Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Nano-bio interactions: a neutrophil-centric view

Abstract

Neutrophils are key components of the innate arm of the immune system and represent the frontline of host defense against intruding pathogens. However, neutrophils can also cause damage to the host. Nanomaterials are being developed for a multitude of different purposes and these minute materials may find their way into the body through deliberate or inadvertent exposure; understanding nanomaterial interactions with the immune system is therefore of critical importance. However, whereas numerous studies have focused on macrophages, less attention is devoted to nanomaterial interactions with neutrophils, the most abundant leukocytes in the blood. We discuss the impact of engineered nanomaterials on neutrophils and how neutrophils, in turn, may digest certain carbon-based materials such as carbon nanotubes and graphene oxide. We also discuss the role of the corona of proteins adsorbed onto the surface of nanomaterials and whether nanomaterials are sensed as pathogens by cells of the immune system.

Known facts

  • Nanomaterials are inevitably cloaked with proteins giving rise to a bio-corona.

  • Nanomaterials can trigger inflammation with activation of the inflammasome.

  • Carbon-based materials may undergo digestion by macrophages or neutrophils.

Open questions

  • Does the innate immune system sense engineered nanomaterials as pathogens?

  • Are nanomaterial-induced neutrophil extracellular traps or NETs good or bad?

  • Can nanomaterials elicit exosome-mediated pro- or anti-inflammatory signals?

Introduction

Inflammation is a complex biological response involving soluble factors and cells that arises in a tissue in response to harmful stimuli including pathogens, toxicants, or dead cells. The process normally leads to recovery and healing. However, inflammation can also lead to persistent tissue damage and may even promote neoplastic transformation1,2. Indeed, the distinction between acute and chronic inflammation is important, not least in toxicology. Inflammation is fundamentally a normal, protective physiological response to injury or infection. However, if inflammatory responses are persistent due to an exaggerated or dysregulated response, including failure of resolution of inflammation, a pathological response occurs3.

Understanding interactions of engineered nanomaterials with the immune system is of considerable relevance both from a toxicological and biomedical perspective4. However, whereas numerous publications have focused on nanomaterial interactions with macrophages, less attention is devoted to neutrophils, despite the fact that neutrophils are key factors in inflammation. In fact, research in recent years has revealed that these cells may also inform and shape adaptive immune response, in addition to their traditional roles as hunters and killers of microbes5. Furthermore, although this has previously been overlooked, neutrophils also express a rich repertoire of so-called pattern recognition receptors or PRRs6. We will focus here on the interactions of engineered nanomaterials with neutrophils, the most abundant of the white blood cells.

Nanomaterial effects on neutrophils

Neutrophils are key factors in inflammation and numerous studies have shown that engineered nanomaterials may elicit acute and/or chronic inflammation in different animal models7. However, despite numerous studies showing tissue infiltration of neutrophils upon exposure to nanoparticles, it can be argued that neutrophils are a somewhat neglected cell in nanotoxicology, as there are relatively few studies on direct interactions of nanomaterials with these cells. Nevertheless, neutrophils are normally the first responders in an inflammatory reaction while macrophages arrive in the second wave of inflammation and serve mainly to remove cell debris and to promote tissue healing8. Similarly, it is worth noting that macrophages are not the only cells that are involved in the clearance of nanoparticles from the blood; in fact, a recent study showed that neutrophils also play a major role in nanoparticle clearance, at least in some mouse strains9. Notably, although neutrophils are cleared from the circulation via the liver and spleen, evidence has been put forward that the bone marrow is a major site of neutrophil clearance10. It follows that nanoparticles that are cleared from the circulation by neutrophils could end up in the bone marrow and yet the bone marrow is frequently overlooked as a possible site for the sequestration of nanoparticles, as particle uptake by macrophages in the liver or spleen is usually in focus11.

Girard and colleagues12,13,14,15 have published a series of papers in which various metal and metal oxide nanoparticles including nanoparticles of titanium dioxide, zinc oxide, and silver were shown to activate neutrophils and/or to inhibit neutrophil apoptosis. In contrast, gold nanoparticles were found to activate or accelerate neutrophil apoptosis16. Needless to say, careful attention to endotoxin contamination of the tested particles is required17. Other authors have shown that silver nanoparticles differently affect distinct subpopulations of neutrophils18. Fromen et al.19 documented interactions between injected nanoparticles and circulating neutrophils, which could drive particle clearance but could also alter neutrophil responses in a mouse model of acute lung injury. The attachment of poly(ethylene glycol) (PEG) onto the surface of nanoparticles is commonly thought to prevent particle opsonization and macrophage uptake. However, a recent study suggested, instead, that neutrophils preferentially internalized PEGylated particles (i.e., polystyrene microspheres) in the presence of human plasma20. Notably, when the authors used model cell lines such as HL-60 or THP-1 cultured in standard cell medium supplemented with 10% fetal bovine serum, PEGylation reduced uptake of the particles. However, when these cells were cultured in human plasma, the PEGylated particles were more avidly taken up, in line with the results obtained with primary cells20. This suggests that nanomedicine approaches based on PEGylation of nanoparticles need to be reconsidered—perhaps the administered particles with their “shield” of surface-attached polymers are being sequestered by neutrophils in the blood? Bisso et al.21 conducted an in-depth study of nanomaterial interactions with human neutrophils focusing on polymeric and liposomal particles ranging in size from 20 nm to 5 µm. The authors found that nanoparticles were readily internalized by neutrophils ex vivo in the absence of serum proteins, and that the internalization was size-dependent insofar as a significant increase in uptake of the 200 nm particles was observed over particles < 100 nm in diameter. The inclusion of albumin in the cell culture medium prevented uptake of polystyrene particles and reduced the uptake of liposomal nanoparticles, but enhanced neutrophil uptake of poly(lactic-co-glycolic acid) (PLGA) particles. Notably, particle-laden neutrophils (i.e., 1 µg/mL of polystyrene particles or 5 µg/mL of liposomes) were found to undergo normal degranulation upon stimulation with conventional agonists21.

Carbon-based nanomaterials, including carbon nanotubes (CNTs), are widely studied in nanotoxicology22 and these materials were shown to trigger apoptosis and/or autophagic cell death in macrophages (Box 1). Less is known in regards to neutrophils. In a recent study conducted in the frame of the Horizon2020 project BIORIMA, the toxicity of three multi-walled CNTs (MWCNTs) with varying physicochemical properties was evaluated in neutrophils vs. macrophages. Macrophages were susceptible only to the fiber-like MWCNTs, but neutrophil cell viability was significantly affected by all three CNTs, both long and tangled (Keshavan et al., manuscript in preparation). Thus, although macrophages are capable of ingesting nanomaterials and are widely used as a model in nanotoxicology, neutrophils should not be ignored.

Bio-corona formation on nanoparticles

Nanomaterials promptly adsorb biomolecules leading to the formation of a so-called bio-corona23. The binding of proteins or other biomolecules to nanoparticle surfaces may thereby afford a new “identity” to the nanoparticle24. Deng et al.25 showed that poly(acrylic acid)-coated gold nanoparticles bind fibrinogen, a protein involved in blood clot formation, in a charge-dependent manner, inducing unfolding of the protein, and that binding to integrin receptors on the surface of the monocytic cell line, THP-1 leads to activation of the nuclear factor-κB pathway and secretion of the pro-inflammatory cytokine tumor necrosis factor-α. In a comprehensive study using a panel of silica and polystyrene nanoparticles of various sizes and surface modifications, Tenzer et al.26 could show that plasma protein adsorption occurs very rapidly, and that it affects hemolysis, thrombocyte activation, cellular uptake, and endothelial cell death. Vlasova et al.27 reported that adsorbed plasma proteins influenced neutrophil responses caused by polymer-coated, single-walled CNTs (SWCNTs). Specifically, the adsorption of IgG resulted in neutrophil activation, as determined by degranulation and release of myeloperoxidase (MPO). Similarly, protein adsorption modulated neutrophil responses toward carboxylated, non-PEGylated SWCNTs28. Lara et al.29 employed an immuno-mapping technique to study epitope presentation of two major proteins in the serum corona, low-density lipoprotein (LDL) and immunoglobulin G. The authors could show that both proteins displayed functional motifs allowing for recognition of the bio-corona on silica nanoparticles by LDL receptor and Fc-γ receptor I, respectively. On the other hand, others have pointed out that the bio-corona could shield targeting ligands on nanoparticles30. However, recent studies suggested clever ways in which to circumvent this problem31,32. Furthermore, purposeful surface modification of CdSe/ZnS quantum dots to induce a protein misfolding event in the bio-corona enabled receptor-mediated endocytosis of the particles33. Bisso et al.21 reported that the presence of serum reduced the ex vivo uptake of poly(styrene) nanoparticles and liposomes by neutrophils and enhanced the uptake of micro- and nanosized PLGA particles. However, the composition of the bio-corona and the role of specific proteins for neutrophil uptake, or lack thereof, was not examined. Furthermore, neutrophils were found to preferentially internalize PEGylated particles20. The authors noted that this is linked to factor(s) in human plasma and provided some evidence for a role of complement. Complement factors also facilitate phagocytosis of apoptotic cells and microbes4.

