BORRELIA-BURGDORFERI INDUCES THE PRODUCTION AND RELEASE OF PROINFLAMMATORY CYTOKINES IN CANINE SYNOVIAL EXPLANT CULTURES

Canine synovial membrane explants were exposed to high-or low-passage Borrelia burgdorferi for 3, 6, 12, and 24 h. Spirochetes received no t reatment, were UV light irradiated for 16 h, or,were sonicated prior t o addition to synovial explant cultures. In explant tissues, mRNA leve ls for the proinflammatory cytokines tumor necrosis factor alpha (TNF- alpha), interleukin-1 alpha (IL-1 alpha), IL-1 beta, and IL-8 were sur veyed semiquantitatively by reverse transcription-PCR. Culture superna tants were examined for numbers of total and motile (i.e., viable) spi rochetes, TNF-like and IL-l-like activities, polymorphonuclear neutrop hil (PMN) chemotaxis-inducing activities, and IL-8. During exposure to synovial explant tissues, the total number of spirochetes iri the sup ernatants decreased gradually by similar to 30%, and the viability als o declined. mRNAs for TNF-alpha, IL-alpha, IL-1 beta, and IL-8 were up -regulated in synovial explant tissues within 3 h after infection with untreated or UV light-irradiated Bi burgdorferi, and mRNA levels corr esponded to the results obtained with bioassays. During 24 h of coincu bation, cultures challenged with untreated dr UV light irradiated spir ochetes produced similar levels of TNF-like and IL-l-like activities. In contrast, explant tissues exposed to untreated B. burgdorferi gener ated significantly higher levels of chemotactic factors after 24 h of incubation than did explant tissues exposed to UV light-treated spiroc hetes. In identical samples, a specific signal for IL-8, was identifie d by Western blot analysis. High-and low-passage borreliae did not dif fer in their abilities to induce proinflammatory cytokines. No differe nce in cytokine induction between untreated and sonicated high-passage spirochetes was observed, suggesting that fractions of the organism c an trigger the production and release of inflammatory mediators. The t itration of spirochetes revealed a dose-independent cytokine response, where 10(3) to 10(7) B. burgdorferi organisms induced similar TNF-lik e activities but only 10(7) spirochetes induced measurable IL-1-like a ctivities. The release of chemotactic factors was dose dependent and w as 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-1 alpha, and IL-1 beta in the synovium but that the interaction of viable spirochetes wi th synovial cells leads to the release of IL-8, which probably is a pr ime initiator of PMN migration during acute Lyme arthritis.