RAG1 and colitis: Transgenic mice expressing tumor necrosis factor induced protein 3 (TNFAIP3; aka A20) in intestinal epithelial cells under the villin promoter (v-TNFAIP3) develop colitis on the recombination activating 1 (RAG1) deficient background (v-TNFAIP3 x RAG1-/-) [6].