IL6 and rheumatoid arthritis: Tocilizumab is a humanized monoclonal antibody that inhibits IL-6 signaling, including production of CRP.2 In patients with RA, tocilizumab treatment normalizes CRP levels as long as the free serum tocilizumab concentration remains ≥1 μg/mL.4 This suggests that CRP levels are a useful biomarker of tocilizumab activity.