Celiac disease: quantity matters.

Celiac disease (CD) is caused by uncontrolled immune responses to the gluten proteins in wheat and related cereals. Gluten is a complex mixture of gliadin and glutenin proteins and most modern wheat varieties contain up to 100 highly related, but distinct gluten proteins. Invariably, these gliadin and glutenin proteins contain immunogenic peptides, particularly so after the peptides have been modified by the enzyme tissue transglutaminase (TG2). This modification results in the conversion of glutamine residues in the gluten peptides into the negatively charged glutamic acid. This generates peptides that bind strongly to the disease predisposing HLA-DQ2.5 or -DQ8 molecules and this facilitates the induction of disease-inducing CD4 T cell responses, a hallmark of CD. It is well-known that the HLA-DQ genotype determines the risk of disease development. Moreover, the abundance of immunogenic peptides in the gluten proteins is likely linked to the observation that polyclonal T cell responses to multiple gluten peptides are usually found in patients with CD. However, not all patients respond to the same set of peptides. Here, I propose a model that integrates these observations and links them to the highly variable clinical spectrum of symptoms that are associated with CD. Moreover, I discuss whether it is feasible to alter wheat and/or gluten to make it suitable for consumption by CD patients.