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Induction of Inflammasome-dependent Pyroptosis by Carbon Black Nanoparticles*

Open AccessPublished:April 27, 2011DOI:https://doi.org/10.1074/jbc.M111.238519
      Inhalation of nanoparticles has been implicated in respiratory morbidity and mortality. In particular, carbon black nanoparticles are found in many different environmental exposures. Macrophages take up inhaled nanoparticles and respond via release of inflammatory mediators and in some cases cell death. Based on new data, we propose that exposure of macrophages (both a macrophage cell line and primary human alveolar macrophages) to carbon black nanoparticles induces pyroptosis, an inflammasome-dependent form of cell death. Exposure of macrophages to carbon black nanoparticles resulted in inflammasome activation as defined by cleavage of caspase 1 to its active form and downstream IL-1β release. The cell death that occurred with carbon black nanoparticle exposure was identified as pyroptosis by the protective effect of a caspase 1 inhibitor and a pyroptosis inhibitor. These data demonstrate that carbon black nanoparticle exposure activates caspase 1, increases IL-1β release after LPS priming, and induces the proinflammatory cell death, pyroptosis. The identification of pyroptosis as a cellular response to carbon nanoparticle exposure is novel and relates to environmental and health impacts of carbon-based particulates.

      Introduction

      Macrophages are critical regulators of local immune homeostasis. They are highly adaptive components of the innate immune system and respond in diverse ways to pathogens and other potential danger signals (
      • Opitz B.
      • van Laak V.
      • Eitel J.
      • Suttorp N.
      ,
      • Harada R.N.
      • Repine J.E.
      ,
      • Twigg 3rd, H.L.
      ). In the lung, the alveolar macrophage is the first line of defense against environmental exposures. Alveolar macrophages phagocytose particulate matter, release inflammatory cytokines, and interact with other cells and molecules through the expression of surface receptors. One way in which an immune response is generated in alveolar macrophages is through the phagocytosis of deposited particles within the respiratory tract (
      • Sibille Y.
      • Reynolds H.Y.
      ).
      The nanoparticle industry has expanded substantially in recent years. A variety of engineered carbon nanoparticles is used in consumer products such as car tires, rubber, and printer toner cartridges (
      • Loeffler J.
      • Hedderich R.
      • Fiedeler U.
      • Malsch I.
      • Túquerres G.
      • Koskinen J.
      • Linden M.
      • Lojkowski W.
      • Moritz T.
      • Zins M.
      • Bernabeu E.
      • Larena A.
      ). Nanoparticles are also being used as novel means of drug delivery. Additionally, carbonaceous nanoparticles are present as an environmental contaminant. Combustion processes are a significant source of carbon nanoparticles. Elemental carbon-based nanoparticles with a diameter of less than 100 nm are a major part of diesel exhaust and ambient pollution (
      • Möller W.
      • Brown D.M.
      • Kreyling W.G.
      • Stone V.
      ).
      Particulate ambient pollution is known to cause adverse health effects in susceptible individuals and aggravates existing respiratory conditions such as asthma and chronic obstructive pulmonary disease (
      • Hussain S.
      • Thomassen L.C.
      • Ferecatu I.
      • Borot M.C.
      • Andreau K.
      • Martens J.A.
      • Fleury J.
      • Baeza-Squiban A.
      • Marano F.
      • Boland S.
      ). Even moderate levels of ambient air particulates are known to induce acute adverse health effects such as mortality in heart and lung diseases and chronic lung morbidity (
      • Lundborg M.
      • Johard U.
      • Låstbom L.
      • Gerde P.
      • Camner P.
      ). Ultrafine particles are unique in their ability to bypass mucociliary clearance mechanisms and penetrate into deeper regions of the respiratory tract (
      • Lippmann M.
      • Yeates D.B.
      • Albert R.E.
      ,
      • Oberdörster G.
      ,
      • Ferin J.
      • Oberdörster G.
      • Penney D.P.
      ,
      • Oberdörster G.
      • Ferin J.
      • Lehnert B.E.
      ). Although bulk elemental carbon is considered chemically inert (as in diamond and graphite), seemingly inert substances have been shown to elicit an inflammatory response when exposure occurs with nanoscale particles compared with an equivalent mass dose of larger particles (
      • Ferin J.
      • Oberdörster G.
      • Penney D.P.
      ,
      • Oberdörster G.
      • Ferin J.
      • Lehnert B.E.
      ,
      • Beck-Speier I.
      • Dayal N.
      • Karg E.
      • Maier K.L.
      • Schumann G.
      • Schulz H.
      • Semmler M.
      • Takenaka S.
      • Stettmaier K.
      • Bors W.
      • Ghio A.
      • Samet J.M.
      • Heyder J.
      ,
      • Stone V.
      • Shaw J.
      • Brown D.M.
      • Macnee W.
      • Faux S.P.
      • Donaldson K.
      ,
      • Renwick L.C.
      • Brown D.
      • Clouter A.
