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M G Netea

Publications and source records attributed to M G Netea.

72 records · Page 4Linked to original sources
PubMed1998

Lipopolysaccharide-induced production of tumour necrosis factor and interleukin-1 is differentially regulated at the receptor level: the role of CD14-dependent and CD14-independent pathways.

Cytokine production induced via CD14-dependent and CD14-independent pathways was investigated in mouse peritoneal macrophages incubated with lipopolysaccharide (LPS) or lipid A. Different LPS receptors appear to be responsible for production of tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 alpha (IL-1 alpha) and IL-1 beta. TNF-alpha production is essentially CD14 dependent, both in the presence or absence of plasma. In the presence of plasma, endotoxin-induced IL-1 production is mediated by CD14-dependent mechanisms, while in its absence both CD14-dependent and CD14-independent pathways are involved. Lipid A stimulates cytokine synthesis through both CD14-dependent and CD14-independent mechanisms, but its action is weaker than that of LPS, indicating that the polysaccharide moiety may be necessary for proper stimulation of mouse macrophages by endotoxin.

Animals↗
PubMed1998

Increased interleukin-1alpha and interleukin-1beta production by macrophages of low-density lipoprotein receptor knock-out mice stimulated with lipopolysaccharide is CD11c/CD18-receptor mediated.

Immune mechanisms, including production of pro-inflammatory cytokines such as interleukin-1 (IL-1) and tumour necrosis factor (TNF), play an important role in early atherogenesis. The study of the mechanisms responsible for the increased cytokine production capacity of hypercholesterolemic hosts is therefore crucial for finding new strategies aimed to stop the development of atherosclerosis. We assessed the lipopolysaccharide (LPS)-induced cytokine production of macrophages from low-density lipoproteins (LDL)-receptor knock-out (LDLR-/-) mice, which have a seven- to ninefold higher plasma LDL concentration. Macrophages of LDLR-/- mice produced approximately twofold more IL-1alpha and IL-1beta in response to LPS when compared with macrophages of control mice (LDLR+/+). TNF-alpha synthesis was only slightly increased. Removal of CD14 by phospholipase C treatment of cells decreased cytokine production by 50% (IL-1) to 80% (TNF), but the differences between LDLR-/- and LDLR+/+ remained the same. In contrast, treatment of cells with anti-CD11c monoclonal antibody inhibited the IL-1alpha and IL-1beta production in LDLR-/- mice towards normal values, while no effect could be seen on TNF. In conclusion, LDLR-/- macrophages stimulated with LPS synthesize more IL-1alpha and IL-1beta than controls and this phenomenon is mediated by the CD11c/CD18 receptor.

Animals↗
PubMed1998

Recombinant murine granulocyte colony-stimulating factor protects against acute disseminated Candida albicans infection in nonneutropenic mice.

The effect of recombinant granulocyte colony-stimulating factor (rG-CSF) on acute disseminated Candida albicans infection in nonneutropenic mice was investigated. Mice treated with a single dose of rG-CSF showed a significantly reduced mortality (28% vs. 90%; P < .001). The outgrowth of C. albicans from the kidneys, spleens, and livers of rG-CSF-treated mice was significantly reduced (log cfu/g of kidney, 5.54 vs. 7.13; P < .001), as were circulating tumor necrosis factor-alpha and interleukin-1beta. After rG-CSF, the kidneys showed fewer infectious infiltrates, enhanced granulocyte influx, and almost complete absence of hyphal outgrowth. During peritoneal C. albicans infection, rG-CSF enhanced influx of granulocytes to the site of infection, and exudate granulocytes showed increased oxygen radical production. These results indicate that rG-CSF enhances host resistance to disseminated candidiasis in nonneutropenic mice through activation of granulocytes and their recruitment to the site of infection.

Animals↗
PubMed1998

Posttranscriptional down-regulation of tumor necrosis factor-alpha and interleukin-1beta production in acute meningococcal infections.

