Interleukin-3 induces antimicrobial activity against Leishmania amazonensis and Trypanosoma cruzi and tumoricidal activity in human peripheral blood-derived macrophages

Endogenous overexpression of an active phosphorylated form of DNA polymerase β under oxidative stress in Trypanosoma cruzi

Trypanosoma cruzi is exposed during its life to exogenous and endogenous oxidative stress, leading to damage of several macromolecules such as DNA. There are many DNA repair pathways in the nucleus and mitochondria (kinetoplast), where specific protein complexes detect and eliminate damage to DNA. One group of these proteins is the DNA polymerases. In particular, Tc DNA polymerase β participates in kinetoplast DNA replication and repair. However, the mechanisms which control its expression under oxidative stress are still unknown. Here we describe the effect of oxidative stress on the expression and function of Tc DNA polymerase β To this end parasite cells (epimastigotes and trypomastigotes) were exposed to peroxide during short periods of time. Tc DNA polymerase β which was associated physically with kinetoplast DNA, showed increased protein levels in response to peroxide damage in both parasite forms analyzed. Two forms of DNA polymerase β were identified and overexpressed after peroxide treatment. One of them was phosphorylated and active in DNA synthesis after renaturation on polyacrylamide electrophoresis gel. This phosphorylated form showed 3-4-fold increase in both parasite forms. Our findings indicate that these increments in protein levels are not under transcriptional control because the level of Tc DNA polymerase β mRNA is maintained or slightly decreased during the exposure to oxidative stress. We propose a mechanism where a DNA repair pathway activates a cascade leading to the increment of expression and phosphorylation of Tc DNA polymerase β in response to oxidative damage, which is discussed in the context of what is known in other trypanosomes which lack transcriptional control.

Exposure of Trypanosome cruzi to oxidative stress leads to damage of several macromolecules such as DNA. DNA polymerases play a very important role in DNA repair after oxidative damage. One of them is Tc DNA polymerase β. In this work, two form of this DNA polymerase were identified and overexpressed in T. cruzi cells after hydrogen peroxide treatment been one of them a phosphorylated and highly active form. The increment of Tc DNA polymerase β was not correlated with changes in mRNA levels, indicating absence of transcriptional control. We propose a mechanism where hydrogen peroxide treatment activates a pathway leading to expression and phosphorylation of Tc DNA polymerase β in response to oxidative damage.

Elevated serum levels of macrophage migration inhibitory factor are associated with progressive chronic cardiomyopathy in patients with Chagas disease

Clinical symptoms of chronic Chagas disease occur in around 30% of the individuals infected with Trypanosoma cruzi and are characterized by heart inflammation and dysfunction. The pathogenesis of chronic chagasic cardiomyopathy (CCC) is not completely understood yet, partially because disease evolution depends on complex host-parasite interactions. Macrophage migration inhibitory factor (MIF) is a pleiotropic proinflammatory cytokine that promotes numerous pathophysiological processes. In the current study, we investigated the link between MIF and CCC progression.

Immunohistochemical analysis demonstrated MIF overexpression in the hearts from chronically T. cruzi-infected mice, particularly those showing intense inflammatory infiltration. We also found that MIF exogenously added to parasite-infected murine macrophage cultures is capable of enhancing the production of TNF-α and reactive oxygen species, both with pathogenic roles in CCC. Thus, the integrated action of MIF and other cytokines and chemokines may account for leukocyte influx to the infected myocardium, accompanied by enhanced local production of multiple inflammatory mediators. We further examined by ELISA the level of MIF in the sera from chronic indeterminate and cardiomyopathic chagasic patients, and healthy subjects. CCC patients displayed significantly higher MIF concentrations than those recorded in asymptomatic T. cruzi-infected and uninfected individuals. Interestingly, increased MIF levels were associated with severe progressive Chagas heart disease, in correlation with elevated serum concentration of high sensitivity C-reactive protein and also with several echocardiographic indicators of left ventricular dysfunction, one of the hallmarks of CCC. Our present findings represent the first evidence that enhanced MIF production is associated with progressive cardiac impairment in chronic human infection with T. cruzi, strengthening the relationship between inflammatory response and parasite-driven pathology. These observations contribute to unravel the elements involved in the pathogenesis of CCC and may also be helpful for the design of novel therapies aimed to control long-term morbidity in chagasic patients.

