guide version 4.0. 2009.
- Çetereisi D, Karlioglu N, Gelincik A, Michelland S, Önay-Uçar E, Ertek B, et al. Proteomic Identification of Allergenic Proteins of Morus alba L. Pollenexacerbation. Asian Pac J Allergy Immunol. 2019;37(4):205-11.
- Plant Guide [Internet]. USDA, NRCS. 2003.
- CABI. Morus alba 2019 [10-12-2020]. Available from: https://www.cabi.org/isc/datasheet/34816.
- Muñoz FJ, Delgado J, Palma JL, Giménez MJ, Monteseirín FJ, Conde J. Airborne contact urticaria due to mulberry (Morus alba) pollen. Contact Dermatitis. 1995;32(1):61.
- El-Qutob D, Bartolome B, Cuesta J, Mir A, Alberola A, Pastor-Vargas C. Identification of a Lipid Transfer Protein as a New Allergen From Morus alba Pollen. J Investig Allergol Clin Immunol. 2017;27(4):263-5.
- WHO/IUIS. Morus alba (Mor a 2) 2020 [updated 07-12-202011-12-2020]. Available from: http://allergen.org/viewallergen.php?aid=1044.
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- Prasad R, Verma SK, Dua R, Kant S, Kushwaha RA, Agarwal SP. A study of skin sensitivity to various allergens by skin prick test in patients of nasobronchial allergy. Lung India. 2009;26(3):70-3.
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- Halonen M, Stern DA, Wright AL, Taussig LM, Martinez FD. Alternaria as a major allergen for asthma in children raised in a desert environment. Am J Respir Crit Care Med. 1997;155(4):1356-61.
- Mansouritorghabeh H, Jabbari-Azad F, Sankian M, Varasteh A, Farid-Hosseini R. The Most Common Allergenic Tree Pollen Grains in the Middle East: A Narrative Review. Iran J Med Sci. 2019;44(2):87-98.
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- Andallu B, Suryakantham V, Lakshmi Srikanthi B, Reddy GK. Effect of mulberry (Morus indica L.) therapy on plasma and erythrocyte membrane lipids in patients with type 2 diabetes. Clin Chim Acta. 2001;314(1-2):47-53.
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