Viruses are natural nanoparticles and it is not surprising that a bio-corona of proteins may form on viruses in various biological fluids, or that the bio-corona may affect immune responses to viruses34. Indeed, the adsorbed bio-corona could be considered as part of the motifs that are sensed by immune cells. Hence, the boundaries between pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) apparently begin to dissolve at the nano-bio interface, as both engineered and natural nanoparticles (i.e., viruses) adsorb host proteins on their surface. This topic is discussed in more detail below.

Exosomes: message in a bottle

Exosomes are nanosized extracellular vesicles that are naturally secreted by cells and they may play a particularly important role in conveying information between immune cells35. Exosomes were initially thought to fulfill a janitorial function by providing the cell with a means of getting rid of non-functional proteins and other molecules. Subsequent studies suggested important roles of exosomes in intercellular communication and the interest in exosomes and other microvesicles has escalated in the past two decades due to their emerging roles in health and disease36. Exosomes thus harbor specific proteins and nucleic acids, mostly small RNAs, such as ribosomal RNA, transfer RNA, microRNA, and mRNA molecules36. Exosomes from activated neutrophils were recently reported to acquire surface-bound neutrophil elastase (NE) and the exosomes were shown to degrade extracellular matrix components causing the hallmarks of chronic obstructive pulmonary disease37. Exosomal NE was much more potent than free NE. In the latter study, neutrophils were activated with the bacterial peptide, formyl-methionine-leucine-phenylalanine (fMLP), a known neutrophil agonist. Whether or not such exosome-mediated pathological responses occur following nanomaterial exposure merits close attention; several studies have shown that CNTs cause pulmonary inflammation as well as airway remodeling38. In a seminal study, Zhu et al.39 reported that exosomes were generated in significant numbers in the lungs of mice exposed to iron oxide nanoparticles, and noted that the exosomes were quickly transferred to the systemic circulation, thereby conveying immune activation in extrapulmonary organs. The authors inferred that the exosomes were of macrophage origin, although further studies are warranted to discern the source of nanoparticle-induced exosomes and whether neutrophils are also involved. Studies have shown that different metal or metal oxide nanoparticles may elicit varying cellular patterns of inflammation and one cannot a priori assume that macrophages are the only cell type at play40. In another recent study, ZnO nanoparticles were found to trigger neutrophilic inflammation in rats and numerous microRNAs were shown to be selectively up- or downregulated in serum exosomes from ZnO-exposed animals when compared with controls41. Using single-particle inductively coupled plasma-mass spectrometry and other techniques, Logozzi et al.42 reported that primary human macrophages are capable of endocytosis of gold nanoparticles (20 nm) with subsequent discharge of the nanoparticles via exosomes. Further studies are required to determine whether this is a general phenomenon and to what extent the exosomal content of nanoparticles correlates with the delivered dose. Nevertheless, it is conceivable that exosomes could be exploited as biomarkers of exposure to nanoparticles42.

Neutrophil traps: a necessary nuisance?

Brinkmann et al.43 reported 15 years ago that neutrophils kill pathogens extracellularly by releasing so-called neutrophil extracellular traps or NETs. NETs are comprised a backbone of nuclear chromatin decorated with antimicrobial proteins such as MPO and NE. In addition to the classical or most commonly studied form of NADPH oxidase-dependent NETs, which contain nuclear chromatin, some studies have shown that neutrophils under certain conditions release NETs comprising mitochondrial DNA44,45.

NET formation is frequently viewed as a specialized form of neutrophil cell death that is distinct from apoptosis and necrosis46, and this cell death has been dubbed NETosis. This has led to some confusion in the literature, as the term NETosis is commonly equated with NET formation, and to further compound the situation, some authors refer to “vital NETosis”47,48. Indeed, as the terms suicidal and vital NETosis are controversial, it is advisable to simply refer to neutrophil formation of NETs with or without attendant cell death. On the other hand, it is well established that the stimulation of neutrophils with phorbol 12-myristate 13-acetate (PMA) leads to a caspase-independent, non-apoptotic form of cell death49,50. Recent studies suggest some commonalities between NET formation and other forms of programmed cell death (Box 1). Hence, gasdermin D, a pore-forming protein and a key executor of pyroptosis, is required for NET formation in neutrophils stimulated with PMA51,52. Furthermore, anti-neutrophil cytoplasmic antibodies trigger NETs via receptor-interacting protein kinase 1/3 and MLKL, key factors in necroptosis53, although it is important to note in this context that different stimuli may trigger different pathways of NET formation54,55.

NETs are thought to play a role during infection by allowing neutrophils to capture and kill pathogens extracellularly43,56. However, mounting evidence suggests that uncontrolled or excessive production of NETs, or defective degradation or removal of NETs, is related to the exacerbation of inflammation and the development of several diseases57. Hakkim et al.58 reported that impairment of DNaseI-mediated NET degradation is associated with systemic lupus erythematosus. Excessive formation of NETs, on the other hand, could clog blood vessels and provide a scaffold for thrombus formation59, whereas a recent study has shown that both DNase1 and DNase1-like 3 are capable of degrading NETs in circulation60. We found that NETs are handled differently by macrophages and dendritic cells with LL-37-dependent uptake followed by intracellular degradation in the former case, and extracellular, DNase1L3-mediated degradation of NETs in the latter case (Lazzaretto et al., manuscript in preparation). NETs were shown to prime T cells and reduce the activation threshold to specific antigens61. TLR9, an intracellular sensor that functions to alert the immune system of viral and bacterial infections by binding to DNA, was not involved. Nevertheless, this suggests that NETs may serve as a link between the innate and adaptive immune system. Furthermore, and in support of this notion, a recent study showed that deposition of cell-free DNA through neutrophil formation and ejection of NETs occurs at the site of immunization and drives the activity of aluminum adjuvant (alum), thereby enhancing adjuvant-induced adaptive immune responses62.

Can nanomaterials trigger NETs? Early work suggested that rod-shaped gold nanoparticles, as well as cationic lipid nanoparticles, are capable of triggering NETs, but compelling evidence was not presented as it is difficult to distinguish between neutrophil cell death with (passive) release of intracellular contents vs. the production of NETs63,64. Naturally, endotoxin contamination also needs to be excluded. More recently, agglomerates of endotoxin-free superparamagnetic iron oxide nanoparticles (SPIONs) were shown to elicit NETs, albeit at a very high concentration (200 µg/mL)65. Importantly, stabilization of the SPIONs with human serum albumin prevented NET formation. The authors also found that agglomerates of SPIONs triggered NET formation in vivo in an animal model, and that the particles were “glued” together by the NETs, and they suggested that such SPION-NET co-aggregates might occlude blood vessels65. The study highlights the need for careful particle design and passivation strategies to make nanoparticles safe for intravenous use. Muñoz et al.66 reported that nanodiamonds (10 nm) cause plasma membrane damage and signs of lysosomal instability in neutrophils, and found that these nanoparticles triggered the formation of NETs at high concentrations of nanoparticles (200 µg/mL). In contrast, larger particles (100–1000 nm) were relatively inert. The smaller particles also triggered inflammation following subcutaneous injection of a high dose (1 mg) into the foot pads of mice, but the swelling was resolved after 1–2 weeks66. The relevance of these findings is difficult to judge due to the high doses that were applied. It is worth noting that nanodiamonds were recently shown to be well-tolerated in sub-acute and chronic duration studies in rodents and non-human primates following intravenous injections67.

