Type:
Whole Allergen
Whole Allergen
g201 Barley
g201 Barley Scientific Information
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
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