As a result of oral administration of saliva from Crohn's disease patients or ulcerative colitis patients to sterile mice, it was found that Th1 cells are markedly increased in the large intestine. Furthermore, from the intestinal bacterial flora of mice in which this increase in Th1 cells was observed, the inventors succeeded in isolating bacteria that would cause strong Th1 cell induction in the large intestine when colonized in the intestinal tract.クローン病患者又は潰瘍性大腸炎患者由来の唾液を、無菌マウスに経口投与した結果、大腸においてＴｈ１細胞が著増することを見出した。さらに、このＴｈ１細胞の増加が見られたマウスの腸内細菌叢から、腸管に定着すると大腸で強いＴｈ１細胞の誘導を引き起こすことになる細菌を単離することに成功した。
