Tumor necrosis factor is required for the priming of peritoneal macrophages by trehalose dimycolate.

Trehalose dimycolate (TDM), a glycolipid present in the cell wall of Mycobacterium spp., is a powerful immunostimulant. We have developed an original model of macrophage activation where TDM is injected in vivo to prime peritoneal macrophages. These primed macrophages do not express inducible NO synthase (NOS II), however, they can be fully activated, i.e. induced to express NOS II and to develop a NOS II-dependent antiproliferative activity, following in vitro exposure to low concentrations of LPS. In a previous paper, we have shown that TDM-priming of mouse peritoneal macrophages is mediated by the sequential production of IL-12 and IFN-gamma. In the present paper, we investigated the role of TNF in the priming of macrophages by TDM. By semi-quantitative RT-PCR, we have shown that TDM injection induced transcription of TNF-alpha in peritoneal cells. TNF-mRNA levels peaked 5 hours after TDM injection and remained elevated for at least 32 hours. TNF expression was absolutely necessary for macrophage priming, as injection of an anti-TNF monoclonal antibody, 4 h before and 20 hours after TDM injection, prevented LPS-dependent activation of macrophages in vitro. This result was confirmed by the inability of TDM to prime macrophages from LT-alpha/TNF-alpha knockout (LT/TNFKO) mice. In addition, analysis of LT/TNFKO mice treated with TDM revealed that induction of the IL-12 transcript in their peritoneal cells and expression of a functional NADPH oxidase in macrophages are TNF-independent events.

Differential cytostatic effects of NO donors and NO producing cells.

A 3-h exposure to NO donors (spermine-NO, DETA-NO, or SNAP), or to NOS II-expressing cells (activated macrophages or EMT6 cells) reversibly inhibited DNA synthesis in K562 tumor cells. In GSH-depleted K562 cells, cytostasis remained reversible when induced by DETA-NO or NOS II activity, but became irreversible after exposure to spermine-NO or SNAP. Only SNAP and spermine-NO efficiently inhibited GAPDH, an enzyme with a critical thiol, in GSH-depleted cells. Thus, the irreversible cytostasis induced in GSH-depleted cells by spermine-NO or SNAP can be tentatively attributed to S-nitrosating or oxidizing species derived from NO. However, these species did not contribute significantly to the early antiproliferative effects of macrophages. Ribonucleotide reductase, a key enzyme in DNA synthesis. has been shown to be inhibited by NO. Supplementation of the medium with deoxyribonucleosides to bypass RNR inhibition restored DNA synthesis in target cells exposed to DETA-NO and NO-producing cells, but was inefficient for GSH-depleted cells previously submitted to spermine-NO or SNAP. These cells also exhibited a persistent depletion of the dATP pool. In conclusion, GSH depletion reveals striking qualitative differences in the nature of the toxic effectors released by various NO sources, questioning the significance of S-nitrosating or oxidizing nitrogen oxides in NOS II-dependent cytostasis.

Interleukin-12 synthesis is a required step in trehalose dimycolate-induced activation of mouse peritoneal macrophages.