DNA repair BER pathway inhibition increases cell death caused by oxidative DNA damage in Trypanosoma cruzi

Trypanosoma cruzi, a parasitic protozoan, is the etiological agent of Chagas disease, an endemic and neglected pathology in Latin America. It presents a life cycle that involves a hematophagous insect and man as well as domestic and wild mammals. The parasitic infection is not eliminated by the immune system of mammals; thus, the vertebrate host serves as a parasite reservoir. Additionally, chronic processes leading to dysfunction of the cardiac and digestive systems are observed. To establish a chronic infection some parasites should resist the oxidative damage to its DNA exerted by oxygen and nitrogen free radicals (ROS/RNS) generated in host cells. Till date there are no reports directly showing oxidative DNA damage and repair in T. cruzi. We establish that ROS/RNS generate nuclear and kinetoplastid DNA damage in T. cruzi that may be partially repaired by the parasite. Furthermore, we determined that both oxidative agents diminish T. cruzi cell viability. This effect is significantly augmented in parasites subsequently incubated with methoxyamine, a DNA base excision repair (BER) pathway inhibitor, strongly suggesting that the maintenance of T. cruzi viability is a consequence of DNA repair mechanisms.

EFFECT OF HYPOXIA ON MACROPHAGE INFECTION BY LEISHMANIA AMAZONENSIS

In the present study, we compared the effect of 5% oxygen tension (hypoxia) with a normal tension of 21% oxygen (normoxia) on macrophage infection by the protozoan parasite Leishmania amazonensis. Macrophages from different sources (human cell line U937, murine cell line J774, and murine peritoneal macrophages) exposed to hypoxia showed a reduction of the percentage of infected cells and the number of intracellular parasites per cell. Observations on the kinetics of infection indicated that hypoxia did not depress L. amazonensis phagocytosis but induced macrophages to reduce intracellular parasitism. Furthermore, hypoxia did not act synergistically with gamma-interferon and bacterial lipopolysaccharides in macrophages to induce killing of parasites. Experiments also indicated no correlation between nitric oxide production and control of infection in macrophages under hypoxic condition. Thus, we have provided the first evidence that hypoxia, which occurs in various pathological conditions, can alter macrophage susceptibility to a parasitic infection.

Sodium stibogluconate (Pentostam) potentiates oxidant production in murine visceral leishmaniasis and in human blood

Sodium stibogluconate (Sbb), a leishmanicidal drug, was studied for its in vivo effect on the formation of reactive oxygen species (ROS), assessed by chemiluminescence (CL) in the whole blood of mice infected with Leishmania infantum. Stimulation of ROS formation induced ex vivo by zymosan particles or the protein kinase C activator phorbol myristate acetate (PMA) was reduced by approximately 25% (P < 0.05) after infection of mice. Treatment of infected mice with Sbb (50 to 400 mg/kg of body weight) enhanced the blood CL induced by zymosan and PMA (47 to 96%, P < 0.01). The drug potentiation effect also occurred in uninfected mice. In vitro treatment of normal human blood with Sbb (1, 10, or 100 microg/ml) for 1 h primed the CL response to PMA (29 to 54%). The priming effect of Sbb was also observed on the production of superoxide by isolated polymorphonuclear leukocytes stimulated either by PMA and zymosan or by the chemoattractants N-formyl-Met-Leu-Phe and platelet-activating factor. These data provide the first evidence of priming of the phagocyte respiratory burst by Sbb. This novel property of Sbb may contribute to the drug's leishmanicidal effect.

Comparison of different staining procedures for the flow cytometric analysis of U-937 cells infected with different Leishmania-species

The human macrophage cell line U-937 infected with different Leishmania species, Leishmania mexicana amazonensis (Lma), Leishmania donovani (Ld) and Leishmania infantum (Li), was analyzed by flow cytometry (FCM). Leishmania spp. were labeled with different stains prior to the infection of the U-937 cells (BCECF-Am, PKH2-GL and SYTO 17) or after the infection (AO, FITC-conjugated monoclonal antibodies, PI). Infected cells were analyzed by flow cytometry, fluorescence microscopy and in parallel microscopically after Giemsa staining. The data obtained by these two methods were compared to decide which method is mostly appropriate for detection and estimation of the infection rate. Three fluorescent stains were suitable: BCECF-Am, SYTO 17 and FITC-conjugated MoAb with 0.02% digitonin. None of the vital stains gave evaluable results after 3 days of incubation.

