The goal of this collaborative proposal is to create a novel 120,000 peptide chip for use in the diagnosis, prognosis, and treatment of Crohn’s disease. The peptides will be both random and specific to gut bacterial proteins implicated in complicated Crohn’s disease. Patients with Crohn’s disease have a distinctive pattern of antibody binding to random peptides in the chip, called an immunosignature. We propose that the immunosignature will be a much more sensitive and specific method of diagnosis and prognosis than any currently available methods. Moreover, we propose that changes in the signature over time will reflect disease activity and response to therapy.