Human neutrophil (PMN) oxygen radical production and the cytoskeleton

Maitake beta-glucan promotes recovery of leukocytes and myeloid cell function in peripheral blood from paclitaxel hematotoxicity

Bone marrow myelotoxicity is a major limitation of chemotherapy. While granulocyte colony stimulating factor (G-CSF) treatment is effective, alternative approaches to support hematopoietic recovery are sought. We previously found that a beta-glucan extract from maitake mushroom Grifola frondosa (MBG) enhanced colony forming unit-granulocyte monocyte (CFU-GM) activity of mouse bone marrow and human hematopoietic progenitor cells (HPC), stimulated G-CSF production and spared HPC from doxorubicin toxicity in vitro. This investigation assessed the effects of MBG on leukocyte recovery and granulocyte/monocyte function in vivo after dose intensive paclitaxel (Ptx) in a normal mouse. After a cumulative dose of Ptx (90-120 mg/kg) given to B6D2F1mice, daily oral MBG (4 or 6 mg/kg), intravenous G-CSF (80 microg/kg) or Ptx alone were compared for effects on the dynamics of leukocyte recovery in blood, CFU-GM activity in bone marrow and spleen, and granulocyte/monocyte production of reactive oxygen species (ROS). Leukocyte counts declined less in Ptx + MBG mice compared to Ptx-alone (p = 0.024) or Ptx + G-CSF treatment (p = 0.031). Lymphocyte levels were higher after Ptx + MBG but not Ptx + G-CSF treatment compared to Ptx alone (p < 0.01). MBG increased CFU-GM activity in bone marrow and spleen (p < 0.001, p = 0.002) 2 days after Ptx. After two additional days (Ptx post-day 4), MBG restored granulocyte/monocyte ROS response to normal levels compared to Ptx-alone and increased ROS response compared to Ptx-alone or Ptx + G-CSF (p < 0.01, both). The studies indicate that oral MBG promoted maturation of HPC to become functionally active myeloid cells and enhanced peripheral blood leukocyte recovery after chemotoxic bone marrow injury.

Effects of CNI-1493 on human granulocyte functions

During acute bacterial infections such as sepsis and meningitis, activation of inflammatory mediators such as nitric oxide (NO) plays a crucial role in both pathogenesis and host defense. We have previously reported that CNI-1493, a macrophage deactivator, reduced mortality in infant rats infected with Haemophilus influenzae type b (Hib) with associated decrease in the number of granulocytes in the infected tissue. The aim of the present study was to investigate how CNI-1493 affects granulocytes and macrophages in vitro. Murine macrophages (RAW 264.7) pre-incubated with CNI-1493 prior to activation with lipopolysaccharide (LPS)/interferon gamma (IFNgamma) had decreased NO production measured as NO(2)(-)/NO(3)(-) levels and reduction in inducible NO-synthase (iNOS) expression. Reactive oxygen species (ROS) production was increased in formylmethionyl-leucyl-phenylalanine (FMLP)-stimulated granulocytes following CNI-1493 treatment, whereas F-actin content, motility and chemotaxis were decreased under the same conditions. The effects of CNI-1493 on both NO production in LPS/IFNgamma-activated macrophages and ROS production, F-actin content, motility and chemotaxis in granulocytes, may contribute to the reduced inflammatory response and increased survival in Hib-infected animals treated with CNI-1493.

The effect of selective phosphodiesterase isoenzyme inhibition on neutrophil function in vitro

Neutrophil-derived proteases such as neutrophil elastase (NE) and matrix metalloproteinase (MMP) are implicated in the pathogenesis of Chronic Obstructive Pulmonary Disease (COPD). In this study, the effects of selective phosphodiesterase (PDE) inhibition on NE and MMP-9 release, as well as Myeloperoxidase (MPO) activity and integrin-mediated neutrophil adhesion to human umbilical vein endothelial cells (HUVECs), were investigated. Human neutrophils were treated with PDE inhibitors (10(-11)-10(-4)M) in the absence and presence of TNF-alpha (tumour necrosis factor) (100 U ml(-1)) for 30 min, prior to fMLP activation. After 45 min, the cells were removed and NE, MPO and MMP-9 release assessed. In the adhesion studies, the neutrophils were radio-labelled with 51Cr, stimulated and immediately transferred to cultured HUVEC monolayers for 30 min, prior to assessment of adhesion. TNF-alpha (100 U ml(-1)) acted synergistically with fMLP in stimulating azurophil degranulation with respect to both MPO activity (P<0.01) and NE release (P<0.01). In contrast, an additive effect was observed with TNF-alpha and fMLP with regard to MMP-9 release and neutrophil adhesion to HUVECs. The PDE4 inhibitors, roflumilast, roflumilast N-oxide, cilomilast and rolipram significantly suppressed MPO, NE and MMP-9 release in both the presence and absence of TNF-alpha (P<0.05; n=6-10) and also reduced neutrophil adhesion to HUVECs. In contrast, milrinone, a PDE3 inhibitor and the non-selective PDE inhibitor, theophylline did not inhibit azurophil degranulation under any of the experimental conditions. These data provide further evidence that selective PDE4 isoenzyme inhibitors can inhibit neutrophil degranulation, effects not shared by PDE3 inhibitors or theophylline.