Trehalose dimycolate (TDM), a glycolipid present in the cell wall of Mycobacterium spp., is a powerful immunostimulant. TDM primes murine macrophages (Mphi) to produce nitric oxide (NO) and to develop antitumoral activity upon activation with low doses of lipopolysaccharide (LPS). In this study, we investigated the ability of TDM to induce interleukin 12 (IL-12) and the role of this cytokine in TDM-induced activation of murine Mphi. RNA isolated from peritoneal exudate cells (PEC) collected at different times after TDM injection was used to determine IL-12 (p35 and p40 subunits) and gamma interferon (IFN-gamma) mRNA levels by semiquantitative reverse transcriptase-PCR. Constitutive expression of IL-12p35 was observed in PEC from untreated as well as from TDM-injected mice. In contrast, expression of the IL-12p40 subunit was almost undetectable in control PEC but was dramatically upregulated in PEC from TDM-injected mice. IL-12p40 expression peaked at 8 h and subsided to baseline levels at 39 h postinjection. TDM was also able to induce IFN-gamma expression; however, kinetics of induction of IFN-gamma was different from that of IL-12p40. Maximal levels of IFN-gamma mRNA were reached by 24 h and did not return to baseline by 4 days. In addition, pretreatment of mice with neutralizing monoclonal antibodies directed against IL-12 (C15.6.7 and C15.1.2) blocked IFN-gamma mRNA induction in PEC from TDM-treated mice. We further determined if the induction of IL-12 and/or IFN-gamma contributes to the in vivo priming effect of TDM on peritoneal Mphi. TDM-injected mice were treated in vivo with anti-IL-12 or anti-IFN-gamma (XMG.1.6) monoclonal antibodies. TDM-primed Mphi were then activated in vitro with LPS and tested for their ability to produce NO and to develop cytostatic activity toward cocultivated L1210 tumor cells. Priming of Mphi by TDM was completely blocked by in vivo neutralization of either IL-12 or IFN-gamma as demonstrated by an absence of tumoricidal activity and NO production by TDM-elicited Mphi in the presence of LPS. Taken together our results show that TDM, a defined molecule from M. tuberculosis, induces in vivo production of IL-12. Moreover, synthesis of IL-12 mediates TDM priming of mouse peritoneal Mphi through IFN-gamma induction.

Differential responsiveness of human and rat mesothelioma cell lines to recombinant interferon-gamma.

Recombinant human interferon-gamma (r-hu-IFN-gamma) has been found to exert an antitumor action in vivo in early stages of human malignant mesothelioma, and an antiproliferative effect in vitro. In order to study the mechanisms of cytostasis in mesothelioma cells, we examined two IFN-gamma-controlled metabolic pathways known to mediate growth arrest in various cell types, measuring production of the antiproliferative compound nitric oxide (NO) and degradation of tryptophan in nine human mesothelioma cell lines (HMCLs) displaying different sensitivities to the antiproliferative effect of r-hu-IFN-gamma. Two rat mesothelioma cell lines were also studied. IFN-gamma receptor was present and functional in HMCLs, regardless of their sensitivity to the growth-inhibitory effect of r-hu-IFN-gamma. However, no NO synthase activity or the resulting antiproliferative molecule NO were induced in HMCLs treated either with r-hu-IFN-gamma alone or with a combination of r-hu-IFN-gamma and other cytokines, and/or with lipopolysaccharide (LPS). In responsive HMCLs, r-hu-IFN-gamma induced strong indoleamine-2,3-dioxygenase (IDO) activity, which causes rapid degradation of tryptophan; however, the correlation between r-hu-IFN-gamma-mediated growth arrest and IDO induction was not absolute. In rat mesothelioma cells, NO synthase was induced in response to murine IFN-gamma + interleukin-1beta (IL-1beta) treatment, and played a role in the cytokine-mediated antiproliferative activity. However, NO production did not seem to be the unique antiproliferative mechanism induced by cytokines in these cells. Our results indicate that two classical pathways accounting for some of the cytostatic effects of IFN-gamma in rodent cells are not efficient in human mesothelioma cells, and suggest that cytokine-induced growth inhibition is mediated by a different pathway in HMCLs.

Protection by glutathione against the antiproliferative effects of nitric oxide. Dependence on kinetics of no release.