We recently provided first evidence that graphene oxide (GO) can trigger NETs in primary human neutrophils, indicating that the immune system can “sense” even a two-dimensional material (Fig. 1). Hence, we could show that low doses of micrometer-sized GO sheets triggered NETs in primary human neutrophils more effectively than small GO with nanosized lateral dimensions68. Both materials were produced under sterile conditions and were proven to be endotoxin-free. Interestingly, the large GO sheets initiated the oxidation of cholesterol in the plasma membrane of neutrophils as evidenced by time-of-flight secondary ion mass spectrometry (ToF-SIMS) furthermore, the release of NETs was reduced by Trolox, a potent lipid antioxidant68. Neumann et al.69 previously reported that methyl-β-cyclodextrin (MβCD), a cholesterol-depleting agent, triggered the formation of NETs in a manner that was independent of the NADPH oxidase (i.e., insensitive to pharmacological inhibition using diphenylene iodonium [DPI]). To study the signaling pathway underlying the formation of NETs in GO-exposed cells, we explored the effect of DPI on NET formation in neutrophils exposed to GO, PMA, or MβCD. DPI was found to block PMA-induced production of NETs, as expected, and blocked the production of NETs in neutrophils exposed to the small GO sheets68. However, NET formation in MβCD-treated cells and in cells incubated with large GO was unaffected by DPI, indicating that NADPH oxidase activation is not required. Interestingly, the mitochondria-targeted antioxidant MitoTEMPO significantly reduced the production of NETs by GO. Mitochondrial reactive oxygen species (ROS) are also required for calcium ionophore-induced NETs70. In a companion paper, we showed that small and large GO are degraded in an MPO-dependent manner in NETs purified from activated neutrophils71. Neutrophils can also enzymatically digest CNTs (discussed below). Thus, it appears that neutrophils are capable of handling at least some carbon-based nanomaterials as pathogens, leading to the destruction of the offending agents72.

Fig. 1: Neutrophils capture graphene oxide sheets in extracellular traps.
figure1

ac Confocal images of neutrophils incubated in the presence of large GO sheets (12.5 μg/mL). Cells were stained with antibodies to neutrophil elastase (NE) followed by a secondary FITC-labeled antibody (green) and counterstained with DAPI (blue) for visualization of cell nuclei. d Light and fluorescence microscopy images superimposed to show the presence of GO. e Scanning electron microscopy (SEM) image of neutrophils exposed to GO (12.5 μg/mL). The arrow points to a large GO sheet that has been “captured” in a network of chromatin fibers (i.e., NETs). Reproduced from Mukherjee et al.68, with permission from Elsevier

Neutrophil degradation of nanomaterials

The membrane-bound NADPH oxidase generates ROS that are instrumental for the killing of ingested pathogens. Degranulation with the release of MPO is also an important feature of the microbicidal actions of neutrophils73. In addition to its role in antimicrobial defense, MPO is also reported to be involved in the degradation of CNTs and the clearance of CNTs from the lungs was markedly less efficient in MPO-deficient mice when compared with wild-type mice74. Neutrophil-mediated destruction of CNTs was first described by Kagan et al.75. Subsequently, MPO-dependent degradation of PEGylated CNTs was reported and this was suggested to occur in a two-step process whereby the polymers were first removed from the CNTs by NE followed by the degradation of the CNTs themselves by MPO76. Eosinophils can also digest CNTs77. Furthermore, CNTs and GO were shown to undergo acellular degradation in NETs purified from activated neutrophils71,78 (Fig. 2). In a recent study, GO functionalized with fMLP was shown to stimulate neutrophil degranulation leading to degradation (Martin et al., manuscript in preparation). Even graphene can undergo neutrophil-mediated degradation, although the process is considerably slower when compared with GO79. The latter studies were conducted ex vivo using human neutrophils. Notably, a recent in vivo study has shown that GO (20 mg/kg) administered subcutaneously elicits an inflammatory reaction in mice in response to implantation consistent with a foreign body reaction80. The latter study did not evaluate biodegradation of the implanted materials. Girish et al.81, on the other hand, explored biodegradation after intravenously injecting graphene (20 mg/kg) into mice by using a Raman confocal imaging approach. The authors noted graphene engulfment by tissue-bound macrophages and found that degradation was prominent after 90 days. Tuning the properties of graphene-based materials to achieve optimal performance while maintaining an acceptable degree of biocompatibility and biodegradability remains an important challenge in the field82.

Fig. 2: Nano-bio interactions: from coronation to degradation.
figure2

This schematic diagram depicts nanoparticles with or without a protein corona (PC) and/or a polymer coating (i.e., poly(ethylene glycol) or PEG) interacting with neutrophils (left) vs. macrophages (right). Neutrophils release neutrophil extracellular traps (NETs) consisting of nuclear chromatin decorated with granule proteins such as myeloperoxidase (MPO), and recent studies have shown that carbon nanotubes (CNTs) and graphene oxide (GO) are captured and digested in NETs in an MPO-dependent manner71,78. The NADPH oxidase (commonly abbreviated as NOX) is a multiprotein complex expressed in phagocytes that catalyzes the generation of superoxide. Superoxide, in turn, dismutates to form hydrogen peroxide and MPO catalyzes the formation of hypochlorous acid, a freely diffusible oxidant that is microbicidal and also is responsible for the degradation of carbon-based nanomaterials124. In addition, superoxide and nitric oxide, produced by inducible nitric oxide synthase (iNOS), react to form peroxynitrite, which was shown to digest nanomaterials in macrophages125. Macrophages emit pro-inflammatory IL-1β through an inflammasome-dependent mechanism (a cytosolic protein complex shown outside the cell for clarity). Neutrophils and macrophages release exosomes, thus providing a further means of cell-to-cell communication and propagation of inflammation. Recent work has shown that neutrophil-derived exosomes express neutrophil elastase (NE) on the surface; these exosomes degrade extracellular matrix more readily when compared with free NE37

Inflammasomes: double-edged swords

How do nanomaterials and other exogenous substances trigger inflammation? Numerous studies have shown that the inflammasome, originally described by Tschopp and colleagues83, is a key signaling hub that regulates innate immunity and inflammation84. The inflammasomes are multiprotein complexes that are activated in response to diverse pathogen- and host-derived danger signals leading to the activation of caspase-1 with processing of cytosolic pro-IL-1β and secretion of pro-inflammatory IL-1β85. NLRP3, in particular, responds to a diverse array of different stimuli including crystalline and particulate matter such as uric acid crystals, silica, asbestos, and alum, as well as to pathogens86,87,88,89. NLRP3 is also a sensor of various nanomaterials90. Indeed, not only long and rigid CNTs but also ultrathin GO sheets and spherical carbon particles are able to trigger NRLP3-dependent IL-1β secretion in human macrophages91,92,93 (Fig. 2). However, less is known regarding inflammasome activation in neutrophils. Neutrophils are capable of activating the NLRC4 inflammasome in response to bacterial challenge, but this occurs without the induction of pyroptosis94. On the other hand, NE cleaves gasdermin D in neutrophils95, thus providing an alternative route to pyroptosis in these cells. Indeed, it should be noted that the production of IL-1β is not exclusively dependent on caspase-196. Thus, neutrophil-derived serine proteases are also involved in the processing of IL-1 family cytokines, and serine proteases and/or caspases may be involved in neutrophils depending upon the stimulus97.

How big is a speck? ASC (apoptosis-associated speck-like protein containing a CARD) is a CARD (caspase recruitment domain) carrying protein of 22 kDa that is involved in the recruitment of pro-caspase-1 to the inflammasome. ASC was described 20 years ago as a protein that could be visualized as a small spot or speck in the cytosol of apoptotic cells98. Intriguingly, although inflammasome activation was originally believed to take place in the cytosol of cells, subsequent studies have shown that cells may transmit inflammation in a prion-like manner via extracellular ASC. These micrometer-sized clumps of ASC proteins continued to stimulate caspase-1 activation extracellularly and stimulated further inflammasome activation in neighboring macrophages that had ingested the ASC oligomers99,100. Extracellular ASC was found in tissues of patients with inflammatory diseases and autoantibodies to ASC developed in some patients with autoimmune pathologies. Thus, as pointed out previously, danger signals come in many shapes and sizes101. It should therefore not come as a surprise that the immune system is capable of responding to synthetic (nano)particles.

