Higher Monocyte Expression of TLR2 and TLR4, and Enhanced Pro-inflammatory Synergy of TLR2 with NOD2 Stimulation in Sarcoidosis

Introduction  Sarcoidosis is an inflammatory disease of unknown etiology. However, an infectious cause has been proposed suggesting a role for pattern-recognition receptors, such as Toll-like receptors (TLRs) and nucleotide-binding domain, leucin-rich repeat containing family proteins (NLRs), in the pathogenesis. Objective  Our aim was to investigate whether differences in TLR2 and TLR4 expression, and the response to TLR2, TLR4, and NOD2 stimulation, are associated with sarcoidosis. Materials and Methods  Blood mononuclear cells from sarcoidosis patients (n = 24) and healthy subjects (n = 19) were incubated with the TLR2 ligands PGN and Pam3CSK4, the TLR4 ligand LPS, the NOD2 ligand MDP, or medium alone. After 16 h, monocyte TLR2 and TLR4 expression and cytokine secretion, including TNFα, IL-1β, IL-6, IL-8, IL-10, and IL-12p70, were measured using flow cytometry and cytometric bead array. Results  TLR2 and TLR4 expression at baseline was significantly higher in patients. Combined TLR2 and NOD2 stimulation induced a four-fold higher secretion of TNFα and a 13-fold higher secretion of IL-1β in patients. Additionally, there was a synergistic effect of TLR2 with NOD2 stimulation on induction of IL-1β in patients, whereas IL-10 was synergistically induced in healthy subjects. Conclusion  Increased TLR expression and enhanced secretion of pro-inflammatory cytokines after combined TLR2 and NOD2 stimulation may be related to the pathogenesis of sarcoidosis. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. This study was supported by the Swedish Heart–Lung Foundation, King Oscar II Jubilee Foundation, the Swedish Research Council, the U.S. National Institutes of Health (Grant No. 1 R21 HL077579-01), the Stockholm County Council and Karolinska Institutet.