      • Donaldson K.
      ). Carbon black (CB)
      The abbreviations used are: CB
      carbon black
      NALP3
      NACHT domain, leucine-rich-repeat (LRR) domain, and pyrin domain (PYD)-containing protein 3
      ROS
      reactive oxygen species
      YVAD
      benzyloxycarbonyl-Tyr-Val-Ala-Asp(OMe)-fluoromethyl ketone
      TEM
      transmission electron microscopy
      BET
      Brunauer-Emmett-Teller
      DLS
      dynamic light scattering
      XRD
      x-ray diffraction.
      nanoparticles can cause cytotoxic injury, increase levels of proinflammatory chemokines, and inhibit cell growth (
      • Yamawaki H.
      • Iwai N.
      ).
      There are several explanations for this increased toxicity, including the increased surface area of nanoparticles (
      • Oberdörster G.
      ,
      • Oberdörster G.
      • Ferin J.
      • Lehnert B.E.
      ,
      • Stone V.
      • Shaw J.
      • Brown D.M.
      • Macnee W.
      • Faux S.P.
      • Donaldson K.
      ,
      • Beck-Speier I.
      • Dayal N.
      • Karg E.
      • Maier K.L.
      • Roth C.
      • Ziesenis A.
      • Heyder J.
      ,
      • Hussain S.
      • Boland S.
      • Baeza-Squiban A.
      • Hamel R.
      • Thomassen L.C.
      • Martens J.A.
      • Billon-Galland M.A.
      • Fleury-Feith J.
      • Moisan F.
      • Pairon J.C.
      • Marano F.
      ,
      • Koike E.
      • Kobayashi T.
      ,
      • Mauderly J.L.
      • Snipes M.B.
      • Barr E.B.
      • Belinsky S.A.
      • Bond J.A.
      • Brooks A.L.
      • Chang I.Y.
      • Cheng Y.S.
      • Gillett N.A.
      • Griffith W.C.
      • Henderson R.F.
      • Mitchell C.E.
      • Nikula K.J.
      • Thomassen D.G.
      ,
      • Moss O.R.
      • Wong V.A.
      ,
      • Oberdörster G.
      • Oberdörster E.
      • Oberdörster J.
      ). In a previous study, acute adverse effects of different types of carbonaceous nanoparticles instilled in mice strongly correlated with particle size and surface area (
      • Stoeger T.
      • Reinhard C.
      • Takenaka S.
      • Schroeppel A.
      • Karg E.
      • Ritter B.
      • Heyder J.
      • Schulz H.
      ). A surface area threshold of ∼20 cm2 was defined for acute lung inflammation in mice below which no inflammatory responses were observed (
      • Stoeger T.
      • Reinhard C.
      • Takenaka S.
      • Schroeppel A.
      • Karg E.
      • Ritter B.
      • Heyder J.
      • Schulz H.
      ). CB nanoparticles showed higher surface reactivity compared with a similar dose of larger particles (
      • Brown D.M.
      • Dickson C.
      • Duncan P.
      • Al-Attili F.
      • Stone V.
      ). CB nanoparticles have also been shown to induce oxidative stress in alveolar macrophages, and it is believed that this capacity for oxidation may be mediated by particle surface functionality (
      • Koike E.
      • Kobayashi T.
      ,
      • Barlow P.G.
      • Clouter-Baker A.
      • Donaldson K.
      • Maccallum J.
      • Stone V.
      ,
      • Ma J.Y.
      • Ma J.K.
      ,
      • Ito T.
      • Ikeda M.
      • Yamasaki H.
      • Sagai M.
      • Tomita T.
      ,
      • Aam B.B.
      • Fonnum F.
      ,
      • Dick C.A.
      • Brown D.M.
      • Donaldson K.
      • Stone V.
      ). A recent study showed that the oxidative potency of CB nanoparticles correlates with their surface area and inflammatory responses (
      • Stoeger T.
      • Takenaka S.
      • Frankenberger B.
      • Ritter B.
      • Karg E.
      • Maier K.
      • Schulz H.
      • Schmid O.
      ). A possible mechanism for CB particle-related inflammation involves direct and indirect reactive oxygen species (ROS) generation by particle-cell interactions, which in turn activates redox-sensitive transcription of proinflammatory genes (
      • Stoeger T.
      • Takenaka S.
      • Frankenberger B.
      • Ritter B.
      • Karg E.
      • Maier K.
      • Schulz H.
      • Schmid O.
      ). ROS have been implicated as the cause of significant inflammation and, in some cases, cell death (
      • Martinon F.
      • Mayor A.
      • Tschopp J.
      ).
      One possible outcome of macrophage exposure to nanoparticles is cell death. Cell death may be categorized according to several characteristics including noninflammatory or proinflammatory and accidental or programmed. Apoptosis, perhaps the best characterized of these mechanisms, is a programmed and noninflammatory process. It is characterized by distinctive DNA cleavage as well as activation of the executioner caspases 3 and 9 (
      • Martinon F.
