Abstract
Neutrophil surveillance is central to nanoparticle clearance. Silver nanoparticles (AgNP) have numerous uses, however conflicting evidence exists as to their impact on neutrophils and whether they trigger damaging inflammation. Neutrophil’s importance in innate defence and regulating immune networks mean it’s essential we understand AgNP’s impact on neutrophil function. Human neutrophil viability following AgNP or Ag Bulk treatment was analysed by flow cytometry and AnV/PI staining. Whilst AgNP exposure did not increase the total number of apoptotic neutrophils, the number of late apoptotic neutrophils was increased, suggesting AgNP increase transit through apoptosis. Mature (CD16bright/CD62Lbright), immature (CD16dim/CD62Lbright) and apoptotic (CD16dim/CD62Ldim) neutrophil populations were evident within isolated neutrophil preparations. AgNP exposure significantly reduced CD62L staining of CD16bright/CD62Lbright neutrophils, and increased CD16 staining of CD16dim/CD62Lbright populations, suggesting AgNPs trigger neutrophil activation and maturation, respectively. AgNP exposure dramatically increased IL-8, yet not classical pro-inflammatory cytokine release, suggesting AgNP triggers neutrophil activation, without pro-inflammation or damaging, necrotic cell death. For the first time, we show AgNPs differentially affect distinct sub-populations of circulating human neutrophils; activating mature neutrophils with the emergence of CD16bright/CD62Ldim neutrophils. This may stimulate particle clearance without harmful inflammation, challenging previous assumptions that silver nanomaterials induce neutrophil toxicity and damaging inflammatory responses.
Highlights
Analyses of the impact of particles, either nanoparticle or air pollution, on biological systems have recognised the importance of neutrophil surveillance in particle clearance
CD62L expression is gradually lost as neutrophils transit the circulation and age, and CD62Ldim neutrophils are preferentially eliminated from the circulation by macrophage clearance in the spleen, liver and bone marrow[8,10]
We investigated the impact of silver nanoparticles on circulating human neutrophil heterogeneity and the emergence of neutrophil subsets, by assessing CD16 and CD62L cell surface expression
Summary
Analyses of the impact of particles, either nanoparticle or air pollution, on biological systems have recognised the importance of neutrophil surveillance in particle clearance. As the first line of defence against invading pathogens, circulating neutrophils are rapidly recruited to sites of inflammation associated with infection or particle exposure[2] They become activated, and phagocytose and destroy microbes by releasing proteases, cationic defence peptides and reactive oxygen species[3]. Billions of neutrophils are mobilised from the bone marrow daily under normal homeostasis, and peripheral blood contains a heterogeneous population of neutrophils at various stages of maturity, mobility and activity[8] These can be distinguished by their differential expression of cell surface markers. CD62L expression is gradually lost as neutrophils transit the circulation and age, and CD62Ldim neutrophils are preferentially eliminated from the circulation by macrophage clearance in the spleen, liver and bone marrow[8,10]. Plasticity in neutrophil function and phenotype has been documented, and the prevalence of neutrophils in different sub-populations can alter in response to environmental factors (reviewed by7); neutrophils are clearly more versatile and dynamic than previously anticipated
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