D-098. The Toll-Like Receptor Signaling Pathway Mediates Release of Inflammatory Mediators in Human Monocytes Stimulated with Borrelia burgdorferi Spirochetes

V. A. Dennis¹, S. Dixit¹, S. O. Brein², X. Alvarez¹, B. Pahar¹, M. Philipp¹;
¹Tulane Natl. Primate Res. Ctr., Covington, LA, ²Tulane Univ., New Orleans, LA.

Infection with Borrelia burgdorferi, the agent of Lyme disease, results in the activation of inflammatory pathways that lead to the release of cytokines and chemokines and an influx of inflammatory cells. Lipoproteins of B. burgdorferi signal through the Toll-Like Receptor (TLR) pathway for inflammatory mediator production by macrophages. The objective of this study was to determine whether or not B. burgdorferi spirochetes (Bb) also signal through the TLR pathway, and if so, what components of this pathway are directly involved in the production of inflammatory mediators in macrophages in response to Bb. We first focused on MyD88, an adapter molecule that is essential in the TLR pathway for the induction of inflammatory mediators by TLR ligands. Our results revealed by real-time PCR, confocal microscopy and flow cytometry that MyD88 was maximally expressed in THP1 cells at 24 hr after stimulation of these cells with Bb. RNA interference (RNAi) of the MyD88 gene in THP1 cells revealed that silencing of the MyD88 gene using small interfering RNA resulted in 20%, 35% and 80% down-modulation of the production of TNF-α, IL-8 and IL-6, respectively in THP1 cells in response to Bb. RNAi silencing of TLR1, TLR2 or TLR5 further revealed that silencing of the TLR1 and TLR2 genes alone or combined, but not the TLR5 gene caused a down-regulation of IL-6, IL-8 and TNF-α in Bb-stimulated THP1 cells. Our results demonstrate that MyD88, TLR1 and TLR2 are, in part, involved in activation of the inflammatory response by B. burgdorferi spirochetes, and that there are alternative pathways also regulating inflammation in Lyme disease.