      • Mayor A.
      • Tschopp J.
      ,
      • Fink S.L.
      • Cookson B.T.
      ). In contrast to apoptosis, necrosis is defined as an accidental and proinflammatory form of cell death in which the plasma membrane loses its integrity, allowing rapid fluid influx, leading to cell swelling and lysis (
      • Fink S.L.
      • Cookson B.T.
      ,
      • Kepp O.
      • Galluzzi L.
      • Zitvogel L.
      • Kroemer G.
      ,
      • Bergsbaken T.
      • Fink S.L.
      • Cookson B.T.
      ). Pyroptosis is a recently described mechanism of cell death, sharing unique characteristics with both necrosis and apoptosis (
      • Fink S.L.
      • Cookson B.T.
      ,
      • Kepp O.
      • Galluzzi L.
      • Zitvogel L.
      • Kroemer G.
      ,
      • Bergsbaken T.
      • Fink S.L.
      • Cookson B.T.
      ,
      • Schroder K.
      • Tschopp J.
      ,
      • Suzuki T.
      • Franchi L.
      • Toma C.
      • Ashida H.
      • Ogawa M.
      • Yoshikawa Y.
      • Mimuro H.
      • Inohara N.
      • Sasakawa C.
      • Nuñez G.
      ). It is defined by its dependence on inflammasome activation and caspase 1 activity. Inflammasomes, which can differ in their subunit composition, have been shown to activate caspase 1, which in the setting of a microbial stimulus activates the proinflammatory cytokines IL-1β and IL-18 (
      • Kepp O.
      • Galluzzi L.
      • Zitvogel L.
      • Kroemer G.
      ,
      • Bergsbaken T.
      • Fink S.L.
      • Cookson B.T.
      ,
      • Cassel S.L.
      • Joly S.
      • Sutterwala F.S.
      ). Like apoptosis, pyroptosis is a form of programmed cell death. But unlike apoptosis, pyroptosis is characterized by loss of membrane integrity. This is due to caspase 1-dependent insertion of a pore into the membrane, leading to fluid influx, cell swelling, and lysis (
      • Fink S.L.
      • Cookson B.T.
      ). Pyroptosis ultimately leads to release of cellular contents and inflammation (
      • Fink S.L.
      • Cookson B.T.
      ,
      • Kepp O.
      • Galluzzi L.
      • Zitvogel L.
      • Kroemer G.
      ,
      • Bergsbaken T.
      • Fink S.L.
      • Cookson B.T.
      ,
      • Suzuki T.
      • Franchi L.
      • Toma C.
      • Ashida H.
      • Ogawa M.
      • Yoshikawa Y.
      • Mimuro H.
      • Inohara N.
      • Sasakawa C.
      • Nuñez G.
      ,
      • Fink S.L.
      • Cookson B.T.
      ,
      • Miao E.A.
      • Leaf I.A.
      • Treuting P.M.
      • Mao D.P.
      • Dors M.
      • Sarkar A.
      • Warren S.E.
      • Wewers M.D.
      • Aderem A.
      ).
      The recent expansion of the nanotechnology industry as well as the continually growing sources of combustion derived pollution warrants investigation into the potential health effects of these nanoparticles. In this study we examined the effect of CB nanoparticles on the inflammasome and pyroptosis. The data show that macrophage exposure to 20 ± 6 nm CB nanoparticles induces caspase 1 activation and IL-1β release and the proinflammatory form of cell death, pyroptosis.

      DISCUSSION

      In this study we found that CB nanoparticles induced cell death in macrophages and that this occurred in the absence of any detectable transition metals. These data show that after phagocytosis of the CB nanoparticles, macrophages increased in size; that is, the opposite of the cellular condensation associated with apoptosis. Macrophage exposure to CB nanoparticles led to inflammasome activation, as characterized by caspase 1 activation and IL-1β release. The identification of the cell death undergone by exposed cells as pyroptosis was confirmed by the inhibiting effects of both a caspase 1 inhibitor and a pyroptosis inhibitor on CB nanoparticle-induced cell death (Fig. 6B).
      A daily dose of CB in the working environment can be as large as 120 μg/kg person, assuming a threshold limiting value for respirable carbon black of 2.5 mg/m3 (
      • Vesterdal L.K.
      • Folkmann J.K.
      • Jacobsen N.R.
      • Sheykhzade M.
      • Wallin H.
      • Loft S.
      • Møller P.
      ). Additionally, an 8-h average amount of elemental carbon detected on a heavily traveled roadway in Harlem was 6.2 μg/m3 (
      • Kinney P.L.
      • Aggarwal M.
      • Northridge M.E.
      • Janssen N.A.
      • Shepard P.
      ), which corresponds to the alveoli burden of 7 μg, assuming a respiratory volume of 0.7 m3/h and 0.2 alveolar deposition fraction for 20-nm particles based on a human deposition model (
      • Cassee F.R.
      • Frijer J.I.
