In this paper we show that Clostridium perfringens epsilon-toxin accumulates predominantly in the mouse kidney, where it is distributed mainly in glomeruli, capillaries, and collecting ducts. Although some pycnotic and exfoliated epithelial cells were observed in distal tubuli and collecting ducts, there were no findings indicative of severe renal injury. Bilateral nephrectomy increased the mouse lethality of the toxin, suggesting that the kidney contributes to the host defense against the lethal toxicity of epsilon-toxin.Epsilon-toxin produced by Clostridium perfringens types B and D is a potent toxin that is responsible for rapidly fatal enterotoxemia in livestock (17,22). The toxin has been well defined in terms of the proteolytic activation of epsilon-protoxin (7, 10), its pore-forming ability in Madin-Darby canine kidney (MDCK) cell membranes (12, 18) and artificial lipid bilayers (19), and its heptamerization in detergent-insoluble glycosphingolipid-enriched microdomains (10, 11). However, the pathogenic mechanisms involved in the lethality of epsilontoxin remain largely unknown, except that it exhibits toxicity towards neuronal cells (2,8,9) and blood vessels in the brains of mice and rats (1, 3, 4). Besides massive necrosis in the brain, pulpy kidneys are noticeable in animals that have died due to enterotoxemia (22). Epsilon-toxin exhibits cytotoxicity towards MDCK cells derived from dog renal distal tubules or collecting ducts but not towards any other cell lines (17,21,24). Moreover, epsilon-toxin was reported to be most abundant in the kidneys when intravenously (i.v.) administered to mice (13). However, nothing is known about its nephrotoxicity.The aim of this study was to determine the distribution of epsilon-toxin in the mouse kidney and also its nephrotoxicity. Male ddY mice (4 weeks old; SLC Japan, Shizuoka, Japan) were used. The epsilon-protoxin and epsilon-toxin used in this study were recombinant toxins, which were purified, activated, and labeled with [␥-35 S]ATP as described previously (11). The intravenous 50% lethal dose of epsilon-toxin was determined to be approximately 20 ng per mouse. The time to death after challenge estimated for mice susceptible to 15 ng of epsilontoxin was 8.3 Ϯ 0.4 h (mean Ϯ standard error [SE], n ϭ 5), and that for mice receiving 500 ng of epsilon-toxin was 0.35 Ϯ 0.01 h (mean Ϯ SE, n ϭ 5).First, we examined, by whole-body autoradiography (WBA), whether epsilon-toxin is accumulated predominantly in the mouse kidney in accordance with the results obtained by others using a different methodology (13). One hundred nanograms of 35 S-epsilon-toxin or 35 S-epsilon-protoxin was i.v. injected into a mouse through a tail vein. The mouse given 35 S-epsilontoxin was frozen in dry ice-acetone at approximately 1 h postinjection (p.i.) immediately after death. The mouse given 35 Sepsilon-protoxin was sacrificed by cervical dislocation at 1 h p.i., followed by freezing in dry ice-acetone. Frozen sections (50 m each) were prepared with an autocryotome (NA-500F; Nakagawa Seisaku...