Cell proliferation in colonic crypts of germ-free and conventional mice--preliminary report

The influence of normal microbial flora on cell proliferation in mouse colonic crypts was assessed by a comparison of conventional and germ-free animals. The following characteristics of the crypts were measured: length, diameter in the middle, number of columns, number of cell per one column, percentage of goblet cells, mitotic and labelling index distribution and average cell cycle time for the proliferative compartment. It has been found that the crypts in conventional mice are longer than in their germ-free counterparts, while their diameter and percentage of goblet cells were similar in both animal groups. The mitotic index was lower in germ-free mice, as well as the labelling index. The average cell cycle time was about 1.7-fold shorter in conventional animals than in germ-free animals. This result was verified using computer simulation model; it turned out that the change in average cell cycle time could be solely responsible for all the observed differences between germ-free and conventional animals. It seems therefore that normal microbial flora stimulates cell proliferation in mouse colon, most probably due to shortening of the average cell cycle.