      • Subramaniam R.
      • Asgharian B.
      • Miller F.J.
      • van Bree L.
      • Rombout P.J.
      ). In the current study 30 μg/cm2 of CB nanoparticles were applied to cell culture wells. Although it is difficult to compare these doses with the mass/mass and mass/volume concentrations discussed above, it is within the mass range that is observed in occupational and environmental settings but does represent a substantial dose for respirable carbon black.
      Pyroptosis, a proinflammatory form of cell death, proceeds through the activation of the inflammasome, leading to cleavage of caspase 1 into its active form. Once activated, caspase 1 cleaves the proinflammatory cytokines IL-1β and IL-18 into their active forms, allowing for their release into the extracellular environment. Although indicative of caspase 1 activation, the release of these inflammatory cytokines is not required for caspase 1 activation or pyroptosis. The production of pro-IL-1β and pro-IL-18 is mediated by toll-like receptors. The release of active IL-1β and IL-18 associated with pyroptosis in previous reports (
      • Suzuki T.
      • Franchi L.
      • Toma C.
      • Ashida H.
      • Ogawa M.
      • Yoshikawa Y.
      • Mimuro H.
      • Inohara N.
      • Sasakawa C.
      • Nuñez G.
      ,
      • Miao E.A.
      • Leaf I.A.
      • Treuting P.M.
      • Mao D.P.
      • Dors M.
      • Sarkar A.
      • Warren S.E.
      • Wewers M.D.
      • Aderem A.
      ,
      • Sauer J.D.
      • Witte C.E.
      • Zemansky J.
      • Hanson B.
      • Lauer P.
      • Portnoy D.A.
      ,
      • Silveira T.N.
      • Zamboni D.S.
      ,
      • Ngai S.
      • Batty S.
      • Liao K.C.
      • Mogridge J.
      ,
      • Whitfield N.N.
      • Byrne B.G.
      • Swanson M.S.
      ,
      • Rupper A.C.
      • Cardelli J.A.
      ,
      • Fink S.L.
      • Bergsbaken T.
      • Cookson B.T.
      ,
      • Bergsbaken T.
      • Cookson B.T.
      ,
      • Fink S.L.
      • Cookson B.T.
      ) has all included toll-like receptor stimulatory effects of microbial antigens. Thus, although priming cells with LPS before nanoparticle exposure allows for an additional confirmation of caspase 1 activation, inflammasome activation can occur separately from LPS priming. This is supported by previous reports showing that caspase 1-induced cell death may proceed independently of IL-1β and IL-18 secretion when a microbial stimulus is not present (
      • Fink S.L.
      • Cookson B.T.
      ,
      • Monack D.M.
      • Navarre W.W.
      • Falkow S.
      ).
      Pyroptosis is characterized by a loss of membrane integrity (
      • Fink S.L.
      • Cookson B.T.
      ,
      • Kepp O.
      • Galluzzi L.
      • Zitvogel L.
      • Kroemer G.
      ,
      • Bergsbaken T.
      • Fink S.L.
      • Cookson B.T.
      ,
      • Fink S.L.
      • Cookson B.T.
      ). Although the exact mechanism of this remains unknown, it has been demonstrated that membrane pore formation occurs, leading to cell swelling and necrosis-like lysis. Our data supports pyroptosis after CB nanoparticle exposure with evidence of cell swelling, caspase 1 activation, and cell death.
      There have been a number of inflammasomes characterized with different subunits. Although this study does not specify which inflammasome CB nanoparticles activate, it has been shown that particulate matter including silica, asbestos, monosodium urate crystals, cholesterol crystals (
      • Cassel S.L.
      • Joly S.
      • Sutterwala F.S.
      ,
      • Duewell P.
      • Kono H.
      • Rayner K.J.
      • Sirois C.M.
      • Vladimer G.
      • Bauernfeind F.G.
      • Abela G.S.
      • Franchi L.
      • Nuñez G.
      • Schnurr M.
      • Espevik T.
      • Lien E.
      • Fitzgerald K.A.
      • Rock K.L.
      • Moore K.J.
      • Wright S.D.
      • Hornung V.
      • Latz E.
      ,
      • Cassel S.L.
      • Eisenbarth S.C.
      • Iyer S.S.
      • Sadler J.J.
      • Colegio O.R.
      • Tephly L.A.
      • Carter A.B.
      • Rothman P.B.
      • Flavell R.A.
      • Sutterwala F.S.
      ), and aluminum adjuvants (
      • Eisenbarth S.C.
      • Colegio O.R.
      • O'Connor W.
      • Sutterwala F.S.
      • Flavell R.A.
      ) induce a caspase 1-dependent inflammatory response mediated by the NALP3 inflammasome (
      • Martinon F.
      • Mayor A.
      • Tschopp J.
      ,
      • Cassel S.L.
      • Joly S.
      • Sutterwala F.S.
      ,
      • Martinon F.
      • Gaide O.
      • Pétrilli V.
      • Mayor A.
