Viable microbes are required to develop chronic T cell mediated intestinal inflammation in most experimental colitis models (i.e., Il-10−/−, Il2−/−, Tcrab−/−, Naïve CD4+ T cell transfer to Rag1/2−/−, Tlr5−/−, TnfΔARE mice) in which GF mice have no inflammation but develop progressive intestinal inflammation after colonization with complex microbiota [11–16]. This evidence concerns the gene RAG1 and colitis.