Saito S, et al. - The purpose of this study is to report the development of a test for evaluating the strength of IL-6 signal inhibition and examination of the variables related to IL-6 signaling in rheumatoid arthritis (RA) patients who were treated with tocilizumab (TCZ). Evaluation of the proportion of pSTAT3-positive CD4+ T cells under IL-6 stimulation is a highly sensitive and valuable method for ascertaining differences in the strength of IL-6 signal inhibition in patients treated with TCZ. It is proposed that different TCZ treatment intervals were necessary to lower disease activity in each group of patients, and these outcomes also indicate that the IL-6 signaling pathway may differ in each RA patient. This test may support strategies for optimizing TCZ treatment in RA patients.