An in vitro chemotaxis assay revealed monocyte migration in response to RA synovial fluid, which was attenuated by pre-incubation for 30 min with an anti-CCL2 neutralizing antibody; no such effect was seen with anti-CCN1 neutralizing antibody (Fig. 1D), implying that CCL2 is an important factor in monocyte infiltration during RA. Here, CCL2 is linked to rheumatoid arthritis.