CX3CL1 and rheumatoid arthritis: In RA patients, fractalkine has been detected in the synovial fluid, in peripheral blood and in inflamed synovial membranes, often at concentrations several times higher than those seen in other arthropathies, including OA (Endres et al. 2010; Nanki et al. 2002; Ruth et al. 2001; Yano et al. 2007).