Human TLR8 is activated upon recognition ofBorrelia burgdorferiRNA in the phagosome of human monocytes

• DOI: 10.1189/jlb.0413206
• Publication Date: 2013-08-02T05:02:09Z
• Authors: Jorge L Cervantes; Carson J La Vake; Bennett Weinerman; Stephanie Luu; Caitlin O'Connell; Paulo H Verardi; Juan C Salazar
• Keywords: Male; Lyme Disease; 0303 health sciences; Transcription, Genetic; Interferon-beta; Monocytes; 3. Good health; RNA, Bacterial; 03 medical and health sciences; HEK293 Cells; Interleukin-1 Receptor-Associated Kinases; Toll-Like Receptor 7; Toll-Like Receptor 8; Borrelia burgdorferi; Gene Knockdown Techniques; Phagosomes; Myeloid Differentiation Factor 88; Humans; Female

ABSTRACT Phagocytosed Borrelia burgdorferi (Bb), the Lyme disease spirochete, induces a robust and complex innate immune response in human monocytes, which TLR8 cooperates with TLR2 induction of NF-κB-mediated cytokine production, whereas is solely responsible for transcription IFN-β through IRF7. We now establish role Bb RNA TLR8-mediated IFN-β. First, using TLR2-transfected HEK.293 cells, were unable to phagocytose intact Bb, we observed activation by lipoprotein-rich borrelial lysates synthetic ligands but not live spirochetes. Purified RNA, DNA, triggered activation. Neither these 2 induced TLR7. Using purified monocytes then show that phagocytosed as well equivalent amounts delivered into phagosome polyethylenimine (PEI), secretion TNF-α. The was markedly impaired naturally deficient IRAK-4 cells knockdown expression small interfering RNA. confocal microscopy provide evidence colocalizes internalized both early (EEA1) late endosomes (LAMP1). Live bacterial staining indicates spirochetal does transfer from cytosol. fluorescent dextran particles phagosomal integrity Bb-infected affected. demonstrate, first time, ligand spirochete within vacuole TLR8-MyD88 pathway.