In vivo gluten challenge in coeliac disease

Abstract

In vivo gluten challenge has been used since the early 1950s to study the role of cereal fractions in celiac disease. While early studies relied on crude indicators of celiac toxicity, the advent of jejunal biopsy and sophisticated immunohistochemical techniques has allowed accurate studies to be performed. Studies to determine the nature of the cereal component that is toxic to patients with celiac disease have concentrated on wheat because of its nutritional importance. A number of in vitro studies indicated the presence of one or more celiac-activating epitopes with the N-terminus of the A-gliadin molecule. In vivo challenge with three synthetic peptides subsequently indicated the toxicity of a peptide corresponding to amino acids 31 to 49 of A-gliadin. In vivo gluten challenge is the gold standard for the assessment of celiac toxicity; however, jejunal biopsy is a relatively invasive procedure, thus, other methods have been investigated. Direct infusion of the rectum with gluten has been shown to result in an increase in mucosal intraepithelial lymphocytes, occurring only in celiac patients. This method has been used to study the celiac toxicity of gliadin subfractions. The in vitro technique of small intestinal biopsy organ culture is also a useful tool and appears to give the same results as in vivo challenge. The importance of tiny amounts of gliadin in the diet, such as that which occurs in wheat starch, has been studied by in vivo challenge; this technique has clarified the position of oats in the gluten-free diet. Several studies suggest that this cereal may be included in the diet of most adult celiac patients. Studies of the transport of gliadin across the enterocyte following ingestion or challenge suggest that gliadin may be metabolized by a different pathway in celiac disease. This could result in an abnormal presentation to the immune system, triggering a pathogenic rather than a tolerogenic response.

Wheat gliadin induces apoptosis of intestinal cells via an autocrine mechanism involving Fas–Fas ligand pathway

“…This is an interesting finding in view of future studies aimed at the understanding of the immune modulating activities exerted by Gl–PT. As reported by several in vitro and in vivo studies [42–45], the sequences ‐Gln‐Gln‐Gln‐Pro‐ and/or ‐Pro‐Ser‐Gln‐Gln‐ are known to be a common feature of toxic gliadin‐derived peptides. Interestingly, remarkable homologies were identified between these toxic sequences and the protective amino acid sequence within the ‘1157 Da’ peptide (H 2 N‐gln‐gln‐pro‐gln‐) [17,18,40].…”

How gluten-free is gluten-free, and what does this mean to coeliac patients?

“…Individual variation and clinical heterogeneity of coeliac patients pose difficult problems for an attempt to find an acceptable threshold value for trace amounts of gluten to be allowed in gluten-free foods [1]. Challenge studies and dietary survey studies [7,[9][10][11][12][13] have shown that a daily intake of 100 mg or more of gliadin was sufficient to elicit typical coeliac changes, whereas a daily intake of gliadin of 4-14 mg did not cause smallintestinal mucosal damage in coeliac patients [10]. Unlike food allergy, in coeliac disease there appears to be a low-level threshold of gluten that might be acceptable for the majority of coeliac patients.…”

“…Wheatstarch-based bread-flour mixtures containing traces of gluten are more palatable than zero-gluten preparations, and they are preferred by patients in some countries (e.g. the UK and Finland) [11,13]. However, clinical data at present are not sufficient to back up the 200 parts per million (ppm) (200 mg/kg) threshold value suggested by the present Codex Alimentarius standard for foods rendered gluten-free (draft proposal 1998; compare with Stern and colleagues [1]).…”

The immune recognition of gluten in coeliac disease

“…Current understanding indicates that different gluten peptides are involved in the disease process in a different manner, some fragments being ‘toxic’ and others ‘immunogenic’. Specifically, a fragment is defined ‘toxic’ if it is able to induce mucosal damage either when added in culture to duodenal mucosal biopsy [22], or when administered in vivo on proximal and distal intestine [6,23,24], whereas a fragment is defined ‘immunogenic’ if it is able to specifically stimulate HLA‐DQ2‐ [25–28] or DQ8‐ [29–31] restricted T cell lines and T cell clones derived from jejunal mucosa or peripheral blood of coeliac patients. More in detail, as concerns ‘toxicity’, using in vitro jejunal biopsy organ culture, it was demonstrated that α‐, β‐, γ‐, and ω‐gliadins have a decreasing toxicity and the presence of similar N‐terminal aminoacid sequence in rye and barley prolamins suggests that a certain amino acid sequence may constitute the toxic determinant [32,33].…”