Denis Girard

Cell surface expression of intermediate filament proteins vimentin and lamin B1 in human neutrophil spontaneous apoptosis.

Neutrophils represent an important source of autoantigens for antineutrophil cytoplasmic antibody associated with vasculitis. To date, two cytoskeletal proteins, vinculin and vimentin, have been reported to be expressed on the cell surfaces of activated macrophages, platelets, and apoptotic T lymphocytes. However, such cell surface expression has never been studied in human neutrophils. As we recently demonstrated that different cytoskeletal proteins were cleaved in apoptotic neutrophils, we hypothesized that some of these were expressed on the cell surface of apoptotic neutrophils. Herein, we found that among vinculin, paxillin, gelsolin, vimentin, lamin B1, α‐tubulin, and β‐tubulin, only the two intermediate filament (INFIL) proteins, vimentin and lamin B1, are expressed on the cell surface of 24‐h aged neutrophils [spontaneous apoptosis (SA)]. By monitoring intracellular expression of vimentin and lamin B1 during SA, we found that these two proteins were cleaved and that such cleavage was reversed by the pan caspase inhibitor N‐benzyloxy‐carbonyl‐V‐A‐D‐O‐methylfluoromethyl ketone (z‐VAD‐fmk). When neutrophil apoptosis was delayed or suppressed by lipopolysaccharide or the cytokines granulocyte‐colony stimulating factor (G‐CSF), granulocyte macrophage (GM)‐CSF, or interleukin‐4, the loss of intracellular expression of vimentin and lamin B1 was prevented. The INFIL proteins were absent from the cell surface when neutrophil apoptosis was delayed. Addition of z‐VAD‐fmk significantly decreased the cell surface expression of vimentin and lamin B1 during SA. This study provides the first evidence that apoptotic neutrophils express cytoskeletal proteins on their surface, opening the possibility that these cells may participate in the development of autoantibodies directed against cytoskeletal proteins, a condition frequently reported in several inflammatory diseases.

Leishmania donovani Promastigotes Evade the Antimicrobial Activity of Neutrophil Extracellular Traps

Upon their recruitment to a site of infection and their subsequent activation, neutrophils release DNA and a subset of their granule content to form filamentous structures, known as neutrophil extracellular traps, which capture and kill microorganisms. In this study, we show that Leishmania promastigotes induced the rapid release of neutrophil extracellular traps from human neutrophils and were trapped by these structures. The use of Leishmania mutants defective in the biosynthesis of either lipophosphoglycan or GP63 revealed that these two major surface promastigote virulence determinants were not responsible for inducing the release of the surface protease neutrophil extracellular traps. We also demonstrate that this induction was independent of superoxide production by neutrophils. Finally, in contrast to wild-type Leishmania donovani promastigotes, mutants defective in lipophosphoglycan biosynthesis were highly susceptible to the antimicrobial activity of neutrophil extracellular traps. Altogether, our data suggest that neutrophil extracellular traps may contribute to the containment of L. donovani promastigotes at the site of inoculation, thereby facilitating their uptake by mononuclear phagocytes.

In Vivo and In Vitro Roles of IL-21 in Inflammation

IL-21 is a cytokine known to mediate its biological action via the IL-21R, composed of a specific chain, IL-21Rα, and the common γ-chain (CD132). Recent data suggest that IL-21 possesses proinflammatory properties. However, there is no clear evidence that IL-21 induces inflammation in vivo and, curiously, the interaction between IL-21 and neutrophils has never been investigated, despite the fact that these cells express CD132 and respond to other CD132-dependent cytokines involved in inflammatory disorders. Using the murine air pouch model, we found that IL-21 induced inflammation in vivo, based on recruitment of neutrophil and monocyte populations. In contrast to LPS, administration of IL-21 into the air pouch did not significantly increase the concentration of IL-6, CCL5, CCL3, and CXCL2. We demonstrated that HL-60 cells expressed IL-21Rα, which is down-regulated during their differentiation toward neutrophils, and that IL-21Rα is not detected in neutrophils. Concomitant with this, IL-21 induced Erk-1/2 phosphorylation in HL-60 cells, but not in neutrophils. To eliminate the possibility that IL-21 could activate neutrophils even in the absence of IL-21Rα, we demonstrated that IL-21 did not modulate several neutrophil functions. IL-21-induced Erk-1/2 phosphorylation was not associated with proliferation or differentiation of HL-60 toward neutrophils, monocytes, or macrophages. IL-21Rα was detected in human monocytes and monocyte-derived macrophages, but IL-21 increased CXCL8 production only in monocyte-derived macrophages. We conclude that IL-21 is a proinflammatory cytokine, but not a neutrophil agonist. We propose that IL-21 attracts neutrophils indirectly in vivo via a mechanism independent of IL-6, CCL3, CCL5, and CXCL2 production.

S100A8 and S100A9 Induce Cytokine Expression and Regulate the NLRP3 Inflammasome via ROS-Dependent Activation of NF-κB(1.).

