Recognition of Borrelia burgdorferi, the Lyme Disease Spirochete, by TLR7 and TLR9 Induces a Type I IFN Response by Human Immune Cells

Abstract

Borrelia burgdorferi is the spirochetal agent of Lyme disease, a multisystemic disorder characterized by inflammation. Using global transcriptional profiling, we characterized the response of human PBMCs exposed to B. burgdorferi in an ex vivo coculture system. The expression profiles induced by B. burgdorferi were marked by the intense up-regulation of IFN-responsive transcripts and transcripts involved in the JAK/STAT signaling pathway. Transcript levels of IFN-α, IFN-β, and IRF7, and protein concentrations of IFN-α, were significantly elevated relative to those in unstimulated PBMCs. The induction of IFN-α was completely dependent upon phagocytosis of B. burgdorferi. Addition of a soluble type I IFN receptor, B18R, did not abolish the induction of IFN-inducible genes, indicating that B. burgdorferi directly elicits enhanced expression of these genes independently of type I IFN feedback signaling. Inhibitors of either TLR7 or TLR9 significantly reduced B. burgdorferi-stimulated IFN-α protein expression and transcription of IFN-induced genes. Simultaneous inhibition of both TLR7 and TLR9 completely abrogated IFN-α induction. The IFN-α-producing populations in PBMCs were identified as plasmacytoid dendritic and CD14+CD11c+ cells. These results reveal a TLR7/9-dependent signaling pathway used by human PBMCs to initiate a type I IFN response to the extracellular bacterium B. burgdorferi.

Phagosomal signaling byBorrelia burgdorferiin human monocytes involves Toll-like receptor (TLR) 2 and TLR8 cooperativity and TLR8-mediated induction of IFN-β

“…Specific immunoregulatory DNA sequences (IRSs; Integrated DNA Technologies) (31) were used to block TLR7 signaling (IRS661: 5′-TGCTTGCAAGCTTGCAAGCA-3′), TLR7 and TLR8 (IRS957: 5′-TGCTTG-AC-ATCCTGGAGGGGTTGT-3′), and TLR9 (IRS869: 5′-TCCTGGAGGGGTTGT-3′) as described by Petzke et al (22). A non-TLR-specific oligodeoxyribonucleotide sequence was used as a control, in the same concentration as the TLR inhibitor.…”

“…Bacteria can elicit type I IFNs either by activating TLRs (11,12) or through TLR-independent recognition of bacterial pathogenassociated molecular patterns (PAMPs) within the host cell cytosol (11,18). We and others have begun to demarcate the pathways by which live Bb induces type I IFNs in both mouse and human cells (7,(19)(20)(21)(22). Miller et al (20) demonstrated that live Bb induces transcription of several ISGs in bone marrow-derived murine macrophages (BMDMs) independent of both MyD88 (20) and TRIF (21) yet requiring the transcription factor IFN regulatory factor (IRF) 3.…”

“…Miller et al (20) demonstrated that live Bb induces transcription of several ISGs in bone marrow-derived murine macrophages (BMDMs) independent of both MyD88 (20) and TRIF (21) yet requiring the transcription factor IFN regulatory factor (IRF) 3. Using Bb-infected human peripheral blood mononuclear cells (PBMCs), Petzke et al (22) provided evidence that human plasmacytoid dendritic cells (pDCs) are a principal source of IFN-α in response to phagocytosed live spirochetes and demonstrated that transcription and secretion of this type I IFN was inhibited by blocking TLR7 and TLR9. These two TLRs, together with TLR8, make up a family of endosomal pattern recognition receptors that are capable of generating MyD88-dependent type I IFNs by sensing pathogen-derived nucleic acids (23,24).…”

“…To explore this possibility, we took advantage of the availability of specific inhibitory DNA-oligonucleotide sequences (IRSs) that have the ability to block ligation of TLR7, TLR8, or TLR9 (31,32). These inhibitors were recently used by Petzke et al (22) to demonstrate that induction of IFN-α in Bb-infected pDCs is dependent on TLR7 and TLR9. For these experiments, we first corroborated that healthy volunteers' monocytes expressed TLR7 and TLR8 and very little TLR9 (27) (Table S1).…”

The role of Toll-like receptors in skin diseases

“…Niedobór TRIF nie wpływa jednak, w przeciwieństwie do niedoboru MyD88, na osłabienie odpowiedzi na infekcję krętkami u myszy [36]. W rozpoznaniu Borrelia burgdorferi biorą udział również receptory TLR7 i TLR9, indukując wydzielanie interferonu przez komórki immunologiczne [37].…”