Rheumatoid arthritis (RA) is a systemic, chronic inflammatory disease that is characterized by T helper 17 (Th17) cell- and osteoclast-induced joint destruction and inflammation. In RA, several cytokines (interleukin (IL)-1, 6,17, and tumor necrosis factor (TNF)) are involved in almost all aspects of articular inflammation and destruction. This study aimed to evaluate the combinatorial effect of TNF and IL-6 inhibitors on the differentiation and activation of Th17 cells and osteoclasts in the context of RA, and to identify the RA-related mechanisms through IL-6 signaling. Tetrahydropapaverine (THP) showed direct binding to TNF in screening-ELISA, and SPR and TNF-neutralization assays. In a previous study, the therapeutic effect of gp130-targeting LMT-28 was confirmed in RA. Combinatorial treatment with LMT-28 and THP reduced the arthritis index and showed protective effects against bone and cartilage destruction in CIA mice. The secretion levels of TNF, IL-6, and IL-1 beta significantly decreased upon combinatorial treatment with LMT-28 and THP. Further, the LMT-28 and THP combination suppressed the differentiation and activation of Th17 cells in mouse splenocytes and human PBMCs. In human RA-FLS, the LMT-28 and THP combination inhibited cell proliferation and downregulated IL-6 and/or TNF-mediated signaling relative to that observed upon independent treatment with LMT-28 or THP. Furthermore, the combination of LMT-28 and THP significantly inhibited the differentiation of mouse bone marrow monocytes (BMMs) into osteoclasts. In conclusion, the LMT-28 and THP combination can attenuate RA through the inhibition of Th17 differentiation and osteoclastogenesis, and suppression of IL-6 or TNF-induced signaling pathways. This combinatorial therapy could be used as a new strategy for the treatment of RA. (C) 2019 Elsevier Inc. All rights reserved.