FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W2954005276> ?p ?o ?g. }

• W2954005276 abstract "Article2 July 2019Open Access Source DataTransparent process Malaria inflammation by xanthine oxidase-produced reactive oxygen species Maureen C Ty Maureen C Ty Department of Microbiology, New York University School of Medicine, New York, NY, USA Search for more papers by this author Marisol Zuniga Marisol Zuniga Department of Microbiology, New York University School of Medicine, New York, NY, USA Search for more papers by this author Anton Götz Anton Götz Department of Microbiology, New York University School of Medicine, New York, NY, USA Search for more papers by this author Sriti Kayal Sriti Kayal Department of Biotechnology and Medical Engineering, National Institute of Technology, Rourkela, Odisha, India Search for more papers by this author Praveen K Sahu Praveen K Sahu Center for the Study of Complex Malaria in India, Ispat General Hospital, Rourkela, Odisha, India Search for more papers by this author Akshaya Mohanty Akshaya Mohanty Infectious Diseases Biology Unit, Institute of Life Sciences, Bhubaneswar, Odisha, India Search for more papers by this author Sanjib Mohanty Sanjib Mohanty Center for the Study of Complex Malaria in India, Ispat General Hospital, Rourkela, Odisha, India Search for more papers by this author Samuel C Wassmer Samuel C Wassmer Department of Infection Biology, London School of Hygiene & Tropical Medicine, London, UK Search for more papers by this author Ana Rodriguez Corresponding Author Ana Rodriguez [email protected] orcid.org/0000-0002-0060-3405 Department of Microbiology, New York University School of Medicine, New York, NY, USA Search for more papers by this author Maureen C Ty Maureen C Ty Department of Microbiology, New York University School of Medicine, New York, NY, USA Search for more papers by this author Marisol Zuniga Marisol Zuniga Department of Microbiology, New York University School of Medicine, New York, NY, USA Search for more papers by this author Anton Götz Anton Götz Department of Microbiology, New York University School of Medicine, New York, NY, USA Search for more papers by this author Sriti Kayal Sriti Kayal Department of Biotechnology and Medical Engineering, National Institute of Technology, Rourkela, Odisha, India Search for more papers by this author Praveen K Sahu Praveen K Sahu Center for the Study of Complex Malaria in India, Ispat General Hospital, Rourkela, Odisha, India Search for more papers by this author Akshaya Mohanty Akshaya Mohanty Infectious Diseases Biology Unit, Institute of Life Sciences, Bhubaneswar, Odisha, India Search for more papers by this author Sanjib Mohanty Sanjib Mohanty Center for the Study of Complex Malaria in India, Ispat General Hospital, Rourkela, Odisha, India Search for more papers by this author Samuel C Wassmer Samuel C Wassmer Department of Infection Biology, London School of Hygiene & Tropical Medicine, London, UK Search for more papers by this author Ana Rodriguez Corresponding Author Ana Rodriguez [email protected] orcid.org/0000-0002-0060-3405 Department of Microbiology, New York University School of Medicine, New York, NY, USA Search for more papers by this author Author Information Maureen C Ty1, Marisol Zuniga1, Anton Götz1, Sriti Kayal2, Praveen K Sahu3, Akshaya Mohanty4, Sanjib Mohanty3, Samuel C Wassmer5 and Ana Rodriguez *,1 1Department of Microbiology, New York University School of Medicine, New York, NY, USA 2Department of Biotechnology and Medical Engineering, National Institute of Technology, Rourkela, Odisha, India 3Center for the Study of Complex Malaria in India, Ispat General Hospital, Rourkela, Odisha, India 4Infectious Diseases Biology Unit, Institute of Life Sciences, Bhubaneswar, Odisha, India 5Department of Infection Biology, London School of Hygiene & Tropical Medicine, London, UK *Corresponding author. Tel: +1 (646) 5016997; Fax: +1 (646) 5074645; E-mail: [email protected] EMBO Mol Med (2019)11:e9903https://doi.org/10.15252/emmm.201809903 PDFDownload PDF of article text and main figures. Peer ReviewDownload a summary of the editorial decision process including editorial decision letters, reviewer comments and author responses to feedback. ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InMendeleyWechatReddit Figures & Info Abstract Malaria is a highly inflammatory disease caused by Plasmodium infection of host erythrocytes. However, the parasite does not induce inflammatory cytokine responses in macrophages in vitro and the source of inflammation in patients remains unclear. Here, we identify oxidative stress, which is common in malaria, as an effective trigger of the inflammatory activation of macrophages. We observed that extracellular reactive oxygen species (ROS) produced by xanthine oxidase (XO), an enzyme upregulated during malaria, induce a strong inflammatory cytokine response in primary human monocyte-derived macrophages. In malaria patients, elevated plasma XO activity correlates with high levels of inflammatory cytokines and with the development of cerebral malaria. We found that incubation of macrophages with plasma from these patients can induce a XO-dependent inflammatory cytokine response, identifying a host factor as a trigger for inflammation in malaria. XO-produced ROS also increase the synthesis of pro-IL-1β, while the parasite activates caspase-1, providing the two necessary signals for the activation of the NLRP3 inflammasome. We propose that XO-produced ROS are a key factor for the trigger of inflammation during malaria. Synopsis Although malaria is a high inflammatory disease, during in vitro infection, macrophages fail to secrete inflammatory cytokines, suggesting that other factors contribute to the observed inflammation in patients. Oxidative stress cooperates with the parasite to induce an inflammatory response. Plasmodium falciparum infected erythrocytes (iRBC) do not induce a pro-inflammatory response in macrophages. Reactive oxygen species (ROS) produced by the enzyme xanthine oxidase (XO) result in macrophages secreting pro-inflammatory cytokines and chemokines. Addition of both iRBC and ROS results in the activation of the inflammasome and secretion of IL-1β in macrophages. ROS acting as signal 1 (generating pro-IL-1β) and iRBC as signal 2 (generating IL-1β). Introduction Malaria induces an extremely high inflammatory response which, coupled to the sequestration of Plasmodium falciparum-infected red blood cells (iRBC), plays a key role in the life-threatening pathologies associated with this disease (Clark, 2007; Clark et al, 2008). A remarkable paradox in malaria research is that the strong inflammatory cytokine response and high fevers in patients cannot be modeled in vitro, where incubation of the parasite with immune cells results in little to no response in immune cells, such as macrophages (Scragg et al, 1999; Couper et al, 2010; Zhou et al, 2012) or dendritic cells (Elliott et al, 2007; Giusti et al, 2011; Götz et al, 2017). It is important to note that older publications showing in vitro inflammation were latter attributed to mycoplasma contamination of the cultures (Rowe et al, 1998). The levels of oxidative stress in the circulation of malaria patients are elevated, as it is evident by the presence of high concentrations of plasma malondialdehyde, a by-product of lipid peroxidation, that is indicative of elevated oxidative stress (Narsaria et al, 2012). There are several sources of oxidative stress described in malaria: Plasmodium growth in erythrocytes (Atamna & Ginsburg, 1993), the macrophage oxidative burst (Kharazmi et al, 1987), and the upregulation of oxidative enzymes in the host (Iwalokun et al, 2006). Although they can all generate reactive oxygen species (ROS) during malaria, the relative contributions of each during infection are not known. Upregulation of xanthine oxidase (XO), a host oxidative enzyme, has been documented in the circulation of malaria patients, infected monkeys, and mice (Tubaro et al, 1980; Srivastava et al, 1992; Siddiqi et al, 1999; Iwalokun et al, 2006). The enzyme precursor of XO, xanthine dehydrogenase, is upregulated by activation of type I IFN receptor very early upon Plasmodium infection in mice (Guermonprez et al, 2013), suggesting that early sensing of malaria results in increased oxidative stress. In general, oxidative stress is known to cause inflammation through the destruction of tissues and release of danger signals by necrotic cells (Mittal et al, 2014). Here, we show an alternative mechanism where oxidative stress directly activates human macrophages to release inflammatory cytokines, identifying extracellular ROS a potent trigger of inflammation. In the context of malaria, we