CCL2 and rheumatoid arthritis: The chemotaxis, survival and proliferation pathways in mononuclear cells can be activated by chemokines [44], including chemokine ligand 2 (CCL2, also known as monocyte chemoattractant protein-1 (MCP-1), a critical regulator in the process of monocyte migration and infiltration to the site of RA inflammation, as CCL2/MCP-1 is produced at significantly higher levels in blood, synovial fluid and synovial tissue from patients with RA compared with samples from non-RA controls [45,46].