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Infection and Immunity, March 2000, p. 1207-1214, Vol. 68, No. 3
Department of
Bacteriology1 and Department of Medicine
II,2 Nara Medical University, Kashihara,
Nara 634-8521, Japan
Received 1 October 1999/Returned for modification 29 October
1999/Accepted 12 November 1999
In a previous study, we showed that infection with Shiga toxin
(Stx)-producing Escherichia coli O157:H7 (strain
SmrN-9) caused neurologic symptoms in malnourished mice
with positive immunoreactions of Stx2 in brain tissues. The present
study explores the mechanism of how Stx injures the vascular
endothelium to enter the central nervous system in mice. Oral infection
with strain SmrN-9 elicited a tumor necrosis factor alpha
(TNF-
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Pathogenic Mechanism of Mouse Brain Damage Caused by Oral
Infection with Shiga Toxin-Producing Escherichia coli
O157:H7
) response in the blood as early as 2 days after infection,
while Stx was first detected at 3 days postinfection. In the
brain, TNF-
was detected at day 3, and its quantity was increased
over the next 3 days. Frozen sections of the brains from moribound mice
contained high numbers of apoptotic cells. Glycolipids recognized by an
anti-Gb3 monoclonal antibody were extracted from the brain, and
purified Stx2 was able to bind to the glycolipids. In human umbilical
vascular endothelial cells (HUVEC) cultured with fluorescein-labeled
Stx2 (100 ng/ml), TNF-
(20 U/ml) significantly facilitated the
intracellular compartmentalization of fluorescence during 24 h of
incubation, suggesting the enhanced intracellular processing of Stx2.
Consequently, higher levels of apoptosis in HUVEC were found at
48 h. Short-term exposure of HUVEC to Stx2 abrogated their
apoptotic response to subsequent incubation with TNF-
alone
or TNF-
and Stx2. In contrast, primary exposure of HUVEC to TNF-
followed by exposure to Stx2 alone or TNF-
and Stx2 induced
apoptosis at the same level as obtained after 48-h incubation
with these two agents. These results suggest that the rapid production
of circulating TNF-
after infection induces a state of competence in
vascular endothelial cells to undergo apoptosis, which
would be finally achieved by subsequent elevation of Stx in the blood.
In this synergistic action, target cells must be first exposed to
TNF-
. Such cell injury may be a prerequisite to brain damage
after infection with Stx-producing E. coli
O157:H7.
*
Corresponding author. Mailing address: Department of
Bacteriology, Nara Medical University, 840, Shijyocho, Kashihara, Nara 634-8521, Japan. Phone: 81-744-29-8839. Fax: 81-744-29-7375. E-mail: eijikita{at}nmu-gw.cc.naramed-u.ac.jp.
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