CCL5 and rheumatoid arthritis: Exposure of SF to synovial fluid of RA patients has been shown to activate the JAK-STAT signaling pathway [41,42] and the receptors of many cytokines and chemokines that play important roles in the pathogenesis of RA—such as IL-6, RANTES, MCP-1, IP-10, OSM, and IFNs—directly transmit signals via the JAK-STAT pathway [43].