CX3CL1 and rheumatoid arthritis: CX3CL1, also known as Fractalkine, is primarily secreted by endothelial cells and neurons [43], and is closely associated with the pathogenesis of inflammatory diseases such as atherosclerosis, renal fibrosis, rheumatoid arthritis, and both acute and chronic neurodegenerative diseases of the central nervous system (CNS) [44].