The regulation of tumor necrosis factor-alpha (TNF) and interleukin-1beta (IL-1beta) production was studied in patients with meningococcal disease. Circulating TNF and IL-1beta normalized within 1 day. TNF mRNA and IL-1beta mRNA in white blood cells decreased over 3-4 days. During the acute stage, TNF and IL-1beta production in stimulated whole blood cultures was down-regulated. After 4-5 days, this production was restored. The down-regulation was unlikely to be caused by circulating IL-6 and IL-10, as these cytokines normalized within 2-3 days. TNF mRNA in stimulated cultures during the acute stage, with down-regulated production, did not differ from that at recovery, with restored production. In contrast, the down-regulated production of IL-1beta was associated with significantly lower IL-1beta mRNA levels. Thus, TNF and IL-1beta production are differentially regulated. Whereas TNF production is regulated posttranscriptionally, IL-1beta production is also regulated at the mRNA level.

Anti-Bacterial Agents↗
PubMed1998

Modulation of the pro- and anti-inflammatory cytokine balance by amphotericin B.

Amphotericin B is an antifungal drug associated with side effects such as fever and chills, symptoms which may be mediated by pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) and tumour necrosis factor-alpha (TNFalpha). We assessed the capacity of amphotericin B to modulate production of these pro-inflammatory cytokines as well as the anti-inflammatory IL-1 receptor antagonist (IL-1ra), induced by LPS, heat-killed Candida albicans or Staphylococcus aureus. The results of the present study show that amphotericin B slightly increased the production of pro-inflammatory cytokines by human mononuclear cells (PBMC), whereas the production of the anti-inflammatory cytokine IL-1ra was significantly inhibited. This results in a shift towards pro-inflammatory cytokine production, as indicated by a decreased IL-1ra/IL-1beta ratio. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) indicated that levels of IL-1beta and TNFalpha mRNA were increased. In conclusion, amphotericin B is able to cause a shift towards pro-inflammatory cytokine production by human PBMC. This may explain the side effects, such as fever and chills, observed after treatment of patients with amphotericin B.

Amphotericin B↗
PubMed1998

Lipoprotein(a) inhibits lipopolysaccharide-induced tumor necrosis factor alpha production by human mononuclear cells.

Lipoproteins can bind lipopolysaccharide (LPS) and decrease LPS-stimulated cytokine production. Lipoprotein(a) [Lp(a)] was as potent as low-density lipoproteins (LDL) in inhibiting LPS-stimulated tumor necrosis factor synthesis by human mononuclear cells. The kinetics of LPS inhibition by Lp(a) was similar to that of LDL. This suggests that circulating Lp(a) may be an important factor determining the amplitude of the response to LPS in humans.

Humans↗
PubMed1997

The role of hyperuricemia in the increased cytokine production after lipopolysaccharide challenge in neutropenic mice.

Patients with severe granulocytopenia are more susceptible to severe infections and sepsis. Proinflammatory cytokines such as tumor necrosis factor-alpha (TNF), interleukin-1 alpha (IL-1 alpha), and IL-1 beta play an important role in the pathophysiology of sepsis. The profile of these proinflammatory cytokines after lipopolysaccharide (LPS) challenge in cyclophosphamide-induced neutropenic mice was assessed, and possible mechanisms responsible for the modified cytokine production were studied. After LPS, both circulating concentrations of TNF and IL-1 alpha in neutropenic mice were 50% to 200% higher than those of controls, whereas IL-1 beta concentrations were not modified. The kinetics of cytokine production were similar in neutropenic and control animals. The susceptibility of neutropenic mice to an LPS challenge was increased. The observed overproduction of TNF and IL-1 alpha was not due to a direct effect of cyclophosphamide treatment. Because circulating concentrations of uric acid were increased in the neutropenic mice, the effect of hypouricemic treatment with allopurinol and sodium bicarbonate was investigated; such treatment in neutropenic mice challenged with LPS was followed by an improved survival and a reduced proinflammatory cytokine production towards the concentrations in control mice. Hyperuricemia induced by repeated administrations of uric acid in normal mice led to an increased TNF production after LPS. In conclusion, neutropenic mice respond with enhanced cytokine production and increased susceptibility to an LPS challenge, and hyperuricemia probably plays an important role in this phenomenon.