Pretreatment by L-buthionine sulfoximine (BSO), which inactivates gamma-glutamylcysteine synthetase and, therefore, inhibits glutathione (GSH) synthesis, greatly increased the sensitivity of tumor cells to the antiproliferative effects of several NO-donating compounds. The sensitization that resulted from depletion of cellular GSH pools was observed in tumor cells exhibiting different degrees of resistance to NO. In contrast, GSH depletion of tumor target cells did not affect their sensitivity to the cytostatic activity of activated macrophages and other NO-producing cells (EMT6 cells treated by interferon gamma and LPS). The kinetics for NO generation is a parameter that may differentiate NO-producing cells and short-lived NO donors. To study the relationship between the magnitude of NO fluxes and the increased toxicity on BSO-pretreated cells, two NO-releasing zwitterions derived from polyamines (NONOates) with different half-lives were selected. NO fluxes as a function of time were simulated, according to the donor half-life and initial concentration, and antiproliferative effects on control and BSO-treated cells were compared. GSH depletion increased the sensitivity of tumor cells in the case of the less stable NO donor only. We, thus, propose that intracellular GSH is specifically protective against high fluxes of NO.

Activity of nitric oxide-generating compounds against encephalomyocarditis virus.

Nitric oxide (NO) generated by two NO donors (sodium nitroprusside or S-nitroso-L-glutathione) was shown to exert a dose-dependent inhibition of encephalomyocarditis virus growth in L-929 cells. This activity was not due to the cytotoxic or direct virucidal effects of NO donors. L-929 cells were shown to produce NO endogenously, but this low level of production did not counter encephalomyocarditis virus replication.

Role of trehalose dimycolate-induced interferon-alpha/beta in the restriction of encephalomyocarditis virus growth in vivo and in peritoneal macrophage cultures.

Preventive intraperitoneal trehalose dimycolate (TDM) treatment of mice, inoculated with encephalomyocarditis (EMC) virus by the same route, caused restriction of virus growth in the peritoneum, which was correlated to IFN production in peritoneal fluids prior to infection. Peritoneal macrophages from TDM-treated mice (TDM-PM) spontaneously secreted IFN-alpha/beta in large amounts. By their supernatants, TDM-PM could transfer an antiviral state against EMC virus to permissive resident peritoneal macrophages from control mice. IFN-alpha/beta produced by TDM-PM was found to be involved in this transfer activity. TDM-PM also exerted a strong antiviral effect on EMC virus-infected L-929 cells, which increased with time and the macrophage-target cell ratio. This activity also occurred by an IFN-alpha/beta-dependent mechanism. These data point to the role of IFN-alpha/beta production prior to EMC virus infection in the antiviral activities of TDM-PM and, more generally, in the outcome of viral infection.

Phosphatidylinositolmannoside-based liposomes induce no synthase in primed mouse peritoneal macrophages.

Liposomes prepared from phosphatidylinositolmannosides (extracted from BCG) and cholesterol are efficiently endocytosed by macrophages. Phagocytosis of particles or microbes modifies macrophage metabolism and in some cases, delivers potent stimulating signals to macrophages. We examined the effect of phosphatidylinositolmannoside-based liposomes on three macrophage functions especially important for host defenses: nitric oxide production, oxidative burst and TNF-alpha secretion. Phosphatidylinositolmannoside-based liposomes, added as empty vesicles, induced a strong NO synthase activity in mouse peritoneal macrophages primed either by interferon-gamma or by trehalose dimycolate. They also induced a moderate production of TNF-alpha. Phosphatidylinositolmannosides conferred activating properties to pH-sensitive liposomes. In contrast, liposomes composed of phosphatidylcholine and phosphatidylserine were unable to activate primed macrophages.

Role of calcium in the activation of mouse peritoneal macrophages: induction of NO synthase by calcium ionophores and thapsigargin.

