Effects of intestinal bacteria on the development of colonic neoplasm II. Changes in the immunological environment.

To study the effects of intestinal bacteria on the development of colonic neoplasm, we have established gnotobiotic mice with a single species of intestinal bacteria. In the previous study, the incidence of colonic adenoma induced with 1,2-dimethylhydrazine (DMH) in the gnotobiotic mice with Lactobacillus acidophilus, gnotobiotic mice with Escherichia coli and germ-free mice were 30, 50 and 74%, respectively. In this study, 7-week-old mice in each group were sacrificed without the administration of DMH to examine the constituents of immuno-competent cells in various mouse organs using flow cytometry. In the gnotobiotic mice, CD3 intermediate interleukin (IL)-2Rbeta positive cells were observed predominantly in the liver. In the gnotobiotic mice with L. acidophilus, Mac-1 positive Gr-1 positive cells were observed predominantly in the colonic lamina propria. The activation of extrathymic T cells in the liver and granulocytes in the colonic mucosa may be related to anti-neoplastic effects of L. acidophilus in this experimental model.