Agranulocytosis↗
PubMed1997

Interleukin 1 beta, tumour necrosis factor-alpha and interleukin 1 receptor antagonist in newly diagnosed insulin-dependent diabetes mellitus: comparison to long-standing diabetes and healthy individuals.

Interleukin 1 beta (IL-1) and tumour necrosis factor alpha (TNF) are important for the beta cell lysis in insulin-dependent diabetes mellitus (IDDM), while IL-1 receptor antagonist (IL-1ra) is considered protective by blocking the effects of IL-1. Serum concentrations and ex-vivo production of IL-1, TNF and IL-1ra were examined in 10 newly diagnosed IDDM (ND-IDDM) patients, and compared with 11 long-standing IDDM (LS-IDDM) patients and 14 healthy volunteers. Ex-vivo LPS-stimulated production of IL-1 in ND-IDDM patients was significantly increased compared with LS-IDDM patients and healthy controls, while TNF and IL-1ra synthesis did not differ significantly. IL-1ra/IL-1 ratio was significantly decreased in ND-IDDM, and returned to normal values in the LS-IDDM group. Circulating concentrations of IL-1ra in LS-IDDM patients were increased. These data suggest a proinflammatory imbalance in ND-IDDM patients and this may play an important role in beta cell loss.

Acute Disease↗
PubMed1997

The effects of dexamethasone and chlorpromazine on tumour necrosis factor-alpha, interleukin-1 beta, interleukin-1 receptor antagonist and interleukin-10 in human volunteers.

Tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) are pro-inflammatory cytokines that play an important role in severe infections, whereas IL-1 receptor antagonist (IL-1ra) and IL-10 are anti-inflammatory cytokines that counteract their effects. Chlorpromazine and dexamethasone protect mice against lethal endotoxaemia by decreasing circulating concentrations of TNF-alpha and IL-1 beta. We investigated whether administration of chlorpromazine or dexamethasone to human volunteers is able to modulate the lipopolysaccharide (LPS)-stimulated cytokine production capacity in whole blood. Blood samples were taken before and several time-points after medication. Circulating cytokine concentrations were low in all samples. LPS-induced TNF-alpha and IL-1 beta production in whole blood was inhibited by dexamethasone treatment, while chlorpromazine had no effect. When peripheral blood mononuclear cells were stimulated in vitro with LPS, the addition of chlorpromazine (1-100 ng/ml) had no modulatory action on TNF-alpha, IL-1 beta, IL-1ra or IL-10 synthesis. The chlorpromazine concentrations measured in circulation of volunteers were eight to 40 times lower than the concentrations shown to be effective in mice. In conclusion, chlorpromazine inhibits TNF-alpha and IL-1 beta production in mice at concentrations that cannot be reached in humans, thus precluding its usage in clinical anti-cytokine strategies. In contrast, dexamethasone is an effective inhibitor of pro-inflammatory cytokine production.

Adult↗
PubMed1997

Hyperlipoproteinemia enhances susceptibility to acute disseminated Candida albicans infection in low-density-lipoprotein-receptor-deficient mice.