Bacterial lipopolysaccharide (LPS) has been recognized as one of the most potent activating signals for mouse peritoneal macrophages. In macrophages primed by interferon-gamma (IFN-gamma) or trehalose dimycolate (TDM), LPS induces NO synthase and the events associated with a high nitric oxide output: antitumor and antiparasitic activities. In the present report, it is shown that drugs (calcium ionophores or thapsigargin) which elevate the concentration of cytosolic calcium, [Ca2+]i, induce NO synthase and antitumor activities in primed macrophages, mimicking LPS action. Calcium ionophores and thapsigargin trigger NO synthase activity in macrophages primed in vivo by TDM, in thioglycollate-elicited macrophages primed in vitro by IFN-gamma, and in IFN-gamma-treated EMT6 adenocarcinoma cells. However, activation of TDM-primed macrophages by LPS does not seem to involve calcium fluxes: (i) no change in [Ca2+]i was detectable in TDM-primed macrophages loaded with Fura-2 and exposed to LPS, and (ii) activation of TDM-primed macrophages by LPS can be obtained in the presence of 4 mM EGTA. NO synthase expression is thus controlled in primed macrophages by two different pathways; calcium ionophores can replace LPS but do not act through the same intracellular cascade.

Antiviral action of trehalose dimycolate against EMC virus: role of macrophages and interferon alpha/beta.

Preventive treatment of mice with trehalose 6,6' dimycolate (TDM), an immunomodulator of bacterial origin, enhances their resistance to encephalomyocarditis (EMC) virus infection. The protective effect of TDM is totally abolished by the injection of silica particles in mice, demonstrating the role of macrophages in the antiviral action of TDM. In vitro, peritoneal macrophages from mice treated with TDM (TDM-PM) exhibit an intrinsic antiviral activity against EMC virus, while resident peritoneal macrophages (RES-PM) are permissive to this virus. Greater amounts of interferon are detected in supernatants of cultures of TDM-PM than of RES-PM. Neutralization of interferon (IFN) by addition in vitro of anti-IFN alpha/beta serum markedly reduces the antiviral activity of TDM-PM. These results indicate that interferon alpha/beta is involved in the intrinsic anti-EMC virus activity of peritoneal macrophages from mice treated with TDM.

LPS-induced activation of primed murine peritoneal macrophages is modulated by prostaglandins and cyclic nucleotides.

Murine peritoneal macrophages primed in vivo by trehalose dimycolate (TDM) express cytostatic activity against tumor cells after treatment in vitro with 10 ng/ml lipopolysaccharide (LPS) during a 4-hr period (activation step). There is a strict correlation (P < 0.0001) between acquisition of antitumoral activity and induction of NO synthase quantified by its end products citrulline and NO2-. LPS also stimulates the release of cyclooxygenase products which exert a retroinhibitory action on NO synthase and cytostatic activities, as judged by an increase of both parameters by indomethacin (1 microM) and a decrease by externally added PGE2 (1 microM). LPS increases cellular and extracellular cAMP levels through an indomethacin-sensitive pathway, pointing to cAMP as a second messenger in the retroinhibitory action of LPS-induced prostaglandins. In fact, the addition of 8-bromo-cAMP or of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine during the activation step decreases NO synthase activity; however, at the same time these drugs increase the apparent efficiency of NO as an antitumor agent.

Low response of BALB/c macrophages to priming and activating signals.

Trehalose dimycolate (TDM), a mycobacterial glycolipid, is a powerful macrophage-priming agent. However, its efficiency seems limited in the case of BALB/c mice. Peritoneal macrophages harvested from TDM-treated BALB/c mice did not control BCG growth in vitro as efficiently as similar macrophages from two other mouse strains, (B6 x D2)F1 and C57BL/6, which are respectively Bcgr and Bcgs. BALB/c macrophages elicited by TDM also exhibited a low capacity to produce hydrogen peroxide and, after activation by lipopolysaccharide (LPS), weak cytostatic activity against P815 mastocytoma cells. Finally, alkaline phosphodiesterase, a marker of resident and inflammatory macrophages, was still expressed at a high level in macrophages of BALB/c mice treated with TDM. Low responsiveness of BALB/c macrophages to stimuli was not observed with TDM only; activation for tumor cytotoxicity of thioglycolate-elicited macrophages from BALB/c mice required also higher doses of interferon-gamma, and LPS. L-Arginine-dependent production of nitric oxide was inducible in macrophages from BALB/c mice, but the conditions required for its induction were more stringent. Thus, the reduced antiproliferative effects of BALB/c macrophages may be due to uncomplete induction of NO synthase after suboptimal stimulation.