S100A8 and S100A9 are cytoplasmic proteins expressed by phagocytes. High concentrations of these proteins have been correlated with various inflammatory conditions, including autoimmune diseases such as rheumatoid arthritis and Crohn’s disease, as well as autoinflammatory diseases. In the present study, we examined the effects of S100A8 and S100A9 on the secretion of cytokines and chemokines from PBMCs. S100A8 and S100A9 induced the secretion of cytokines such as IL-6, IL-8, and IL-1β. This secretion was associated with the activation and translocation of the transcription factor NF-κB. Inhibition studies using antisense RNA and the pharmacological agent BAY-117082 confirmed the involvement of NF-κB in IL-6, IL-8, and IL-1β secretion. S100A8- and S100A9-mediated activation of NF-κB, the NLR family, pyrin domain-containing 3 (NLRP3) protein, and pro-IL-1β expression was dependent on the generation of reactive oxygen species. This effect was synergistically enhanced by ATP, a known inflammasome activator. These results suggest that S100A8 and S100A9 enhance the inflammatory response by inducing cytokine secretion of PBMCs.

Activation of human neutrophils by titanium dioxide (TiO2) nanoparticles.

This paper describes the in vitro effects of titanium dioxide (TiO(2)) nanoparticles (NPs) upon human neutrophils. Kinetic experiments revealed no cell necrosis after 24h of treatment with TiO(2) (0-100 microg/ml). In contrast, TiO(2)-induced change in cellular morphology in a concentration-dependent manner in neutrophils over time, indicating its potential to activate these cells. To further support this, we demonstrated that TiO(2) markedly and rapidly induced tyrosine phosphorylation events, including phosphorylation of two key enzymes, p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinases-1/2 (Erk-1/2). We also determined the effects of TiO(2) on two neutrophil functions requiring a longer exposure period between NPs and cells: apoptosis and cytokine production. Interestingly, at concentrations >or=20 microg/ml, TiO(2) inhibited neutrophil apoptosis in a concentration-dependent manner after 24h of treatment. Supernatants from TiO(2)-induced neutrophils were harvested after 24h and tested for the presence of 36 different analytes (cytokines, chemokines) using an antibody array assay. TiO(2) treatment increased production of 13 (36%) analytes, including IL-8, which exhibited the greatest increase ( approximately 16 x control cell levels). The increased production of IL-8 was confirmed by ELISA. We conclude that TiO(2) exerts important neutrophil agonistic properties in vitro.

Mechanisms involved in interleukin-15-induced suppression of human neutrophil apoptosis: role of the anti-apoptotic Mcl-1 protein and several kinases including Janus kinase-2, p38 mitogen-activated protein kinase and extracellular signal-regulated kinases-1/2

Interleukin‐15 (IL‐15) is a pro‐inflammatory cytokine known as a general inhibitor of apoptosis, which possesses potential therapeutic properties. Although IL‐15 was previously found to be a human neutrophil agonist, its mode of action remains unknown. Herein, we were interested in elucidating the mechanisms by which it delays neutrophil apoptosis. IL‐15 was found to induce tyrosine phosphorylation events and to prevent loss of the anti‐apoptotic Mcl‐1 protein expression. Using different signal transduction inhibitors, we found that Janus kinase (Jak)‐2, Jak‐3, p38 mitogen‐activated protein kinase (MAPK) and extracellular signal‐regulated kinase (ERK), but not G proteins, are involved in IL‐15‐induced suppression of apoptosis. Furthermore, we found that IL‐15 activates Jak‐2, p38 MAPK and ERK‐1/2, but, unlike granulocyte macrophage‐colony‐stimulating factor (GM‐CSF), it does not activate signal transducer and activator of transcription (STAT)‐5a/b. We conclude that IL‐15 delays neutrophil apoptosis via several pathways, and that Mcl‐1 and several kinases contribute to this. We also conclude that, unlike GM‐CSF, IL‐15 does not activate the Jak‐2/STAT‐5 pathway found to be important in neutrophil signaling.

Mechanisms Involved in Spontaneous and Viscum album Agglutinin-I-Induced Human Neutrophil Apoptosis: Viscum album Agglutinin-I Accelerates the Loss of Antiapoptotic Mcl-1 Expression and the Degradation of Cytoskeletal Paxillin and Vimentin Proteins Via Caspases

