1. Wheat-based foods are broken down in the stomach and the upper part of the small intestine called the duodenum. Gluten is broken down in the duodenum.
2. Some of the partially digested food travels to the next segment of the small intestine called the jejunum.
3. In the jejunum, structures called villi with surface-bound enzymes break food down into complex molecules the body absorbs.
4. Gluten adheres to the tips of villi where enzymes break it down into simpler molecules called peptides. Some of the peptides, called 33-MER, cannot be broken down any further. This is true for all persons whether they suffer from celiac sprue or not.
5. Absorption cells in the gut lumen absorb 33-MER peptides and pass them into the tissues of the lamina propria. Antigen presenting cells (APC), part of the body's immune system, target foreign substances in the body for response by the immune system. APC do this by binding with the foreign substance, and then send biochemical signals to white blood cells to attack. In nearly all people with celiac sprue, APC bind with 33-MER only if the APC carry a protien called DQ2.
6. Once the intestinal wall absorbs 33-MER peptides, APC in celiac sprue patients signal white blood cells to attack. The result is eventual desctruction of absorption cells and villi in the intestinal wall.
Credit: Kirk Woellert, National Science Foundation