Helen L Wright1, Andrew L Cross1, Steven W Edwards1, Robert J Moots2. 1. Institute of Integrative Biology, University of Liverpool and Institute of Ageing and Chronic Disease, University Hospital Aintree, Liverpool, UK. 2. Institute of Integrative Biology, University of Liverpool and Institute of Ageing and Chronic Disease, University Hospital Aintree, Liverpool, UK. rjmoots@liv.ac.uk.
Abstract
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.
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 RApatients, 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 RApatients 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.
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