Diversity in oat potential immunogenicity: basis for the selection of oat varieties with no toxicity in coeliac disease

BACKGROUND AND AIMS

Coeliac disease (CD) is triggered by an abnormal reaction to gluten. Peptides resulting from partially digested gluten of wheat, barley or rye cause inflammation of the small intestinal mucosa. Previous contradictory studies suggest that oats may trigger the abnormal immunological response in patients with CD. Monoclonal antibodies (moAbs) against the main immunotoxic 33-mer peptide (A1 and G12) react strongly against wheat, barley and rye but have less reactivity against oats. The stated aim of this study is to test whether this observed reactivity could be related to the potential toxicity of oats for patients with CD.

METHODS

In the present study, different oat varieties, controlled for their purity and by their distinct protein pattern, were used to examine differences in moAb G12 recognition by ELISA and western blot. Immunogenicity of oat varieties was determined by 33-mer concentration, T cell proliferation and interferon γ production.

RESULTS

Three groups of oat cultivars reacting differently against moAb G12 could be distinguished: a group with considerable affinity, a group showing slight reactivity and a third with no detectable reactivity. The immunogenicity of the three types of oats as well as that of a positive and negative control was determined with isolated peripheral blood mononuclear T cells from patients with CD by measurement of cell proliferation and interferon γ release. A direct correlation of the reactivity with G12 and the immunogenicity of the different prolamins was observed.

CONCLUSIONS

The results showed that the reactivity of the moAb G12 is proportional to the potential immunotoxicity of the cereal cultivar. These differences may explain the different clinical responses observed in patients suffering from CD and open up a means to identify immunologically safe oat cultivars, which could be used to enrich a gluten-free diet.

In vitro tests indicate that certain varieties of oats may be harmful to patients with coeliac disease

BACKGROUND

The presence of oats in gluten-free diet is controversial. The aim of this work is to evaluate if different varieties of oats exert different toxicity in coeliac disease.

METHODS

Three varieties of oats were tested by two in vitro assay based on the known ability of peptic-tryptic digests of coeliac-active proteins to agglutinate K562 cells and to disrupt lysosomes, respectively.

RESULTS

Avenins from the Italian variety Astra and the Australian variety Mortlook were much more active than the Australian variety Lampton. Gliadin, digested in the same way, certainly displayed more activity than all three avenins, but rice (var. Roma) did not have measurable activity.

CONCLUSIONS

The results indicate that some varieties of oats may be potentially harmful to individuals with coeliac disease and therefore should be excluded from the gluten-free diet required to maintain good health in coeliac disease. It is important to realize that constant, small amounts of active proteins in the diet, such as certain avenins, may prevent complete recovery of the intestinal mucosa in this disease.

Further studies of the in vitro activity of synthetic gliadin peptides in coeliac disease

Studies of in vitro activity of synthetic peptides derived from the A-gliadin structure were carried out using assays based on cultures of foetal chick intestinal mucosa and on incubation with rat liver lysosomes. The peptide corresponding to residues 11-19, displayed very high activity in the chick intestinal assay, but was only weakly active in the lysosomal assay. Peptide 9-19 was highly active in the chick intestinal assay but was only mildly active in the lysosomal assay. Peptide 8-19 was still appreciably active in both assays. The results on this group of peptides suggest the importance of residues 8-12 to activity and possibly also of a N-terminal glutamine residue. The peptide 213-227, found in a sub-fraction of fraction 9, was only weakly active in both assays, indicating that the PSQQ motif was not solely responsible for toxicity. Thus, as the peptide 208-219 was shown previously to be active in the chick intestinal assay, it is likely that the 208-212 region of this peptide is of prime importance in conferring activity. The results show, for the first time, that a nonapeptide from the N-terminal region of A-gliadin is very active in an in vitro model of toxicity in coeliac disease.

Characterization of the gliadin-derived peptides which are biologically active in coeliac disease

Reversed-phase HPLC on C18 silica gel at pH 3.5 was used to separate peptides in fraction 9, a mixture of peptides of unknown composition obtained from an enzymic digest of wheat gliadin. This fraction, which has been shown to be toxic to individuals with coeliac disease, yielded a principal peak as well as many minor peaks after HPLC. The significant peaks were subjected to amino acid analysis. The principal peak obtained was purified by rechromatography at pH 6.0 and shown to contain a dodecapeptide of sequence H-Arg-Pro-Gln-Gln-Pro-Tyr-Pro-Gln-Pro-Gln-Pro-Gln-OH. This peptide may have been derived from regions in the A-gliadin molecule corresponding to amino acids numbered 75-86 or from homologous regions in other gliadin molecules. Preliminary results indicate that it is active in two in vitro models of coeliac disease and that it could be the source of one of the undigested peptides (Hexapeptide II, (Glx)3, (Pro)2, Tyr) obtained from coeliac mucosal digestion of fraction 9. Some active serine-containing peptides were also obtained from chromatography at pH 3.5 and attempts are being made to correlate these with the other undigested peptide (Hexapeptide I) of composition (Glx)3, (Pro)2, Ser, obtained after coeliac mucosal digestion of fraction 9.

A measure of response to perturbation used to assess structural change in some polluted and unpolluted stream fish communities

A new method for measuring structural change in sets of species which have been subjected to natural or experimental perturbation is developed and is shown to be superior to static diversity and evenness measures for this purpose. Three parameters, HΔ', JΔ', and XΔ;} are shown to provide necessary and sufficient information on the severity of a perturbation as well as the uniformity of its effect on all species in the set. When positive and negative changes in species abundance are considered separately, the method is sensitive to compensatory changes which are not detected by static measures.The parameters are then calculated for some data sets on polluted and unpolluted fish communities in second and third order streams from the Clemons Fork watershed in eastern Kentucky. Results indicate that HΔ', the diversity of change over two sampling seasons, is high for perturbed and unperturbed systems, but JΔ' the eveness of change is lower for the communities which were polluted in the second sampling season. Severe pollution results in the suppression of most major fish species, whereas more moderate pollution results in a large number of compensatory changes. The biological basis for such an outcome is discussed, and the notion of these three parameters as the "vital signs" of a healthy ecosystem is presented.

Insular biogeography: of mice and mites

The number of mite species using cricetid rodents in North America is related to the host distributional areas. The age and latitude of the distributional areas have unimportant effects on the number of mite species using a rodent species. The relation between species and areas is analogous to species equilibrium numbers of island faunas.