TNF and rheumatoid arthritis: Regarding the effect of bDMARD therapy on the Wnt signaling in RA, most of the relevant studies were conducted with TNFα inhibitors [34, 41] or an IL-6 receptor (IL-6R) inhibitor, tocilizumab [18, 19], and they showed a decrease in the serum level of Dkk-1 in RA patients undergoing these bDMARD treatments.