      • Tschopp J.
      ,
      • Martinon F.
      • Pétrilli V.
      • Mayor A.
      • Tardivel A.
      • Tschopp J.
      ,
      • Chen G.Y.
      • Nuñez G.
      ). As such, these data suggest that CB nanoparticles activate the NALP3 inflammasome as well, although ongoing studies will further characterize the CB nanoparticle inflammasome. To the best of our knowledge this is the first instance in which nanoparticles have been implicated in inducing pyroptosis (
      • Martinon F.
      • Mayor A.
      • Tschopp J.
      ).
      Several mechanisms of inflammasome activation have been proposed, including the generation of ROS (
      • Hussain S.
      • Thomassen L.C.
      • Ferecatu I.
      • Borot M.C.
      • Andreau K.
      • Martens J.A.
      • Fleury J.
      • Baeza-Squiban A.
      • Marano F.
      • Boland S.
      ,
      • Beck-Speier I.
      • Dayal N.
      • Karg E.
      • Maier K.L.
      • Schumann G.
      • Schulz H.
      • Semmler M.
      • Takenaka S.
      • Stettmaier K.
      • Bors W.
      • Ghio A.
      • Samet J.M.
      • Heyder J.
      ,
      • Hussain S.
      • Boland S.
      • Baeza-Squiban A.
      • Hamel R.
      • Thomassen L.C.
      • Martens J.A.
      • Billon-Galland M.A.
      • Fleury-Feith J.
      • Moisan F.
      • Pairon J.C.
      • Marano F.
      ,
      • Zhou R.
      • Yazdi A.S.
      • Menu P.
      • Tschopp J.
      ,
      • Tschopp J.
      • Schroder K.
      ,
      • Slane B.G.
      • Aykin-Burns N.
      • Smith B.J.
      • Kalen A.L.
      • Goswami P.C.
      • Domann F.E.
      • Spitz D.R.
      ,
      • Hu Y.
      • Mao K.
      • Zeng Y.
      • Chen S.
      • Tao Z.
      • Yang C.
      • Sun S.
      • Wu X.
      • Meng G.
      • Sun B.
      ,
      • Val S.
      • Hussain S.
      • Boland S.
      • Hamel R.
      • Baeza-Squiban A.
      • Marano F.
      ), potassium efflux (
      • Pétrilli V.
      • Papin S.
      • Dostert C.
      • Mayor A.
      • Martinon F.
      • Tschopp J.
      ), cathepsin B (
      • Davis M.J.
      • Swanson J.A.
      ), and phagosomal destabilization (
      • Aam B.B.
      • Fonnum F.
      ,
      • Hornung V.
      • Bauernfeind F.
      • Halle A.
      • Samstad E.O.
      • Kono H.
      • Rock K.L.
      • Fitzgerald K.A.
      • Latz E.
      ,
      • Chen G.Y.
      • Nuñez G.
      ,
      • Cassel S.L.
      • Sutterwala F.S.
      ). Disintegration of the cellular membrane by CB nanoparticles can cause the production of ROS. Aam and Fonnum (
      • Aam B.B.
      • Fonnum F.
      ) showed that low doses of CB nanoparticles activate rat alveolar macrophages to produce ROS. They suggested that the ERK MAPK pathway participates in intracellular signaling leading to the ROS generation. Hornung et al. (
      • Hornung V.
      • Bauernfeind F.
      • Halle A.
      • Samstad E.O.
      • Kono H.
      • Rock K.L.
      • Fitzgerald K.A.
      • Latz E.
      ) demonstrated that the NALP3 inflammasome activation induced by silica crystals and aluminum salts could be replicated via sterile lysosomal damage, implicating intracellular pH or cathepsin B activity in inflammasome activation. Even nanoparticles made from materials that are considered inert in bulk form have been found to induce pulmonary inflammation when exposure occurs with nanoscale particles. Although this study did not find TiO2 nanoparticles to be inflammasome activating in macrophages, Yazdi et al. (
      • Yazdi A.S.
      • Guarda G.
      • Riteau N.
      • Drexler S.K.
      • Tardivel A.
      • Couillin I.
      • Tschopp J.
      ) showed that in human keratinocytes nano-TiO2 activates the NALP3 inflammasome and induces IL-1β. Any or all of the potential mechanisms discussed may apply to the CB nanoparticle mechanism of inflammasome activation. Further investigation into the ROS generated by alveolar macrophages in response to CB nanoparticle exposure is warranted.
      The present study shows that macrophage exposure to CB nanoparticles activates the inflammasome leading to pyroptosis. CB merits further investigation into its mechanisms of inflammation modulation (increased IL-1β release) and pyroptosis. As a primary component in ambient pollution and diesel exhaust and a component of toners in printers used in office buildings worldwide, CB nanoparticles are a critical target for study. A better understanding of their mechanism of inflammasome activation may allow us to appropriately regulate potential health hazards.

      REFERENCES

        • Opitz B.
        • van Laak V.