found that an inflammatory cytokine response could be triggered in macrophages simply by incubation with the plasma of malaria patients and that this response is dependent on XO, since a specific inhibitor of this enzyme can inhibit this response. These results implicate XO as a host-derived source of inflammation in malaria. Accordingly, we observed that patients with elevated XO activity also present high levels of plasma inflammatory cytokines and higher incidence of cerebral malaria. We have also observed that P. falciparum acts as signal 2 and synergizes with ROS which act as signal 1 for the activation of the NLRP3 inflammasome and the release of IL-1β by macrophages. Results To study the inflammatory response induced by P. falciparum, we incubated iRBC in the late developmental schizont stage with human macrophages derived from monocytes isolated from healthy donors. Little to no inflammatory cytokines are produced by these macrophages, which otherwise respond strongly to LPS (Fig 1A) and are fully viable (Appendix Fig S1). Similar results were observed when infected red blood cell lysates (iRBCL), which presumably contain potential pathogen-associated molecular patterns (PAMPs; Gazzinelli et al, 2014), were incubated with the macrophages (Fig 1B). A wide range of ratios of macrophages to iRBCL was tested in two independent experiments finding no detectable cytokine secretion at any concentration (Appendix Fig S2). Priming of macrophages with IFNγ (Fig 1C) or co-incubation with IFNα (Appendix Fig S3) before addition of iRBC (Glass & Natoli, 2015) also does not result in inflammatory cytokine secretion. We also observed that macrophages efficiently phagocytose iRBC (Fig 1D) and that incubation of macrophages with iRBC does not inhibit subsequent activation by LPS (Fig 1E), suggesting that the iRBC do not induce permanent inhibition of macrophage activation. Altogether, these data demonstrate that P. falciparum iRBC do not induce secretion of inflammatory cytokines by human monocyte-derived macrophages in vitro. Figure 1. Plasmodium falciparum-infected erythrocytes do not induce inflammatory cytokine secretion in human monocyte-derived macrophages A, B. Macrophages produce little to no inflammatory cytokines when incubated with either (A) whole iRBC or (B) fresh iRBCL for 24 h. One-way ANOVA with Tukey test for multiple comparisons was performed to determine statistical significance. C. Macrophages were pre-incubated with IFNγ (1,000 U/ml) for 18 h before iRBCL stimulation. One-way ANOVA with Tukey test for multiple comparisons was performed to determine statistical significance. D. Phase-contrast microscopy of macrophages 24 h after the addition of RBC, iRBC, or LPS. Dark hemozoin crystals can be observed within macrophages. Scale bar is 30 μm. E. Macrophages were incubated with iRBCL 24 h before addition of LPS. Paired t-test was performed to determine statistical significance. Data information: Each symbol represents the value obtained for cells from an independent donor in an independent experiment. (A) n = 4; (B) n = 5; (C) n = 3; (E) n = 3. Asterisks indicate significance (*P < 0.05, **P < 0.01, and ***P < 0.001) when values were compared with RBC (A–C) or RBCL (E). Source data are available online for this figure. Source Data for Figure 1 [emmm201809903-sup-0002-SDataFig1.pdf] Download figure Download PowerPoint Malaria induces a “cytokine storm” in patients, where elevated levels of cytokines are found in the bloodstream (Clark, 2007; Clark et al, 2008). This is in contrast with our observations that P. falciparum does not induce even a minimal inflammatory cytokine response in vitro and suggests that other factors must be involved in triggering the host inflammatory response. To study whether ROS, which are produced in large amounts during malaria, could contribute to the activation of the immune cells, we utilized XO, an enzyme involved in the oxidation of hypoxanthine and a potent producer of ROS (Battelli et al, 2016). XO is upregulated in children with malaria, and its levels increase with disease severity (Iwalokun et al, 2006). We observed that incubation of human macrophages in vitro with XO at a typical concentration found in the plasma of patients infected with P. falciparum (0.12 U/ml; Iwalokun et al, 2006) results in an increase of inflammatory cytokine secretion comparable to