CCL2 and rheumatoid arthritis: Macrophages are considered to play a seminal part in cytokine production in the joints of patients with RA and represent a major source for most of the prominent mediators of disease, such as tumor necrosis factor (TNF)-α and interleukin (IL)-6, but also other cytokines and chemokines involved in the disease process, such as IL-1β, IL-8, and chemokine (C-C motif) ligand 2 (CCL2) (59).