Oat sensitivity

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Oat sensitivity represents a sensitivity to the proteins found in oats, Avena sativa. Sensitivity to oats can manifest as a result of allergy to oat seed storage proteins either inhaled or ingested. A more complex condition affects individuals who have gluten-sensitive enteropathy in which there is an autoimmune response to avenin, the glutinous protein in oats similar to the gluten within wheat. Sensitivity to oat foods can also result from their frequent contamination by wheat, barley, or rye particles. [1]

Contents

Oat allergy

Studies on farmers with grain dust allergy and children with atopy dermatitis reveal that oat proteins can act as both respiratory and skin allergens. [2] [3] [4] [5] [6] Oat dust sensitivity in farms found 53% showed reactivity to dust, second only to barley (70%), and almost double that of wheat dust. [7] The 66 kDa protein in oats was visualized by 28 out of 33 sera (84%). However, there was evident non-specific binding to this region and thus it may also represent lectin-like binding. [8] IgA and IgG responses, meanwhile, like those seen to anti-gliadin antibodies in celiac disease or dermatitis herpetiformis, are not seen in response to avenins in atopic dermatitis patients. [9]

Food allergies to oats can accompany atopy dermatitis. [10] Oat avenins share similarities with γ and ω-gliadins of wheat — based on these similarities they could potentiate both enteropathic response and anaphylactic responses. Oat allergy in gluten-sensitive enteropathy can explain an avenin-sensitive individual with no histological abnormality, no T-cell reaction to avenin, bearing the rarer DQ2.5trans phenotype, and with anaphylactic reaction to avenin. [11]

Avenin-sensitive enteropathy

Oat toxicity in people with gluten-related disorders depends on the oat cultivar consumed because the immunoreactivities of toxic prolamins are different among oat varieties. [1] [12] Furthermore, oats are frequently cross-contaminated with the other gluten-containing cereals. [1] Pure oat (labelled as "pure oat" or "gluten-free oat" [13] ) refers to oats uncontaminated with any of the other gluten-containing cereals. [12]

Some cultivars of pure oat could be a safe part of a gluten-free diet, requiring knowledge of the oat variety used in food products for a gluten-free diet. [12] Nevertheless, the long-term effects of pure oats consumption are still unclear [14] and further studies identifying the cultivars used are needed before making final recommendations on their inclusion in the gluten-free diet. [15]

Immunological evidence

Anti-avenin antibodies

In 1992, six proteins were extracted from oats that reacted with a single coeliac sera. Three of the proteins were prolamins, and have been called CIP 1 (gamma avenin), CIP 2, and CIP3. They had the following amino acid sequences:

Antibody recognition sites on three avenins CIP1 (γ-avenin)               P S E Q Y Q P Y P E Q Q Q P F  CIP2 (γ-avenin) T T T V Q Y D P S E Q Y Q P Y P E Q Q Q P F V Q Q Q P P F  CIP3 (α-avenin) T T T V Q Y N P S E Q Y Q P Y

Within the same study, three other proteins were identified, one of them an α-amylase inhibitor as identified by protein homology. A follow-up study showed that most celiacs have anti-avenin antibodies (AVAs), with a specificity and sensitivity comparable to anti-gliadin antibodies. [16] A subsequent study found that these AVAs did not result from cross-reaction with wheat. [17] However, recently it has been found that AVAs drop as soon as Triticeae glutens are removed from the diet. [18] Anti-avenin antibodies declined in treated celiacs on an oat diet in 136 individuals, suggesting oats can be involved in celiac disease when wheat is present, but are not involved when wheat is removed from the diet. The study, however, did find an increased number of patients with higher intraepithelial lymphocytes (IELs, a type of white bloodcell) in the oat-eating cohort. Regardless of whether or not this observation is a direct allergic immune response, by itself this is essentially benign.[ citation needed ]

Cellular immunity

In gluten-sensitive enteropathy, prolamins mediate between T-cells and antigen-presenting cells, whereas anti-transglutaminase antibodies confer autoimmunity via covalent attachment to gliadin. In 16 examined coeliacs, none produced a significant Th1 response. [19] Th1 responses are needed to stimulate T-helper cells that mediate disease. This could indicate that coeliac disease does not directly involve avenin or that the sample size was too small to detect the occasional responder.