How do protozoan parasites survive inside macrophages?

During infections with intracellular microbes, macrophages have two roles. On the one hand, they are important effector cells for the control and killing of intracellular bacteria and protozoan parasites by oxidative and non-oxidative mechanisms. On the other hand, macrophages may also serve as long-term host cells that facilitate the replication and survival of the pathogens, for example, by protecting them against toxic components of the extracellular milieu. In this review, Christian Bogdan and Martin Röllinghoff summarize some of the more recently discovered mechanisms by which intracellular protozoan parasites, such as Leishmania spp, Trypanosoma cruzi and Toxoplasma gondii, manage to exploit macrophages as safe target cells.

Multinucleated giant cell formation induced by IFN-gamma/IL-3 is associated with restriction of virulent Mycobacterium tuberculosis cell to cell invasion in human monocyte monolayers

One of the hallmarks of an effective immune response against Mycobacterium tuberculosis is the formation of granulomas containing multinucleated giant cells. IFN-gamma and interleukin-3 (IL-3) promote Langhans-type multinucleated giant cell formation and have been identified in T cell clones reacting to M. tuberculosis antigens. The ability of human monocytes treated with IFN-gamma and IL-3 to limit the spread of M. tuberculosis in an in vitro infection assay was examined. Monocytes were incubated with control medium, IFN-gamma, TNF-alpha, and calcitriol, a combination permissive to M. tuberculosis growth, or IFN-gamma and IL-3 and infected with a low inoculum of M. tuberculosis (Erdman). IFN-gamma/IL-3 treatment reduced M. tuberculosis CFU relative to both untreated and IFN-gamma/TNF-alpha/calcitriol-treated monocytes. Specifically, CFU were reduced by 79% at 14 days in the IFN-gamma/IL-3 treatment group relative to the IFN-gamma/TNF-alpha/calcitriol treatment group, an effect that was not due to toxic monocyte metabolites. M. tuberculosis growth restriction by IFN-gamma/IL-3-treated monocyte monolayers was associated with the development of Langhans-type multinucleated giant cells. At the light microscope level, dense growth of M. tuberculosis surrounded by a ring of nuclei localized to the center of individual cells. The intracellular location of M. tuberculosis was confirmed by electron microscopy. In contrast, monocyte monolayers treated with IFN-gamma/TNF-alpha/calcitriol consisted of a syncitium of cells containing monocyte aggregates. Nonlocalized linear arrays of M. tuberculosis were observed to be growing throughout such aggregates. These results suggest that physical sequestration of M. tuberculosis by Langhans-type multinucleated giant cells may limit cell to cell spread of this pathogen, thereby restricting growth.

Migration Inhibitory Factor Induces Killing of Leishmania major by Macrophages: Dependence on Reactive Nitrogen Intermediates and Endogenous TNF-α

Macrophage migration inhibitory factor (MIF) is a product of activated T cells, anterior pituitary cells, and macrophages. MIF plays an important role in LPS-induced shock and delayed-type hypersensitivity. Furthermore, MIF exhibits a proinflammatory spectrum of action, promoting TNF-α production by macrophages, and counter-regulates glucocorticoid suppression of cytokine production. Here, we report that purified recombinant MIF activates murine macrophages to kill Leishmania major, with maximal effects at concentrations above 1 μg/ml. This MIF-mediated activation is specific, since it can be blocked completely by anti-MIF mAb. The MIF-mediated activation is dependent on TNF-α produced endogenously by macrophages, because the administration of anti-TNF-α antiserum markedly reduced the MIF effect. No MIF-mediated activation was observed in macrophages derived from TNF receptor p55 knockout mice, thus demonstrating the requirement of the smaller TNF receptor molecule for autocrine TNF-α signaling. A highly specific inhibitor of the inducible nitric oxide synthase (iNOS), l-N6-(1-iminoethyl)lysine, dihydrochloride, also inhibited the action of MIF, suggesting an important role for iNOS in the antiparasitic properties of MIF. In line with this, no MIF-mediated activation was detected analyzing macrophages derived from iNOS-deficient mice. The effect of MIF was blocked completely by the macrophage-deactivating cytokines IL-10, IL-13, and TGF-β. Finally, the expression of MIF mRNA and protein was up-regulated in lymph nodes of mice during the first week after infection with L. major. MIF therefore represents a cytokine involved not only in the recruitment of proinflammatory cells during infection but also in the complex regulation of the antimicrobial activity of these cells.

