**2.1 Gluten**

The major environmental factor responsible for the development of CD is gluten, which is a complex mixture of prolamin and glutelin storage proteins of certain cereals, such as wheat, barley, rye, oats, and their derivates. These common dietary proteins have unusual biochemical properties that include a high abundance of glutamine and proline residues, which render them resistant to degradation by gastrointestinal proteases [20], leaving large peptides. These peptides enter the lamina propria of the small intestine via transcellular or paracellular routes where, in affected individuals, an immune reaction occurs.