Stimulation of antimycobacterial activity in mouse peritoneal macrophages by priming with trehalose dimycolate (TDM).

We examined the potential of two bacterial immunomodulators, trehalose dimycolate (TDM) and lipopolysaccharide (LPS), to stimulate the capacity of mouse peritoneal macrophages to control the growth of the intracellular bacterium, Mycobacterium tuberculosis BCG. Macrophages were obtained from mice innately susceptible (Bcgs) or resistant (Bcgr) to BCG infection. In all mouse strains tested (Bcgr and Bcgs), with the exception of BALB/c (Bcgs), TDM was sufficient to elicit macrophages with strong antimycobacterial activity in vitro. In BALB/c mice, the induction of anti-BCG activity required two signals, TDM and LPS, given in sequence. Our data suggest that additional gene(s), besides the Bcg locus, control macrophage resistance to BCG.

MDP and LPS act synergistically to induce arginine-dependent cytostatic activity in rat alveolar macrophages.

Rat alveolar macrophages can be activated in vitro for cytostatic activity against tumor cells by MDP and LPS acting in synergy. MDP can be substituted for by analogs active as adjuvants. Macrophage activation correlates with an increased production of nitrite and citrulline. NG-monomethyl-L-arginine, a specific inhibitor of the L-arginine metabolism having nitrite and citrulline as end products, abolishes the cytostatic activity. We therefore conclude that, in this model, the main effector mechanism of the cytostatic activity is mediated by molecules derived from L-arginine through the newly described NOo-generating pathway.

Production of an arginine-derived relaxing factor induced by IFN-gamma plus endotoxin in murine adenocarcinoma EMT 6 cells.

Treatment of EMT 6 mammary adenocarcinoma cells with Interferon-gamma (IFN-gamma, 10 U.ml-1) plus endotoxin lipopolysaccharide (LPS, 100 ng.ml-1) induces concomitantly a growth arrest and production of citrulline and nitrite from L-arginine. A similar L-arginine-dependent metabolism is responsible for the vascular smooth muscle relaxing effect of stimulated endothelial cells. We therefore investigated the ability of EMT 6 cells to induce the relaxation of endothelium-denuded rat aortic rings precontracted with noradrenaline (1 microM). Pretreatment of EMT 6 cells with IFN-gamma + LPS increased their relaxing potency by 5-10 times. The relaxin effects of control and treated EMT 6 cells were entirely counteracted by NG-monomethyl-L-arginine (300 microM), a specific inhibitor of nitrite and citrulline production from L-arginine, and by methylene blue (10 microM) and LY 83583 (10 microM), two inhibitors of NOo-induced activation of guanylate cyclase. The effect of NG-monomethyl-L-arginine was reversed by L- but not D-arginine (1 mM). It is concluded that IFN-gamma + LPS increase the production of a relaxing factor in EMT 6 cells through the L-arginine-NOo-synthase pathway.

Prenatal and postnatal corticosteroid therapy to prevent neonatal necrotizing enterocolitis: a controlled trial.

