Collectively, the data presented here suggest that the IL-17A producing cells play a major role in the pathogenesis of CD, that both gluten and CD associated bacteria provoke an IL-17A response in the intestinal mucosa of CD patients and that the magnitude of the adverse IL-17A reaction to gluten is markedly influenced by the composition of the resident microbiota and the amount of CD associated bacteria present. This evidence concerns the gene IL17A and Cowden disease.