IL6 and rheumatoid arthritis: Currently, C-reactive protein (CRP) level is used clinically as a biomarker of IL-6 activity and inflammation in RA.4 After binding to IL-6 receptor (IL-6R), IL-6 stimulates the synthesis of CRP through activation of the Janus kinase signaling pathway.1 Elevated IL-6 levels in patients with RA correlate with disease activity.