Immunomodulating effect of killed, apathogenic Escherichia coli, strain Nissle 1917, on the macrophage system]

The influence of formaldehyde-killed Escherichia coli strain Nissle 1917 (SK 22) on macrophages of C57BL/6 mice was investigated in vitro. It has been shown that SK 22 activated macrophages derived from bone marrow produced Interleukin-6 with high efficiency. In addition, SK 22 stimulated macrophages to secrete tumor necrosis factor, as measured by a bioassay. Furthermore, macrophages were activated by SK 22 to produce a 3 fold amount of oxygen radicals compared to the spontaneous oxygen radical production. In contrast to this finding, the phagocytic capacity of these macrophages was only slightly increased. The specific lysis of P 815 tumor cells by peritoneal macrophages after coincubation with SK 22 was measured using tumor cells prelabelled with radioactive 51Cr. The results of the in vitro experiments presented clearly show that the E. coli preparation SK 22 is an efficient immunomodulator of the unspecific immune system.