Immune-mediated mechanisms

• Celiac disease – prolamines (gliadin peptides) – transglutaminase-IgA antibodies (see Tab. 3)

- Systemic detection

- Local intestinal detection

• Food allergy to wheat or other cereal types

- Systemic detection

- Local intestinal detection

Type I – e.g. wheat flour, wheat pollen, gluten, gliadin (e.g. ω-5 gliadin), other allergens (differential diagnosis: gluten substitutes, e.g. lupin flour, corn)

Type IV – e.g. wheat flour, wheat pollen, other allergens

Non-immune-mediated mechanisms

• Non-celiac disease gluten intolerance – no glutaminase-IgA antibody production (gluten sensitivity without celiac disease or food allergy)

e.g. gluten ataxia, myopathy, irritable bowel syndrome

• Fructan-induced abdominal symptoms

- Fructooligosaccharide and fructopolysaccharide, e.g. irritable bowel syndrome

• Small intestinal bacterial overgrowth, carbohydrate malassimilation

Immunologically active prolamins, which are only partially digestible by humans, are found in various cereal types. They include gliadin in wheat, secalin in rye, hordein in barley and avenin in oat, whereby immunological reactivity in celiac disease decreases according to the sequence given here from wheat through to oat and is determined by the patient’s sensitivity. Therefore, a gluten-free diet in celiac disease always includes at least wheat, spelt, rye and barley, whereas only wheat (gliadin) needs to be specifically avoided in wheat-mediated food allergy, but not rye and barley, assuming there is no crossreactivity with other cereal types.

In the case of gluten sensitivity (hitherto) classified as non-immunological, the specific IgA antibodies to transglutaminase and endomysium are negative, whereas approximately 50% of patients exhibit nonspecifically elevated antibodies to gliadin as well as occasional HLA-DQ2/DQ8 positivity. It is not yet known whether this form of gluten sensitivity is triggered by local immunological mechanisms after all or whether it is the result of a simple permeability disorder in the gastrointestinal tract (another disease?). IgA, Immunoglobulin A; HLA, human leukocyte antigen