Deactivation of primed respiratory burst response of goldfish macrophages by leukocyte-derived macrophage activating factor(s)

Macrophage activation factors (MAF), induced maximal priming of the respiratory burst response in GMCL after 6 h of stimulus, but by 24 or 48 h no priming effect was observed. Bacterial lipopolysaccharide (LPS) also primed the respiratory burst of goldfish macrophages, but the kinetics of priming were different from that induced by MAF. LPS induced a gradual increase in priming potential over 48 h of cultivation. Co-stimulation of macrophages with MAF and LPS resulted in enhanced priming of respiratory burst activity compared to either factor alone; however, the kinetics of priming were similar to those induced by MAF only. The MAF antagonized the ability of LPS to prime the respiratory burst over extended cultivation. The priming kinetics of the respiratory burst induced by MAF and/or LPS were not unique to GMCL, but were also similar for primary cultures of IVDKM. Respiratory burst deactivated macrophages-mounted potent nitric oxide response, indicating that this deactivation event was selective for respiratory burst activity. Autocrine factors produced by MAF-activated macrophages augmented priming of the respiratory burst, suggesting that deactivation of primed respiratory burst responses was not due to cytokine mediators produced by activated macrophages, but was most likely an intracellular deactivation event. Furthermore, production of reactive intermediates by activated fish macrophages was biphasic; with maximal ROI production occurring 6 h after stimulus, and maximal RNI occurring 72 h after stimulus. Our results indicate that activated fish macrophages mount sequential antimicrobial responses that are selectively deprogrammed once maximal induction has occurred. The ability to selectively deactivate ROI production without affecting subsequent RNI production may play an important role in host defense: regulating the duration of ROI production, and thus minimizing host tissue damage in an otherwise futile attempt to eliminate ROI resistant pathogens.

Cytokine gene expression during infection of mice lacking CD4 and/or CD8 with Trypanosoma cruzi

The expression of lymphokine genes during infection of virulent (Tulahuén) or mild (CA-I) strains of T. cruzi was studied in mice lacking CD4 and/or CD8 molecules. The increased susceptibility of CD4- and CD4-CD8- mice to infection with CA-I or Tulahuén was parallelled by diminished IFN-gamma mRNA levels. Nitric oxide release and inducible nitric oxide synthase mRNA accumulation by cells from Tulahuén infected CD4- mice was also diminished. CD8- (but not CD4-CD8- mice) showed an increased IL-4 and IL-10 mRNA accumulation upon infection with both strains of T. cruzi. A 'Th2-like' response (higher IL-4 and IL-10 mRNA to IFN-gamma mRNA ratio), was also observed when cells from noninfected CD8- mice were stimulated with T cell mitogens.

Pneumocystis carinii-induced activation of the respiratory burst in human monocytes and macrophages

Human monocytes and monocyte-derived macrophages were studied for their ability to phagocytose Pneumocystis carinii and produce superoxide (O2-) during the process. One x 10(6) freshly isolated monocytes, incubated with 0.1-3.75 x 10(6) P. carinii cysts, increased O2- production in a dose-related way. Antibodies were essential for the process since opsonized, but not unopsonized, pneumocysts induced O2- production significantly above the response obtained by lung tissue from rats (10.7 and 4.9 versus 3.0 fmol/cell per 90 min). The difference between pneumocysts opsonized in untreated versus complement-depleted serum was not significant (10.7 versus 12.6 fmol/cell per 90 min). Monocyte-derived macrophages also activated the respiratory burst when stimulated with pneumocysts, and this effect could be significantly increased, from 4.2 to 8.8 fmol/cell per 90 min, when cells were primed with interferon-gamma (IFN-gamma). Cells primed with IL-3 also increased O2- production, though to a lesser extent. In contrast, granulocyte-macrophage colony-stimulating factor (GM-CSF) had only a small effect on the respiratory burst in cells stimulated with P. carinii. Priming with IFN-gamma increased the rate of phagocytosis in macrophages. After incubation for 90 min or more, however, the percentage of cells with phagocytic vacuoles was only slightly higher in IFN-gamma-primed cells. When examined by electron microscopy (EM), most vacuoles contained partially or totally degraded pneumocysts. In conclusion, we have demonstrated the ability of monocytes and monocyte-derived macrophages to ingest and degrade pneumocysts, activating the respiratory burst during the process.

