Protein kinase C has both stimulatory and suppressive effects on macrophage superoxide production.

Unlike resident peritoneal macrophages (RPM) or tumor necrosis factor alpha (TNF alpha)-primed bone marrow-derived macrophages (BMM), unprimed BMM do not generate superoxide in response to the protein kinase C (PKC) activator, phorbol myristate acetate (PMA). However, these cells do contain significant levels of PKC activity. In contrast to PMA, zymosan induces the generation of superoxide in unprimed BMM, as well as in TNF alpha-primed BMM and RPM. Staurosporine, a potent PKC inhibitor, failed to affect the zymosan-induced production of superoxide by unprimed and TNF alpha-primed BMM and RPM, in spite of substantial inhibition of PMA-induced superoxide production by the primed BMM and RPM. However, when PKC was depleted from unprimed BMM by prolonged (24 h) treatment with phorbol dibutyrate (PdBt) (10(-7) M) the ability of zymosan to induce the production of superoxide was greatly diminished. Such a result could be interpreted as suggesting a role for PKC in the zymosan-induced response, a conclusion which contrasts with the inhibitor data. However, PKC depletion, in this case, is achieved via the PdBt-induced activation of PKC. It is thus possible that it is the initial activation of PKC, rather than its depletion, that suppresses superoxide production. Consistent with this interpretation, the co-stimulation of unprimed BMM with both zymosan and PMA resulted in a reduced superoxide release compared to zymosan alone. The activation of PKC therefore appears to have a suppressive effect on the generation of superoxide by unprimed cells. We thus conclude that PKC is not required for zymosan-induced superoxide production by either primed or unprimed macrophages and suggest that PKC may be involved in regulatory mechanisms restricting superoxide production by macrophages. However, since PMA alone can initiate the release of superoxide from primed BMM and RPM, it would appear that PKC can mediate both stimulatory and suppressive signals for macrophage superoxide production.     

Regulation of the growth and differentiation of a human monocytic cell line by lymphokines. I. Induction of superoxide anion production and chemiluminescence

The U937 human monocytic cell line was studied to determine its ability to generate a respiratory burst after stimulation with phorbol myristate acetate (PMA) or opsonized zymosan. U937 cells cultured in normal medium produced virtually no superoxide anion or chemiluminescence in response to either stimulus. In contrast, U937 cells cultured in medium containing soluble factors from activated lymphocytes produced significant O2- and chemiluminescence when stimulated with PMA or opsonized zymosan. The chemiluminescence in response to PMA was maximal in U937 cells precultured with these soluble factors for 3 days, whereas maximal responsiveness to opsonized zymosan was not observed until 5 to 6 days of lymphokine exposure. Although this ability to generate a respiratory burst persisted for a number of days in U937 cells that were subsequently recultured in normal medium, this responsiveness was gradually lost in the continued absence of these factors. The data indicate that the U937 monocytic cell line can be activated or induced to differentiate by soluble factors released by activated lymphocytes. In the process, these cells acquire the ability to generate a respiratory burst. The U937 cell line may serve as a useful model for the study of the ontogeny and regulation of the respiratory burst during human monocytic differentiation.     

Priming of the respiratory burst of bone marrow-derived macrophages is associated with an increase in protein kinase C content.

The biochemical mechanism(s) underlying the priming of the macrophage for an enhanced PMA-induced respiratory burst is not understood. Because the cellular receptor for PMA is thought to be protein kinase C (PKC), we have investigated the effects of priming agents on cellular PKC levels. Sonicates from unprimed bone marrow-derived macrophages (BMM) were found to contain PKC activity (309 +/- 51 pmol 32P-incorporated/mg/min; mean +/- SE, n = 17) as measured by the phospholipid-, diacylglycerol-, and calcium-dependent phosphorylation of histone. Exposure of BMM to priming agents such as TNF-alpha, LPS, and granulocyte/macrophage-CSF resulted in a significant increase in both histone-phosphorylating activity and levels of immunoreactive PKC protein in these cells. A minimum of 6-h exposure, with an increasing effect up to 48 h, was required for a detectable increase in PKC level. The activity from primed BMM, like that of the untreated cells, was predominantly cytosolic. The kinetics and concentration dependence of the priming agent-induced increase in the PKC content of BMM closely paralleled the enhancing effects of these agents on the PMA-stimulated respiratory burst. Furthermore, CSF-1, a cytokine that does not prime BMM, failed to increase PKC activity. We propose that the exposure of BMM to priming agents leads to an increase in the expression of a stimulatory isozyme(s) of PKC, resulting in an enhanced ability to mount a respiratory burst in response to stimulation with PMA.     