Evidence that there are exceptional cases came in a 2004 study on oats. [11] The patients drafted for this study were those who had symptoms of celiac disease when on a "pure-oat" challenge, therefore not representative of a celiac sample. This study found that four patients had symptoms after oat ingestion, and three had elevated Marsh scores for histology and avenin responsive T-cells, indicating avenin-sensitive enteropathy (ASE). All three patients were the DQ2.5/DQ2 (HLA DR3-DQ2/DR7-DQ2) phenotype. Patients with DQ2.5/DQ2.2 tend to be the most prone toward gluten sensitive enteropathy (GSE), have the highest risk for GS-EATL, and shows signs of more severe disease at diagnosis.[ citation needed ] While the DQ2.5/DQ2 phenotype represents only 25% of celiac patients, it accounts for all of the ASE celiacs, and 60-70% of patients with GS-EATL.[ citation needed ] Synthetic avenin peptides were synthesized either in native or deamidated form, and the deamidated peptides showed higher response.

DQ2.5/T-cell receptor recognition from 2 Oat-sensitive coeliacs TCR-Site1                             Y Q P Y P E Q E~E~P F V TCR-Site2                           Q Y Q P Y P E Q Q Q P F V Q Q Q Q Antibody recognition site(see above) CIP2 (γ-avenin) T T T V Q Y D P S E Q Y Q P Y P E Q Q Q P F V Q Q Q P P F

The overlap of the antibody and T-cell sites, given trypsin digestion of avenin, suggest this region is dominant in immunity. The TCR-site1 was synthetically made as deamidated ("~E~"), and native peptide requires transglutaminase to reach full activation. Two studies to date have looked at the ability of different oat strains to promote various immunochemical aspects of celiac disease. While preliminary, these studies indicate different strains may have different risks for avenin sensitivity. [20] [21]

See also

Related Research Articles

<span class="mw-page-title-main">Gluten</span> Group of cereal grain proteins

Gluten is a structural protein naturally found in certain cereal grains. Although "gluten" often only refers to wheat proteins, in medical literature it refers to the combination of prolamin and glutelin proteins naturally occurring in all grains that have been proven capable of triggering celiac disease. These include any species of wheat, barley, rye and some oat cultivars, as well as any cross hybrids of these grains. Gluten makes up 75–85% of the total protein in bread wheat.

<span class="mw-page-title-main">Oat</span> Cool weather staple grain, animal feed

The oat, sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name. While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed. Oats are a nutrient-rich food associated with lower blood cholesterol when consumed regularly.

<span class="mw-page-title-main">Coeliac disease</span> Autoimmune disorder that results in a reaction to gluten

Coeliac disease or celiac disease is a long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barley. Classic symptoms include gastrointestinal problems such as chronic diarrhoea, abdominal distention, malabsorption, loss of appetite, and among children failure to grow normally. This often begins between six months and two years of age. Non-classic symptoms are more common, especially in people older than two years. There may be mild or absent gastrointestinal symptoms, a wide number of symptoms involving any part of the body, or no obvious symptoms. Coeliac disease was first described in childhood; however, it may develop at any age. It is associated with other autoimmune diseases, such as Type 1 diabetes mellitus and Hashimoto's thyroiditis, among others.

<span class="mw-page-title-main">Gluten-free diet</span> Diet excluding proteins found in wheat, barley, and rye

A gluten-free diet (GFD) is a nutritional plan that strictly excludes gluten, which is a mixture of prolamin proteins found in wheat, as well as barley, rye, and oats. The inclusion of oats in a gluten-free diet remains controversial, and may depend on the oat cultivar and the frequent cross-contamination with other gluten-containing cereals.

Food intolerance is a detrimental reaction, often delayed, to a food, beverage, food additive, or compound found in foods that produces symptoms in one or more body organs and systems, but generally refers to reactions other than food allergy. Food hypersensitivity is used to refer broadly to both food intolerances and food allergies.

<span class="mw-page-title-main">Gliadin</span>

Gliadin is a class of proteins present in wheat and several other cereals within the grass genus Triticum. Gliadins, which are a component of gluten, are essential for giving bread the ability to rise properly during baking. Gliadins and glutenins are the two main components of the gluten fraction of the wheat seed. This gluten is found in products such as wheat flour. Gluten is split about evenly between the gliadins and glutenins, although there are variations found in different sources.

<span class="mw-page-title-main">Whole grain</span> Cereal containing endosperm, germ, and bran

A whole grain is a grain of any cereal and pseudocereal that contains the endosperm, germ, and bran, in contrast to refined grains, which retain only the endosperm.

<span class="mw-page-title-main">Wheat allergy</span> Medical condition

Wheat allergy is an allergy to wheat which typically presents itself as a food allergy, but can also be a contact allergy resulting from occupational exposure. Like all allergies, wheat allergy involves immunoglobulin E and mast cell response. Typically the allergy is limited to the seed storage proteins of wheat. Some reactions are restricted to wheat proteins, while others can react across many varieties of seeds and other plant tissues. Wheat allergy is rare. Prevalence in adults was found to be 0.21% in a 2012 study in Japan.