        • Eitel J.
        • Suttorp N.
        Am. J. Respir. Crit. Care Med. 2010; 181: 1294-1309
        • Harada R.N.
        • Repine J.E.
        Chest. 1985; 87: 247-252
        • Twigg 3rd, H.L.
        Semin. Respir. Crit. Care Med. 2004; 25: 21-31
        • Sibille Y.
        • Reynolds H.Y.
        Am. Rev. Respir. Dis. 1990; 141: 471-501
        • Loeffler J.
        • Hedderich R.
        • Fiedeler U.
        • Malsch I.
        • Túquerres G.
        • Koskinen J.
        • Linden M.
        • Lojkowski W.
        • Moritz T.
        • Zins M.
        • Bernabeu E.
        • Larena A.
        Nanoroad SME European Project. European Union, Brussels, Belgium2010
        • Möller W.
        • Brown D.M.
        • Kreyling W.G.
        • Stone V.
        Part Fibre Toxicol. 2005; 2: 7
        • Hussain S.
        • Thomassen L.C.
        • Ferecatu I.
        • Borot M.C.
        • Andreau K.
        • Martens J.A.
        • Fleury J.
        • Baeza-Squiban A.
        • Marano F.
        • Boland S.
        Part. Fibre Toxicol. 2010; 7: 10
        • Lundborg M.
        • Johard U.
        • Låstbom L.
        • Gerde P.
        • Camner P.
        Environ Res. 2001; 86: 244-253
        • Lippmann M.
        • Yeates D.B.
        • Albert R.E.
        Br. J. Ind. Med. 1980; 37: 337-362
        • Oberdörster G.
        Ann. Occup. Hyg. 1994; 38 (421-402): 601-615
        • Ferin J.
        • Oberdörster G.
        • Penney D.P.
        Am. J. Respir. Cell Mol. Biol. 1992; 6: 535-542
        • Oberdörster G.
        • Ferin J.
        • Lehnert B.E.
        Environ. Health Perspect. 1994; 102: 173-179
        • Beck-Speier I.
        • Dayal N.
        • Karg E.
        • Maier K.L.
        • Schumann G.
        • Schulz H.
        • Semmler M.
        • Takenaka S.
        • Stettmaier K.
        • Bors W.
        • Ghio A.
        • Samet J.M.
        • Heyder J.
        Free Radic. Biol. Med. 2005; 38: 1080-1092
        • Stone V.
        • Shaw J.
        • Brown D.M.
        • Macnee W.
        • Faux S.P.
        • Donaldson K.
        Toxicol. In Vitro. 1998; 12: 649-659
        • Renwick L.C.
        • Brown D.
        • Clouter A.
        • Donaldson K.
        Occup. Environ. Med. 2004; 61: 442-447
        • Yamawaki H.
        • Iwai N.
        Circ. J. 2006; 70: 129-140
        • Beck-Speier I.
        • Dayal N.
        • Karg E.
        • Maier K.L.
        • Roth C.
        • Ziesenis A.
        • Heyder J.
        Environ. Health Perspect. 2001; 109: 613-618
        • Hussain S.
        • Boland S.
        • Baeza-Squiban A.
        • Hamel R.
        • Thomassen L.C.
        • Martens J.A.
        • Billon-Galland M.A.
        • Fleury-Feith J.
        • Moisan F.
        • Pairon J.C.
        • Marano F.
        Toxicology. 2009; 260: 142-149
        • Koike E.
        • Kobayashi T.
        Chemosphere. 2006; 65: 946-951
        • Mauderly J.L.
        • Snipes M.B.
        • Barr E.B.
        • Belinsky S.A.
        • Bond J.A.
        • Brooks A.L.
        • Chang I.Y.
        • Cheng Y.S.
        • Gillett N.A.
        • Griffith W.C.
        • Henderson R.F.
        • Mitchell C.E.
        • Nikula K.J.
        • Thomassen D.G.
        Research Report (Health Effects Institute). 1994; (discussion pp. 77–97): 1-75
        • Moss O.R.
        • Wong V.A.
        Inhal. Toxicol. 2006; 18: 711-716
        • Oberdörster G.
        • Oberdörster E.
        • Oberdörster J.
        Environ. Health Perspect. 2005; 113: 823-839
        • Stoeger T.
        • Reinhard C.
        • Takenaka S.
        • Schroeppel A.
        • Karg E.
        • Ritter B.
        • Heyder J.
        • Schulz H.
        Environ. Health Perspect. 2006; 114: 328-333
        • Brown D.M.
        • Dickson C.
        • Duncan P.
        • Al-Attili F.
        • Stone V.
        Nanotechnology. 2010; 21 (215104/215101–215104/215109)
        • Barlow P.G.
        • Clouter-Baker A.
        • Donaldson K.
        • Maccallum J.
        • Stone V.
        Part Fibre Toxicol. 2005; 2: 11
        • Ma J.Y.
        • Ma J.K.