Interleukin 4 receptor signaling in human monocytes and U937 cells involves the activation of a phosphatidylcholine-specific phospholipase C: a comparison with chemotactic peptide, FMLP, phospholipase D, and sphingomyelinase

Interleukin 4 (IL-4) diminishes cytokine activation of human macrophage. IL-4 binding to monocyte IL-4R is associated with protein kinase C (PKC) translocation to a nuclear fraction. The cleavage of diacyglycerol (DAG), an activator of PKC, from membrane phospholipids was investigated to define the proximal events of IL-4R signaling. IL-4 induced a statistically significant time-and dose-dependent generation of DAG. The IL-4-triggered production of DAG was not derived from phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis, since neither cytosolic calcium flux nor liberation of inositol phosphates was detected in response to IL-4. Experiments were performed using [14C-methyl]choline-labeled U937 cells and monocytes to determine whether IL-4R activated phospholipase C (PLC), PLD, or PLA2 to use membrane phosphatidylcholine (PC) to form DAG. IL-4 induced a time- and dose-dependent increase of phosphocholine (pchol) with concomitant degradation of membrane PC (p < 0.05 compared with control). The finding that the peak reduction of PC was equivalent to peak production of pchol suggested that IL-4R signaling involved the activation of a PC-specific PLC. Changes in choline (chol) or lyso-PC and glycerolphosphocholine, the respective products of PC cleavage by PLD or PLA2, were not detected in IL-4-treated cells. In contrast, exogenous PLD induced an increase in chol and concomitant loss of membrane PC. Additional investigation suggested that IL-4R signaling does not involve PLD. In cells labeled with L-lyso-3-PC 1-[1-14C]palmitoyl, PLD but not IL-4, increased the production of phosphatidic acid (PA) and phosphatidyl-ethanol when pretreated with ethanol. Propranolol, an inhibitor of phosphatidate phosphohydrolase, and calyculin A, a phosphatase 1 and 2A inhibitor, blocked DAG production in response to FMLP but not to IL-4. In propranolol pretreated cells, PMA but not IL-4 triggered the production of PA and lowered the amount of DAG. Evidence that PLA2 is not coupled to IL-4R is the detection of arachidonate production in response to FMLP but not to IL-4. Furthermore, IL-4R is not coupled to sphingomyelinase (SMase) since IL-4, unlike exogenous SMase, did not generate ceramide but induced the hydrolysis of PC to pchol that was comparable to exogenous PLC. In summary, IL-4R signaling in monocytes and U937 cells involves PLC and not PLD, PLA2, or SMase, and it uses PC and not PIP2 to form DAG.

Cytokines in the treatment of leishmaniasis: from studies of immunopathology to patient therapy

The genus Leishmania, an obligate intramacrophage parasite, causes a wide spectrum of clinical diseases. It is worldwide in distribution and causes 20 million new cases annually with an at risk population of approximately 1.5 billion persons. The most severe forms are associated with high morbidity, mortality and relapses with conventional therapy. The therapeutic issues and responses to standard and alternative therapies are reviewed. Recent developments in molecular biology and immunology methods employed in the study of leishmaniasis have defined an intricate interaction of the parasite with host immune system. Perturbation of the host immune responses may be part of the survival mechanisms of Leishmania. In murine model, the finding of T helper cells that differ by their panel of cytokines has allowed a more precise definition of immunopathogenesis of leishmaniasis. Preliminary data from leishmaniasis patients lend support to this concept of altered immunomodulation. Furthermore, the data from leishmaniasis patients lend support to this concept of altered enhancement of therapeutic response by interferon-gamma has provided a new approach for treatment of patients using recombinant cytokines and for the study of the disease. Current research for early diagnosis, alternative therapies and need for vaccines are reviewed in the context of the immunopathology of leishmaniasis.

