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Infect. Immun., 01 1998, 247-258, Vol 66, No. 1
RK Straubinger, AF Straubinger, BA Summers, HN Erb, L Harter and MJ Appel
Canine synovial membrane explants were exposed to high- or low-passage
Borrelia burgdorferi for 3, 6, 12, and 24 h. Spirochetes received no
treatment, were UV light irradiated for 16 h, or were sonicated prior to
addition to synovial explant cultures. In explant tissues, mRNA levels for
the proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha),
interleukin-1alpha (IL-1alpha), IL-1beta, and IL-8 were surveyed
semiquantitatively by reverse transcription-PCR. Culture supernatants were
examined for numbers of total and motile (i.e., viable) spirochetes,
TNF-like and IL-1-like activities, polymorphonuclear neutrophil (PMN)
chemotaxis-inducing activities, and IL-8. During exposure to synovial
explant tissues, the total number of spirochetes in the supernatants
decreased gradually by approximately 30%, and the viability also declined.
mRNAs for TNF-alpha, IL-1alpha, IL-1beta, and IL-8 were up-regulated in
synovial explant tissues within 3 h after infection with untreated or UV
light-irradiated B. burgdorferi, and mRNA levels corresponded to the
results obtained with bioassays. During 24 h of coincubation, cultures
challenged with untreated or UV light-irradiated spirochetes produced
similar levels of TNF-like and IL-1-like activities. In contrast, explant
tissues exposed to untreated B. burgdorferi generated significantly higher
levels of chemotactic factors after 24 h of incubation than did explant
tissues exposed to UV light-treated spirochetes. In identical samples, a
specific signal for IL-8 was identified by Western blot analysis. High- and
low-passage borreliae did not differ in their abilities to induce
proinflammatory cytokines. No difference in cytokine induction between
untreated and sonicated high-passage spirochetes was observed, suggesting
that fractions of the organism can trigger the production and release of
inflammatory mediators. The titration of spirochetes revealed a
dose-independent cytokine response, where 10(3) to 10(7) B. burgdorferi
organisms induced similar TNF-like activities but only 10(7) spirochetes
induced measurable IL-1-like activities. The release of chemotactic factors
was dose dependent and was initiated when tissues were infected with at
least 10(5) organisms. We conclude that intact B. burgdorferi or fractions
of the bacterium can induce the local up-regulation of TNF-alpha,
IL-1alpha, and IL-1beta in the synovium but that the interaction of viable
spirochetes with synovial cells leads to the release of IL-8, which
probably is a prime initiator of PMN migration during acute Lyme arthritis.
Copyright © 1998, American Society for Microbiology
Borrelia burgdorferi induces the production and release of proinflammatory cytokines in canine synovial explant cultures
James A. Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA. rks4@cornell.edu
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