Colony stimulating factor-1 stimulates diacylglycerol generation in murine bone marrow-derived macrophages, but not in resident peritoneal macrophages

Colony stimulating factor-1 (CSF-1) stimulates DNA synthesis in murine bone marrow-derived macrophages (BMM); however, unlike BMM, murine resident peritoneal macrophages (RPM) undergo a poor proliferative response. It has previously been shown that phosphatidylinositol-4,5-bisphosphate hydrolysis is not associated with CSF-1 action in BMM. In this report we demonstrate that, despite a lack of inositol trisphosphate generation, CSF-1 transiently elevated both [3H]myristoyl- and [3H]arachidonyl-diacylglycerol (DAG) in BMM in a dose-dependent fashion. CSF-1 failed, however, to stimulate an increase in either species of DAG in RPM. Thus, DAG could be a second messenger for the proliferative action of CSF-1 in macrophages. Other mitogenic agents, 12-0-tetradecanoyl phorbol 13-acetate (TPA) and exogenous phospholipase C, also increased BMM levels of [3H]myristoyl- and [3H]arachidonyl-DAG. The nonmitogenic agents, lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha) and zymosan, had different effects on the generation of either species of DAG in BMM. LPS failed to elevate either form, TNF-alpha increased only [3H]arachidonyl-DAG, while zymosan stimulated levels of both species of DAG. It therefore appears that increased diacylglycerol generation may be necessary, but perhaps not sufficient, for macrophage proliferation.     

Rat macrophage treatment with lipopolysaccharide leads to a reduction in respiratory burst product secretion and a decrease in NADPH oxidase affinity

The effect of LPS on the respiratory burst in resident rat peritoneal macrophages has been examined. Rat macrophages secreted high levels of both O2- and H2O2 in response to triggering with phorbol esters, opsonized zymosan, and immune complexes. After culture in vitro with LPS these macrophages exhibited a marked diminution in their capacity to secrete high levels of respiratory burst products. The LPS-mediated loss of secretory activity was apparent after 2 hr of exposure to LPS and was inhibitable by polymyxin B in a dose-dependent fashion. The effect was not selective for any triggering agent type as inhibition of secretory activity occurred after triggering with PMA, zymosan and immune complexes. PGE2 added at levels secreted by the macrophages in response to LPS also inhibited respiratory burst product secretion. In addition, indomethacin prevented the LPS-mediated inhibition of secretion. Because the inhibition of secretion was common to all triggering agents tested, this suggested that the basis for the impaired secretion was at a level other than the receptor for the triggering agent. Both LPS and PGE2 treatment of the macrophages increased the Km of the oxidase for NADPH (1.7- to 2.3-fold) without affecting significantly the Vmax of the enzyme. These data suggest that stimulation of rat peritoneal macrophages by LPS results in an impaired ability to secrete respiratory burst products as a result of a PGE2-mediated decrease in NADPH oxidase affinity and that this alteration is independent of alterations in tumoricidal activity.     

