Effects of tocilizumab on neutrophil function and kinetics

Eur J Clin Invest. 2017 Oct;47(10):736-745. doi: 10.1111/eci.12799. Epub 2017 Aug 31.


Background: Decreases in circulating neutrophils (polymorphonuclear leucocytes, PMNs) have been reported in patients treated with the anti-interleukin-6 receptor (IL-6R) antibody tocilizumab (TCZ); the mechanism for this is unclear. We hypothesize that TCZ reduces circulating neutrophils by affecting margination and/or bone marrow trafficking without affecting neutrophil function or apoptosis.

Materials and methods: Eighteen healthy subjects were randomized to single intravenous dose of TCZ 8 mg/kg (n = 12) or placebo (n = 6) on day 0. On day 4, each subject had autologous indium-111-labelled neutrophils re-injected, and their kinetics quantified with longitudinal profiling in a whole body gamma-counter. TCZ-treated subjects were divided into two groups according to the extent of reduction in neutrophil count.

Results: Mean day 4 neutrophil counts, as % baseline, were 101·9%, 68·3% and 44·2% in the placebo, TCZ-PMN-'high' and TCZ-PMN-'low' groups, respectively (P < 0·001). Following TCZ, neutrophil function, activation and apoptosis ex vivo were all unaffected. In vivo, there were no differences in early blood recovery or margination to liver/spleen and bone marrow; however, later neutrophil re-distribution to bone marrow was markedly reduced in the TCZ-PMN-low group (peak pelvic count as % day 4 count on: day 5, 188% placebo vs. 127% TCZ-PMN-low, P < 0·001; day 10, 180% placebo vs. 132% TCZ-PMN-low, P < 0·01), with a trend towards higher liver/spleen neutrophil retention.

Conclusions: We have demonstrated for the first time in humans that IL-6R blockade affects neutrophil trafficking to the bone marrow without influencing neutrophil functional capacity.

Keywords: Interleukin-6; neutrophil; tocilizumab; trafficking.

Publication types

  • Comparative Study
  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Antibodies, Monoclonal, Humanized / administration & dosage*
  • Antibodies, Monoclonal, Humanized / pharmacokinetics
  • Apoptosis / drug effects*
  • Cell Movement / drug effects*
  • Healthy Volunteers
  • Humans
  • Infusions, Intravenous
  • Kinetics
  • Male
  • Middle Aged
  • Neutrophils / cytology
  • Neutrophils / drug effects*
  • Neutrophils / physiology
  • Reference Values
  • Sensitivity and Specificity
  • Single-Blind Method
  • Young Adult


  • Antibodies, Monoclonal, Humanized
  • tocilizumab