Zhao X, Gu M, Xu X, et al. - Investigators tried to find out the contributions of CCL2, CCL3, CCL4 and their cognate receptors in circulating monocyte chemotaxis and knee osteoarthritis (KOA) development. They identified the expression patterns of the chemokine receptors in CD14+CD16− circulating monocytes from KOA patients and healthy volunteers Utilizing flow cytometry staining. Utilizing chemokine neutralizing antibodies (NA) and receptor antagonists, the role of chemokines and their cognate receptors in the chemotaxis of CD14+CD16− circulating monocytes was evaluated in vitro and in vivo. The evidence showed that, analogous to the CCL2/CCR2 axis, CCL3 built-in osteoarthritic knees can chemoattract circulating monocytes to the inflamed synovium through CCR1.