Activation and proliferation signals in murine macrophages: relationships among c-fos and c-myc expression, phosphoinositide hydrolysis, superoxide formation, and DNA synthesis

Murine bone marrow-derived macrophages (BMM) undergo DNA synthesis in response to growth factors such as colony stimulating factor-1 (CSF-1) and granulocyte-macrophage CSF (GM-CSF). These macrophages can also be "activated," but without subsequent DNA synthesis, by a number of other agents, including lipopolysaccharide (LPS), concanavalin A, zymosan, formyl-methionyl-leucyl-phenylalanine (FMLP), and the Ca2+ ionophore, A23187. When BMM are treated with a range of stimuli, there is some, although not perfect, correlation between transient elevations in both c-myc mRNA and c-fos mRNA levels and increases in DNA synthesis. However, enhanced DNA synthesis and oncogene expression are readily dissociated from rises in inositol phosphates and, by implication, phospholipase C-mediated hydrolysis of phosphatidyl inositol 4,5-bisphosphate. Superoxide formation in BMM can also be dissociated from the other responses and does not necessarily depend on protein kinase C activation.     

Age-related alterations in superoxide anion generation in mouse peritoneal macrophages studied by repeated stimulations and heat shock treatment.

The ability of thioglycollate-elicited peritoneal macrophages (PM) from young and senescent mice to generate superoxide anions (O2-) under repeated stimulation or thermal stress was studied using either zymosan, opsonized zymosan (OZ), or phorbol myristate acetate (PMA). A diminished capacity to recover from repeated stimulation was found with aging. When stimulated for a second time 24 hours after the primary stimulation, PM from young animals generated 80% of the initial O2- responses to either zymosan, or OZ. Under the same conditions, PM from senescent mice generated 62% of the initial O2- produced in response to zymosan, and 45% in response to OZ. In both age groups the response to a second PMA stimulation comprised only 10% of the primary response. A considerably diminished capacity to generate O2- was also demonstrated in PM from senescent mice after recovery from exposure to thermal stress. Exposure to 42.5 degrees C for 20 minutes was found to be the threshold temperature for irreversible loss of activity in senescent PM, whereas at this temperature, PM from young animals recovered up to 70% of their O2- generating activity. Since NADPH oxidase and superoxide dismutase activities were only mildly affected by the hyperthermia in all age groups, they could not account for the age-related decline in the recovery from stress. Age-related alterations in signal transduction or receptor alterations could possibly play a primary role in this decline.     

Cyclosporin A inhibits phorbol ester-induced activation of superoxide production in resident mouse peritoneal macrophages.

Peritoneal resident macrophages from mice are sensitive to inhibition by cyclosporin A (CsA) of phorbol 12-myristate 13-acetate (PMA)-stimulated oxidative burst. Inhibition was assessed in terms of superoxide anion (O2.-) and H2O2 production. Key findings were as follows. (a) CsA inhibited in a dose-dependent manner the production of O2.- when cells were stimulated with PMA. CsA did not alter the respiratory burst induced by other stimuli (zymosan, concanavalin A and fMet-Leu-Phe). It was verified that CsA itself had no scavenger effect. (b) A concomitant decrease in H2O2 liberation following CsA exposure was found. This inhibition was observed both in the initial rate of synthesis and in the accumulation after 15 min of incubation. (c) NADPH oxidase activity in the crude supernatant was unaffected by the previous incubation of macrophages with CsA. CsA does not inhibit glucose transport measured as 14CO2 production. (d) The production of O2.- was strongly dependent on the glucose concentration. Sodium oleate also stimulated O2.- production in resident macrophages. These data might be correlated with the inhibitory effect of CsA upon other functions of macrophages.     

Macrophage colony-stimulating factor (M-CSF) enhances the capacity of murine macrophages to secrete oxygen reduction products

The capacity of macrophage colony-stimulating factor (M-CSF) to enhance respiratory burst activity in peritoneal macrophages was measured. Macrophages incubated for 48 hr or more with concentrated L cell-conditioned medium as a source of M-CSF released two to three times as much O2- in response to PMA as did unexposed macrophages. Stimulation was noted at concentrations of colony-stimulating activity from 0.1 to 2000 U/ml and was maximal at 10 to 100 U/ml. Purified, endotoxin-free CSF enhanced secretion to a similar degree as unpurified L cell-conditioned medium. Release of O2- by M-CSF macrophages occurred over 60 min and was triggered by opsonized zymosan as well as PMA. H2O2 release was also enhanced in macrophages exposed to both unpurified and purified M-CSF. These data indicate that M-CSF enhances the capacity of mature macrophages to release oxygen reduction products, and they are consistent with reports that CSF can stimulate the release of other secretory products.     

