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Mice have been extensively employed as an animal model of renal damage caused by Shiga toxins. In this study, we examined the role of the proinflammatory cytokine tumor necrosis factor alpha (TNF-␣) in the development of toxin-mediated renal disease in mice. Mice pretreated with TNF-␣ and challenged with Shiga toxin type 1 (Stx1) showed increased survival compared to that of mice treated with Stx1 alone. Conversely, mice treated with Stx1 before TNF-␣ administration succumbed more quickly than mice given Stx1 alone. Increased lethality in mice treated with Stx1 followed by TNF-␣ was associated with evidence of glomerular damage and the loss of renal function. No differences in renal histopathology were noted between animals treated with Stx1 alone and the TNF-␣ pretreatment group, although we noted a sparing of renal function when TNF-␣ was administered before toxin. Compared to that of treatment with Stx1 alone, treatment with TNF-␣ after toxin altered the renal cytokine profile so that the expression of proinflammatory cytokines TNF-␣ and interleukin-1␤ (IL-1␤) increased, and the expression of the anti-inflammatory cytokine IL-10 decreased. Increased lethality in mice treated with Stx1 followed by TNF-␣ was associated with higher numbers of dUTP-biotin nick end labeling-positive renal tubule cells, suggesting that increased lethality involved enhanced apoptosis. These data suggest that the early administration of TNF-␣ is a candidate interventional strategy blocking disease progression, while TNF-␣ production after intoxication exacerbates disease.Shiga toxins are a family of genetically and functionally related cytotoxic proteins expressed by the enteric pathogens Shigella dysenteriae serotype 1 and certain serotypes of Escherichia coli. Antigenic similarity to Shiga toxin expressed by S. dysenteriae serotype 1 is used to define Shiga toxin type 1 (Stx1) and type 2 (Stx2) expressed by Shiga toxin-producing E. coli (STEC) (44). Shiga toxins consist of a single A subunit in noncovalent association with a pentamer of B subunits. B subunits mediate binding to the neutral glycolipid receptor globotriaosylceramide (Gb 3 ), while the A subunit possesses an N-glycosidase activity (38). Following toxin internalization and routing to the endoplasmic reticulum (ER), a fragment of the toxin A subunit generated by furin or a furin-like protease is translocated across the ER membrane and mediates the cleavage of a single adenine residue (A4256 in the rat) from the 28S rRNA component of ribosomes (39). Stx-induced depurination leads to the disruption of elongation factor-dependent aminoacyl-tRNA binding to nascent polypeptides (30). Thus, Shiga toxins are potent protein synthesis inhibitors, with 50% cytotoxic doses measured in pg/ml amounts for many cell types in vitro. Shiga toxins also activate the ribotoxic and ER stress pathways, which are important in the activation of proinflammatory cytokine/chemokine production and apoptosis (6,22,41).The ingestion of small quantities of Stx-producing bacteria may lead to the devel...