The activity of wheat gliadin peptides in in vitro assays for coeliac disease.

A fraction of a peptic-tryptic-pancreatinic digest of wheat gliadin (fraction 9), known to be toxic to individuals with coeliac disease, together with synthetic peptides containing key gliadin sequences, were tested for their effects on foetal chick intestine and on rat liver lysosomes. Fraction 9 and a dodecapeptide corresponding to residues 75-86 of A-gliadin (RPQQPYPQPQPQ) were the only peptides to display appreciable activity in both assays. A synthetic hexapeptide corresponding to residues 77-82 was only weakly toxic to lysosomes and non-toxic to chick duodenum. A decapeptide corresponding to residues 76-85 was non-toxic in both assays. Two serine-containing peptides containing the key sequence PSQQ were also tested but were found to be non-toxic, as was the hexapeptide PSQQQP. The results suggest that the key sequences QQQP and PSQQ are not sufficient by themselves to cause activity. Further tests on synthetic peptides will be necessary to define the sequences of highest toxicity.