CCL2 and rheumatoid arthritis: The role of CCR4 in inducing migration has been shown utilizing different disease models; for example, in prostate cancer, tumor-associated macrophages promote metastasis via the activation of the CCL2-CCR2 or the CCR4 axis, whereas circulating monocytes from patients with rheumatoid arthritis (RA) showed a high expression of CCR4, suggesting that CCR4-dependent migration is required for monocyte recruitment to the joint [40, 41].