MIF production by dendritic cells is differentially regulated by Toll-like receptors and increased during rheumatoid arthritis

Macrophage migration inhibitory factor (MIF) is clearly associated with rheumatoid arthritis (RA) disease severity. However, the regulation of MIF during the course of RA has not been subjected to similar scientific scrutiny. The aim of our study was to investigate the role of various Toll-like receptors (TLRs) and inflammatory mediators on MIF production by dendritic cells (DCs) in healthy controls and RA patients. DCs were cultured from 12 healthy donors and 12 RA patients. Triggering via TLR mediated pathways was achieved using various TLR specific ligands alone or in combination: Pam3Cys for TLR2, LPS and recombinant extra domain A containing fibronectin for TLR4 and Poly(I:C) and R848 for TLR3 and TLR7, respectively. In addition, iDCs from healthy controls were incubated with various cytokines, RANKL and CD40L for 48 h. MIF levels were measured using an ELISA assay. Stimulation of DCs by TLR4 ligands resulted in higher MIF production compared to immature DCs from healthy controls (p<0.002) and RA patients (p<0.002). DCs from RA patients produced higher MIF levels than healthy controls both at the immature stage (p<0.04) as well after full maturation via TLR2 (p<0.04) and TLR4 (p<0.001) triggering. Incubation with TLR3 and TLR7 ligands resulted in a significantly decreased secretion of MIF in RA patients and controls. Simultaneous incubation of TLR4 with either TLR3 or TLR7 ligands resulted in a decrease of MIF secretion when compared to TLR4 stimulation alone. The secretion of MIF increased when DCs were stimulated with TNF-alpha, RANKL and CD40L. The secretion of MIF by dendritic cells is differentially regulated by TLRs. In addition, TNF-alpha, RANKL, and CD40L augment MIF production by DCs and thus play a potential role in the amplification of the inflammatory loop in RA.