Adenosine regulates the respiratory burst of cytokine-triggered human neutrophils adherent to biologic surfaces

The effect of adenosine on the respiratory burst was investigated using human neutrophils adherent to serum-coated surfaces. Adenosine caused complete suppression of the respiratory burst elicited by TNF-alpha, FMLP, or CSF for granulocytes; partial suppression of the response to CSF for granulocytes/macrophages, Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, or uncoated polystyrene surfaces; and no suppression of the response to PMA. In most experiments, 4.7 x 10(-7) M and 2.5 x 10(-8) M adenosine caused 50% suppression of H2O2 release in response to TNF-alpha and FMLP, respectively, and 10 microM caused 100% suppression. Preexposure of neutrophils to ADP blocked the inhibitory effect of adenosine. With adherent neutrophils, there is a prolonged lag period in the onset of the respiratory burst in response to cytokines. Adenosine was fully suppressive if its addition was delayed past the first third of this lag period, or if it was removed during the last third of the lag period. A 10-min pulse with adenosine was most inhibitory when delivered in the middle third of the lag period. Dihydrocytochalasin B abolished the suppressive effect of adenosine on H2O2 release in response to FMLP. Thus adenosine, at concentrations found in human plasma, is a potent but selective inhibitor of the respiratory burst of adherent human neutrophils in response to physiologic, soluble stimuli, and ADP is a potentially physiologic counter-suppressant. Adenosine appears to exert most of its effect during a discrete interval within the lag period before onset of the respiratory burst, and may affect the coupling of agonist receptors to the cytoskeleton.     

Activation and proliferation signals in murine macrophages: stimulation of glucose uptake by hemopoietic growth factors and other agents

Purified colony-stimulating factor (CSF-1) (or macrophage colony stimulating factor [M-CSF]) stimulated the glucose uptake of murine bone marrow-derived macrophages (BMM) and resident peritoneal macrophages (RPM) as measured by 3H-2-deoxyglucose (2-DOG) uptake. Similar concentrations of CSF-1 stimulated the 2-DOG uptake and DNA synthesis in BMM. Other purified hemopoietic growth factors, granulocyte-macrophage CSF (GM-CSF) and interleukin-3 (IL-3) (or multi-CSF), and the tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), even though differing in their mitogenic capabilities on BMM, were also stimulators of 2-DOG uptake in BMM and RPM. The nonmitogenic agents, lipopolysaccharide (LPS) and concanavalin A (Con A), were also active. The inhibition by cytochalasin B and by high concentrations of D-glucose suggest that the basal and stimulated 2-DOG uptake occurred via a carrier-facilitated D-glucose transport system. The responses of the two macrophage populations to the hemopoietic growth factors and to the other agents were quite similar, suggesting that events that are important for the induction of DNA synthesis are not tightly coupled to the earlier rise in glucose uptake. For the BMM, the ability of a particular agent to stimulate glucose uptake did not parallel its ability to promote cell survival. However, stimulation of glucose uptake could still be a necessary but insufficient early macrophage response for cell survival and subsequent DNA synthesis.     

Hyperoxia alters effect of calcium on rat alveolar macrophage superoxide production

