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Whole Allergen

g201 Barley

g201 Barley Scientific Information

Type:

Whole Allergen

Display Name:

Barley

Route of Exposure:

Inhalation

Family:

Poaceae

Species:

Hordeum vulgare

Latin Name:

Hordeum vulgare

Other Names:

Four-rowed barley, Spring barley, Winter barley, six-rowed barley, two-rowed barley, Scotch barley

Summary

Barley, a self-pollinating crop belonging to the Poaceae family, is an annual monocotyledonous herb. The flowering period of barley typically ranges from June to July. It is native to North Africa and western Asia and is regarded as a sustainable crop in Europe, Africa, Asia, and America. It thrives best in the temperate climate; well-drained clay loams and loams are considered optimal for its cultivation. Exposure to barley pollen has been reported to cause respiratory symptoms in atopic individuals. Hor v 5, a 30 kDa protein, has been identified as an allergenic molecule present in barley pollen. Furthermore, barley pollen has been found to be cross-reactive with Kentucky bluegrass, perennial ryegrass, maize, rye, triticale, common wheat, oat, rapeseed, common sunflower, and flax.

Allergen

Nature

Barley (Hordeum vulgare), a grain crop, is an annual monocotyledonous herb with broad leaves, short stems and awns, thick and short spike, tough ear rachis, and large grains (1, 2). The spike of barley possesses a series of spikelets (sets of three) attached at the nodes to every other side of the rachis. Florets are found to be present in each of these spikelets. In the six-rowed barley, the florets are usually fertile and further develop into kernels; this further paves the development of six rows of kernels. However, in two-rowed barley, the lateral florets are infertile, and therefore the central floret in each triplet grows as the kernel. The barley kernels are enclosed in a seed coat (testa) which tightly fuses with the pericarp (outer tissue of the grain). Furthermore, the grain is covered by the husk, attached tightly to the pericarp (3). The flowering period of barley has been reported to be usually from June to July (4). Pollination of barley is found to be usually through self-pollination (5).

Barley is extensively used in the brewing industry for malt production. Moreover, barley as a straw cereal is also used as a component in animal feeds (6).

Taxonomy

The Poaceae family consists of around 12,000 species and 780 genera and comprises several grain-producing agricultural species like barley, wheat, rice, and maize (7). 

Taxonomic tree of Barley (Hordeum vulgare) (8)

Domain

Eukaryota

Kingdom

Plantae

Phylum

Spermatophyta

Subphylum

Angiospermae

Class

Monocotyledonae

Order

Cyperales

Family

Poaceae

Genus

Hordeum

Taxonomic tree of Barley (Hordeum vulgare) (8)

Tissue

Grasses usually generate granular surfaced pollen grains, spherical to oval in shape and single-pored (5). The barley pollen grains typically range between 86 to 122 µm (5). According to the WHO/IUIS database, Hor v 5, a 30 kDa allergenic protein molecule has been found to be present in the barley pollen (9).

Epidemiology

Worldwide distribution

Around 20% of the general population and almost 40% of the atopic individuals are impacted by allergic sensitization due to grass pollens (10).

According to an Ireland-based study, the West Meath region has been reported to have a high prevalence of barley sensitization among patients with symptomatic rhinitis (19%) as 30% of the production of Irish barley is yielded from this region (11).

A study conducted in Turkey reported sensitization to barley pollens among 19.5% (105/539) of children with respiratory allergy (12). 

Risk factors

People (like farmers) with direct exposure to cultivated grass fields (Hordeum, Triticum, Secale) or residing in proximity to these fields can develop sensitivity and allergic symptoms (5). 

Environmental Characteristics

Living environment

Barley is cultivated in temperate climates worldwide at 350 to 4050 m above sea level (13). This grass is found to be both drought and salinity tolerant; therefore, considered a major cereal in many dry areas of the world (14). Barley thrives in soil with a pH ranging from 6.0 to 8.5. Moreover, well-drained clay loams and loams are considered optimal for barley cultivation (15). 

