Systematic analysis highlights the key role of TLR2/NF-κB/MAP kinase signaling for IL-8 induction by macrophage-like THP-1 cells under influence of Borrelia burgdorferi lysates

Abstract

Lyme borreliosis is a spirochetal infection caused by the Borrelia burgdorferi sensu lato complex that can proceed towards an inflammatory joint manifestation known as Lyme arthritis. Production of chemokines orchestrating neutrophil infiltration is supposed to be key to early arthritic pathogenesis. Using PMA-differentiated macrophage-like THP-1 (mTHP-1) cells we identified by antibody array methodology or mRNA analysis IL-8, GRO-α, NAP-2, and SDF-1α as being among those chemokines that are upregulated by bacterial lysates obtained from B. burgdorferi. Based on these observations, we set out to characterize in detail mechanisms mediating IL-8 release in this cellular model. TLR2 blocking antibodies, analysis of p65 translocation, and electromobility-shift analysis revealed activation of the TLR2/NF-κB axis by B. burgdorferi. The functional importance of this pathway was substantiated by suppression of IL-8 after inhibition of IκB kinase. Notably, MAP kinases, specifically the MEK1/2–ERK1/2 pathway, were essential for IL-8 secretion. Those data were confirmed by using freshly isolated adherent peripheral blood mononuclear cells. On the contrary, B. burgdorferi-induced IL-8 in mTHP-1 was unlikely related to flagellin, α3β1-integrin signaling, lipopolysaccharide, bacterial DNA, NOD1/NOD2 agonists, or to intermediate production of IL-1β and TNF-α. Induction of IL-8 by B. burgdorferi was not due to amplification of constitutive AP-1 DNA-binding activity detectable in mTHP-1 cells. Data presented herein validate that TLR2, particularly on mTHP-1 cells, holds a central position in mediating IL-8 secretion associated with extracellular B. burgdorferi and beyond that suggest inhibition of IκB kinase and MEK1/2 kinases as promising pharmacological strategies aiming at IL-8 in early Lyme arthritis.