The effect of hyperoxia on the Ca2+ dependence of stimulated superoxide anion radical (O2-.) production (the respiratory burst) of rat alveolar macrophages was investigated. Enhancement of the concanavalin A (con A)-stimulated respiratory burst by extracellular Ca2+ was suppressed by O2 exposure. Similarly, the inhibitory effect of verapamil on the con A-stimulated respiratory burst was reduced by O2 exposure. O2 exposure also inhibited con A stimulation that was independent of Ca2+ entry. Exposure to O2 also caused a decline in O2-. production stimulated by either A23187 or phorbol myristate acetate (PMA). With A23187 stimulation, extracellular Ca2+ was essential for either air-exposed (control) or O2-exposed cells. With PMA, stimulation was independent of extracellular Ca2+ for either air or O2-exposed macrophages and verapamil did not inhibit. Free intracellular Ca2+ concentration ([Ca2+]i) was measured in control and O2-exposed alveolar macrophages. Hyperoxic exposure did not alter [Ca2+]i in unstimulated cells. In controls, con A stimulated an immediate increase in [Ca2+]i followed by a rapid decrease and a second rise and fall. The second elevation was suppressed by verapamil or ethyleneglycol-bis (beta-aminoethylether)-N,N'-tetraacetic acid or O2 exposure. The results of both the respiratory burst assays and measurement of con A-stimulated changes in [Ca2+]i suggest that Ca2+ entry involved in stimulus-response coupling is suppressed in cellular O2 toxicity.     

Regulation of respiratory burst in murine peritoneal macrophages: differential sensitivity to phorbol diesters by macrophages in different states of functional activation

Activation of macrophages either in vivo or in vitro can modulate the capacity to generate and secrete reactive oxygen intermediates including H2O2 and O2-. Thus, the cellular and biochemical components requisite for execution of the respiratory burst must be regulated during the activation process. In the present report, we have examined murine peritoneal macrophages in different stages of activation for their sensitivity to stimulants of respiratory burst known to activate protein kinase c (i.e., phorbol dibutyrate or diacylglycerol). The results demonstrated that more highly activated macrophages showed, in addition to greater magnitude of H2O2 or O2- production, a two- to fourfold greater sensitivity to these stimuli. While more active macrophages also exhibited a higher rate of H2O2 secretion, the time at which secretion was measured did not account for or modulate the heightened sensitivity. The increased sensitivity to stimulation was dependent upon the stage of activation and not on the agent used to elicit the macrophages. Increased sensitivity of the more active macrophage populations was also seen when physiologic stimuli (i.e., insoluble immune complexes or unopsonized zymosan) were used. These findings indicate that macrophage activation for H2O2 secretion modulates the sensitivity to stimulation such that more H2O2 is produced in a shorter time and at a lower concentration of stimulus, thereby heightening the inflammatory response in several independent ways. Because all the stimuli employed in the present study have in common the ability to activate protein kinase c (either directly or indirectly), the data also suggest that this form of macrophage activation may involve, at least in part, modulation of the stimulus-response coupling mechanisms which utilize this enzyme.     

Stimulation of macrophage H2O2 release by resident thymocytes: effect of a soluble factor distinct from interferon-gamma

Activated T cells are known to stimulate macrophage oxidative metabolism and antimicrobial activity through release of interferon-gamma (IFN-gamma). In contrast, the role of nonactivated T cells in regulating macrophage effector functions is less well defined. We have previously reported that a low molecular weight soluble factor derived from resident (nonactivated) thymocytes enhances macrophage receptor-mediated phagocytosis. In the present study, we examined the capacity of resident murine thymocytes to stimulate the respiratory burst and microbicidal activity of peritoneal macrophages. Macrophages cultured for 1-2 days with cell-free thymocyte supernatant (TS) released two to three times more H2O2 in response to PMA or opsonized zymosan than did control macrophages. The H2O2-stimulating factor in TS was distinguished from IFN-gamma by its heat stability (100 degrees C, 20 min), approximate MW of 2400 Da (gel filtration high-pressure liquid chromatography), and absence of interferon activity in both antiviral and enzyme-linked immunosorbent assays. TS-treated macrophages, however, did not exhibit a greater capacity to kill or inhibit the intracellular growth of Toxoplasma gondii, indicating that the thymocyte factor did not fully activate macrophage microbicidal mechanisms. These data suggest that thymocytes can increase the respiratory burst capacity of macrophages in the absence of antigen-specific immune responses.     

