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Celiac disease is understood to be an immune response to certain proteins which occur in a group of cereals; most commonly they are glutens (wheat), secalins (rye) and hordeins (barley). A clinical test for celiac examines serum levels of two specific antibodies: Deamidated Gliadin peptide Ab IgG and Tissue Transglutaminase Ab IgA.

Is it possible to test positive for the above antibodies while being sensitive (raise an immune response) only to hordeins?

There are two components to this question:

  • Can a person be sensitive to hordeins while being unaffected by either wheat gluten or rye (secalins)?
  • Would the above test produce a positive result given only hordein-specific antibodies? In other words, is the test specific to wheat gluten antibodies or will antibodies to any gluten epitope produce a positive result?

The reason behind this question in a short case history:

  • Mature adult subject experienced mild/intermittent IBS symptoms, onset vaguely extending back several years. Diet notably included regular/daily consumption of wheat/rye products as well as intermittent (2-3/week) beer (barley).
  • Recent clinical screening for celiac (serum levels of Deamidated Gliadin peptide Ab IgG and Tissue Transglutaminase Ab IgA) performed to investigate cause of suspected osteoporosis; both antibody levels assessed as positive.
  • Symptoms apparently abated within about one week following an initial dietary change successfully removing only barley gluten (beer), while regular consumption of wheat/rye continued.

Observations suggest a specific response only to barley, and raises the question about specificity of the clinical antibody test.

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  • $\begingroup$ You might find this answer to a related question to be of interest — it doesn't address celiac directly, but it does answer the first part of your question. $\endgroup$ – tyersome Jan 20 at 4:30
  • $\begingroup$ @tyersome it does help with general understanding. Still hoping for an on-point answer to reconcile some specific facts and observations. $\endgroup$ – Anthony X Jan 21 at 0:31
  • $\begingroup$ I would recommend editing your question to focus on the IBS specific portions — since you already learned the answer to 1. and 2. I recommend rewriting your post to include that information and delete extraneous material. (The website keeps track of edits so you don't need to have an 'Edit' section.) This will show people that you have done your research and allow people to focus on what you still don't know, rather than getting distracted by questions for which you already know the answers. ——— Specifically, I would delete anything not relevant to understanding your final paragraph. $\endgroup$ – tyersome Jan 22 at 0:31
  • $\begingroup$ @tyersome Thanks for the suggestion; hope my latest edit does the job $\endgroup$ – Anthony X Jan 22 at 3:43
  • $\begingroup$ You're welcome — this is much better! (+1) It's great that you've put in so much effort to improve your question. The only other suggestion I can make at this point is to include references for the background statements you make. In particular, references that describe the basis for the clinical tests might allow someone with the correct background to rapidly come up with an answer for you. This also provides a resource for other users and documents all the work you've put into your question! ——— I hope you get a good answer soon. 😊 $\endgroup$ – tyersome Jan 22 at 4:55
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1) Can a person be sensitive to barley hordeins, while being unaffected by wheat gluten or rye secalins?

Possibly, but I haven't found a documented case.

According to What is gluten? (Journal of Gastroenterology and Hepatology, 2017):

A variety of sequences from α, γ, and ω gliadins, as well as from the glutenins, have been identified to activate coeliac disease. However, several hundred gluten peptides are predicted to be immunogenic and trigger the T-cell mediated response.6 The most immunodominant T-cell epitope is from α gliadin, although T-cell cross-reactivity against gluten-derived, secalin-derived, and hordein-derived peptides have been confirmed. Additionally, within each grain, there exists a distinct hierarchy of immunostimulatory gluten peptides.6 Of all the peptides known to stimulate the T-cell response in coeliac disease, a given patient may react to only a few.

However, according to Coeliac disease: immunogenicity studies of barley hordein and rye secalin‐derived peptides (International Journal of Experiemntal Pathology, 2016):

In conclusion, barley hordein and rye secalin appear to contain CD toxic epitopes that are found in wheat gluten, as demonstrated by the observed cross‐reactivity of CD‐derived gluten‐sensitive small intestinal T‐cell lines to wheat gliadin, barley hordein and rye secalin‐derived peptides.

2) Are the blood tests specific to wheat gluten antibodies?

I can't say for deamidated gliadin peptide Ab IgG test, but tissue transglutaminase antibodies IgA test (anti-tTG IgA) is not specific for wheat gluten; antibodies can be triggered by wheat gliadins, barley hordeins and rye secalins.

Gluten peptides (gliadins, hordeins, secalins) bind to tissue transglutaminase which deamidates them. Individuals with celiac disease have HLA DQ2/DQ8 dendritic cells, which present deamidated peptides to T cells, which stimulate B cells to produce antibodies against tissue transglutaminase:

In CD, deamidation of gluten by tissue transglutaminase (tTG) in the small-bowel lamina propria promotes presentation of gluten peptides (gliadin in wheat, secalin in rye and hordein in barley) by HLA-DQ2 or HLA-DQ8 dendritic cells to pathogenic local CD4+ T cells...The most widely used serological test is anti-tTG IgA (Medscape)

3) Can barley affect the gut differently than wheat?

Possibly.

Nutrition and Celiac Disease (Nutrients, 2014):

There is very limited data looking at the effect of barley hordein or rye secalin on CD outcomes in the published literature (e.g., [66,67]), but evidence exists that these prolamins induce effects different to wheat gluten, at least at an immunologic level.

4) Do positive DGP and TTG test confirm celiac disease?

The specificity of IgG deaminated gliadin peptide (DGP) is 98% and of IgA tissue transglutaminase (TTG) 95% (American Family Physician, 2014), so when both tests are positive, celiac disease is very likely. The final diagnosis is by histological examination of a tissue sample obtained by duodenal biopsy.

5) Is it possible that, in celiac disease, symptoms disappear after removing only beer, but not wheat and rye from the diet?

It could be possible to have celiac disease confirmed by blood tests without any symptoms despite consuming wheat, barley and rye. Beer could trigger symptoms by irritating the bowel, not by gluten, but by alcohol or other substances, like in people with irritable bowel syndrome (American Journal of Gastroenterology, 2013).

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  • $\begingroup$ Thanks for the comprehensive answer. I was hoping for a more definitive answer, but this is very helpful and useful info. $\endgroup$ – Anthony X Jan 31 at 23:51

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