Barley
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.
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.
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.
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.
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%.
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.
Atopic Dermatitis
There are rare reports of urticaria from beer in atopic patients. In one case report, a patient suffered a severe anaphylactic reaction upon beer ingestion.
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.
Cross-Reactivity
Barley cross-reactivity has been demonstrated to wheat, rye, oats and Job’s tears (also known as adlay). 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. The barley 10 kDa was likely to be the classic LTP, also known as Hor v 14.
References
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