Decoding danger at the nanoscale

Cells of the immune system are equipped with PRRs that monitor the extracellular or intracellular environment for signs of infection or “danger”. Toll-like receptors (TLRs) are present both on cell surfaces and in endosomal compartments, whereas retinoid acid-inducible gene-I-like receptors and nucleotide-binding and oligomerization domain-like receptors (NLRs) are present in the cytosol102. Furthermore, soluble scavenging receptors have been described103,104. PRRs presumably evolved to discriminate between foreign intruders and “self,” but they also recognize DAMPs released from stressed or damaged cells105. It has been estimated that a single cell may express as many as 50 distinct PRRs, thus testifying to the importance of sensing “danger”106. Nanomaterials—with or without a corona of proteins or other biomolecules—may be considered as a particular case of danger signals that are able to trigger sterile inflammatory responses. Indeed, we have previously postulated that engineered nanomaterials may present nanomaterial-associated molecular patterns or NAMPs to cells of the immune system107. Thus, in analogy with microorganisms (bacteria, viruses) displaying PAMPs and damaged or stressed cells releasing DAMPs, we postulated that engineered nanomaterials coated with a corona of biomolecules may act as nanoparticle-associated molecular patterns or NAMPs107. The notion of nanomaterial-associated molecular patterns has captured the attention of several other authors108,109,110,111. The fact that nanoparticles with an adsorbed corona of proteins may display epitopes that are sensed by the immune system is of considerable interest, as this may point toward a systematic understanding of nano-bio interactions112. It may also be worthwhile to explore whether nanoparticles per se present molecular patterns that are decoded by the immune system. Indeed, emerging studies suggest that some nanoparticles could act as protein mimics capable of engaging with intra- or extracellular receptors113, and the combination of experimental and theoretical studies promises to shed light on this exciting topic114,115. Using a proteomics approach, He et al.116 found that carbon-based nanomaterials (i.e., single-walled carbon nanohorns, SWCNTs, and MWCNTs) bound to glycoprotein nonmetastatic melanoma protein B (GPNMB, also known as osteoactivin) in macrophages. The authors suggested that GPNMB serves as an intracellular PRR for these nanomaterials. We have recently demonstrated, by using a transcriptomics approach, that SWCNTs prompted the upregulation and secretion of chemokines in primary human macrophages, and we provided evidence for direct binding of CNTs to TLR2/4117. The nanomaterials used were endotoxin-free. Taken together, these results give credence to the idea that nanomaterials may act as NAMPs107. Interestingly, computational studies predicted that the binding of carbon-based nanostructures to proteins is guided mainly by hydrophobic interactions114. More specifically, we and others have analyzed the association of CNTs and other carbon nanostructures to TLRs117,118. Turabekova et al.118 predicted that the hydrophobic pockets of some TLRs might be capable of binding pristine SWCNTs and C60 fullerenes (Fig. 3). Furthermore, we suggested that ion-pair interactions with positively charged residues might strengthen the binding of carboxylated CNTs to TLRs117. It will certainly be important to study whether engineered nanomaterials also engage with neutrophil PRRs.

Fig. 3: Macrophage sensing of single-walled carbon nanotubes as pathogens.
figure3

Computational modeling of a SWCNT bound to the extracellular domains of TLR1/TLR2 (a). The nanotube is surrounded by amino acids of mostly hydrophobic nature giving rise to strong van der Waals interactions (b). The results shown in c depict one of the best binding poses obtained by molecular docking of carboxylated SWCNTs with TLR4117. Interestingly, the highest scoring binding mode of SWCNT and TLR4 shared several similarities with the experimentally resolved structure of TLR3 in complex with double-stranded RNA (d)126. These findings suggest that TLR4 homodimers may engage with SWCNTs through a tweezer-like mechanism. It is noted that these modeling results were derived in the absence of a protein corona in order to elucidate direct binding to TLRs. The efficiency of protein adsorption is well-known to be proportional to the diameter of the nanotubes127. Therefore, the small diameter of these SWCNTs may limit protein adsorption, thus leaving a sufficient surface for the direct interaction with TLRs117. Panel a and b are from Turabekova et al.118 with permission from The Royal Society of Chemistry. Results shown in panel c are from ref. 117 while results in panel d were generated based on ref. 126

It is worth noting that nanoparticles can also be exploited for the removal of DAMPs such as cell-free DNA that is expelled from dying cells to ameliorate inflammatory diseases initiated by the inappropriate activation of TLR signaling. Hence, Liang et al.119 prepared cationic nanoparticles composed of the block copolymer of PLGA and poly(2-(diethylamino)ethyl methacrylate), and found that these particles had a high DNA-binding capacity. Furthermore, when injected intravenously the cationic nanoparticles could alleviate symptoms in animal models of arthritis. These results, along with previous work by other investigators, suggest that cationic nanoparticles may act as nucleic acid scavengers120,121. Further studies are needed to formally address whether the acquisition of a protein corona on scavenger particles navigating the blood stream would interfere with or promote nucleic acid binding.

Concluding remarks

Neutrophils are key effector cells of the innate arm of the immune system and play important roles in host defense against pathogens, and yet, paradoxically, they are also involved in numerous pathological conditions characterized by chronic inflammation. Studies in recent years have shown that nanomaterials can modulate and activate neutrophils and other immune cells. Moreover, activated neutrophils may capture and digest certain carbon-based nanomaterials. Neutrophils also play a role in particle clearance in the systemic circulation (at least in mice). Understanding the interactions between nanomaterials and neutrophils is important for the development of safe and effective nanomaterials for biomedical applications.

The nanotoxicology literature is replete with publications on the negative impact of nanomaterials, often referencing the pro-inflammatory effects of the materials, even when studies are performed in cell culture where coordinated immune reactions cannot occur. However, it is important to note that inflammation as such is not a detrimental response. Therefore, one should not seek to prevent (acute) inflammation at every cost. Instead, careful design of nanomaterials is required in order to avoid chronic, adverse reactions. Furthermore, nanomaterials may be exploited to harness immune responses to ameliorate chronic inflammation and/or autoimmune diseases, and leverage immune responses toward cancer cells122,123.

References

  1. 1.

    Nathan, C. Points of control in inflammation. Nature 420, 846–852 (2002).

    CAS  PubMed  Article  Google Scholar 

  2. 2.

    Medzhitov, R. Origin and physiological roles of inflammation. Nature 454, 428–435 (2008).

    CAS  Article  Google Scholar 

  3. 3.

    Bhattacharya, K., Andón, F. T., El-Sayed, R. & Fadeel, B. Mechanisms of carbon nanotube-induced toxicity: focus on pulmonary inflammation. Adv. Drug Deliv. Rev. 65, 2087–2097 (2013).

    CAS  PubMed  Article  Google Scholar 

  4. 4.

    Boraschi, D. et al. Nanoparticles and innate immunity: new perspectives on host defence. Semin. Immunol. 34, 34–51 (2017).

    Article  CAS  Google Scholar 

  5. 5.

    Nathan, C. Neutrophils and immunity: challenges and opportunities. Nat. Rev. Immunol. 6, 173–182 (2006).

    CAS  PubMed  Article  Google Scholar 

  6. 6.

    Thomas, C. J. & Schroder, K. Pattern recognition receptor function in neutrophils. Trends Immunol. 34, 317–328 (2013).

    CAS  PubMed  Article  Google Scholar 

  7. 7.

    Leso, V., Fontana, L. & Iavicoli, I. Nanomaterial exposure and sterile inflammatory reactions. Toxicol. Appl. Pharmacol. 355, 80–92 (2018).

    CAS  PubMed  Article  Google Scholar 

  8. 8.

    Underhill, D. M. & Goodridge, H. S. Information processing during phagocytosis. Nat. Rev. Immunol. 12, 492–502 (2012).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  9. 9.

