Influence of the indigenous microbiota on amounts of protein, DNA, and alkaline phosphatase activity extractable from epithelial cells of the small intestines of mice.

Germfree mice housed in isolators under controlled environmental and nutritional conditions were associated with an intestinal microflora. These associated animals and germfree mice drawn from the same population were used in experiments in which saline extracts of cells from the small intestine were assayed for alkaline phosphatase activity and for protein and DNA content. Epithelial cells were harvested from the intestines sequentially from the villous tips to the crypts of Lieberkühn. In all preparations, germfree animals yielded from one and one-third to one and one-half times the mass (wet weight) of cells yielded by associated mice. Likewise, for all preparations, extracts of the mass of cells from germfree mice contained more protein and DNA per milliliter than did extracts from associated animals. The ratio of the amount of extractable protein or DNA per milliliter of extract to the total wet weight of the cells in milligrams was about the same, however, for preparations from germfree and associated animals. All preparations from germfree animals yielded higher total alkaline phosphatase activities than those from associated mice. When related to the amount of DNA in the cells, the enzymatic activities were slightly but not significantly higher in preparations from germfree animals, except for preparations of cells removed from the tips of the villi. When related to the amount of protein in the extracts, the enzymatic activity (i.e., specific activity) was about the same in preparations from germfree and from associated mice, except (again) for preparations of cells removed from the tips of the villi. In the latter preparations, the specific alkaline phosphatase activities and enzymatic activities calculated relative to the amount of DNA were substantially higher for germfree animals than for mice with a microflora. Individual intestinal epithelial cells from germfree and associated animals, except those close to the villous tips, contain about the same alkaline phosphatase activity. Therefore, germfree mice must yield more activity of such microvillous enzymes than do mice with a microflora, partly because enterocytes at the tips of the villi in germfree mice contain more protein with enzymatic activity than do cells in a comparable location in mice with a microflora. In addition, the small intestines of germfree mice contain more activity of enzymes such as alkaline phosphatase than do those of associated animals because the small intestines of the former animals contain more enterocytes than do those of the latter.