Recent studies have suggested the use of lipoproteins as an adjuvant treatment of lethal gram-negative infections. However, other important microorganisms for the etiology of sepsis, such as Candida species, grow better in lipid-rich environments. We investigated the effect of hyperlipoproteinemia on systemic candidiasis in low-density-lipoprotein-receptor-deficient (LDLR-/-) mice, in which the loss of the receptor results in a seven- to ninefold-higher plasma LDL level than that in their wild-type littermates (C57BL/6J). LDLR-/- mice died earlier, and the outgrowth of Candida albicans in the kidneys and livers of LDLR-/- mice was significantly higher compared with that of controls. After infection, circulating cytokine concentrations were significantly higher in LDLR-/- mice. In vitro, C. albicans grew better in plasma samples of LDLR-/- mice than in control plasma samples and peritoneal macrophages of LDLR-/- mice challenged with heat-killed C. albicans produced more cytokines than did those of controls. This latter phenomenon was probably due to increased binding of yeast cells to macrophages of LDLR-/- mice. These data suggest that hyperlipoproteinemia is deleterious in systemic candidiasis.

Acute Disease↗
PubMed1996

Low-density lipoprotein receptor-deficient mice are protected against lethal endotoxemia and severe gram-negative infections.

Lipoproteins can bind lipopolysaccharide (LPS) and decrease the LPS-stimulated production of pro-inflammatory cytokines. We investigated the effect of increased plasma concentrations of low-density-lipoproteins (LDL) on survival and cytokine production after a lethal challenge with either LPS or live Gram-negative bacteria in LDL receptor deficient mice (LDLR-/-). The LDLR-/- mice challenged with LPS had an eightfold increased LD50 when compared with the wild type controls (C57Bl/6J), while tumor necrosis factor alpha (TNFalpha) and interleukin-1 alpha (IL-1 alpha) plasma concentrations were decreased twofold. LDLR-/- mice had significantly lower and delayed mortality than control mice after infection with Klebsiella pneumoniae. No differences in the outgrowth of bacteria in the organs were present between the two groups, while circulating cytokine concentrations were decreased twofold in LDLR-/- mice. In contrast, the LPS-stimulated in vitro production of cytokines by peritoneal macrophages of LDLR-/- mice was significantly increased compared with controls. This increase was associated with enhanced specific binding of LPS to the macrophages of LDLR-/- mice. In conclusion, endogenous LDL can protect against the lethal effects of endotoxin and Gram-negative infection. At least part of this protection is achieved through decreased in vivo production of pro-inflammatory cytokines, in spite of increased cytokine production capacity.

Animals↗
PubMed1996

A semi-quantitative reverse transcriptase polymerase chain reaction method for measurement of MRNA for TNF-alpha and IL-1 beta in whole blood cultures: its application in typhoid fever and exentric exercise.

Whole blood cultures are used to study cytokine stimulation and release ex vivo. In the present study this method was compared with a more direct approach and a quantitative reverse transcriptase polymerase chain reaction (RT-PCR) was used to assess mRNA expression for IL-1 beta and tumour necrosis factor alpha (TNF-alpha) and mRNA in whole blood. Stimulation of whole blood from normal donors with lipopolysaccharide (LPS) at various time intervals showed a parallel rise of immunogenic IL-1 beta and TNF-alpha as well as a rise of mRNA expression for IL-1 beta and TNF-alpha with peak levels for IL-1 beta after 4-6 h stimulation and for mRNA TNF-alpha expression after 2 h stimulation. These methods were used to explore cytokine production during the course of typhoid fever and after a 5 km run. In both conditions circulating cytokine concentrations were not influenced, but the TNF-alpha and IL-1 beta mRNA gene expression in circulating whole blood cells was increased in patients with typhoid fever. The LPS-stimulated production of TNF-alpha and IL-1 beta was decreased in both but there was no change for the mRNA content in whole blood for these cytokines. These findings demonstrate that RT-PCR is an attractive method to study the gene expression of cytokines in whole blood, an increased TNF-alpha and IL-1 beta gene expression is present in typhoid fever, and that the LPS stimulated downregulation of cytokines in exercise and typhoid fever may be mediated by post-transcriptional processes.

