Background and objectives Rheumatoid arthritis (RA) is the most common chronic inflammatory rheumatism. Identification of autoantigens targeted by RA autoantibodies has been of major interest. Alpha-enolase (ENO1) is considered as a pivotal autoantigen in early RA. Whatever the nature of this molecule, its role in RA pathophysiology remains unknown. The main objective of this study was to investigate the in vitro effects of soluble ENO1 on peripheral blood mononuclear cells (PBMCs) from healthy donors and RA patients in order to determine the potential pathogenic role of ENO1.

Materials and methods PBMCs of healthy donors or RA patients were cultured with ENO1 or control. ELISA and transcriptomic analysis were performed to assess the pro- or anti-inflammatory effect of ENO1. Moreover, flow cytometry analysis, experiments of receptor inhibition and ELISA were performed to determine the target cell population and receptor of ENO1.

Results Firstly, we showed that ENO1 has the ability to induce the production of a large amount of pro-inflammatory cytokines and chemokines, and to activate the innate immune system on PBMCs from healthy donors. ENO1 also exhibits this pro-inflammatory effect on cells from RA patients. Then, we demonstrated that ENO1, which exclusively bound monocytes, exhibited a LPS-like action mediated by TLR4. More precisely, the effects of ENO1 specifically involved the CD14-dependent TLR4 pathway.

Conclusions Together, these findings illustrate for the first time that ENO1 triggers in vitro an inflammatory response mediated by monocytes through the CD14-dependent TLR4 pathway and contribute to elucidate the role of this autoantigenin the RA pathophysiological mechanisms.