the one induced by LPS (Fig 2A). A dose–response analysis showed that increasing the concentrations of XO results in increased cytokine secretion by macrophages (Appendix Fig S4). Figure 2. Exposure to ROS promotes cytokine secretion from human macrophages and from PBMC A–E. Cytokine secretion of macrophages (A–D) or PBMC (E) incubated with the indicated stimuli for 24 h. RBC, iRBC, RBCL, iRBCL, XO, hypoxanthine (Hyx), the anti-oxidants N-acetyl-l-cysteine (NAC), and 1-thioglycerol (1-TG), and heat inactivated (HI) XO were added to macrophages for 24 h. Febuxostat (Feb) was pre-incubated for 30 min with XO before addition to macrophages. Each symbol represents the value obtained for cells from an independent donor in an independent experiment. Insets show paired samples by donor in two different conditions. Blue asterisks indicate significance when values were compared with RBCL (A, E) or XO (B–D). Gray asterisks mark comparison with control (B–D). (A) n = 7; (B–E) n = 3. One-way ANOVA with Tukey test for multiple comparisons was performed to determine statistical significance (*P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001). Source data are available online for this figure. Source Data for Figure 2 [emmm201809903-sup-0003-SDataFig2.pdf] Download figure Download PowerPoint Increasing the concentration of hypoxanthine, the substrate for XO, results in higher levels of cytokine secretion (Fig 2B), while incubation with the specific inhibitor of XO febuxostat (Osada et al, 1993) results in decreased cytokine release (Fig 2C). These results confirm the XO specificity of the observed response and exclude the possibility that the cytokine secretion was caused by contamination of the XO. Furthermore, inactivation of XO activity by heat treatment and addition of anti-oxidants, either membrane permeant or not, decreases cytokine secretion by macrophages incubated with XO (Fig 2D), indicating that the inflammatory activity is mediated by XO-produced ROS. We also studied the response of whole peripheral blood mononuclear cells (PBMCs) to P. falciparum iRBC, whole or lysate, finding a weak cytokine response which was not significantly different than the RBC controls. PBMC also responded strongly to XO stimulation (Fig 2E). XO produces ROS in the form of superoxide, which rapidly dismutates to H2O2 (Knowles et al, 1969) and permeates cell membranes reaching the cytosol (Bienert et al, 2007). We observed that cytokine secretion was not induced by the addition of H2O2 (Appendix Fig S5), which is short-lived within cells (Rhee et al, 2005). However, incubation of macrophages with XO for different times revealed that cytokine secretion requires exposure to the enzyme for at least 15 min (Fig 3A), suggesting that a prolonged exposure to ROS is necessary for the activation of the inflammatory response. Figure 3. Prolonged exposure to extracellular ROS induces cytokine secretion A. XO was incubated with macrophages for the indicated times, when wells were washed twice and media was replaced. Supernatants were collected for cytokine determinations 24 h later (n = 3). Error bars show standard deviation. Kruskal–Wallis statistical method was used for statistical analysis. Blue asterisks indicate significance when values were compared with time 0 (*P < 0.05). B. Diagram shows experimental set up with macrophages in the bottom of the well and XO added either in the dialysis cassette (DC, blue) or the well (black). XO activity panels show that the enzyme did not leak through the DC membrane. Secretion of IL-6 and TNF was measured 24 h after addition of XO in each compartment. A representative result of two independent experiments is shown. Source data are available online for this figure. Source Data for Figure 3 [emmm201809903-sup-0004-SDataFig3.pdf] Download figure Download PowerPoint Since intracellular ROS are a well-characterized second messenger in the signaling cascade for immune cell activation (Schieber & Chandel, 2014), we next determined whether cytokine secretion could be triggered strictly by extracellular ROS or if it required intracellular production of these reactive molecules. We observed that physical separation of XO from macrophages through a dialysis membrane did not interfere with macrophage activation, indicating that extracellular ROS can induce cytokine secretion in macrophages (Fig 3B). These