Type:
Whole Allergen
Whole Allergen
f6 Barley
f6 Barley Scientific Information
Display Name:
Barley
Route of Exposure:
Ingestion
Family:
Poaceae
Species:
Hordeum vulgare
Latin Name:
Hordeum vulgare
Summary
Barley is an important cereal crop of the Poaceae family (also containing rice, wheat and maize), which is used mainly for animal feed and in the brewing and distilling industry. Few reports of allergy to barley exist, most frequently these are patients with an occupational respiratory allergy known as Baker's asthma, or from ingesting beer. The main barley allergens include lipid transfer proteins (LTPs), which likely remain intact after the malting and brewing process.
Allergen
Nature
Barley is a member of the Poaceae family, which includes many significant grain-producing cultivated species such as rice (Oryza sativa), wheat (Triticum spp.) and maize (Zea mays) (1). Barley is one of the top four cereal crops produced worldwide, with a global production of over 141 million tons and is mainly used as animal feed and in malting for the brewing and distilling industries (2). It is also consumed in foods such as stews, soups, bread and biscuits in the Middle East, Europe and Asia (3).
Taxonomy
Taxonomic tree of Barley (4) |
|
|---|---|
Domain |
Eukaryota |
Kingdom |
Plantae |
Phylum |
Tracheophyta |
Subphylum |
Spermatophytina |
Class |
Magnoliopsida |
Order |
Poales |
Family |
Poaceae |
Genus |
Hordeum |
Taxonomic tree of Barley (4) |
|---|
Epidemiology
Worldwide distribution
The majority of case reports about barley allergy have focused on adult patients with respiratory allergy known as baker's asthma induced by barley flour, or with allergy from beer containing barley. Two cases of barley allergy have been reported in children who displayed severe anaphylactic reactions. However, few studies have evaluated barley allergy in relation to the level of barley-specific IgE and, to date, the prevalence of barley allergy has not been evaluated in a population-based study (3).
Clinical Relevance
Few reports of allergy to barley exist, most frequently these are patients with respiratory allergy known as Baker's asthma induced by barley flour, or from ingesting beer containing barley (3).
Barley is a source of gluten (along with wheat, rye and oats), and should therefore be avoided in patients with gluten-related disorders such as celiac disease and non-celiac gluten sensitivity (5).
Allergic rhinitis
One large-scale, multi-center case study in Korean children and adolescents showed that barley was the cause of 0.2% of immediate-type food allergy. A study including 42 Korean children (20 with clinically defined barley allergy and 22 atopic controls) demonstrated that levels of barley IgE were significantly higher in the allergic group vs the control group. After ingestion of barley in the allergic group, symptoms were mostly cutaneous (90.0%) or respiratory (40.0%), with anaphylaxis being observed in 35.0% (3).
Asthma
Baker’s asthma is one of the most common forms of occupational asthma, with the annual incidence in the UK estimated to be 290–450 cases per million. It usually occurs in workers who have been sensitized to flour and by workers who are atopic. Asthma symptoms are usually preceded by rhinitis, conjunctivitis and skin irritation. The specific IgE antibodies most often found in Baker’s asthma are against cereal flours such as wheat, rye or barley, with wheat flour being the most prominent (6).
Atopic Dermatitis
There are rare reports of urticaria from beer in atopic patients (7, 8). In one case report, a patient suffered a severe anaphylactic reaction upon beer ingestion (9-12).
Prevention and Therapy
Prevention strategies
Patients with Baker’s asthma are advised to avoid barley allergen or minimize exposure. This can be achieved by technical dust control, relocation of the baker to a less exposed task, or by wearing respiratory protection. Due to the large quantity of dust in most bakeries in relation to the amount of allergen exposure needed to elicit symptoms in sensitized workers, changing employment is often the solution (6).
Molecular Aspects
Allergenic molecules
Table adapted from Allergome.org (13), detailing barley seed allergens
Allergen |
Type |
Mass (kDa) |
|---|---|---|
Hor v 14 |
Lipid transfer protein |
9 |
Hor v 15 |
α-amylase inhibitor |
16 |
Hor v 16 |
α-amylase |
47.8 |
Hor v 17 |
β-amylase |
57.3 |
Hor v 18kDa |
Unknown |
18 |
Hor v 21 |
Gliadin |
33.1 |
Hor v 28 |
α-amylase inhibitor |
15.1 |
Hor v 32 |
Peroxiredoxin |
24 |
Hor v 33 |
Trypsin inhibitor |
45 |
Hor v 36 |
Glutenin |
35 |
Hor v 37 |
Thionin |
14.5 |
Hor v 39 |
Serine protease inhibitor |
9.3 |
Hor v 7k-LTP |
Lipid transfer protein |
13 |
Hor v BDAI |
α-amylase inhibitor |
16.4 |
Hor v BTI |
Trypsin inhibitor |
16 |
Hor v GBSS_I |
Starch syntase |
66 |
Allergen |
Type |
Mass (kDa) |
|---|
In an early study, several protein bands have been identified in case reports using immunoblotting and cross-reactivity experiments with barley-allergic patients. A 16 kDa protein band in barley was identified as major component in Baker’s asthma, but not in barley-allergy. Conversely, a 10 kDa protein was identified in barley allergy but not Baker’s asthma (Curioni et al, 1999). The 10 kDa protein was likely the same protein as described later, which is an LTP named Hor v 14 is now considered the classic barely LTP (Navarro et al, 2021)
Two major proteins in beer attributed to barley are protein Z4 (now known as Hor v 33) and lipid transfer protein (LTP) 1 (Garcia-Casado et al, 2001). In a later study, LTP1 was named Hor v 7k-LTP and is associated with severe symptoms. In addition to the LTPs, several barley allergens have been described including α- and β-amylase, gliadin, glutenin, peroxiredoxin, thionin, and trypsin inhibitor (11).
A barley allergen associated with Baker’s asthma was identified as a 14.5 kDa inhibitor of α-amylase (14, 15).
Cross-reactivity
Barley cross-reactivity has been demonstrated to wheat, rye, oats and Job’s tears (also known as adlay) (3, 16). A case report from a patient with clinically defined beer and Rosaceae allergy had serum which cross-reacted with a 10 kDa protein from apple and peach (likely LTPs, but unknown at the time) and LTP from peach peel, carrot and broccoli (Asero et al, 2001). The barley 10 kDa was likely to be the classic LTP, also known as Hor v 14 (11).
Compiled By
Author: RubyDuke Communications
Reviewer: Dr. Michael Thorpe
Last reviewed: June 2022
References
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