The result of orally administering saliva derived from a Crohn's disease patient or an ulcerative colitis patient to germ-free mice has revealed that Th1 cells markedly increased in the colons. Further, from the bacterial microbiota in the intestines of the mice in which such an increase in Th1 cells were observed, bacteria have been successfully isolated which caused strong Th1 cell induction in the colon upon intestinal colonization.