results expand the traditional view where activation of toll-like receptors (TLRs) or cytokine receptors induce intracellular ROS that act as second messengers, resulting in NFkB-mediated cytokine secretion (Nathan & Cunningham-Bussel, 2013). To study the relevance of XO-produced ROS during P. falciparum infection, we first determined the relation between oxidative stress resulting from XO activity in the plasma of malaria patients and the levels of inflammatory cytokines. XO activity was measured by detecting ROS produced by plasma XO after addition of excess concentrations of its substrate, hypoxanthine. Under these conditions, the assay reflects the levels of oxidative stress produced by XO that are not quenched by anti-oxidants in the plasma, providing a measurement of the oxidant/anti-oxidant balance for each patient sample. We observed that two cytokines, TNF and IL-8, showed a significant correlation with plasma XO activity (Fig 4A), suggesting an involvement of this enzyme in malaria-induced inflammation. We also observed that patients with cerebral malaria showed higher levels of XO activity compared to patients with uncomplicated malaria (Fig 4B), suggesting a role for oxidative stress in the pathogenesis of this complication. Figure 4. XO inflammatory activity in malaria patients and relation to cerebral malaria A. Plasma levels of TNF and IL-8 from patients with uncomplicated (black circles, n = 14) or cerebral (red circles, n = 9) malaria correlate with levels of XO-produced ROS detected in each sample. ROS is expressed as fold change over plasma from healthy controls. Uncomplicated malaria, gray circles, cerebral malaria, red circles. B. Levels of XO activity in malaria patients correlate with disease severity UM (uncomplicated malaria, n = 14) and CM (cerebral malaria, n = 9). Error bars show standard deviation. C. Plasma from malaria patients induces macrophages to secrete cytokines, which are inhibited by a XO-specific inhibitor. Plasma from a healthy control (HP) and from three patients: P1 (with cerebral malaria), P2, and P3 (both with uncomplicated malaria), was pre-incubated for 30 min with febuxostat (Feb) or alone at 37°C before addition to macrophages at 1:2 dilution in media for 30 min. Cells were washed and cytokine secretion measured in triplicates after 24 h of incubation. Data information: Linear regression (A), Mann–Whitney test (B), and unpaired t-tests (C) were performed to determine statistical significance (*P < 0.05, **P < 0.01). Source data are available online for this figure. Source Data for Figure 4 [emmm201809903-sup-0005-SDataFig4.pdf] Download figure Download PowerPoint To determine whether plasma XO in malaria patients is responsible for triggering an inflammatory response in macrophages, we incubated plasma from malaria patients with macrophages in vitro. We observed that plasma samples from malaria patients can induce inflammatory cytokine secretion in macrophages that is inhibited by febuxostat (Fig 4C), indicating that XO is required for the generation of this response. Interestingly, the sample with higher levels of XO activity (twofold increase over healthy control plasma samples) corresponded to a patient with cerebral malaria and also induced a higher inflammatory response in macrophages. The plasma from the two patients with uncomplicated malaria presented lower levels of XO activity and inflammation in vitro. It is important to note that no parasites or infected cells were added to this assay, suggesting that at least part of the inflammatory response triggered during malaria is not induced directly by the parasite. Next, we investigated how oxidative stress contributes to inflammation in the context of malaria, where macrophages are simultaneously exposed to ROS and Plasmodium. We observed that when macrophages are incubated with P. falciparum iRBCL in the presence of XO, a synergistic increase is observed in the secretion of IL-1β, but not of TNF, IL-6, or IL-10 (Fig 5A). Although iRBCL alone did not induce secretion of IL-1β, it increased the secretion of this cytokine in response to XO by 20-fold. This increase is specific of iRBCL and dependent on its concentration (Fig 5B), indicating that infected, but not uninfected, erythrocytes synergize with ROS leading to increased release of IL-1β. Co-incubation of macrophages with XO and iRBCL also induced