Differential mitogen-activated protein kinase stimulation by Fc gamma receptor IIa and Fc gamma receptor IIIb determines the activation phenotype of human neutrophils

Fc gamma Rs mediate immune complex-induced tissue injury. The hypothesis that Fc gamma RIIa and Fc gamma RIIIb control neutrophil responses by activating mitogen-activated protein kinases was examined. Homotypic and heterotypic cross-linking of Fc gamma RIIa and/or Fc gamma RIIIb resulted in a rapid, transient increase in ERK and p38 activity, with maximal stimulation between 1 and 3 min. Fc gamma RIIa and Fc gamma RIIIb stimulated distinct patterns of ERK and p38 activity, and heterotypic cross-linking failed to stimulate synergistic activation of either ERK or p38 activity. Both Fc gamma RIIa and Fc gamma RIIIb required activation of a nonreceptor tyrosine kinase and phosphatidylinositol 3-kinase for stimulation of ERK and p38. Inhibition of ERK activation with PD98059 enhanced H2O2 production stimulated by homotypic and heterotypic Fc gamma R cross-linking. Inhibition of p38 with SB203580 attenuated H2O2 production stimulated by Fc gamma RIIIb or heterotypic cross-linking, but had no effect on Fc gamma RIIa-stimulated H2O2 production. On the other hand, PD98059 inhibited actin polymerization stimulated by Fc gamma R cross-linking, while SB203580 had no effect. Inhibition of actin polymerization with cytochalasin D enhanced p38 activity stimulated by either Fc gamma RIIa or Fc gamma RIIIb, but cytochalasin D only enhanced H2O2 production stimulated by Fc gamma RIIIb. Our data indicate that Fc gamma RIIa and Fc gamma RIIIb independently activate ERK and p38. The two receptors demonstrate different efficacies for ERK and p38 activation, and they do not act cooperatively. ERK and p38 provide stimulatory and inhibitory signals for neutrophil responses to immune complexes. In addition, these data indicate that actin reorganization may play a role in mediating p38-dependent activation of respiratory burst upon stimulation of Fc gamma RIIIb in neutrophils.

Salmonella pathogenicity island 2-dependent evasion of the phagocyte NADPH oxidase

A type III protein secretion system encoded by Salmonella pathogenicity island 2 (SPI2) has been found to be required for virulence and survival within macrophages. Here, SPI2 was shown to allow Salmonella typhimurium to avoid NADPH oxidase-dependent killing by macrophages. The ability of SPI2-mutant bacteria to survive in macrophages and to cause lethal infection in mice was restored by abrogation of the NADPH oxidase-dependent respiratory burst. Ultrastructural and immunofluorescence microscopy demonstrated efficient localization of the NADPH oxidase in the proximity of vacuoles containing SPI2-mutant but not wild-type bacteria, suggesting that SPI2 interferes with trafficking of oxidase-containing vesicles to the phagosome.

Yops of Yersinia enterocolitica inhibit receptor-dependent superoxide anion production by human granulocytes

