T cell stimulatory bacteria colonizing in the human oral cavity

Colonization with microbes of oral origin can be seen in the intestine of patients with several diseases such as IBD, liver cirrhosis and colon cancer. The colonized oral bacteria may affect the intestinal and systemic immune systems. In this study, we have searched for T cell stimulatory bacterial species colonizing in the human oral cavity. For this purpose, saliva samples were obtained from healthy donors and patients with Crohn's disease (CD), and inoculated into germ-free (GF) mice. A saliva sample from one CD patient induced a marked accumulation of TH1 cells in the colonic lamina propria of the inoculated mice. Several bacterial species were specifically observed in the gut microbiome of mice inoculated with the CD patient saliva, not in mice with other saliva samples. To isolate TH1 cell-inducing bacterial strains, we cultured cecal contents from the mice inoculated with the CD patient saliva, and succeeded in isolation of 8 individual bacterial strains. In GF mice inoculated with a mixture of the isolated 8 strains, a significant increase in Th1 cells was observed. Among 8 strains, Klebsiella pneumoniae strain was the major colonizer in the intestine of mice inoculated with the CD patient saliva. In mice monocolonized with the Klebsiella pneumoniae strain, we observed a sufficient induction of TH1 cells. Therefore, the Klebsiella pneumonia strain can be a taxonomic biomarker for CD.