synergistic production of the chemokines IL-8, CCL5, and CCL2 (Fig 5C), which are essential in the recruitment and activation of leukocytes to sites of inflammation (Luster, 1998) and are also elevated during malaria (Ioannidis et al, 2014). Figure 5. ROS and Plasmodium falciparum-infected erythrocytes generate synergistic secretion of IL-1β and chemokines A–C. Cytokine and chemokine secretion by macrophages after 24 h incubation with the indicated stimuli. (B) IL-1β levels after addition of increasing concentration of RBCL or iRBCL (1:2, 1:4, and 1:8 macrophage:iRBCL). One-way ANOVA with Tukey test for multiple comparisons was performed to determine statistical significance. Asterisks indicate significance when values are compared with XO + RBCL (*P < 0.05 and ***P < 0.001). Each symbol represents the value obtained for cells from an independent donor in an independent experiment. (A) n = 4; (B) n = 2; (C) n = 4. Insets show paired samples by donor in two different conditions. Source data are available online for this figure. Source Data for Figure 5 [emmm201809903-sup-0006-SDataFig5.pdf] Download figure Download PowerPoint Elevated levels of IL-1β lead to inflammatory events such as fever, increased circulating neutrophils, upregulation of surface markers in cells, extensive nitric oxide production, and elevated levels of CRP and inflammatory cytokines (Dinarello, 1996, 2009; Cahill & Rogers, 2008), which are all common in malaria (Mackintosh et al, 2004). We propose that elevated levels of IL-1β induced by ROS contribute to the systemic inflammation in malaria. The expression and release of IL-1β are mediated through the standard two-checkpoint model of priming and activation (He et al, 2016). Priming, considered signal 1, is classically mediated by the activation of TLRs, whose downstream signaling leads to the translocation of NFκB and the production of pro-IL-1β. Activation, or signal 2, promotes the assembly of a multimeric protein complex called the inflammasome, culminating in the autocatalyzation of caspase-1, the subsequent cleavage of pro-IL-1β, and the release of bioactive IL-1β (Broz & Dixit, 2016). Gene expression analysis of macrophages incubated with XO shows greatly augmented IL-1β transcripts that are not much further increased when iRBCL are added (Fig 6A). Detection of pro-IL-1β protein in macrophages reveals that its presence is dependent on XO, but not on iRBCL (Fig 6B), indicating that XO is acting as signal 1 in macrophages. In contrast, activation of caspase-1 in macrophages is dependent on iRBCL, but not on XO (Fig 6C), assigning the function of signal 2 to iRBCL. This model is consistent with the synergistic increase in IL-1β secretion that is observed after the addition of iRBCL to XO-treated macrophages (Fig 5A and B). These data indicate that priming of macrophages is achieved by exposure to extracellular ROS, which promotes the production of pro-IL-1β, while the presence of infected erythrocytes mobilizes the inflammasome, propelling to the activation of caspase-1 and the consequent cleavage and release of bioactive IL-1β. Figure 6. ROS prime macrophages for Plasmodium falciparum-infected erythrocytes activation of the NLRP3 inflammasome A. Gene expression analysis of macrophages incubated with the indicated stimuli expressed as fold change over RBCL. Dotted red line indicates 2-fold increase in RNA expression. B. Western Blot analysis of pro-IL-1β. Relative abundance is the average of three independent experiments with different donors. Error bars show standard deviation. C. FLICA analysis of activated caspase-1. Results are representative of two independent experiments with different donors. D. Two distinct siRNAs against NLRP3 and an irrelevant control siRNA were utilized to knock down RNA levels by lipofectamine transfection in macrophages that were later incubated with iRBCL, or RBCL as control, with or without XO, before quantification of secreted IL-1β. Results are representative of two independent experiments with different donors. E. Diagram of macrophage inflammasome activation by XO and iRBC. Source data are available online for this figure. Source Data for Figure 6 [emmm201809903-sup-0007-SDataFig6.pdf] Download figure Download PowerPoint NLRP3 has consistently been implicated as a sensor for inflammasome activation in monocytes from both P. falciparum and