Effects of IL-6 and IL-6 blockade on neutrophil function in vitro and in vivo

Rheumatology (Oxford). 2014 Jul;53(7):1321-31. doi: 10.1093/rheumatology/keu035. Epub 2014 Mar 7.


Objectives: Reports on the regulation of neutrophil function by IL-6 are often conflicting. Therapeutic inhibition of IL-6 in RA is associated with occasional neutropenia, but the mechanisms underlying this observation are poorly understood. This study investigated interactions between IL-6, the anti-IL-6 receptor agent tocilizumab (TCZ) and neutrophils in vitro and in vivo.

Methods: Neutrophils were isolated from healthy controls and incubated in vitro with pharmacologically relevant concentrations of IL-6 or TCZ. Neutrophils were also isolated from RA patients, including a cohort following TCZ therapy. Apoptosis was measured by annexin V/propidium iodide (PI) flow cytometry; phagocytosis was measured by incubating apoptotic neutrophils with THP-1-derived macrophages; chemotaxis was measured using cell migration through hanging-cell inserts towards IL-8 and cell surface proteins, including adhesion molecules CD11b (αMβ2 integrin) and CD62L (L-selectin) were measured by flow cytometry.

Results: IL-6 (10-100 ng/ml) did not affect the rate of neutrophil apoptosis, priming of the respiratory burst or adhesion molecule expression nor act as a neutrophil chemoattractant. However, IL-6 enhanced signal transducer and activator of transcription 3 (STAT3) activation and neutrophil migration towards IL-8. TCZ in vitro did not induce apoptosis or phagocytosis of neutrophils, nor did it have a significant effect upon apoptosis or cell surface molecule expression. Neutrophil functions in ex vivo neutrophils from RA patients receiving TCZ treatment were unaffected.

Conclusion: Therapeutic blockade of IL-6, while inducing a transient neutropenia, does not directly affect neutrophil functions associated with host defence. TCZ-associated neutropenia cannot be explained by direct induction of apoptosis by TCZ, induction of apoptosis following depletion of IL-6, nor increased phagocytosis of neutrophils.

Keywords: IL-6; neutropenia; neutrophil; rheumatoid arthritis; tocilizumab.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Antibodies, Monoclonal / adverse effects
  • Antibodies, Monoclonal / pharmacology
  • Antibodies, Monoclonal / therapeutic use
  • Antibodies, Monoclonal, Humanized / adverse effects
  • Antibodies, Monoclonal, Humanized / pharmacology*
  • Antibodies, Monoclonal, Humanized / therapeutic use*
  • Apoptosis / drug effects
  • Apoptosis / physiology
  • Arthritis, Rheumatoid / drug therapy*
  • Arthritis, Rheumatoid / pathology
  • Arthritis, Rheumatoid / physiopathology
  • Case-Control Studies
  • Cell Movement / drug effects
  • Cell Movement / physiology
  • Chemotaxis / drug effects
  • Chemotaxis / physiology
  • Female
  • Humans
  • In Vitro Techniques
  • Interleukin-6 / antagonists & inhibitors*
  • Interleukin-6 / immunology
  • Interleukin-6 / pharmacology*
  • Male
  • Middle Aged
  • Neutropenia / etiology
  • Neutrophils / drug effects*
  • Neutrophils / pathology
  • Neutrophils / physiology
  • Phagocytosis / drug effects
  • Phagocytosis / physiology
  • STAT3 Transcription Factor / metabolism
  • Signal Transduction / drug effects
  • Signal Transduction / physiology


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • Interleukin-6
  • STAT3 Transcription Factor
  • STAT3 protein, human
  • tocilizumab