Change in serum IL-6 after administration of tocilizumab. Serum IL-6 increased after tocilizumab infusion and reached steady state at different levels in patients with RA (●; n = 5), patients with Castleman disease (■; n = 28), and healthy volunteers (▵; n = 4). Points and error bars show geometric means plus or minus SEs. *Samples from healthy volunteers were drawn on day 7.