Plasmodium vivax malaria patients (Ataide et al, 2014; Hirako et al, 2015). To determine whether NLRP3 is the inflammasome sensor molecule activated by P. falciparum in macrophages, we transfected human monocyte-derived macrophages with siRNA to knockdown expression of NLRP3. We achieved a 50% reduction in NLRP3 mRNA expression (Appendix Fig S6). When NLRP3-siRNA-transfected macrophages were incubated with both iRBCL and XO, they fail to secrete IL-1β compared to cells transfected with control siRNA (Fig 6D), implicating NLRP3 as the sensor that recognizes the parasite and leads the formation of the inflammasome in human macrophages. Conversely, the levels of other inflammatory cytokines and chemokines were not changed by NLRP3-siRNA transfection (Appendix Fig S7), which suggests that the increase observed in response to XO and iRBC stimulation (Fig 5C) is independent of IL-1β. Taken together, these results indicate that in human macrophages, extracellular ROS function as a signal 1, triggering the production of pro-IL-1β, while Plasmodium provides signal 2 for the activation of the NLRP3 inflammasome, resulting in the activation of caspase-1, which cleaves pro-IL-1β into mature IL-1β (Fig 6E). Discussion Since the host inflammatory response contributes decisively to the pathology caused by Plasmodium infection (Mackintosh et al, 2004), understanding the mechanisms causing inflammation in malaria is of crucial importance. However, progress has been hindered by the lack of an in vitro model of inflammation since incubation of the parasite with macrophages or dendritic cells results in little to no response (Scragg et al, 1999; Elliott et al, 2007; Couper et al, 2010; Giusti et al, 2011; Zhou et al, 2012). Although PBMC incubation with iRBC results in detectable cytokine responses, which have been previously attributed mainly to monocytes and γδ-T cells (D'Ombrain et al, 2008; Stanisic et al, 2014), we found that they were not statistically significant and much lower than the responses observed to LPS. Several pathogen-associated molecular patterns have been identified in P. falciparum, including GPI anchors, hemozoin, and parasite DNA (Gazzinelli et al, 2014). When purified from iRBC, these molecules are able to induce inflammatory cytokine responses from immune cells in vitro (Gazzinelli et al, 2014); however, these in vitro assays frequently use high concentrations of purified molecules that do not correspond to physiological concentrations of parasite and a direct comparison of purified molecules and whole iRBC or iRBCL were not performed. It is also possible that whole parasites are able to inhibit specific responses by these active molecules. Their relative contribution to malaria-induced inflammation and pathology in patients remains unclear (Erdman et al, 2008). Considering the strong inflammatory responses observed in malaria patients, other factors beyond the parasite and infected erythrocytes must be involved in triggering the host inflammatory response. Our results point to oxidative stress, and in particular, extracellular ROS, as a trigger of inflammation in malaria since they are abundantly produced during infection and, as we describe here, are potent inducers of inflammatory cytokines. An important r" @default.
• W2954005276 created "2019-07-12" @default.
• W2954005276 creator A5007697425 @default.
• W2954005276 creator A5009417128 @default.
• W2954005276 creator A5011506453 @default.
• W2954005276 creator A5016246281 @default.
• W2954005276 creator A5021360176 @default.
• W2954005276 creator A5024247402 @default.
• W2954005276 creator A5027617404 @default.
• W2954005276 creator A5031492297 @default.
• W2954005276 creator A5082178864 @default.
• W2954005276 date "2019-07-02" @default.
• W2954005276 modified "2023-10-16" @default.
• W2954005276 title "Malaria inflammation by xanthine oxidase‐produced reactive oxygen species" @default.
• W2954005276 cites W1515994079 @default.
• W2954005276 cites W1583717072 @default.
• W2954005276 cites W1963775811 @default.
• W2954005276 cites W1964166589 @default.
• W2954005276 cites W1964465730 @default.
• W2954005276 cites W1966459680 @default.
• W2954005276 cites W1966495986 @default.
• W2954005276 cites W1966728092 @default.
• W2954005276 cites W1967321177 @default.
• W2954005276 cites W1976599392 @default.
• W2954005276 cites W1985299940 @default.
