CCL2 and rheumatoid arthritis: Specifically, the top six induced cytokines, the so called six cytokine set [IL-6, regulated upon activation, normal T cell expressed and presumably secreted (RANTES), growth regulated oncogene-alpha (GRO-α), MCP-1, IL-8, and IP-10] were among the 25% most abundant cytokines in RA synovial fluid (out of 48 measured) (39).