Worldwide distribution

Barley has been reported to be originating from North Africa and western Asia (13). It is regarded as a sustainable crop in Europe, Africa, Asia, and America (16).

Barley has been reported to be grown in a wide range of environments that ranges from high elevations of the Himalayas to the deserts of the Middle East (17). Due to its fast growth cycle, barley is regarded as an important crop in Finland (1). In Iraq, barley is reported to be one of the major crops in terms of area under cultivation, consumption, industrial utilization, and production (16). Furthermore, in Pakistan, barley is majorly cultivated as a source of grain and straw for small ruminants (14).

Furthermore, as per a Madrid-based aerobiological survey, barley pollen was detected in the atmosphere of Madrid, Spain (18). 

Route of Exposure

Main

The route of exposure for barley pollens is through inhalation (19, 20).

Clinical Relevance

Poaceae family has been reported to produce a large amount of pollen in the air, thus resulting in respiratory allergies (21). Barley has been reported to cause respiratory symptoms (20).

Respiratory symptoms

According to a New Zealand-based study conducted on 167 farmers, barley crop exposure was found to be responsible for respiratory symptoms like breathing problems (31.1%), shortness of breath (18.9%), chronic bronchitis (14.4%), and organic dust toxic syndrome (13.2%) (20).

Prevention and Therapy

Prevention strategies

Avoidance

One of the main measures to be taken is to cut down the amounts of pollen in the respiratory system. During pollen season, allergic patients are suggested to stay indoors or wear a mask outdoors to avoid pollen allergens. In worsening conditions, patients may be advised to move to a non-pollen area (22).

Molecular Aspects

Allergenic molecules       

To date (17/01/2022), Hor v 5 has been identified and listed as an allergenic molecule from barley pollen (Hordeum vulgare) according to the WHO/IUIS database and is represented in the table below (9).

Allergen

Biochemical name

Molecular weight

Hor v 5

-

 30 kDa

Allergen

Biochemical name

Molecular weight

Additionally, Hor v 2 (group 2 allergen) (23, 24), Hor v 4 (group 4 allergen) (25), and Hor v 13 (group 13 allergen) (23, 26) have also been identified as allergens from barley pollen.

Cross-reactivity

According to a study, barley pollen has been found to be cross-reactive with Kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne), maize (Zea mays), rye (Secale cereale), wheat-rye hybrid (Triticale), common wheat (Triticum aestivum), oat (Avena sativa), rapeseed (Brassica napus), common sunflower (Helianthus annus) and flax (Linum usitatissimum) (27).

Compiled By

Author: Turacoz Healthcare Solutions

Reviewer: Dr.Christian Fischer

 

