This invention relates transgenic animals that overexpress TL1A in a tissue specific manner to model inflammatory bowel disease (IBM such as colitis, Crohn's disease and ulcerative colitis, fibrosis, and related inflammatory diseases and conditions. TL1A transgenic animals constitutively express both TL1A and GFP in lymphoid and myeloid cell lineages, allowing convenient identification and sorting of immune cells involved in IBD disease progression, such as T-cells, antigen presenting cells (APC), and dendritic cells (DC). TL1A transgenic animals may be induced to exhibit gross fibrosis, or isolated cells may be implanted into immunodeficient mice to establish colitis.