    Jones, S. W. et al. Nanoparticle clearance is governed by Th1 / Th2 immunity and strain background. J. Clin. Invest. 123, 3061–3073 (2013).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  10. 10.

    Furze, R. C. & Rankin, S. M. The role of the bone marrow in neutrophil clearance under homeostatic conditions in the mouse. FASEB J. 22, 3111–3119 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  11. 11.

    Tavares, A. J. et al. Effect of removing Kupffer cells on nanoparticle tumor delivery. Proc. Natl Acad. Sci. USA 114, E10871–E10880 (2017).

    CAS  PubMed  Article  Google Scholar 

  12. 12.

    Gonçalves, D. M., Chiasson, S. & Girard, D. Activation of human neutrophils by titanium dioxide (TiO2) nanoparticles. Toxicol In Vitro. 24, 1002–1008 (2010).

    PubMed  Article  CAS  Google Scholar 

  13. 13.

    Babin, K., Antoine, F., Goncalves, D. M. & Girard, D. TiO2, CeO2 and ZnO nanoparticles and modulation of the degranulation process in human neutrophils. Toxicol. Lett. 221, 57–63 (2013).

    CAS  PubMed  Article  Google Scholar 

  14. 14.

    Goncalves, D. M. & Girard, D. Zinc oxide nanoparticles delay human neutrophil apoptosis by a de novo protein synthesis-dependent and reactive oxygen species-independent mechanism. Toxicol In Vitro. 28, 926–931 (2014).

    CAS  PubMed  Article  Google Scholar 

  15. 15.

    Babin, K., Goncalves, D. M. & Girard, D. Nanoparticles enhance the ability of human neutrophils to exert phagocytosis by a Syk-dependent mechanism. Biochim. Biophys. Acta 1850, 2276–2282 (2015).

    CAS  PubMed  Article  Google Scholar 

  16. 16.

    Noël, C., Simard, J. C. & Girard, D. Gold nanoparticles induce apoptosis, endoplasmic reticulum stress events and cleavage of cytoskeletal proteins in human neutrophils. Toxicol In Vitro. 31, 12–22 (2016).

    PubMed  Article  CAS  Google Scholar 

  17. 17.

    Gonçalves, D. M. & Girard, D. Evidence that polyhydroxylated C60 fullerenes (fullerenols) amplify the effect of lipopolysaccharides to induce rapid leukocyte infiltration in vivo. Chem. Res. Toxicol. 26, 1884–1892 (2013).

    PubMed  Article  CAS  Google Scholar 

  18. 18.

    Fraser, J. A. et al. Silver nanoparticles promote the emergence of heterogeneic human neutrophil sub-populations. Sci. Rep. 8, 1–14 (2018).

    CAS  Article  Google Scholar 

  19. 19.

    Fromen, C. A. et al. Neutrophil-particle interactions in blood circulation drive particle clearance and alter neutrophil responses in acute inflammation. ACS Nano. 11, 10797–10807 (2017).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  20. 20.

    Kelley, W. J., Fromen, C. A., Lopez-Cazares, G. & Eniola-Adefeso, O. PEGylation of model drug carriers enhances phagocytosis by primary human neutrophils. Acta Biomater. 79, 283–293 (2018).

    CAS  PubMed  Article  Google Scholar 

  21. 21.

    Bisso, P. W., Gaglione, S., Guimarães, P. P. G., Mitchell, M. J. & Langer, R. Nanomaterial interactions with human neutrophils. ACS Biomater. Sci. Eng. 4, 4255–4265 (2018).

    CAS  Article  Google Scholar 

  22. 22.

    Bhattacharya, K. et al. Biological interactions of carbon-based nanomaterials: from coronation to degradation. Nanomedicine 12, 333–351 (2016).

    CAS  PubMed  Article  Google Scholar 

  23. 23.

    Barbero, F. et al. Formation of the protein corona: the interface between nanoparticles and the immune system. Semin. Immunol. 34, 52–60 (2017).

    CAS  PubMed  Article  Google Scholar 

  24. 24.

    Fadeel, B. Hide and seek: nanomaterial interactions with the immune system. Front. Immunol. 10, 133 (2019).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  25. 25.

    Deng, Z. J., Liang, M., Monteiro, M., Toth, I. & Minchin, R. F. Nanoparticle-induced unfolding of fibrinogen promotes Mac-1 receptor activation and inflammation. Nat. Nanotechnol. 6, 39–44 (2011).

    CAS  PubMed  Article  Google Scholar 

  26. 26.

    Tenzer, S. et al. Rapid formation of plasma protein corona critically affects nanoparticle pathophysiology. Nat. Nanotechnol. 8, 772–781 (2013).

    CAS  PubMed  Article  Google Scholar 

  27. 27.

    Vlasova, I. I. et al. Adsorbed plasma proteins modulate the effects of single-walled carbon nanotubes on neutrophils in blood. Nanomedicine 12, 1615–1625 (2016).

    CAS  PubMed  Article  Google Scholar 

  28. 28.

    Lu, N., Sui, Y., Tian, R. & Peng, Y. Y. Adsorption of plasma proteins on single-walled carbon nanotubes reduced cytotoxicity and modulated neutrophil activation. Chem. Res. Toxicol. 31, 1061–1068 (2018).

    CAS  PubMed  Article  Google Scholar 

  29. 29.

    Lara, S. et al. Identification of receptor binding to the biomolecular corona of nanoparticles. ACS Nano. 11, 1884–1893 (2017).

    CAS  PubMed  Article  Google Scholar 

  30. 30.

    Salvati, A. et al. Transferrin-functionalized nanoparticles lose their targeting capabilities when a biomolecule corona adsorbs on the surface. Nat. Nanotechnol. 8, 137–143 (2013).

    CAS  PubMed  Article  Google Scholar 

  31. 31.

    Tonigold, M. et al. Pre-adsorption of antibodies enables targeting of nanocarriers despite a biomolecular corona. Nat. Nanotechnol. 13, 862–869 (2018).

    CAS  PubMed  Article  Google Scholar 

  32. 32.

    Oh, J. Y. et al. Cloaking nanoparticles with protein corona shield for targeted drug delivery. Nat. Commun. 9, 1–9 (2018).

    Article  CAS  Google Scholar 

  33. 33.

    Prapainop, K., Witter, D. P. & Wentworth, P. A chemical approach for cell-specific targeting of nanomaterials: small-molecule-initiated misfolding of nanoparticle corona proteins. J. Am. Chem. Soc. 134, 4100–4103 (2012).

    CAS  PubMed  Article  Google Scholar 

  34. 34.

    Ezzat, K. et al. The viral protein corona directs viral pathogenesis and amyloid aggregation. Nat. Commun. 10, 2331 (2019).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  35. 35.

    Théry, C., Ostrowski, M. & Segura, E. Membrane vesicles as conveyors of immune responses. Nat. Rev. Immunol. 9, 581–593 (2009).

    PubMed  Article  CAS  Google Scholar 

  36. 36.

    van Niel, G., D’Angelo, G. & Raposo, G. Shedding light on the cell biology of extracellular vesicles. Nat. Rev. Mol. Cell Biol. 19, 213–228 (2018).

    PubMed  Article  CAS  Google Scholar 

  37. 37.

    Genschmer, K. R. et al. Activated PMN exosomes: pathogenic entities causing matrix destruction and disease in the lung. Cell 176, 113–126 (2019).

    CAS  PubMed  Article  Google Scholar 

  38. 38.

    Shvedova, A. A., Pietroiusti, A., Fadeel, B. & Kagan, V. E. Mechanisms of carbon nanotube-induced toxicity: focus on oxidative stress. Toxicol. Appl. Pharmacol. 261, 121–133 (2012).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  39. 39.

    Zhu, M. et al. Exosomes as extrapulmonary signaling conveyors for nanoparticle-induced systemic immune activation. Small 8, 404–412 (2012).

    CAS  PubMed  Article  Google Scholar 

  40. 40.

    Cho, W. S. et al. Metal oxide nanoparticles induce unique infammatory footprints in the lung: important implications for nanoparticle testing. Environ. Health Perspect. 118, 1699–1706 (2010).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  41. 41.