To determine whether prenatal corticosteroid therapy would reduce the incidence of neonatal necrotizing enterocolitis (NEC), we assigned a total of 466 women admitted in premature labor either to receive placebo (group A, n = 256), if delivery was expected to occur within 24 hours of admission, or to receive betamethasone (group B, n = 210) if delivery was expected to take place more than 24 hours after admission. All women were free of severe medical complications or drug therapy; cases of intrauterine growth retardation or premature rupture of the membranes were excluded. Their newborn infants, excluding malformed, congenitally infected, and growth-retarded infants, were enrolled in the study unless they had died before the age of 10 postnatal days. Babies born to group A mothers (n = 248) were further assigned to a treatment group (group A1, n = 130) receiving dexamethasone, 2 mg/kg/day by intravenous injection during the first 7 days of life, or to a control group (group A2, n = 118) receiving 10% dextrose solution placebo. Group B infants (prenatal betamethasone, n = 205) received neither treatment nor placebo. The incidence of NEC in group A1 was 6.9% (9/130), and in group A2 it was 14.4% (17/118) (p less than 0.05). In group B the incidence was 3.4% (7/205); this was much lower than in group A2 (p less than 0.01) and lower than in group A combined (10.4%) (p less than 0.01). There was no death from NEC and no surgical intervention among group B patients. The mortality rate for group A1 (11%) was lower than for group A2 (56%) (p less than 0.02). There were fewer indications for surgical intervention for NEC in group A1 than in group A2. Histologic studies confirmed bowel ischemia in all specimens analyzed. These data support the hypothesis that the incidence of NEC is significantly reduced after prenatal steroid treatment. Although postnatal therapy with steroids does not decrease the incidence as effectively as prenatal therapy, it improves clinical outcome of NEC.

Antiproliferative activity of gamma-interferon combined with lipopolysaccharide on murine adenocarcinoma: dependence on an L-arginine metabolism with production of nitrite and citrulline.

Growth of the murine adenocarcinoma EMT6 was moderately inhibited by up to 32 units/ml of gamma-interferon (IFN-gamma). However, EMT6 growth was blocked by as low as 2 U/ml of IFN-gamma, when added with lipopolysaccharide. In the same time, the combination IFN-gamma + lipopolysaccharide induced synergistically the production of nitrite and citrulline by EMT6 cells. Synthesis of the two products was correlated with IFN-gamma concentrations. It required exogenous L-arginine and was inhibited by a methylated L-arginine derivative, NG-monomethyl-L-arginine. Inhibition was specific since urea synthesis was not reduced by NG-monomethyl-L-arginine. The L-arginine-dependent pathway was involved in EMT6 cytostasis mediated by IFN-gamma + lipopolysaccharide because cytostasis expression required L-arginine and was inhibited by NG-monomethyl-L-arginine.

Photoaffinity labelling of macrophages and B-lymphocytes using 125I-labelled aryl-azide derivatives of muramyldipeptide.

Two 125I-labelled aryl-azide derivatives of MDP have been synthesized. Photoaffinity labelling experiments demonstrated cell surface binding sites for muramylpeptides on activated B-lymphocytes and intracellular muramylpeptides binding protein(s) of 40-45 kD in rat alveolar macrophages.

Cytostatic product(s) released by activated macrophages, unrelated to interleukin 1, tumor necrosis factor alpha, and interferon-alpha/beta.

Murine peritoneal macrophages activated for cytotoxicity by trehalose dimycolate in vivo and lipopolysaccharide in vitro released cytostatic factor(s) against EMT6 target cells, in 8-hr conditioned medium (CM). The cytostatic factor(s) completely blocked DNA synthesis by EMT6 cells within 16 hr. Other cell lines are less sensitive (P815 and R-L929) or resistant (KB and HT29) to the cytostatic effect of CM. The anti-proliferative activity of CM had a MW greater than 10,000 Da, as judged by ultrafiltration. It was destroyed by proteases and strongly inhibited by P815 cell product(s). Conditioned media from nonactivated macrophages were not cytostatic against EMT6 cells. No relationship was found between cytostatic factor(s) in CM and interleukin 1 (IL-1), tumor necrosis factor alpha (TNF-alpha), and interferon-alpha/beta (IFN-alpha/beta): the growth of EMT6 cells was unaffected by Hu.r.IL-is and Hu.r.TNF-alpha and was only slightly inhibited by IFN-alpha/beta. Furthermore, cytostatic CM contained low levels of TNF and IFN activities. Finally, antibodies raised against murine IFN-alpha/beta had no effect on the cytostatic activity of CM.