Viscum album agglutinin-I (VAA-I) is a plant lectin that possesses interesting potential therapeutic properties and immunomodulatory activities. We have recently found that VAA-I is a potent inducer of human neutrophil apoptosis, but the mechanism(s) involved require further elucidation. In this study, we found that VAA-I alters mitochondrial transmembrane potential and increases intracellular levels of reactive oxygen species (ROS). Despite these observations, treatment with the mitochondrial stabilizer, bongkrekic acid, or with catalase, known to degrade H2O2, fails to reverse VAA-I-induced apoptosis. Moreover, VAA-I was found to induce apoptosis in PLB-985 cells deficient in gp91phox, indicating that the lectin acts via an ROS-independent mechanism. Pretreatment of neutrophils with brefeldin A, an inhibitor of vesicular transport, was found to reverse VAA-I-induced apoptosis. Protein expression of Mcl-1 was decreased by VAA-I. The role of caspases in the degradation of cytoskeletal proteins during both spontaneous and VAA-I-induced neutrophil apoptosis was also investigated. Paxillin and vimentin were markedly degraded by VAA-I when compared with neutrophils that undergo spontaneous apoptosis, but not vinculin or α- and β-tubulin. Caspases were involved in cytoskeletal protein degradation because preincubation with the pan-caspase inhibitor N-benzyloxycarbonyl-V-A-D-O-methylfluoromethyl ketone was found to reverse protein cleavage. We conclude that VAA-I needs to be internalized to mediate apoptosis and that its activity is not dependent on a cell surface receptor-mediated pathway. Also, we conclude that VAA-I induces apoptosis by ROS-independent and Mcl-1-dependent mechanisms and that caspases are involved in cytoskeletal protein degradation in both spontaneous and VAA-I-induced neutrophil apoptosis.

Induction of neutrophil degranulation by S100A9 via a MAPK-dependent mechanism.

S100A9 is a proinflammatory protein, expressed abundantly in the cytosol of neutrophils and monocytes. High extracellular S100A9 concentrations have been correlated with chronic inflammatory diseases such as rheumatoid arthritis and Crohns disease, as well as with phagocyte extravasation. This study tested the hypothesis that S100A9 induces degranulation in human neutrophils. S100A9 was found to up‐regulate the surface expression of CD35 and CD66b, proteins contained in secretory vesicles and specific/gelatinase granules, respectively. In addition, gelatinase and albumin, stored, respectively, in specific/gelatinase granules and secretory vesicles, were detected in the supernatants of neutrophils stimulated with S100A9. In contrast, stimulation with S100A9 had no effect on CD63 expression or MPO secretion, two proteins contained in azurophilic granules. S100A9 induced the phosphorylation of the MAPKs, ERK1/2, p38, and JNK. Inhibition of p38 and JNK but not ERK1/2, with specific inhibitors (SB203580, JNKII, and PD98059, respectively), blocked neutrophil degranulation induced by S100A9. Taken together, these results support the hypothesis and clearly indicate that S100A9 induces the degranulation of secretory and specific/gelatinase granules but not of azurophilic granules in a process involving p38 and JNK and further support its classification as a DAMP.

Damage-Associated Molecular Pattern S100A9 Increases Bactericidal Activity of Human Neutrophils by Enhancing Phagocytosis

The damage-associated molecular-pattern S100A9 is found at inflammatory sites in infections and various autoimmune diseases. It is released at very high concentrations in the extracellular milieu by activated neutrophils and monocytes in response to various agents. This proinflammatory protein is found in infected mucosae and tissue abscesses where it acts notably as a potent neutrophil activator. In this study, we examined the role of S100A9 in the control of infections. S100A9 was found to increase human neutrophil bactericidal activity toward Escherichia coli. Although S100A9 induced the accumulation of reactive oxygen species over time through the activation of NADPH oxidase, its antimicrobial activity was mediated mainly by enhancing the efficiency of neutrophil phagocytosis. Interestingly, S100A9 did not act by increasing cell surface expression of CD16, CD32, or CD64 in neutrophils, indicating that its biological effect in FcR-mediated phagocytosis is independent of upregulation of FcγR levels. However, S100A9-induced phagocytic activity required the phosphorylation of Erk1/2, Akt, and Syk. Taken together, our results demonstrate that S100A9 stimulates neutrophil microbicidal activity by promoting phagocytosis.

Spectroscopic and photophysical properties of some new rhodamine derivatives in cationic, anionic and neutral micelles

Abstract The spectroscopic and photophysical characterization of rhodamine 123 (dye 1 ), 4,5-dibromorhodamine methyl ester (dye 2 ) and 4,5-dibromorhodamine n-butyl ester (dye 3 ) are reported in homogeneous media like water and some alcohols and also in microheterogeneous media; anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral triton X-100 (TX) micelles. The selective biodistribution of these ionic drugs in tissues and membranes strongly influence their photosentisizing properties which have been part of our earlier studies. Results suggest that the hydrogen bonding capability of the amino end group lone pair of these dyes dominates in water. All these dyes interact with anionic SDS micelles. The interaction is mainly electrostatic in nature. At low SDs concentrations (below c.m.c.), dye-SDS aggregate formation takes place. But above c.m.c. only the monomeric dye form is observed. The penetration of dye 3 in SDS is a little less compared to dyes 1 and 2 . Dyes 2 and 3 show a finite interaction with CTAB micelle unlike dye 1 . With neutral TX micelles all the dyes form strong complexes. The fluorescence quantum yield ( Φ F ) of these three dyes in TX is lower. In time-resolved fluorescence experiments, two lifetimes are observed. The effects of the TX concentration on the fluorescence decay are measured. The decay associated spectra of dye 2 in TX are obtained by global compartmental analysis. The dye-surfactant interaction mechanisms are also discussed.