The virulence plasmid-borne genes encoding Yersinia adhesin A (YadA) and several Yersinia secreted proteins (Yops) are involved in the inhibition of phagocytosis and killing of Yersinia enterocolitica by human granulocytes. One of these Yops, YopH, dephosphorylates multiple tyrosine-phosphorylated proteins in eukaryotic cells and is involved in the inhibition of phagocytosis of Y. enterocolitica by human granulocytes. We investigated whether antibody- and complement-opsonized plasmid-bearing (pYV+) Y. enterocolitica inhibits O2- production by human granulocytes in response to various stimuli and whether YopH is involved. Granulocytes were preincubated with mutant strains unable to express YadA or to secrete Yops or YopH. O2- production by granulocytes during stimulation was assessed by measuring the reduction of ferricytochrome c. PYV+ Y. enterocolitica inhibited O2- production by granulocytes incubated with opsonized Y. enterocolitica or N-formyl-Met-Leu-Phe (f-MLP). This inhibitory effect mediated by pYV did not affect receptor-independent O2- production by granulocytes in response to phorbol myristate acetate, indicating that NADPH activity remained unaffected after activation of protein kinase C. The inhibition of f-MLP-induced O2- production by granulocytes depends on the secretion of Yops and not on the expression of YadA. Insertional inactivation of the yopH gene abrogated the inhibition of phagocytosis of antibody- and complement-opsonized Y. enterocolitica by human granulocytes but not of the f-MLP-induced O2- production by granulocytes or tyrosine phosphorylation of granulocyte proteins. These findings suggest that the specific targets for YopH are not present in f-MLP receptor-linked signal transduction and that other Yop-mediated mechanisms are involved.

The MultiScreen filtration system to measure chemoattractant-induced release of leukocyte granule enzymes by differentiated HL-60 cells or normal human monocytes

A variety of chemoattractants initiate chemotaxis by selective binding to chemoattractant receptors (CARs), a subfamily of seven transmembranous G-protein coupled receptors (7TM-GPCRs) expressed in the leukocyte plasma membrane. Whatever the chemoattractant, signaling leading to chemotaxis involves several common biological steps which occur within seconds to minutes of CAR ligand binding. Though each step can be used to study the progress of the chemotaxis activation process. only certain biological events are suitable for monitoring chemotaxis signaling on large sample numbers as required for drug screening. An example of such is the release of granule enzymes by leukocytes in response to a CAR ligand. In this study, promyelocytic HL-60 cells were employed to set up a 96-well microplate methodology using filtration instead of centrifugation to collect the extracellular fluid together with the cell-released enzymes. Undifferentiated HL-60 cells were found not to respond to any of the CAR ligands. With various types of HL-60 cells which had differentiated along the neutrophilic or monocytic pathways, a large enzyme release was dose-dependently triggered by fMLF or C5a, but none of the tested CC or CXC chemokines. The highest responsiveness was found for neutrophilic HL-60 cells differentiated with dibutyryl cyclic AMP. With normal human monocytes (prepared from the blood of healthy donors by leukapheresis and elutriation), the granule enzyme release response was large to fMLF or C5a, substantial to MCP-1, low to RANTES or MIP-1alpha, but insignificant to Eotaxin, IL-8 and GROalpha. The method readily measures N-acetyl-beta-D-glucosaminidase, beta-D-glucuronidase and elastase activities, and requires approximately five times fewer cells than classical methods, a very important feature when normal human cells are to be used in screening assays. The method was also adapted to large scale screening of antagonists such as cyclosporins A and H for fMLF-mediated signaling using HL-60 cells and monocytes, and truncated (9-76) MCP-1 for MCP-1-mediated signaling using monocytes.

Eotaxin-2 activates chemotaxis-related events and release of reactive oxygen species via pertussis toxin-sensitive G proteins in human eosinophils

Eosinophils play an important role in allergic and autoimmune diseases. They are activated by distinct chemokines, leading to the immigration into the inflamed tissue, and mediate tissue damage by releasing reactive oxygen species. Recently, eotaxin was found to have the broadest spectrum of activities of all eosinophil-activating CC chemokines. In this study we investigated the effect of the novel CC chemokine, eotaxin-2, on eosinophil effector functions and compared its activity with eotaxin. Using nitrobenzoxadiazole-phallacidin staining and flow cytometry, we show that eotaxin-2 induced rapid and transient actin polymerization, a prerequisite for cell migration and modulation of the respiratory burst, in eosinophils in the same range of efficacy as observed for eotaxin. Eotaxin-2 induced the release of reactive oxygen species in a dose-dependent manner; half maximal and maximal release were found at 50 ng/ml and 500 ng/ml, respectively. Surprisingly, the efficacy of eotaxin-2 was comparable to that of eotaxin and C5a. Release of reactive oxygen species was inhibited by pertussis toxin, indicating the involvement of Gi proteins in the signaling of eotaxin-2. Moreover, the anti-CC chemokine receptor 3 (CCR3) monoclonal antibody, 7B11, was able to inhibit transient rise in the cytosolic Ca2+ concentration and the release of reactive oxygen species following stimulation with eotaxin-2. Therefore, eotaxin-2 represents a potent CC chemokine for human eosinophils activating chemotaxis-related events, such as actin polymerization, and the respiratory burst via the CCR3. Moreover, the efficacy of eotaxin-2 seems to be in the same range as that of eotaxin which might re-evaluate the recent profile of activity of CC chemokines in the activation of human eosinophils.

