What happens if a celiac eats wheat?

Various symptoms: When patients with celiac disease eats gluten, they get "villious atrophy", the finger-like projections in their small intestine shrink and fail to properly absorb nutrients. This can result in symptoms of: "1) those due to malabsorption, and (2) those due to malnutrition including vitamin and mineral defiencies".

New antibodies: For whatever reason a celiac will develop antibodies to some of the many proteins in wheat & these attack their digestive tissues as if they were wheat. If they stay away from wheat for long enough, the tissues heal & symptoms improve. Any new exposure to wheat can generate a new & large burst of antibodies that starts the injury/symptoms all over again.