        J. Environ. Sci. Health C Environ Carcinog Ecotoxicol. Rev. 2002; 20: 117-147
        • Ito T.
        • Ikeda M.
        • Yamasaki H.
        • Sagai M.
        • Tomita T.
        Environ Toxicol. Pharmacol. 2000; 9: 1-8
        • Aam B.B.
        • Fonnum F.
        Arch. Toxicol. 2007; 81: 441-446
        • Dick C.A.
        • Brown D.M.
        • Donaldson K.
        • Stone V.
        Inhal. Toxicol. 2003; 15: 39-52
        • Stoeger T.
        • Takenaka S.
        • Frankenberger B.
        • Ritter B.
        • Karg E.
        • Maier K.
        • Schulz H.
        • Schmid O.
        Environ. Health Perspect. 2009; 117: 54-60
        • Martinon F.
        • Mayor A.
        • Tschopp J.
        Annu. Rev. Immunol. 2009; 27: 229-265
        • Fink S.L.
        • Cookson B.T.
        Infect. Immun. 2005; 73: 1907-1916
        • Kepp O.
        • Galluzzi L.
        • Zitvogel L.
        • Kroemer G.
        Eur. J. Immunol. 2010; 40: 627-630
        • Bergsbaken T.
        • Fink S.L.
        • Cookson B.T.
        Nat. Rev. Microbiol. 2009; 7: 99-109
        • Schroder K.
        • Tschopp J.
        Cell. 2010; 140: 821-832
        • Suzuki T.
        • Franchi L.
        • Toma C.
        • Ashida H.
        • Ogawa M.
        • Yoshikawa Y.
        • Mimuro H.
        • Inohara N.
        • Sasakawa C.
        • Nuñez G.
        PLoS Pathog. 2007; 3: e111
        • Cassel S.L.
        • Joly S.
        • Sutterwala F.S.
        Semin. Immunol. 2009; 21: 194-198
        • Fink S.L.
        • Cookson B.T.
        Cell. Microbiol. 2006; 8: 1812-1825
        • Miao E.A.
        • Leaf I.A.
        • Treuting P.M.
        • Mao D.P.
        • Dors M.
        • Sarkar A.
        • Warren S.E.
        • Wewers M.D.
        • Aderem A.
        Nat. Immunol. 2010; 11: 1136-1142
        • Baltrusaitis J.
        • Usher C.R.
        • Grassian V.H.
        Phys. Chem. Chem. Phys. 2007; 9: 3011-3024
        • Monick M.M.
        • Powers L.S.
        • Barrett C.W.
        • Hinde S.
        • Ashare A.
        • Groskreutz D.J.
        • Nyunoya T.
        • Coleman M.
        • Spitz D.R.
        • Hunninghake G.W.
        J. Immunol. 2008; 180: 7485-7496
        • Monick M.M.
        • Powers L.S.
        • Gross T.J.
        • Flaherty D.M.
        • Barrett C.W.
        • Hunninghake G.W.
        J. Immunol. 2006; 177: 1636-1645
        • Monick M.M.
        • Powers L.S.
        • Walters K.
        • Lovan N.
        • Zhang M.
        • Gerke A.
        • Hansdottir S.
        • Hunninghake G.W.
        J. Immunol. 2010; 185: 5425-5435
        • Hansdottir S.
        • Monick M.M.
        Vitam. Horm. 2011; 86: 217-237
        • Brough D.
        • Rothwell N.J.
        J. Cell Sci. 2007; 120: 772-781
        • Perregaux D.
        • Gabel C.A.
        J. Biol. Chem. 1994; 269: 15195-15203
        • Walev I.
        • Reske K.
        • Palmer M.
        • Valeva A.
        • Bhakdi S.
        EMBO J. 1995; 14: 1607-1614
        • Hornung V.
        • Bauernfeind F.
        • Halle A.
        • Samstad E.O.
        • Kono H.
        • Rock K.L.
        • Fitzgerald K.A.
        • Latz E.
        Nat. Immunol. 2008; 9: 847-856
        • Dostert C.
        • Pétrilli V.
        • Van Bruggen R.
        • Steele C.
        • Mossman B.T.
        • Tschopp J.
        Science. 2008; 320: 674-677
        • Pétrilli V.
        • Papin S.
        • Dostert C.
        • Mayor A.
        • Martinon F.
        • Tschopp J.
        Cell death Differ. 2007; 14: 1583-1589
        • Yazdi A.S.
        • Guarda G.
        • Riteau N.
        • Drexler S.K.
        • Tardivel A.
        • Couillin I.
        • Tschopp J.
        Proc. Natl. Acad. Sci. U.S.A. 2010; 107: 19449-19454
        • Pazár B.
        • Ea H.K.
        • Narayan S.
        • Kolly L.
        • Bagnoud N.
        • Chobaz V.
        • Roger T.
        • Lioté F.
        • So A.
        • Busso N.
        J. Immunol. 2011; 186: 2495-2502
        • Guarda G.
