CCL2 and rheumatoid arthritis: TNF-α is a major factor of RA development within the synovial niche, as human synovial fibroblasts cultured in presence of TNF-α display increased expression of IL-1β, monocyte chemoattractant protein-1 (MCP1), macrophage inflammatory protein-1 alpha (MIP1α), MMP-1, MMP-3 and receptor activator of nuclear factor-κB ligand (RANKL), an osteoclastogenic cytokine, compared to control cells [25].