Nat Med 2000;6:337-342. (March 1, 2000)
see also: BMJ 2000;320:736 (March 18, 2000)
Dr. Anderson and his University of Oxford colleagues used a series of 15 amino acid peptides along the A-gliadin sequence (alpha gluten) to stimulate in patients with celiac disease their peripheral blood mononuclear cells, or PBMCs. The peptides were either unmodified or were treated with tissue transglutaminase, which, in the presence or absence of lysine, will convert glutamine to glutamate.
Researchers successfully stimulated PBMCs in celiac patients who were in remission due to a gluten-free diet with a gluten challenge. Patients were fed wheat bread for either a half day, 3 days, or 10 days, and healthy, non-celiac patients that were fed wheat bread each day for 4 weeks were used as controls. The researchers successfully produced PBMCs from the celiac disease group, who secreted interferon-gamma 6-8 days later, in response to a particular pool of A-gliadin peptides, which had been treated with tissue transglutaminase. A 17-amino-acid peptide, corresponding to the partially deamidated peptide of A-gliadin amino acids 57-73, was optimal for inducing the interferon-gamma secretion, and the responses were restricted to those with HLA-DQ2.
According to Dr. Anderson: On a more general level, the finding that a host enzyme modifies peptides that are then recognized by the immune system suggests that searching for epitopes important in disease may be more complex than simply reading off protein sequences from sequenced genes. Further, modification of the peptide by tissue transglutaminase that is present in the intestinal lining increases binding of the peptide to HLA-DQ. The researchers also point out that T cells that are responsive to the same A-gliadin peptide are readily induced in celiac disease despite many years of following a gluten-free diet, which indicates a persistence of memory T cells that could be caused by continuing exposure to trace amounts of gluten. The researchers only looked at the A-gliadin peptide, and point out that there is a possibility that other peptides that are structurally unrelated to A-gliadin are also important in celiac disease.