• W2954005276 cites W1985776151 @default.
• W2954005276 cites W1993419780 @default.
• W2954005276 cites W2005659566 @default.
• W2954005276 cites W2007416146 @default.
• W2954005276 cites W2015225308 @default.
• W2954005276 cites W2021650047 @default.
• W2954005276 cites W2023039478 @default.
• W2954005276 cites W2023750774 @default.
• W2954005276 cites W2042458891 @default.
• W2954005276 cites W2044508593 @default.
• W2954005276 cites W2047433660 @default.
• W2954005276 cites W2059535228 @default.
• W2954005276 cites W2062723222 @default.
• W2954005276 cites W2065631534 @default.
• W2954005276 cites W2074987160 @default.
• W2954005276 cites W2076904478 @default.
• W2954005276 cites W2077857097 @default.
• W2954005276 cites W2084141237 @default.
• W2954005276 cites W2091049332 @default.
• W2954005276 cites W2091162467 @default.
• W2954005276 cites W2094156327 @default.
• W2954005276 cites W2094908805 @default.
• W2954005276 cites W2095145392 @default.
• W2954005276 cites W2101926861 @default.
• W2954005276 cites W2106541447 @default.
• W2954005276 cites W2106852899 @default.
• W2954005276 cites W2118183269 @default.
• W2954005276 cites W2120063294 @default.
• W2954005276 cites W2135200515 @default.
• W2954005276 cites W2142636542 @default.
• W2954005276 cites W2145598189 @default.
• W2954005276 cites W2148657042 @default.
• W2954005276 cites W2156412035 @default.
• W2954005276 cites W2163330518 @default.
• W2954005276 cites W2164889791 @default.
• W2954005276 cites W2165275387 @default.
• W2954005276 cites W2169458802 @default.
• W2954005276 cites W2175375539 @default.
• W2954005276 cites W2210414257 @default.
• W2954005276 cites W2216289728 @default.
• W2954005276 cites W2252393368 @default.
• W2954005276 cites W2270686920 @default.
• W2954005276 cites W2275772309 @default.
• W2954005276 cites W2431987552 @default.
• W2954005276 cites W2522054313 @default.
• W2954005276 cites W2583179451 @default.
• W2954005276 cites W2595079717 @default.
• W2954005276 cites W2769499678 @default.
• W2954005276 cites W299728681 @default.
• W2954005276 doi "https://doi.org/10.15252/emmm.201809903" @default.
• W2954005276 hasPubMedCentralId "https://www.ncbi.nlm.nih.gov/pmc/articles/6685105" @default.
• W2954005276 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/31265218" @default.
• W2954005276 hasPublicationYear "2019" @default.
• W2954005276 type Work @default.
• W2954005276 sameAs 2954005276 @default.
• W2954005276 citedByCount "37" @default.
• W2954005276 countsByYear W29540052762019 @default.
• W2954005276 countsByYear W29540052762020 @default.
• W2954005276 countsByYear W29540052762021 @default.
• W2954005276 countsByYear W29540052762022 @default.
• W2954005276 countsByYear W29540052762023 @default.
• W2954005276 crossrefType "journal-article" @default.
• W2954005276 hasAuthorship W2954005276A5007697425 @default.
• W2954005276 hasAuthorship W2954005276A5009417128 @default.
• W2954005276 hasAuthorship W2954005276A5011506453 @default.
• W2954005276 hasAuthorship W2954005276A5016246281 @default.
• W2954005276 hasAuthorship W2954005276A5021360176 @default.
• W2954005276 hasAuthorship W2954005276A5024247402 @default.
• W2954005276 hasAuthorship W2954005276A5027617404 @default.
• W2954005276 hasAuthorship W2954005276A5031492297 @default.
• W2954005276 hasAuthorship W2954005276A5082178864 @default.
• W2954005276 hasBestOaLocation W29540052761 @default.
• W2954005276 hasConcept C178790620 @default.
• W2954005276 hasConcept C181199279 @default.
• W2954005276 hasConcept C185592680 @default.

• next