<span class="mw-page-title-main">Triticeae glutens</span> Seed storage protein in mature wheat seeds

Gluten is the seed storage protein in mature wheat seeds. It is the sticky substance in bread wheat which allows dough to rise and retain its shape during baking. The same, or very similar, proteins are also found in related grasses within the tribe Triticeae. Seed glutens of some non-Triticeae plants have similar properties, but none can perform on a par with those of the Triticeae taxa, particularly the Triticum species. What distinguishes bread wheat from these other grass seeds is the quantity of these proteins and the level of subcomponents, with bread wheat having the highest protein content and a complex mixture of proteins derived from three grass species.

<span class="mw-page-title-main">Gluten-related disorders</span> Set of diseases caused by gluten exposure

Gluten-related disorders is the term for the diseases triggered by gluten, including celiac disease (CD), non-celiac gluten sensitivity (NCGS), gluten ataxia, dermatitis herpetiformis (DH) and wheat allergy. The umbrella category has also been referred to as gluten intolerance, though a multi-disciplinary physician-led study, based in part on the 2011 International Coeliac Disease Symposium, concluded that the use of this term should be avoided due to a lack of specificity.

Gluten-sensitive enteropathy–associated conditions are comorbidities or complications of gluten-related gastrointestinal distress. GSE has key symptoms typically restricted to the bowel and associated tissues; however, there are a wide variety of associated conditions. These include bowel disorders, eosinophilic gastroenteritis and increase with coeliac disease (CD) severity. With some early onset and a large percentage of late onset disease, other disorders appear prior to the coeliac diagnosis or allergic-like responses markedly increased in GSE. Many of these disorders persist on a strict gluten-free diet, and are thus independent of coeliac disease after triggering. For example, autoimmune thyroiditis is a common finding with GSE.

Anti-gliadin antibodies are produced in response to gliadin, a prolamin found in wheat. In bread wheat it is encoded by three different alleles, AA, BB, and DD. These alleles can produce slightly different gliadins, which can cause the body to produce different antibodies. Some of these antibodies can detect proteins in specific grass taxa such as Triticeae, while others react sporadically with certain species in those taxa, or over many taxonomically defined grass tribes.

Anti-transglutaminase antibodies (ATA) are autoantibodies against the transglutaminase protein. Antibodies serve an important role in the immune system by detecting cells and substances that the rest of the immune system then eliminates. These cells and substances can be foreign and also can be produced by the body. Antibodies against the body's own products are called autoantibodies. Autoantibodies can sometimes errantly be directed against healthy portions of the organism, causing autoimmune diseases.

<span class="mw-page-title-main">HLA-DQ2</span>

HLA-DQ2 (DQ2) is a serotype group within HLA-DQ (DQ) serotyping system. The serotype is determined by the antibody recognition of β2 subset of DQ β-chains. The β-chain of DQ is encoded by HLA-DQB1 locus and DQ2 are encoded by the HLA-DQB1*02 allele group. This group currently contains two common alleles, DQB1*0201 and DQB1*0202. HLA-DQ2 and HLA-DQB1*02 are almost synonymous in meaning. DQ2 β-chains combine with α-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively.

<span class="mw-page-title-main">Enteropathy-associated T-cell lymphoma</span> Complication of coeliac disease

Enteropathy-associated T-cell lymphoma (EATL), previously termed enteropathy-associated T-cell lymphoma, type I and at one time termed enteropathy-type T-cell lymphoma (ETTL), is a complication of coeliac disease in which a malignant T-cell lymphoma develops in areas of the small intestine affected by the disease's intense inflammation. While a relatively rare disease, it is the most common type of primary gastrointestinal T-cell lymphoma.

The immunochemistry of Triticeae glutens is important in several inflammatory diseases. It can be subdivided into innate responses, class II mediated presentation, class I mediated stimulation of killer cells, and antibody recognition. The responses to gluten proteins and polypeptide regions differs according to the type of gluten sensitivity. The response is also dependent on the genetic makeup of the human leukocyte antigen genes. In gluten sensitive enteropathy, there are four types of recognition, innate immunity, HLA-DQ, and antibody recognition of gliadin and transglutaminase. With idiopathic gluten sensitivity only antibody recognition to gliadin has been resolved. In wheat allergy, the response pathways are mediated through IgE against other wheat proteins and other forms of gliadin.

<span class="mw-page-title-main">Dermatitis herpetiformis</span> Medical condition

Dermatitis herpetiformis (DH) is a chronic autoimmune blistering skin condition, characterised by intensely itchy blisters filled with a watery fluid. DH is a cutaneous manifestation of coeliac disease, although the exact causal mechanism is not known. DH is neither related to nor caused by herpes virus; the name means that it is a skin inflammation having an appearance similar to herpes.

