CCL2 and rheumatoid arthritis: To the best of our knowledge, the current study is the first to investigate the effects of tofacitinib on such a large range of inflammation-associated plasma proteins in RA patients in vivo. Previous in vitro studies have shown tofacitinib to suppress the production of IL-6, IL-17, IFN-γ, CCL2, CXCL9, CXCL10, and CXCL11 by RA T cells, macrophages, and fibroblasts [11–15].