Interleukin-7 enhances antimicrobial activity against Leishmania major in murine macrophages

Recently, it has been shown that interleukin-7 (IL-7) is able to induce secretion of cytokines and tumoricidal activity by human monocytes. This study shows that treatment of murine macrophages infected with Leishmania major with IL-7 without any other stimulus reduced the percentage of infected cells, as well as the parasite burden per cell, in a dose-dependent manner to a limited degree (45% reduction of the number of amastigotes per 100 macrophages). Simultaneous treatment of macrophages with gamma interferon and IL-7 led to nearly complete (> 99%) elimination of amastigotes. Addition of anti-tumor necrosis factor alpha or N omega-monomethyl-L-arginine acetate reversed the leishmanicidal effects of IL-7, and production of nitric oxide was induced in the presence of IL-7.

Effector functions of activated macrophages against parasites

Evidence in experimental animals indicates a major role for cytokine-activated macrophages as effector cells in protective immunity against parasites. Research on cytokine function during this past year has contributed many insights into the immune mechanisms regulating murine macrophage function as well as the effector molecules employed by these cells to kill both intracellular and extracellular parasites.

T-cell and cytokine responses in leishmaniasis

Intracellular pathogens, particularly those that inhabit lymphocytes and macrophages, represent unique challenges to the immune system. Leishmania are protozoan parasites that replicate exclusively in macrophages and are thus in an excellent position to influence lymphocyte responses. T cell responses are critical in determining the outcome of infections with Leishmania. In both murine and human infections, strong T helper type 2 responses have been associated with disease, and a decreased or absent T helper type 2 response has been associated with healing.

IFN-gamma is directly cytostatic to the extracellular form (promastigote) of Leishmania donovani

We investigated the effect of various human cytokines on the in vitro growth of Leishmania donovani (L. donovani) promastigotes. rhIFN-alpha, rhIFN-beta, rhIL-1, rhIL-2, rhIL-3, rhIL-4, rhIL-6 and rhM-CSF had no effect. By contrast, rhIFN-gamma was directly growth inhibitory to L. donovani promastigotes in a dose-dependent manner. Anti-IFN-gamma antibody, but neither anti-IFN-alpha nor anti-IFN-beta antibody, abolished this promastigote growth inhibitory effect of rhIFN-gamma. L. donovani promastigotes were not lysed by rhIFN-gamma as determined by 51Cr-release assay. These data indicate that rhIFN-gamma is cytostatic, not cytotoxic, to L. donovani promastigotes.

Colony-stimulating factors activate human macrophages to inhibit intracellular growth of Histoplasma capsulatum yeasts

Recombinant cytokines and colony-stimulating factors (CSFs) were tested for their abilities to activate human monocytes/macrophages (M phi) to inhibit the intracellular growth of or kill Histoplasma capsulatum yeasts. None of the cytokines or CSFs or combinations of cytokines and CSFs activated M phi fungistatic activity when they were added to M phi monolayers concurrently with yeasts. In contrast, culture of monocytes for 7 days in the presence of interleukin 3, granulocyte-M phi CSF, or M phi CSF stimulated M phi fungistatic (but not fungicidal) activity against H. capsulatum yeasts in a concentration-dependent manner. Optimal activation of M phi by CSFs required 5 days of coculture, and the cultures had to be initiated with freshly isolated peripheral blood monocytes. Culture of monocytes with combinations of CSFs or addition of CSFs during the 24 h of coculture with the yeasts did not further enhance M phi fungistatic activity for H. capsulatum. Addition of gamma interferon or tumor necrosis factor alpha to CSF-activated M phi also did not enhance M phi fungistatic activity. These results suggest that interleukin 3, granulocyte-M phi CSF, and M phi CSF may play a role in the cell-mediated immune response to H. capsulatum by enhancing monocyte/M phi fungistatic activity.