There is strong evidence that cytokines play a key role in the pathogenesis of Crohn's disease (CD). During the previous funding period, we demonstrated that TNF and IL-4 are important mediators of chronic ileitis in SAMP1/YitFc (SAMP) mice. These unique mice spontaneously develop enteritis without the need for genetic or immunological manipulation, and display macroscopic and histological features closely resembling CD. The overall objective of Project 1 is to continue to investigate the expression and function of key pathogenic cytokines involved in the pathogenesis of chronic intestinal inflammation in this spontaneous murine model of CD. In order to achieve our goals we will: 1) Determine the expression and cellular localization of novel cvtokines during ileitis in SAMP mice. We will clearly define the expression, localization, time course, and cellular origin of TL1A, a novel TNF-like factor, and IL-13, a prototypic Th2 cytokine, as well as their receptors, using real-time PCR, ELISA techniques, immunocytochemistry and multi-color FACS analysis. 2) Define the function of these novel cvtokines in the intestinal mucosa of SAMP mice. We will study the ability of TL1A and IL-13 to stimulate the production of IFN-gamma and other adaptive cytokines in isolated mucosal cells (MLN and LPL) and peripheral lymphocytes from SAMP mice. In addition, we will study how TL1A and IL-13 affect epithelial cell function, cytokine production and barrier function, using ex vivo permeability studies. 3) Determine the effect of cvtokine manipulation on the severity of ileitis in SAMP mice. We will investigate the effects of TL1A and IL-13 neutralization using monoclonal antibodies and a novel siRNA gene shutdown retroviral delivery system. We will also generate DR3 or IL-13-deficient SAMP mice to further define the role of these cytokines in the initiation and perpetuation of chronic ileitis in this model. The ultimate goal of Project 1 is to define the key pathogenic role of cytokines in experimental CD, in order to develop disease-modifying treatment modalities for this devastating disease.