CD4 and osteoarthritis: Iguratimod has been demonstrated to successfully suppress IL-6, TNF-α, IL-8, IL-1β, and monocyte chemotactic protein 1 (MCP-1) in various inflammatory cell cultures.23 The relatively new cytokine IL-17, which is secreted by CD4+ T lymphocytes, has been considered equally important to TNF-α, and has been reported as one of the main cytokines in the RA synovial milieu compared with osteoarthritis.24 In addition, other T-cell lineages, such as Th1, CD4+, and CD25+ T-regulatory cells (Treg) and T follicular helper (Tfh) cells, have also been found in the synovium of RA-infected joints.25