    Qiao, Y. et al. Identification of exosomal miRNAs in rats with pulmonary neutrophilic inflammation induced by zinc oxide nanoparticles. Front. Physiol. 9, 1–11 (2018).

    Article  Google Scholar 

  42. 42.

    Logozzi, M. et al. Human primary macrophages scavenge AuNPs and eliminate it through exosomes. A natural shuttling for nanomaterials. Eur. J. Pharm. Biopharm. 137, 23–36 (2019).

    CAS  PubMed  Article  Google Scholar 

  43. 43.

    Brinkmann, V. et al. Neutrophil extracellular traps kill bacteria. Science 303, 1532–1535 (2004).

    CAS  Article  Google Scholar 

  44. 44.

    Yousefi, S., Mihalache, C., Kozlowski, E., Schmid, I. & Simon, H. U. Viable neutrophils release mitochondrial DNA to form neutrophil extracellular traps. Cell Death Differ. 16, 1438–1444 (2009).

    CAS  PubMed  Article  Google Scholar 

  45. 45.

    Lood, C. et al. Neutrophil extracellular traps enriched in oxidized mitochondrial DNA are interferogenic and contribute to lupus-like disease. Nat. Med. 22, 146–153 (2016).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  46. 46.

    Fuchs, T. A. et al. Novel cell death program leads to neutrophil extracellular traps. J. Cell Biol. 176, 231–241 (2007).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  47. 47.

    Clark, S. R. et al. Platelet TLR4 activates neutrophil extracellular traps to ensnare bacteria in septic blood. Nat. Med. 13, 463–469 (2007).

    CAS  PubMed  Article  Google Scholar 

  48. 48.

    Yipp, B. G. et al. Infection-induced NETosis is a dynamic process involving neutrophil multitasking in vivo. Nat. Med. 18, 1386–1393 (2012).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  49. 49.

    Takei, H., Araki, A., Watanabe, H., Ichinose, A. & Sendo, F. Rapid killing of human neutrophils by the potent activator phorbol 12-myristate 13-acetate (PMA) accompanied by changes different from typical apoptosis or necrosis. J. Leukoc. Biol. 59, 229–240 (1996).

    CAS  PubMed  Article  Google Scholar 

  50. 50.

    Fadeel, B., Åhlin, A., Henter, J. I., Orrenius, S. & Hampton, M. B. Involvement of caspases in neutrophil apoptosis: regulation by reactive oxygen species. Blood 92, 4808–4818 (1998).

    CAS  PubMed  Google Scholar 

  51. 51.

    Chen, K. W. et al. Noncanonical inflammasome signaling elicits gasdermin D-dependent neutrophil extracellular traps. Sci. Immunol. 3, eaar6676 (2018).

    PubMed  Article  Google Scholar 

  52. 52.

    Sollberger, G. et al. Gasdermin D plays a vital role in the generation of neutrophil extracellular traps. Sci. Immunol. 3, eaar6689 (2018).

    PubMed  Article  Google Scholar 

  53. 53.

    Schreiber, A. et al. Necroptosis controls NET generation and mediates complement activation, endothelial damage, and autoimmune vasculitis. Proc. Natl Acad. Sci. USA 114, E9618–E9625 (2017).

    CAS  PubMed  Article  Google Scholar 

  54. 54.

    Kenny, E. F. et al. Diverse stimuli engage different neutrophil extracellular trap pathways. Elife 6, e24437 (2017).

    PubMed  PubMed Central  Article  Google Scholar 

  55. 55.

    Van Der Linden, M., Westerlaken, G. H. A., Van Der Vlist, M., Van Montfrans, J. & Meyaard, L. Differential signalling and kinetics of neutrophil extracellular trap release revealed by quantitative live imaging. Sci. Rep. 7, 6529 (2017).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  56. 56.

    Urban, C. F., Reichard, U., Brinkmann, V. & Zychlinsky, A. Neutrophil extracellular traps capture and kill Candida albicans and hyphal forms. Cell. Microbiol. 8, 668–676 (2006).

    CAS  PubMed  Article  Google Scholar 

  57. 57.

    Papayannopoulos, V. Neutrophil extracellular traps in immunity and disease. Nat. Rev. Immunol. 18, 134–147 (2018).

    CAS  Article  Google Scholar 

  58. 58.

    Hakkim, A. et al. Impairment of neutrophil extracellular trap degradation is associated with lupus nephritis. Proc. Natl Acad. Sci. USA 107, 9813–9818 (2010).

    CAS  PubMed  Article  Google Scholar 

  59. 59.

    Fuchs, T. A. et al. Extracellular DNA traps promote thrombosis. Proc. Natl Acad. Sci. USA 107, 15880–15885 (2010).

    CAS  PubMed  Article  Google Scholar 

  60. 60.

    Jiménez-Alcázar, M. et al. Host DNases prevent vascular occlusion by neutrophil extracellular traps. Science 358, 1202–1206 (2017).

    PubMed  Article  CAS  Google Scholar 

  61. 61.

    Tillack, K., Breiden, P., Martin, R. & Sospedra, M. T lymphocyte priming by neutrophil extracellular traps links innate and adaptive immune responses. J. Immunol. 188, 3150–3159 (2012).

    CAS  PubMed  Article  Google Scholar 

  62. 62.

    Stephen, J. et al. Neutrophil swarming and extracellular trap formation play a significant role in alum adjuvant activity. npj Vaccines 2, 1 (2017).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  63. 63.

    Bartneck, M., Keul, H. A., Gabriele, Z. K. & Groll, J. Phagocytosis independent extracellular nanoparticle clearance by human immune cells. Nano Lett. 10, 59–64 (2010).

    CAS  PubMed  Article  Google Scholar 

  64. 64.

    Hwang, T. L., Aljuffali, I. A., Hung, C. F., Chen, C. H. & Fang, J. Y. The impact of cationic solid lipid nanoparticles on human neutrophil activation and formation of neutrophil extracellular traps (NETs). Chem. Biol. Interact. 235, 106–114 (2015).

    CAS  PubMed  Article  Google Scholar 

  65. 65.

    Bilyy, R. et al. Inert coats of magnetic nanoparticles prevent formation of occlusive intravascular co-aggregates with neutrophil extracellular traps. Front. Immunol. 9, 2266 (2018).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  66. 66.

    Muñoz, L. E. et al. Nanoparticles size-dependently initiate self-limiting NETosis-driven inflammation. Proc. Natl Acad. Sci. USA 113, E5856–E5865 (2016).

    PubMed  Article  CAS  Google Scholar 

  67. 67.

    Moore, L. et al. Biocompatibility assessment of detonation nanodiamond in non-human primates and rats using histological, hematologic, and urine analysis. ACS Nano. 10, 7385–7400 (2016).

    CAS  PubMed  Article  Google Scholar 

  68. 68.

    Mukherjee, S. P. et al. Graphene oxide elicits membrane lipid changes and neutrophil extracellular trap formation. Chem 4, 334–358 (2018).

    CAS  Article  Google Scholar 

  69. 69.

    Neumann, A. et al. Lipid alterations in human blood-derived neutrophils lead to formation of neutrophil extracellular traps. Eur. J. Cell Biol. 93, 347–354 (2014).

    CAS  PubMed  Article  Google Scholar 

  70. 70.

    Douda, D. N., Khan, M. A., Grasemann, H. & Palaniyar, N. SK3 channel and mitochondrial ROS mediate NADPH oxidase-independent NETosis induced by calcium influx. Proc. Natl Acad. Sci. USA 112, 2817–2822 (2015).

    CAS  PubMed  Article  Google Scholar 

  71. 71.

    Mukherjee, S. P. et al. Graphene oxide is degraded by neutrophils and the degradation products are non-genotoxic. Nanoscale 10, 1180–1188 (2018).

    CAS  PubMed  Article  Google Scholar 

  72. 72.

    Mukherjee, S. P., Bottini, M. & Fadeel, B. Graphene and the immune system: a romance of many dimensions. Front. Immunol. 8, 1–11 (2017).

    CAS  Article  Google Scholar 

  73. 73.