Functional abnormalities in protein tyrosine phosphatase epsilon-deficient macrophages

Protein tyrosine phosphatase epsilon (PTP epsilon)-deficient mice were generated by targeted deletion of exons 3, 4, and 5 of the Ptpre gene. Mice homozygous for this deletion (Ptpre(Delta3-5)) were fertile, bred and developed normally and exhibited no overt phenotype. However, closer examination of the function of macrophages from these mice revealed a defect in the regulation of the respiratory burst. While bacterial lipopolysaccharide (LPS) or tumour necrosis factor alpha (TNFalpha) were able to prime bone marrow-derived macrophages (BMM) from wild type (Ptpre(+)) macrophages for an enhanced respiratory burst, they were unable to do so in macrophages from PTP epsilon-deficient mice. PTP epsilon-deficient BMM also had abnormalities in cytokine production with a reduced ability to produce TNFalpha and enhanced IL-10 production in response to challenge with LPS. These findings suggest an important role for PTP epsilon in the control of macrophage function.     

Phagocytosis of immunoglobulin G and C3-bound human sperm by human polymorphonuclear leukocytes is not associated with the release of oxidative radicals.

Antisperm antibody (ASA)- and complement (C)-mediated immune injury to human sperm is thought to be caused in part by phagocytic neutrophils. To investigate this process, we co-cultured purified human polymorphonuclear leukocytes (PMN) with swim-up sperm in the presence of ASA-positive and ASA-negative sera and assayed for PMN respiratory burst activity, monitored by the release of superoxide anion (O2-) and hydrogen peroxide (H2O2). Phorbol myristate acetate (PMA) and opsonized zymosan were used as positive controls. Phagocytosis of ASA-positive and C-bound sperm by PMN did not enhance O2- production when compared to incubation of sperm with ASA-negative sera. Phagocytosis of ASA-positive and C-bound sperm also resulted in minimal release of H2O2 when compared with ASA-positive and C-negative sperm that were not phagocytosed. In contrast, PMN were maximally stimulated to release O2- in response to either opsonized zymosan or PMA. The kinetics of PMA-induced O2- release was unaffected by the presence of ASA-positive and C-bound sperm. Cytocentrifuge preparations of PMN incubated with ASA-positive and C-bound sperm revealed limited O2- release at the site of PMN/sperm contact. These results indicated that 1) phagocytosis of motile sperm by PMN requires the binding of both ASA and C to the sperm surface; 2) phagocytosis of ASA-positive and C-positive sperm by PMN fails to release reactive oxygen species; and 3) metabolic processes associated with PMN respiratory burst activity may not be coupled to the ingestion of ASA-positive and C-bound sperm.     

Cytotoxicity testing of wound-dressing materials

A method was developed for testing the cytotoxicity of various bandage-like wound dressings and gel wound dressings. In this method, the ability of human polymorphonuclear neutrophils (PMNs) to initiate a respiratory burst after exposure to the various wound dressings is used as a marker of cytotoxicity. Luminol-amplified chemiluminescence stimulated with opsonised zymosan or phorbol 12-myristate 13-acetate (PMA) is used to measure the degree of activation of the respiratory burst, i.e. the NADPH oxidase activity, after exposure to wound dressings. Opsonised zymosan (material from yeast cell walls) is a phagocytic stimulus that activates the NADPH oxidase by binding to FC-receptors and complement receptors, and functions as an artificial bacterium, whereas PMA activates the NADPH oxidase by direct activation of protein kinase C. NADPH oxidase activity was inhibited by several wound dressings. The down-regulation of the respiratory burst is detrimental to the bactericial effect of PMNs, and can be used as a marker for the cytotoxicity of wound dressing materials.     

Mycobacterium lepraemurium activates macrophages but fails to trigger release of superoxide anion