Non-celiac gluten sensitivity (NCGS) or gluten sensitivity is "a clinical entity induced by the ingestion of gluten leading to intestinal and/or extraintestinal symptoms that improve once the gluten-containing foodstuff is removed from the diet, and celiac disease and wheat allergy have been excluded".

The gluten challenge test is a medical test in which gluten-containing foods are consumed and (re-)occurrence of symptoms is observed afterwards to determine whether and how much a person reacts to these foods. The test may be performed in people with suspected gluten-related disorders in very specific occasions and under medical supervision, for example in people who had started a gluten-free diet without performing duodenal biopsy.

Duodenal lymphocytosis, sometimes called lymphocytic duodenitis, lymphocytic duodenosis, or duodenal intraepithelial lymphocytosis, is a condition where an increased number of intra-epithelial lymphocytes is seen in biopsies of the duodenal mucosa when these are examined microscopically. This form of lymphocytosis is often a feature of coeliac disease but may be found in other disorders.

References

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  2. ↑ Boussault P, Léauté-Labrèze C, Saubusse E, et al. (November 2007). "Oat sensitization in children with atopic dermatitis: prevalence, risks and associated factors". Allergy. 62 (11): 1251–6. doi:10.1111/j.1398-9995.2007.01527.x. PMID   17919139. S2CID   44678077.
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  5. ↑ Pazzaglia M, Jorizzo M, Parente G, Tosti A (June 2000). "Allergic contact dermatitis due to avena extract". Contact Derm. 42 (6): 364. PMID   10871113.
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  11. 1 2 Arentz-Hansen H, Fleckenstein B, Molberg Ø, et al. (October 2004). "The molecular basis for oat intolerance in patients with celiac disease". PLOS Med. 1 (1): e1. doi: 10.1371/journal.pmed.0010001 . PMC   523824 . PMID   15526039.
  12. 1 2 3 Comino I, Moreno Mde L, Sousa C (Nov 7, 2015). "Role of oats in celiac disease". World J Gastroenterol. 21 (41): 11825–31. doi: 10.3748/wjg.v21.i41.11825 . PMC   4631980 . PMID   26557006. It is necessary to consider that oats include many varieties, containing various amino acid sequences and showing different immunoreactivities associated with toxic prolamins. As a result, several studies have shown that the immunogenicity of oats varies depending on the cultivar consumed. Thus, it is essential to thoroughly study the variety of oats used in a food ingredient before including it in a gluten-free diet.
  13. ↑ Ciacci C, Ciclitira P, Hadjivassiliou M, Kaukinen K, Ludvigsson JF, McGough N, et al. (2015). "The gluten-free diet and its current application in coeliac disease and dermatitis herpetiformis". United European Gastroenterol J (Review). 3 (2): 121–35. doi:10.1177/2050640614559263. PMC   4406897 . PMID   25922672.
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  17. ↑ Hollén E, Högberg L, Stenhammar L, Fälth-Magnusson K, Magnusson KE (July 2003). "Antibodies to oat prolamines (avenins) in children with coeliac disease". Scand. J. Gastroenterol. 38 (7): 742–6. doi:10.1080/00365520310003156. PMID   12889560. S2CID   218911012.
  18. ↑ Guttormsen V, Løvik A, Bye A, Bratlie J, Mørkrid L, Lundin KE (2008). "No induction of anti-avenin IgA by oats in adult, diet-treated coeliac disease". Scand. J. Gastroenterol. 43 (2): 161–5. doi:10.1080/00365520701832822. PMID   18224563. S2CID   3421741.
  19. ↑ Kilmartin C, Lynch S, Abuzakouk M, Wieser H, Feighery C (January 2003). "Avenin fails to induce a Th1 response in coeliac tissue following in vitro culture". Gut. 52 (1): 47–52. doi:10.1136/gut.52.1.47. PMC   1773501 . PMID   12477758.
  20. ↑ Silano M, Di Benedetto R, Maialetti F, et al. (November 2007). "Avenins from different cultivars of oats elicit response by coeliac peripheral lymphocytes". Scand. J. Gastroenterol. 42 (11): 1302–5. doi:10.1080/00365520701420750. PMID   17852883. S2CID   38268535.
  21. ↑ Silano M, Dessì M, De Vincenzi M, Cornell H (April 2007). "In vitro tests indicate that certain varieties of oats may be harmful to patients with coeliac disease". J. Gastroenterol. Hepatol. 22 (4): 528–31. doi:10.1111/j.1440-1746.2006.04512.x. PMID   17376046. S2CID   38754601.
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