    Klebanoff, S. J., Kettle, A. J., Rosen, H., Winterbourn, C. C. & Nauseef, W. M. Myeloperoxidase: a front-line defender against phagocytosed microorganisms. J. Leukoc. Biol. 93, 185–198 (2013).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  74. 74.

    Shvedova, A. A. et al. Impaired clearance and enhanced pulmonary inflammatory/fibrotic response to carbon nanotubes in myeloperoxidase-deficient mice. PLoS ONE 7, e30923 (2012).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  75. 75.

    Kagan, V. E. et al. Carbon nanotubes degraded by neutrophil myeloperoxidase induce less pulmonary inflammation. Nat. Nanotechnol. 5, 354–359 (2010).

    CAS  PubMed  Article  Google Scholar 

  76. 76.

    Bhattacharya, K. et al. Enzymatic ‘stripping’ and degradation of PEGylated carbon nanotubes. Nanoscale 6, 14686–14690 (2014).

    CAS  PubMed  Article  Google Scholar 

  77. 77.

    Andón, F. T. et al. Biodegradation of single-walled carbon nanotubes by eosinophil peroxidase. Small 9, 2720–2729 (2013).

    Article  CAS  Google Scholar 

  78. 78.

    Farrera, C. et al. Extracellular entrapment and degradation of single-walled carbon nanotubes. Nanoscale 6, 6974–6983 (2014).

    CAS  PubMed  Article  Google Scholar 

  79. 79.

    Kurapati, R., et al. Degradation of single-layer and few-layer graphene by neutrophil myeloperoxidase. Angew. Chemie Int. Ed. Engl. 57, 11722–11727 (2018).

    CAS  PubMed  Article  Google Scholar 

  80. 80.

    Sydlik, S. A., Jhunjhunwala, S., Webber, M. J., Anderson, D. G. & Langer, R. In vivo compatibility of graphene oxide with differing oxidation states. ACS Nano. 9, 3866–3874 (2015).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  81. 81.

    Girish, C. M., Sasidharan, A., Gowd, G. S., Nair, S. & Koyakutty, M. Confocal Raman imaging study showing macrophage mediated biodegradation of graphene in vivo. Adv. Healthc. Mater. 2, 1489–1500 (2013).

    CAS  PubMed  Article  Google Scholar 

  82. 82.

    Fadeel, B. et al. Safety assessment of graphene-based materials: focus on human health and the environment. ACS Nano. 12, 10582–10620 (2018).

    CAS  PubMed  Article  Google Scholar 

  83. 83.

    Martinon, F., Burns, K. & Tschopp, J. The inflammasome: a molecular platform triggering activation of inflammatory caspases and processing of proIL-β. Mol. Cell. 10, 417–426 (2002).

    CAS  PubMed  Article  Google Scholar 

  84. 84.

    Broz, P. & Dixit, V. M. Inflammasomes: mechanism of assembly, regulation and signalling. Nat. Rev. Immunol. 16, 407–420 (2016).

    CAS  PubMed  Article  Google Scholar 

  85. 85.

    Mangan, M. S. J. et al. Targeting the NLRP3 inflammasome in inflammatory diseases. Nat. Rev. Drug Discov. 17, 588–606 (2018).

    CAS  PubMed  Article  Google Scholar 

  86. 86.

    Martinon, F., Pétrilli, V., Mayor, A., Tardivel, A. & Tschopp, J. Gout-associated uric acid crystals activate the NALP3 inflammasome. Nature 440, 237–241 (2006).

    CAS  PubMed  Article  Google Scholar 

  87. 87.

    Dostert, C. et al. Innate immune activation through Nalp3 inflammasome sensing of asbestos and silica. Science 320, 674–677 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  88. 88.

    Cassel, S. L. et al. The Nalp3 inflammasome is essential for the development of silicosis. Proc. Natl Acad. Sci. USA 105, 9035–9040 (2008).

    CAS  PubMed  Article  Google Scholar 

  89. 89.

    Hornung, V. et al. Silica crystals and aluminum salts activate the NALP3 inflammasome through phagosomal destabilization. Nat. Immunol. 9, 847–856 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  90. 90.

    Sun, B., Wang, X., Ji, Z., Li, R. & Xia, T. NLRP3 inflammasome activation induced by engineered nanomaterials. Small 9, 1595–1607 (2013).

    CAS  PubMed  Article  Google Scholar 

  91. 91.

    Palomäki, J. et al. Long, needle-like carbon nanotubes and asbestos activate the NLRP3 inflammasome through a similar mechanism. ACS Nano. 5, 6861–6870 (2011).

    PubMed  Article  CAS  Google Scholar 

  92. 92.

    Mukherjee, S. P., Kostarelos, K. & Fadeel, B. Cytokine profiling of primary human macrophages exposed to endotoxin-free graphene oxide: size-independent NLRP3 inflammasome activation. Adv. Healthc. Mater. 7, 1700815 (2018).

  93. 93.

    Andón, F. T. et al. Hollow carbon spheres trigger inflammasome-dependent IL-1β secretion in macrophages. Carbon 113, 243–251 (2017).

    Article  CAS  Google Scholar 

  94. 94.

    Chen, K. W. et al. The neutrophil NLRC4 inflammasome selectively promotes IL-1β maturation without pyroptosis during acute Salmonella challenge. Cell Rep. 8, 570–582 (2014).

    CAS  PubMed  Article  Google Scholar 

  95. 95.

    Kambara, H. et al. Gasdermin D exerts anti-inflammatory effects by promoting neutrophil death. Cell Rep. 22, 2924–2936 (2018).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  96. 96.

    Netea, M. G., van de Veerdonk, F. L., van der Meer, J. W. M., Dinarello, C. A. & Joosten, L. A. B. Inflammasome-independent regulation of IL-1-family cytokines. Annu. Rev. Immunol. 33, 49–77 (2015).

    CAS  PubMed  Article  Google Scholar 

  97. 97.

    Bakele, M. et al. Localization and functionality of the inflammasome in neutrophils. J. Biol. Chem. 289, 5320–5329 (2014).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  98. 98.

    Masumoto, J. et al. ASC, a novel 22-kDa protein, aggregates during apoptosis of human promyelocytic leukemia HL-60 cells. J. Biol. Chem. 274, 33835–33838 (1999).

    CAS  PubMed  Article  Google Scholar 

  99. 99.

    Franklin, B. S. et al. The adaptor ASC has extracellular and ‘prionoid’ activities that propagate inflammation. Nat. Immunol. 15, 727–737 (2014).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  100. 100.

    Baroja-Mazo, A. et al. The NLRP3 inflammasome is released as a particulate danger signal that amplifies the inflammatory response. Nat. Immunol. 15, 738–748 (2014).

    CAS  PubMed  Article  Google Scholar 

  101. 101.

    Rettig, L. et al. Particle size and activation threshold: a new dimension of danger signaling. Blood 115, 4533–4541 (2010).

    CAS  PubMed  Article  Google Scholar 

  102. 102.

    Miyake, K. Innate immune sensing of pathogens and danger signals by cell surface Toll-like receptors. Semin. Immunol. 19, 3–10 (2007).

    CAS  PubMed  Article  Google Scholar 

  103. 103.

    Litvack, M. L. & Palaniyar, N. Soluble innate immune pattern-recognition proteins for clearing dying cells and cellular components: implications on exacerbating or resolving inflammation. Innate Immun. 16, 191–200 (2010).

    CAS  PubMed  Article  Google Scholar 

  104. 104.

    Arai, S. & Miyazaki, T. A scavenging system against internal pathogens promoted by the circulating protein apoptosis inhibitor of macrophage (AIM). Semin. Immunopathol. 40, 567–575 (2018).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  105. 105.

    Farrera, C. & Fadeel, B. It takes two to tango: understanding the interactions between engineered nanomaterials and the immune system. Eur. J. Pharm. Biopharm. 95, 3–12 (2015).

    CAS  PubMed  Article  Google Scholar 

  106. 106.

    Silva, A. L. et al. Nanoparticle impact on innate immune cell pattern-recognition receptors and inflammasomes activation. Semin. Immunol. 34, 3–24 (2017).

    CAS  PubMed  Article  Google Scholar 

  107. 107.