Modulation of cytoskeleton assembly capacity and oxidative response in aged neutrophils

Several reports have emphasized that aged polymorphonuclear cells (PMN) exhibit an impairment of superoxide anion (O2-) generation when triggered with formyl-methionyl-leucine-phenylalanine (FMLP) in comparison to the younger counterpart. Since microfilaments and microtubules are involved in PMN-mediated functions, in a group of old donors we assessed the effects of either actin stabilizing and disrupting agents, i.e. phalloidin and cytochalasin B, or microtubule stabilization or disruption by taxol and colchicine, respectively, on FMLP-triggered neutrophil oxidative responsiveness. Results show that phalloidin treatment, at a concentration ranging from 10(-6) to 10(-8) M, gave rise to an inhibition of O2- release by aged PMN, while the same effect was seen in similarly treated young cells at a concentration of 10(-7) M only. On the contrary, cytochalasin B pretreatment led to an enhancement of O2- generation in both young and aged neutrophils, even if to a lower extent in the latter group. At the same time, taxol at 10(-8) M strength inhibited young cell responsiveness, while no effects were induced by colchicine treatment. Quite interestingly, elderly neutrophil function was negatively modulated by both microtubule affecting compounds. Altogether, these findings suggest the possible relevance of cytoskeletal affecting compounds in the modulation of FMLP-stimulated O2- release during senescence.

Enhancing and priming of macrophages for superoxide anion production by taxol

Taxol, an anticancer drug, has been known not only to block cell division by stabilizing microtubules but also to activate murine macrophages to express TNF-alpha, interleukin-1, and to produce nitric oxide (NO). We therefore reasoned that taxol could activate murine macrophages to generate reactive oxygen intermediates, such as superoxide anion (O2-), which are responsible for intracellular killing of pathogenic microbes. Treatment of RAW264.7 cells, murine macrophage cell line, with taxol increased phorbol ester-induced O2- production in a dose dependent manner (approximately 2 fold). In addition, taxol rapidly (< 1 hr) primed RAW264.7 cells to enhance O2- release stimulated with PMA. Taxol also enhanced stimulation of O2- production by FMLP, but not by Con A. This effect was abolished by prior treatment with both superoxide dismutase (SOD) and N-acetyl-L-cystein, a free radical scavenger. To investigate the mechanism of taxol-induced macrophage stimulation, we evaluated the ability of colchicine, a drug that inhibit tubulin polymerization, and cAMP analogues, which is known to depolymerize microtubule. Taxol-induced O2- production was inhibited by the treatment with both colchicine and DB-cAMP. Taken together, these results demonstrated that taxol provides two signals, "priming" and "enhancing", to generate superoxide anion via the stabilization of microtubules in murine RAW264.7 cells

Cutting Edge: Detection of MCP-4 in Dermal Fibroblasts and Its Activation of the Respiratory Burst in Human Eosinophils

CC-chemokines are an important family of proinflammatory mediators that promote the recruitment and activation of human eosinophils in chronic inflammatory diseases. Recently, a novel human CC-chemokine, monocyte chemotactic protein 4 (MCP-4), has been reported that shows amino acid sequence similarities with eotaxin and RANTES, induces chemotaxis of eosinophils, and signals through specific chemokine receptors. In this study, we investigated the effect of MCP-4 on different eosinophil effector functions leading to the activation of the respiratory burst. In human eosinophils, MCP-4 dose dependently induced the production of reactive oxygen species and actin polymerization as a related event. Pretreatment of eosinophils with different enzyme inhibitors interacting with the signal transduction cascade revealed that Gi protein, protein kinase C, tyrosine kinase, and phosphatidylinositol-3-kinase are involved in the signaling following stimulation with MCP-4. In addition, cytokine-stimulated human dermal fibroblasts expressed high levels of MCP-4 mRNA, suggesting that fibroblasts are a physiologic source of MCP-4. Therefore, this study demonstrates that there is an important role of MCP-4 in the activation of eosinophils and that the interaction between dermal fibroblasts and human eosinophils may play an important role within the cytokine network.

