rGly m 4 PR-10, Soy

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Code: f353
Latin name: Glycine max
Common names: A Bet v 1-homologous allergen, Group 1 Fagales-related protein, PR-10 protein, SAM22.

Soybean allergen components

Available ImmunoCAP®:

Summary

Soy is one of the world’s most important legumes. The bean can be used fresh or processed into flour, flakes, grits, sauce, bran, or Soya milk, or pressed for oil. The list of food products presenting allergy risk is expanding. Soya protein has been found in foods that was not supposed to contain it (1).

There are more than 200 varieties of Soya bean (2-3).

Soya bean is not only a food allergen but also an occupational aero-allergen inducing asthma. Soya bean hull allergens were responsible for an outbreak of epidemic asthma in Barcelona (4). Soy may also result in Baker’s Asthma (5).

Soya protein consists of more than 130 phytochemicals (6) and at least 21 allergenic proteins that have been identified (7-8). Seed proteins in Soya bean comprise 3 major fractions that account for 70% to 80% of total protein composition: 11S, 7S and 2S globulins (9-10).

The following allergens have been characterised:

  • Gly m 1 (11).
     
  • Gly m 2 (12).
     
  • Gly m 3 (13).
     
  • Gly m 4 (14).
     
  • Gly m 2S Albumin (8).
     
  • Gly m 39kD (13).
     
  • Gly m Bd28K (15).
     
  • Gly m Bd30K (16).
     
  • Gly m Lectin (17).
     
  • Gly m Bd 60K (18).
     
  • Gly m Oleosin (19).
     
  • Gly m Trypsin Inhibitor (20).
     

Some Soya bean allergens responsible for food allergy are different from those responsible for respiratory allergies. One important Soya bean food allergen is a protein termed P34, which is abundant in the seeds and other parts of the plant (3). This protein is present in significant amounts in all cultivars studied (21).

The allergens involved in occupational asthma caused by Soya bean flour are mainly high-MW proteins that are present in both Soybean hull and flour, and they are different from the allergens causing asthma outbreaks, which are mainly low-MW proteins concentrated in the hull (5). Soybean hulls contain 3 main allergens, with MW’s of 8, 7.5 and 7 kDa (22). The major allergen causing the epidemics in Barcelona, Spain, was a glycopeptide less than 14 kDa in size and found in Soybean dust. This allergen occurs in all parts of the Soybean plant at all stages of growth, but the telae (hulls) and pods are by far the richest source (23,24).

Fresh Soybeans are less allergenic than stored Soybeans, suggesting that new Soybean allergens are created by increases in temperature upon storage and transportation: During the process of harvest, transport and storage, microbial and mold contamination can raise the temperature of Soybeans to 75 °C or higher. This heat could generate 2 new allergen determinants or increases in epitope exposure as a result of conformational changes. The full significance of these new IgE and IgG4 binding proteins has yet to be determined (25).

Gly m 3, a profilin, is a major Soya bean allergen and an important panallergen (12).

Recombinant allergens, which are genetically engineered isoforms resembling allergen molecules from known allergen extracts, have immunoglobulin E (IgE) antibody binding comparable to that of natural allergens and generally show good reactivity in in vitro and in vivo diagnostic tests (26). To date, many different recombinant allergens of various pollens, molds, mites, bee venom, latex and foods have been cloned, sequenced, and expressed.

Recombinant allergens have a wide variety of uses, from the diagnosis and management of allergic patients to the development of immunotherapy to the standardisation of allergenic test products as tools in molecular allergology. Recombinant allergens are particularly useful for investigations in allergies manifesting wide cross-reactivity.


Allergens from Glycine max listed by IUIS*

rGly 1 rGly 2 rGly 3
rGly 4    

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


f353 rGly m 4

Recombinant non-glycosylated protein produced in an E. coli strain carrying a cloned cDNA encoding Glycine max allergen Gly m 4

Common names: A Bet v 1-homologous allergen, Group 1 Fagales-related protein, PR-10 protein, SAM22
Biological function: Plant defence protein, pathogenesis-related protein
Mw: 17 kDa

Allergen description

Gly m 4 (8) belongs to the PR-10 protein family. It has also been designated a Group 1 Fagales-related protein. Pathogenesis-related (PR) proteins of class 10 are abundant in higher plants. Some of these proteins are induced under stress conditions as part of the plant’s defence mechanism. Other homologues are developmentally regulated, and their expression varies in different plant organs. The PR-10 proteins are encoded by multigene families, have a weight of about 17 kDa and are found in the cytosol (27). They are common panallergens in Fagales pollens (Alder, Hornbeam, Beech, Chestnut) and may be present in a number of vegetables and fruits, e.g., Apple and Hazelnut. Pyr c 1, the major allergen from Pear (Pyrus communis), along with Lupine (Lupinus albus), is a homologous Bet v 1 allergen (28-29). Patients suffering from Birch pollen allergy can also exhibit allergic symptoms on exposure to the pollen of trees from the Fagales (Alder, Hazel, Hornbeam) and Oak and Chestnut, because all contain this panallergen. Recombinant marker allergens are therefore of value for more-accurate diagnoses and subsequent immunotherapy (30).

Due to cross-reactivity between Bet v 1 and Gly m 4, sensitisation to other PR-10 proteins might be evaluated using rGly m 4. For example, in a study that evaluated whether Fagales sensitisation occurred within a population not exposed to Birch pollen, combined reactivity to the 3 species was recorded in 80% of this cohort. Reactivity to Bet v 1 was recorded in 84% of the Birch/Hazel/Oak co-reactivity group. Bet v 1 prevalence ranged between 48% and 21% among subgroups of patients coming from different areas (31).

Twenty-two patients, allergic to Birch pollen and with Soy allergy confirmed by means of positive double-blind, placebo-controlled food challenge results (n = 16) or a convincing history (n = 6), were investigated for IgE reactivity to Birch pollen and Soy allergens. ImmunoCAP analysis revealed Gly m 4-specific IgE in 96% (21/22) of the patients. All patients had Bet v 1-specific IgE antibodies, and 23% (5/22) had positive Bet v 2 results. In IgE immuno-blotting, 25% (6/22) of the patients recognised Soya profilin (Gly m 3), and 64% (14/22) recognised other Soya proteins. IgE binding to Soya was at least 80% inhibited by Birch pollen and 60% inhibited by rGly m 4 in 9 of 11 sera tested. Seventy-one percent (67/94) of highly Bet v 1-sensitised patients with Birch pollen allergy were sensitised to Gly m 4, and 9 (9.6%) of those patients reported Soya allergy. The Gly m 4 content in Soya products ranged between 0 and 70 ppm (milligrams per kilogram). The study concludes that Soya bean is another Birch pollen-related allergenic food. Gly m 4 is the major Soy allergen for patients allergic to Birch pollen and also Soy. The content of Gly m 4 in Soy food products strongly depends on the degree of food processing (8).

Ara h 8 is also cross-reactive with Gly m 4 from Soya bean and Pru av 1 from Cherry. Nonetheless, although common binding epitopes do occur for this panallergen, patient-specific IgE epitope patterns also occur (32).

In a study evaluating severe oral allergy syndrome and anaphylactic reactions caused by a Bet v 1-related PR-10 protein in Soya bean, Gly m 4/SAM22, immediate-type allergic symptoms in patients with Birch pollen allergy after ingestion of Soy protein-containing food items were reported to occur from cross-reactivity of Bet v 1-specific IgE to homologous pathogenesis-related proteins, particularly the PR-10 protein Gly m 4/SAM22 (33).

Compiled by Dr Harris Steinman, harris@zingsolutions.com

References

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As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.