Therefore, it is reasonable to assume that CX3CR1 would be more highly expressed on synovial monocytes than on peripheral monocytes, if the increase in synovial CD14+CD16+ monocytes observed here is due to selective migration from the periphery; however, the expression of CX3CR1 mRNA was found to be decreased considerably in synovial monocytes of RA patients (Fig. 4A). Here, CX3CR1 is linked to rheumatoid arthritis.