    Fadeel, B. Clear and present danger? Engineered nanoparticles and the immune system. Swiss Med. Wkly. 142, w13609 (2012).

    PubMed  Google Scholar 

  108. 108.

    Pradeu, T. & Cooper, E. L. The danger theory: 20 years later. Front. Immunol. 3, 287–287 (2011).

    Google Scholar 

  109. 109.

    Gallo, P. M. & Gallucci, S. The dendritic cell response to classic, emerging, and homeostatic danger signals. Implications for autoimmunity. Front. Immunol. 4, 138 (2013).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  110. 110.

    Shirasuna, K., Karasawa, T. & Takahashi, M. Exogenous nanoparticles and endogenous crystalline molecules as danger signals for the NLRP3 inflammasomes. J. Cell. Physiol. 234, 5436–5450 (2019).

    CAS  PubMed  Article  Google Scholar 

  111. 111.

    Vita, A. A., Royse, E. A. & Pullen, N. A. Nanoparticles and danger signals: oral delivery vehicles as potential disruptors of intestinal barrier homeostasis. J. Leukoc. Biol. 106, 95–103 (2019).

  112. 112.

    Nel, A. E. et al. Understanding biophysicochemical interactions at the nano-bio interface. Nat. Mater. 8, 543–557 (2009).

    CAS  PubMed  Article  Google Scholar 

  113. 113.

    Gallud, A. & Fadeel, B. Keeping it small: towards a molecular definition of nanotoxicology. Eur. J. Nanomed. 7, 143–151 (2015).

    CAS  Article  Google Scholar 

  114. 114.

    Xiu, P., Zhou, R., Zhao, Y., Zuo, G. & Kang, S. Interactions between proteins and carbon-based nanoparticles: exploring the origin of nanotoxicity at the molecular level. Small 9, 1546–1556 (2012).

    PubMed  Google Scholar 

  115. 115.

    Yanamala, N., Kagan, V. E. & Shvedova, A. A. Molecular modeling in structural nano-toxicology: interactions of nano-particles with nano-machinery of cells. Adv. Drug Deliv. Rev. 65, 2070–2077 (2013).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  116. 116.

    He, B. et al. Single-walled carbon-nanohorns improve biocompatibility over nanotubes by triggering less protein-initiated pyroptosis and apoptosis in macrophages. Nat. Commun. 9, 2393 (2018).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  117. 117.

    Mukherjee, S. P. et al. Macrophage sensing of single-walled carbon nanotubes via Toll-like receptors. Sci. Rep. 8, 1–17 (2018).

    Article  CAS  Google Scholar 

  118. 118.

    Turabekova, M. et al. Immunotoxicity of nanoparticles: a computational study suggests that CNTs and C60 fullerenes might be recognized as pathogens by Toll-like receptors. Nanoscale 6, 3488–3495 (2014).

    CAS  PubMed  Article  Google Scholar 

  119. 119.

    Liang, H. et al. Cationic nanoparticle as an inhibitor of cell-free DNA-induced inflammation. Nat. Commun. 9, 4291 (2018).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  120. 120.

    Lee, J. et al. Nucleic acid-binding polymers as anti-inflammatory agents. Proc. Natl Acad. Sci. USA 108, 14055–14060 (2011).

    CAS  PubMed  Article  Google Scholar 

  121. 121.

    Holl, E. K. et al. Scavenging nucleic acid debris to combat autoimmunity and infectious disease. Proc. Natl Acad. Sci. USA 113, 9728–9733 (2016).

    CAS  PubMed  Article  Google Scholar 

  122. 122.

    Hubbell, J. A., Thomas, S. N. & Swartz, M. A. Materials engineering for immunomodulation. Nature 462, 449–460 (2009).

    CAS  PubMed  Article  Google Scholar 

  123. 123.

    Getts, D. R., Shea, L. D., Miller, S. D. & King, N. J. C. Harnessing nanoparticles for immune modulation. Trends Immunol. 36, 419–427 (2015).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  124. 124.

    Vlasova, I. I. et al. Enzymatic oxidative biodegradation of nanoparticles: mechanisms, significance and applications. Toxicol. Appl. Pharmacol. 299, 58–69 (2016).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  125. 125.

    Kagan, V. E. et al. Lung macrophages ‘digest’ carbon nanotubes using a superoxide/peroxynitrite oxidative pathway. ACS Nano. 8, 5610–5621 (2014).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  126. 126.

    Liu, L. et al. Structural basis of Toll-like receptor 3 signaling with double-stranded RNA. Science 320, 379–381 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  127. 127.

    Mu, Q. et al. Protein binding by functionalized multiwalled carbon nanotubes is governed by the surface chemistry of both parties and the nanotube diameter. J. Phys. Chem. C 112, 3300–3307 (2008).

    CAS  Article  Google Scholar 

  128. 128.

    Galluzzi, L. et al. Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018. Cell Death Differ. 25, 486–541 (2018).

    PubMed  PubMed Central  Article  Google Scholar 

  129. 129.

    Clarke, P. G. & Clarke, S. Nineteenth century research on cell death. Exp. Oncol. 3, 139–145 (2012).

    Google Scholar 

  130. 130.

    Andón, F. T. & Fadeel, B. Programmed cell death: molecular mechanisms and implications for safety assessment of nanomaterials. Acc. Chem. Res. 46, 733–142 (2013).

    PubMed  Article  CAS  Google Scholar 

  131. 131.

    Hussain, S. et al. Carbon black and titanium dioxide nanoparticles elicit distinct apoptotic pathways in bronchial epithelial cells. Part. Fibre Toxicol. 7, 10 (2010).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  132. 132.

    Luanpitpong, S., Wang, L., Castranova, V. & Rojanasakul, Y. Induction of stem-like cells with malignant properties by chronic exposure of human lung epithelial cells to single-walled carbon nanotubes. Part. Fibre Toxicol. 11, 22 (2014).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  133. 133.

    Shi, J., Gao, W. & Shao, F. Pyroptosis: gasdermin-mediated programmed necrotic cell death. Trends Biochem. Sci. 42, 245–254 (2017).

    CAS  PubMed  Article  Google Scholar 

  134. 134.

    Mirshafiee, V. et al. Toxicological profiling of metal oxide nanoparticles in liver context reveals pyroptosis in Kupffer cells and macrophages versus apoptosis in hepatocytes. ACS Nano. 12, 3836–3852 (2018).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  135. 135.

    Wang, X., Yousefi, S. & Simon, H. U. Necroptosis and neutrophil-associated disorders. Cell Death Dis. 9, 111 (2018).

    PubMed  PubMed Central  Article  Google Scholar 

  136. 136.

    Stockwell, B. R. et al. Ferroptosis: a regulated cell death nexus linking metabolism, redox biology, and disease. Cell 171, 273–285 (2017).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  137. 137.

    Szwed, M., et al. Small variations in nanoparticle structure dictate differential cellular stress responses and mode of cell death. Nanotoxicology 13, 761–782 (2019).

    CAS  PubMed  Article  Google Scholar 

  138. 138.

    Zhang, J. et al. Zinc oxide nanoparticles harness autophagy to induce cell death in lung epithelial cells. Cell Death Dis. 8, e2954 (2017).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

Download references

Acknowledgements

The work is supported by the European Commission’s H2020 program through BIORIMA (grant agreement number 760928) and the Graphene Flagship (grant agreement number 785219), and the Swedish Research Council (grant agreement number 2016-02040). L.D. acknowledges the support of the Marie Skłodowska-Curie Actions Individual Fellowship IMM-GNR (grant agreement number 797914).

Author information

Affiliations

Authors

Contributions

B.F. wrote the paper with input from S.K., P.C., L.S., L.F., and L.D. P.C. and L.S. performed docking studies. L.F. prepared the schematic figure. All co-authors approved the final version of the paper.

Corresponding author

Correspondence to Bengt Fadeel.

Ethics declarations

Conflict of interest

The authors declare that they have no conflict of interest.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Edited by H.-U. Simon

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Keshavan, S., Calligari, P., Stella, L. et al. Nano-bio interactions: a neutrophil-centric view. Cell Death Dis 10, 569 (2019). https://doi.org/10.1038/s41419-019-1806-8

Download citation

Further reading

Search

Quick links