        • Zenger M.
        • Yazdi A.S.
        • Schroder K.
        • Ferrero I.
        • Menu P.
        • Tardivel A.
        • Mattmann C.
        • Tschopp J.
        J. Immunol. 2011; 186: 2529-2534
        • Vesterdal L.K.
        • Folkmann J.K.
        • Jacobsen N.R.
        • Sheykhzade M.
        • Wallin H.
        • Loft S.
        • Møller P.
        Part. Fibre Toxicol. 2010; 7: 33
        • Kinney P.L.
        • Aggarwal M.
        • Northridge M.E.
        • Janssen N.A.
        • Shepard P.
        Environ. Health Perspect. 2000; 108: 213-218
        • Cassee F.R.
        • Frijer J.I.
        • Subramaniam R.
        • Asgharian B.
        • Miller F.J.
        • van Bree L.
        • Rombout P.J.
        Development of a Model for Human and Rat Airway Particle Deposition: Implications for Risk Assessment. National Institute of Public Health and the Environment, Bilthoven, The Netherlands1999
        • Davis M.J.
        • Swanson J.A.
        J. Leukoc. Biol. 2010; 88: 813-822
        • Sauer J.D.
        • Witte C.E.
        • Zemansky J.
        • Hanson B.
        • Lauer P.
        • Portnoy D.A.
        Cell Host Microbe. 2010; 7: 412-419
        • Silveira T.N.
        • Zamboni D.S.
        Infect. Immun. 2010; 78: 1403-1413
        • Ngai S.
        • Batty S.
        • Liao K.C.
        • Mogridge J.
        Febs J. 2010; 277: 119-127
        • Whitfield N.N.
        • Byrne B.G.
        • Swanson M.S.
        Infect. Immun. 2010; 78: 423-432
        • Rupper A.C.
        • Cardelli J.A.
        Infect. Immun. 2008; 76: 2304-2315
        • Fink S.L.
        • Bergsbaken T.
        • Cookson B.T.
        Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 4312-4317
        • Bergsbaken T.
        • Cookson B.T.
        PLoS Pathog. 2007; 3: e161
        • Fink S.L.
        • Cookson B.T.
        Cell. Microbiol. 2007; 9: 2562-2570
        • Monack D.M.
        • Navarre W.W.
        • Falkow S.
        Microbes Infect. 2001; 3: 1201-1212
        • Duewell P.
        • Kono H.
        • Rayner K.J.
        • Sirois C.M.
        • Vladimer G.
        • Bauernfeind F.G.
        • Abela G.S.
        • Franchi L.
        • Nuñez G.
        • Schnurr M.
        • Espevik T.
        • Lien E.
        • Fitzgerald K.A.
        • Rock K.L.
        • Moore K.J.
        • Wright S.D.
        • Hornung V.
        • Latz E.
        Nature. 2010; 464: 1357-1361
        • Cassel S.L.
        • Eisenbarth S.C.
        • Iyer S.S.
        • Sadler J.J.
        • Colegio O.R.
        • Tephly L.A.
        • Carter A.B.
        • Rothman P.B.
        • Flavell R.A.
        • Sutterwala F.S.
        Proc. Natl. Acad. Sci. U.S.A. 2008; 105: 9035-9040
        • Eisenbarth S.C.
        • Colegio O.R.
        • O'Connor W.
        • Sutterwala F.S.
        • Flavell R.A.
        Nature. 2008; 453: 1122-1126
        • Martinon F.
        • Gaide O.
        • Pétrilli V.
        • Mayor A.
        • Tschopp J.
        Semin. Immunopathol. 2007; 29: 213-229
        • Martinon F.
        • Pétrilli V.
        • Mayor A.
        • Tardivel A.
        • Tschopp J.
        Nature. 2006; 440: 237-241
        • Chen G.Y.
        • Nuñez G.
        Nat. Rev. Immunol. 2010; 10: 826-837
        • Zhou R.
        • Yazdi A.S.
        • Menu P.
        • Tschopp J.
        Nature. 2011; 469: 221-225
        • Tschopp J.
        • Schroder K.
        Nat. Rev. Immunol. 2010; 10: 210-215
        • Slane B.G.
        • Aykin-Burns N.
        • Smith B.J.
        • Kalen A.L.
        • Goswami P.C.
        • Domann F.E.
        • Spitz D.R.
        Cancer Res. 2006; 66: 7615-7620
        • Hu Y.
        • Mao K.
        • Zeng Y.
        • Chen S.
        • Tao Z.
        • Yang C.
        • Sun S.
        • Wu X.
        • Meng G.
        • Sun B.
        J. Immunol. 2010; 185: 7699-7705
        • Cassel S.L.
        • Sutterwala F.S.
        Eur. J. Immunol. 2010; 40: 607-611
        • Val S.
        • Hussain S.
        • Boland S.
        • Hamel R.
        • Baeza-Squiban A.
        • Marano F.
        Inhal. Toxicol. 2009; 21: 115-122