Role of tumor necrosis factor alpha in gnotobiotic mice infected with an Escherichia coli O157:H7 strain.

Gnotobiotic mice inoculated with an enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain developed a flaccid paresis, usually culminating in death. The bacteria colonized feces at 10(9) to 10(10) CFU per g (inoculum size: 2.0 x 10(9) CFU/mouse), and Shiga-like toxins (SLTs) were detected in the feces. A microscopic examination of colons showed mild inflammatory cell infiltration, thinning of the intestinal wall, or necrotic foci. Necrosis of tubular cells was noted in these symptomatic mice. Microhemorrhage, thrombosis, and edematous changes of the brain were also seen. Inflammatory cytokines, tumor necrosis factor alpha (TNF-alpha), interleukin 1alpha (IL-1alpha), and IL-6, were detected in the kidney after EHEC infection, but not in the serum. In the brain, only TNF-alpha was detected. When 2.0 x 10(2) CFU of EHEC O157:H7 was fed to germ-free mice, the number of bacteria began to rise rapidly on day 1 and was maintained at 10(8)to 10(9) CFU/g of feces. SLTs were detected in the feces of the mice. However, the mice showed no histological changes and no cytokine responses, similar to what was found for controls. Treatment with TNF-alpha modified the clinical neural signs, histopathological changes, and cytokine responses; mice treated with TNF-alpha developed severe neurotoxic symptoms and had higher frequencies of systemic symptoms and glomerular pathology. Strong cytokine responses were seen in the kidney and brain. Serum cytokines were also detected in this group. In contrast, a TNF-alpha inhibitor (protease inhibitor) inhibited these responses, especially in the brain. However, local synthesis of the cytokines was observed in the kidney. Thus, TNF-alpha and the other proinflammatory cytokines could be important in modifying the disease caused by EHEC.