['We aimed to assess the effect of tocilizumab (TCZ), an IL-6 receptor inhibitor, on B, T, NK and NKT cells in patients with RA and to study the cell type predictors of remission. We also compared NK cells in patients with RA and in controls.', 'RA patients included in the study met the 2010 ACR/European League Against Rheumatism (EULAR) criteria, were receiving stable doses of steroids and had not received rituximab in the previous year. Different B and T cell subsets, NK cells and NKT cells were assessed by flow cytometry along with perforin A and granzyme B to estimate NK cell cytotoxicity.', 'We included 92 RA patients, including 20 requiring TCZ treatment and 15 requiring anti-TNF drugs, and 25 controls. At baseline, the proportion of CD56(dim)CD16(+)CD3(-) NK cells was inversely correlated with the 28-joint DAS (DAS28). In TCZ-treated patients, the baseline proportion of CD3(-)CD56(+) NK cells was inversely correlated with the change in DAS28 at 3 months and the proportion was 3-fold greater for patients with DAS28 remission at 3 months than other patients. Change in the proportion of CD56(bri)CD16(-) NK cells was linearly correlated with change in the DAS28 at 3 months. The baseline proportion of NK cells did not predict change in disease activity at 3 months with anti-TNF therapy. The perforin content in NK cells increased with TCZ treatment.'] Are high levels of natural killer cells associated with response to tocilizumab in patients with severe rheumatoid arthritis?