The CC chemokine antagonist Met-RANTES inhibits eosinophil effector functions through the chemokine receptors CCR1 and CCR3

Eosinophils are predominant effector cells not only in allergic diseases but also in connective tissue diseases. The recruitment of eosinophils to the site of inflammation and release of reactive oxygen species leading to tissue damage and propagation of the inflammatory response are mediated by chemokines. Thus, agents that would be able to inhibit or antagonize chemokine-induced eosinophil activation are interesting as therapeutical agents. We describe the effect of a chemokine receptor antagonist, Met-RANTES, on human eosinophil effector functions in response to RANTES, monocyte chemoattractant protein (MCP)-3 and eotaxin. Met-RANTES was able to inhibit dose-dependently [Ca2+]i transients in eosinophils following stimulation with RANTES, MCP-3 and eotaxin. Whereas maximal and half-maximal inhibitory effect of Met-RANTES following stimulation with RANTES and MCP-3 were observed at 2 micrograms/ml and 1 microgram/ml, respectively, maximal and half-maximal inhibitory effects of Met-RANTES in response to eotaxin were detected at 10 micrograms/ml and 3 micrograms/ml. Moreover, eotaxin-induced [Ca2+]i transients were only half reduced at a Met-RANTES concentration at which RANTES and MCP-3 were completely blocked. Besides its effect on [Ca2+]i transients, Met-RANTES dose-dependently inhibited actin polymerization in eosinophils following chemokine stimulation. Whereas Met-RANTES totally inhibited RANTES- and MCP-3-induced actin polymerization at 5 micrograms/ml, the eotaxin-induced response was only reduced by 50%. However, Met-RANTES inhibited dose-dependently the release of reactive oxygen species in response to RANTES, MCP-3 and eotaxin. Again, eotaxin-induced release of reactive oxygen species, however, was only half reduced at a Met-RANTES concentration (10 micrograms/ml) at which RANTES and MCP-3 were completely blocked. The results of this study show that (1) Met-RANTES is an effective and powerful antagonist of effector functions of human eosinophils following stimulation with RANTES, MCP-3 and eotaxin; (2) Met-RANTES seems to be able to antagonize the response of eosinophils through chemokine receptor 1 (CCR1) preferentially to CCR3; (3) Met-RANTES antagonizes eosinophil but not neutrophil effector functions and might be therefore of interest for a new therapeutical approach to prevent the invasion and destructive power of eosinophils in diseases that are accompanied by eosinophil infiltration such as allergic asthma and connective tissue diseases.

Human eotaxin represents a potent activator of the respiratory burst of human eosinophils

Increased numbers of eosinophils are found in parasitic infections, autoimmune diseases and allergic diseases such as allergic asthma. They are activated by distinct cytokines and chemokines leading to the immigration in the inflamed tissue and mediate tissue damage by releasing reactive oxygen species. Here, the effect of the recently cloned CC chemokine human eotaxin was investigated for its ability to affect different eosinophil effector functions and compared to the CC chemokines MCP-3 and RANTES. Human eotaxin induced chemotaxis of human eosinophils in a dose-dependent manner. The range of efficacy of the CC chemokines compared to the well-known chemotaxin C5a was eotaxin = RANTES > MCP-3 = C5a. In addition, eotaxin induced rapid and transient actin polymerization, a prerequisite for cell migration, in eosinophils in the same range of efficacy as observed for chemotaxis. To investigate whether eotaxin was able to activate the respiratory burst of eosinophils, release of reactive oxygen species was measured by lucigenin-dependent chemiluminescence. Eotaxin induced production of significantly high amounts of reactive oxygen species at a concentration between 10 ng/ml and 500 ng/ml. Surprisingly, the effect of eotaxin was comparable to the well-known eosinophil activator C5a. The range of efficacy of the CC chemokines compared to C5a in the activation of the respiratory burst was eotaxin = C5a > MCP-3 > RANTES. Production of reactive oxygen species was inhibited by pertussis toxin, staurosporin, genestein and wortmannin. Furthermore, eotaxin induced transient increases in intracellular calcium concentration ([Ca2+]i) in human eosinophils. Therefore, pertussis toxin-sensitive Gi-proteins, protein kinase C, tyrosine kinase, phosphatidylinositol-3-kinase and transient increases in [Ca2+]i are involved in the signal transduction of eosinophils following stimulation with eotaxin. In summary, this study reveals the importance of the CC chemokine eotaxin as a potent activator of the respiratory burst, actin polymerization and chemotaxis. Eotaxin, therefore, plays an important role not only by attracting eosinophils to the site of inflammation but also by damaging tissue by its capacity to induce the release of reactive oxygen species.