Abstract: The present invention is directed to the identification of PBMC- and IBD-associated biomarkers that may be used to diagnose inflammatory bowel disease, and optionally, distinguish between PBMCs isolated from a patient with Crohn's disease and PBMCs isolated from a patient with ulcerative colitis. The present invention is further directed to methods of screening, including high throughput methods of screening, for regulatory agents capable of regulating the activity of PBMC- and IBD-associated biomarkers. Provided are compositions of PBMC- and IBD-associated biomarkers, including regulatory agents of at least one PBMC- and IBD-associated biomarker for methods of diagnosis, prognosis, therapeutic intervention and prevention of an inflammatory bowel disease, e.g., Crohn's disease and ulcerative colitis. Moreover, the present invention is also directed to methods that can be used to assess the efficacy of test compounds and therapies in the treatment inflammatory bowel disease, i.e.