Last reviewed: June 2022

References
  1. Holopainen-Mantila U. Composition and structure of barley (Hordeum vulgare L.) grain in relation to end uses. VTT Science. 2015.
  2. Badr A, Rabey HE, Effgen S, Ibrahim H, Pozzi C, Rohde W, et al. On the origin and domestication history of barley (Hordeum vulgare). Molecular biology and evolution. 2000;17(4):499-510.
  3. MacGregor AW. BARLEY. In: Caballero B, editor. Encyclopedia of Food Sciences and Nutrition (Second Edition). Oxford: Academic Press; 2003. p. 379-82.
  4. Nikoleta K, Gëzim K, Silvana T. Pollinosis caused by the representatives of Gramineae family. GSC Biological and Pharmaceutical Sciences. 2020;11(2):334-40.
  5. Damialis A, Konstantinou G. Cereal pollen sensitisation in pollen allergic patients: to treat or not to treat? European annals of allergy and clinical immunology. 2011;43(2):36.
  6. Hrabina M, Jain K, Gouyon B. Cross‐reactivity between pollen allergens from common Pooideae grasses and cultivated cereals. Clinical & experimental allergy reviews. 2008;8(1):18-20.
  7. Devis DL, Davies JM, Zhang D. Molecular features of grass allergens and development of biotechnological approaches for allergy prevention. Biotechnology advances. 2017;35(5):545-56.
  8. CABI. Hordeum vulgare (Barley) pollen 2022 [17/01/2022]. Available from: https://www.cabi.org/isc/datasheet/27662.
  9. WHO/IUIS. Hor v 5. Hordeum vulgare 2019 [17/01/2022]. Available from: http://allergen.org/viewallergen.php?aid=384.
  10. Andersson K, Lidholm J. Characteristics and immunobiology of grass pollen allergens. International archives of allergy and immunology. 2003;130(2):87-107.
  11. Nae A, Hinchion K, Keogh I. A fifteen-year review of skin allergy testing in Irish patients with symptomatic rhinitis. World Journal of Otorhinolaryngology-Head and Neck Surgery. 2021;7(04):338-43.
  12. Yazicioglu M, Oner N, Celtik C, Okutan O, Pala O. Region of Turkey. Asian Pacific Journal of Allergy and Immunology. 2004;22:183-90.
  13. El-Hashash EF, El-Absy KM. Barley (Hordeum vulgare L.) breeding.  Advances in Plant Breeding Strategies: Cereals: Springer; 2019. p. 1-45.
  14. Shafi M, Bakht J, Jalal F, Khan MA, Khattak SG. Effect of nitrogen application on yield and yield components of barley (Hordeum vulgare L.). Pak J Bot. 2011;43(3):1471-5.
  15. USDA. Barley: Hordeum vulgare L. 2016 [18/01/2022]. Available from: https://plants.usda.gov/DocumentLibrary/plantguide/pdf/pg_hovu.pdf.
  16. Mahmood YA, Hassan HN, Mohammed MS. Yield Performance of Barley Hybrids (Hordeum vulgare L.) under Drought stress and non-stressed Conditions. Passer Journal. 2021;3(1):4.
  17. Kohistani AW, Choudhary AK. Influence of applied nitrogen on productivity, profitability and resource-use efficiency in winter barley (Hordeum vulgare) under semi–arid conditions of Afghanistan. Indian Journal of Agricultural Sciences. 2019;89(4):741-4.
  18. Subiza J, Masiello JM, Subiza JL, Jerez M, Hinojosa M, Subiza E. Prediction of annual variations in atmospheric concentrations of grass pollen. A method based on meteorological factors and grain crop estimates. Clin Exp Allergy. 1992;22(5):540-6.
  19. Singh AB, Mathur C. An aerobiological perspective in allergy and asthma. Asia Pacific Allergy. 2012;2(3):210-22.
  20. Kimbell‐Dunn M, Fishwick R, Bradshaw L, Erkinjuntti‐Pekkanen R, Pearce N. Work‐related respiratory symptoms in New Zealand farmers. American journal of industrial medicine. 2001;39(3):292-300.
  21. Garcia-Mozo H. Poaceae pollen as the leading aeroallergen worldwide: A review. Allergy. 2017;72(12):1849-58.
  22. 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.
  23. Mohapatra SS, Lockey RF, Shirley S. Immunobiology of grass pollen allergens. Current allergy and asthma reports. 2005;5(5):381.
  24. Marth K, Focke M, Flicker S, Valenta R. Human monoclonal antibody–based quantification of group 2 grass pollen allergens. Journal of allergy and clinical immunology. 2004;113(3):470-4.
  25. Nandy A, Petersen A, Wald M, Suck R, Kahlert H, Weber B, et al. Primary structure, recombinant expression, and molecular characterization of Phl p 4, a major allergen of timothy grass (Phleum pratense). Biochemical and biophysical research communications. 2005;337(2):563-70.
  26. Petersen A, Suck R, Hagen S, Cromwell O, Fiebig H, Becker W-M. Group 13 grass allergens: structural variability between different grass species and analysis of proteolytic stability. Journal of allergy and clinical immunology. 2001;107(5):856-62.
  27. Astwood J, Mohapatra S, Ni H, Hill R. Pollen allergen homologues in barley and other crop species. Clinical & Experimental Allergy. 1995;25(1):66-72.