Cells, Cultured↗
PubMed1995

Pharmacologic inhibitors of tumor necrosis factor production exert differential effects in lethal endotoxemia and in infection with live microorganisms in mice.

Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) are principal mediators of septic shock; inhibition of TNF-alpha production may ameliorate outcome in severe infections. Pentoxifylline, chlorpromazine, and thalidomide inhibit TNF-alpha production. Their effects were tested in lethal endotoxemia in sensitized mice. Only chlorpromazine significantly improved survival. Chlorpromazine and pentoxifylline significantly reduced postendotoxin circulating TNF-alpha, by 89% and 76%, respectively. Chlorpromazine also significantly reduced IL-1 beta and soluble TNF receptor-P75. No drug improved survival in Klebsiella pneumoniae-infected mice despite significantly lower circulating TNF-alpha concentrations in chlorpromazine- or pentoxifylline-treated animals. The three compounds decreased circulating TNF-alpha in Candida albicans-infected mice, but survival was not influenced. In neutropenic mice, chlorpromazine had no influence on candida in organs, but in normal mice, Candida counts in kidneys were higher in chlorpromazine-treated mice. Thus, inhibition of TNF-alpha production was of no benefit in K. pneumoniae infection and worsened outcome in C. albicans infection.

Animals↗
PubMedDate not supplied

High glucose concentrations increase the tumor necrosis factor-alpha production capacity by human peripheral blood mononuclear cells.

The proinflammatory cytokines tumor necrosis factor-a (TNF) and interleukin-1b (IL-1) play an important role in the pathogenesis of insulin-dependent diabetes mellitus, while TNF is also involved in promoting insulin resistance. It has been recently shown that glucose can induce the synthesis of TNF and IL-6 in human monocytes. The aim of the present study was to investigate the effect of glucose on unstimulated and lipopolysaccharide (LPS)-induced TNF and IL-1 production by human peripheral blood mononuclear cells (PBMC). No effect of glucose on spontaneous release of TNF or IL-I could be observed. The LPS-stimulated production of TNF was enhanced when cells were preincubated with increasing glucose concentrations. In contrast, no effect of glucose preincubation on LPS-induced IL-I synthesis was found. In conclusion, high glucose concentrations can increase the stimulated TNF production capacity, with possible important consequences for patients with diabetes mellitus.

Diabetes Mellitus, Type 1↗
PubMedDate not supplied

Reduced adrenal response and increased mortality after systemic Klebsiella pneumoniae infection in interleukin-6-deficient mice.

During bacterial infections, both the immune system and the hypothalamus-pituitary-adrenal (HPA) axis are activated. The role of IL-6 in the activation of the HPA axis during bacterial sepsis is not fully understood. The aim of the present study was to investigate the role of endogenous IL-6 in a potentially lethal infection with Klebsiella pneumoniae and the concomitant activation of the HPA axis. We examined the mortality of IL-6-/- and IL-6+/+ mice after intravenous (i.v.) infection with K. pneumoniae as well as the bacterial outgrowth in several organs. Subsequently, the influence of endogenous IL-6 on the effect of i.v. administration of K. pneumoniae on the plasma levels of corticosterone and the pro-inflammatory cytokines TNF-alpha and IL-1alpha was investigated in these mice. The present study demonstrates that IL-6-/- mice are more susceptible than IL-6+/+ mice to a systemic Gram-negative infection with K. pneumoniae, leading to increased outgrowth of microorganisms in the organs of the mice. Moreover, this infection is associated with a reduced adrenal response in IL-6-/- mice. We conclude that IL-6-/- mice are more susceptible to Gram-negative bacterial infections, which is mainly due to an impaired recruitment of granulocytes to the site of infection in the absence of IL-6. Furthermore, the reduced adrenal response may be an explanation for the strong inflammatory response with higher TNF-alpha plasma levels in IL-6-/- mice.

Adrenal Glands↗