In addition to orally administered antigens, tolerance to gut microbiota has been reported several years ago by Powrie et al. (42) who demonstrated that adoptive transfer of CD4+CD45RBhigh cells into immunodeficient mice resulted in the development of colitis, and the inflammatory response could be prevented by simultaneous transfer of CD4+CD45RBlow cells, i.e., Treg cells. The gene discussed is CD4; the disease is colitis.