Mycobacterium lepraemurium failed to stimulate a normal respiratory burst when presented to mouse peritoneal or bone marrow macrophages. By comparison, Mycobacterium bovis (strain Bacillus Calmette-Guerin) or Saccharomyces cerevisiae, as expected, stimulated macrophages to release a large amount of superoxide anion (O2-). M. lepraemurium did not interfere with the response to yeast when both microbes were added together to macrophages. The low release of O2- induced by M. lepraemurium was not due to failure of M. lepraemurium to activate or prime macrophages, because exposure of macrophages to M. lepraemurium caused the expected enhancement of O2- release when the macrophages were stimulated by PMA. Similarly, macrophages taken from mice infected with M. lepraemurium were activated, as indicated by high PMA-stimulated O2- release. Macrophages primed in vitro by exposure to Escherichia coli LPS for 24 h did show a moderate O2- response when stimulated by M. lepraemurium, but macrophages primed by exposure to IFN-gamma muramyl dipeptide, or M. lepraemurium showed a weak response when subsequently challenged with M. lepraemurium. The priming effect of M. lepraemurium or LPS decreased substantially after macrophages were cultured in fresh medium for 24 h. Heat killing or opsonization of M. lepraemurium caused the M. lepraemurium to stimulate a high amount of O2- release from LPS-primed macrophages, but heat killing or opsonization of M. lepraemurium had no effect on release of O2- from unprimed macrophages. The results suggest that M. lepraemurium is taken into macrophages by a mechanism that bypasses the FcR and other receptors that are capable of triggering the production of O2-.     

Redox state and O2*- production in neutrophils of Crohn's disease patients

The aim of this in vitro study was to evaluate the intracellular redox state and respiratory burst (RB) in neutrophils of patients with Crohn's disease (CD). The intracellular redox state and RB in neutrophils was assessed by the superoxide anion (O2*-) production induced in these cells after stimulation by various factors related to the molecular mechanisms that, if altered, may be responsible for an abnormal immune response. This can, in part, cause the onset of inflammation and tissue damage seen in CD. This study demonstrated a decreased glutathione/glutathione disulfide (GSH/GSSG) ratio index of an increased oxidative state in CD patient neutrophils. Moreover, our findings showed a decrease in tumor necrosis factor (TNF-alpha)- or phorbol 12-myristate 13-acetate (PMA)-induced O2*- production in CD patient neutrophils adherent to fibronectin as compared with controls. A decreased adhesion was also demonstrated. For this reason, the involvement of altered mechanisms of protein kinase C (PKC) and beta-integrin activation in CD patient neutrophils is suggested. These data also showed that the harmful effects of TNF-alpha cannot be caused by excessive reactive oxygen species (ROS) production induced by neutrophils. Decreased cell viability after a prolonged time of adhesion (20 hrs) was also measured in CD patient neutrophils. The findings of this study demonstrate, for the first time, that granulocyte-macrophage colony-stimulating factor (GM-CSF), a compound recently used in CD therapy, is able to activate the RB for a prolonged time both in control and CD patient neutrophils. Increased viability of CD patient neutrophils caused by GM-CSF stimulation was also observed. In conclusion, our results indicate that decreased O2*- production and adhesion, caused, in part, by an anomalous response to TNF-alpha, together with low GSH level and low cell viability, may be responsible for the defective neutrophil function found in CD patients. This can contribute to the chronic inflammation and relapses that characterize this pathology. A possible role of GM-CSF in inducing O2*- production and in restoring the defensive role of neutrophils in CD patients is suggested.     

Dectin-1 expression and function are enhanced on alternatively activated and GM-CSF-treated macrophages and are negatively regulated by IL-10, dexamethasone, and lipopolysaccharide

Dectin-1 is the major macrophage receptor for beta-glucans and generates a proinflammatory response through the recognition of these carbohydrates on fungal pathogens. We have examined the effects of cytokines and other agents on the expression and functions of dectin-1 in both resident and elicited murine peritoneal macrophages (Mphi). Dectin-1 expression was found to be highly up-regulated by GM-CSF and by the cytokines that induce alternative macrophage activation, IL-4 and IL-13. In contrast, IL-10, LPS, and dexamethasone, but not IFN-gamma, down-regulated the expression of this receptor. Modulation of dectin-1 receptor levels correlated with the ability of these macrophages to bind zymosan and significantly affected the contribution of this receptor to the resultant proinflammatory response, as measured by the production of TNF-alpha, although some Mphi-specific differences were observed. These results correlate with the known effects of these cytokines and other agents on the ability of the immune system to recognize and respond to fungal pathogens.