f416 rTri a 19 Omega-5 Gliadin, Wheat

Allergens within Food of Plant Origin

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  • Latin name: From Triticum aestivum
  • Family: Poaceae
  • Common names: Omega-5 Gliadin, fast omega Gliadin

Wheat allergen components

Available ImmunoCAP®:

Summary

Wheat is one of the major cereal grains belonging to the grass family (Poaceae or Gramineae) and is a staple food item in most diets worldwide. The hexaploid Triticum aestivum is by far the most important of all wheat species, the highest yielding and the widest ranging, as well as the one most suited to bread making. All varieties of wheat contain soluble and insoluble (gluten) proteins. The softer wheat with the lowest protein content, T. aestivum and the varieties closest to it, is used for biscuits, cakes and pastry. Harder wheat with higher protein content is used for bread, semolina, cous-cous, macaroni and pasta. T. durum (Durum wheat) is a source of Italian pasta, Indian chappatis and Chinese noodles.

Wheat, like all other foods, contains a number of proteins. Over 300 proteins have been matched to established protein database information (2) and some have been identified as allergens.

The major proteins in wheat vary in proportion according to the type of wheat. This variability is one reason reactions to different wheat products are not consistent.

Wheat proteins can be classified into different groups:
  • Albumins (water-soluble; not similar to egg or milk albumin).
  • Globulins (salt-soluble, water-insoluble).
  • Glutens (the water/salt-insoluble wheat proteins)
  • Glutens can be further divided into:
  • Gliadins (28-42%; the major prolamin protein in wheat, soluble in 70-90% alcohol).
  • Glutenins (42-62.5%; the major glutenin proteins in wheat, soluble in dilute acid or alkali solutions).

The following allergens have been identified and characterized:

  • Tri a 18 (3).
  • Tri a 19, a gliadin, also known as fast w-gliadin (4-18). 
  • Tri a Chitinase (19).
  • Tri a LTP (20-21).
  • Tri a Germin, a glycoprotein expressed in many plants in response to biotic and abiotic stress (22).

Tri a aA/TI, an alpha-amylase/trypsin inhibitor, (approximately 14-15 kDa in size) (23-28) implicated as a major allergen associated with baker’s asthma (24) and, less commonly, with food allergy (29). In particular, the subunits of the tetrameric alpha-amylase inhibitor, CM2, CM3 and CM16, are known to be major allergens for baker’s asthma.
In Japanese patients with atopic dermatitis, serum IgE bound only to CM3 and not to CM2 and CM16, suggesting that CM3 may be involved in both atopic dermatitis and baker’s asthma (25). 
Tri a Bd 36K, a peroxidase purified from Wheat albumin and an inhalant allergen (30).
Tri a Bd 17K, identified as alpha-amylase inhibitor CM16 (31-32).
Tri a Peroxidase, a 60 kDa protein (33).
Tri m Peroxidase, a 36 kDa seed-specific peroxidase, found specifically in T. monococcum, but also present in flour from diploid, tetraploid (pasta) and hexaploid (bread) wheats. Sensitisation occurs via inhalation. Sera from 6 out of 10 patients hypersensitive to wheat flour were shown to have specific IgE directed to this allergen (34). This allergen is one of the most reactive with some patients’ sera (35).
Tri a TPIS, a triosephosphate isomerase, an allergen via inhalation in bakers (36).


Allergens from Triticum aestivum listed by IUIS*

Tri a 12 Tri a 14 Tri a 18
Tri a 19 Tri a 25 Tri a 26

*International Union of Immunological Societies (www.allergen.org) Jan. 2008.

f416 rTri a 19

Recombinant non-glycosylated protein produced in an E. coli strain carrying a cloned cDNA encoding a part of w-5 gliadin from Triticum aestivum

Common names: w-5 gliadin, fast w-gliadin
Biological function: A plant proline- and glutamine-rich storage protein
Mw: 27 kDa

Allergen description

Gliadins include more than 40 monomeric water/salt-insoluble but ethanol soluble proteins with molecular weights in the range of 30-70 kDa. According to amino acid sequence and electrophoresis mobility they are classified into a-, b-, g-, and w-gliadins, all rich in non-polar amino acids and glutamine. w-gliadins, consisting to about 80 % of the amino acids glutamine, proline and phenylalanine, are almost completely repetitive in sequence. The greater molecular weight and poor content of cysteines distinguish w-gliadins from the sulphur rich a-, b- and g-gliadins. The w-gliadins are further classified as slowly-migrating w-1 and w-2, w-3 and fast-migrating w-4 and w-5. Tri a 19 (w-5 gliadin), a component of the fast w-gliadin fraction, is a major allergen among water/salt-insoluble proteins. rTri a 19, mw ~27 kDa, is a recombinant peptide representing the immuno-dominant part of w-5 gliadin (1). 

IgE antibodies against fast w-gliadin cross-react with g-gliadin and slow w-gliadin (4). Further studies have reported that g-70 and g-35 secalins in rye and g-3 hordein in barley cross-react with w-5 gliadin, suggesting that rye and barley may elicit symptoms in patients sensitized to w-5 gliadin.

In immunoblotting, anti-w-5 gliadin antibodies bound to 70 kDa and 32 kDa proteins in rye and to a 34-kDa protein in barley, but not to any proteins in oats. The cross-reactive proteins were identified as rye g-70 secalin, rye g-35 secalin and barley g-3 hordein, respectively. In ELISA studies, 21/23 (91%) patients with Wheat-Dependent Exercise-Induced Anaphylaxis (WDEIA) showed IgE antibodies to purified g-70 secalin, 19/23 (83%) to g-35 secalin and 21/23 (91%) to g-3 hordein. Skin prick testing gave positive reactions to g-70 secalin in 10/15 (67%) patients, to g-35 secalin in 3/15 (20%) patients and to g-3 hordein in 7/15 (47%) patients (5).

Of the wheat proteins, w-5 gliadin has been reported as a major allergen in Wheat-Dependent Exercise-Induced Anaphylaxis (WDEIA) (1,4-16). Although the mechanism is not fully understood, a study reports that w-5 gliadin-derived peptides are cross-linked by tissue transglutaminase (tTG), which causes a marked increase in IgE antibody binding both in vitro and in vivo. Activation of tTG in the intestinal mucosa during exercise in patients with WDEIA may lead to the formation of large allergen complexes capable of eliciting anaphylactic reactions (11).

In addition, w-5 gliadin has been shown to be a major allergen in children with immediate allergy to ingested wheat. After oral wheat challenge 40 children with suspected wheat allergy presented atopic dermatitis and/or gastrointestinal and/or respiratory symptoms. 19 children (48%) had immediate reactions and 8 children (20%) had delayed hypersensitivity symptoms. Sixteen (84%) of those with immediate symptoms had IgE antibodies to w-5 gliadin whereas none of the children with delayed or negative challenge test results had IgE antibodies to w-5 gliadin. Moreover, in children with wheat induced anaphylaxis, w-5 gliadin seems to be a major sensitizing allergen (17).

Compiled by Dr Harris Steinman, harris@zingsolutions.com

References:

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2009