Leishmania and the macrophage: a marriage of inconvenience

Leishmanicidal and cytotoxic activity of essential oil from the fruit peel of Myrciaria floribunda (H. West ex Willd.) O. Berg: Molecular docking and molecular dynamics simulations of its major constituent onto Leishmania enzyme targets

Cutaneous Leishmaniasis (CL) is a neglected disease characterized by highest morbidity rates worldwide. The available treatment for CL has several limitations including serious side effects and resistance to the treatment. Herein we aimed to evaluate the activity of essential oil from the peel of Myrciaria floribunda fruits (MfEO) on Leishmania amazonensis. The cytotoxic potential of MfEO on host mammalian cells was evaluated by MTT. The in vitro leishmanicidal effects of MfEO were investigated on the promastigote and intracellular amastigote forms. The ultrastructural changes induced by MfEO were evaluated by Scanning Electron Microscopy (SEM). The molecular docking of the major compounds δ-Cadinene, γ-Cadinene, γ-Muurolene, α-Selinene, α-Muurolene and (E)-Caryophyllene onto the enzymes trypanothione reductase (TreR) and sterol 14-alpha demethylase (C14DM) were performed. Our results showed that MfEO presented moderate cytotoxicity for Vero cells and macrophages. The MfEO inhibited the growth of promastigote and the survival of intracellular amastigotes, in a dose- and time- dependent way. The MfEO presented high selectivity towards amastigote forms, being 44.1 times more toxic for this form than to macrophages. Molecular docking analysis showed that the major compounds of MfEO interact with Leishmania enzymes and that δ-Cadinene (δ-CAD) presented favorable affinity energy values over TreR and C14DM enzymes, when compared with the other major constituents. Molecular dynamics (MD) simulation studies revealed a stable binding of δ-CAD with lowest binding free energy values in MMGBSA assay. Our results suggested that δ-CAD may be a potent inhibitor of TreR and C14DM enzymes. Communicated by Ramaswamy H. Sarma.

Anti-Leishmania activity of essential oil of Myracrodruon urundeuva (Engl.) Fr. All.: Composition, cytotoxity and possible mechanisms of action

Myracrodruon urundeuva (Engl.) Fr. All., commonly known as "aroeira-do-sertão", is a medicinal plant from Anacardiaceae family. In this study, the chemical composition of M. urundeuva essential oil (MuEO) was evaluated by gas chromatography-mass spectrometry (GC-MS), as well as its anti-Leishmania potential, cytotoxicity, and macrophage activation capability as possible antiprotozoal mechanism of action were assessed. Fourteen compounds were identified, which constituted 94.87% of total oil composition. The most abundant components were monoterpenes (80.35%), with β-myrcene (42.46%), α-myrcene (37.23%), and caryophyllene (4.28%) as the major constituents. The MuEO inhibited the growth of promastigotes (IC₅₀ 205 ± 13.4 μg mL^-1), axenic amastigotes (IC₅₀ 104.5 ± 11.82 μg mL^-1) and decreased percentage of macrophage infection and number of amastigotes per macrophage (IC₅₀ of 44.5 ± 4.37 μg⋅mL^-1), suggesting significant anti-Leishmania activity. The cytotoxicity of MuEO was assessed by MTT test in Balb/c murine macrophages and by human erythrocytes lysis assay and low cytotoxicity for these cells was observed. The CC₅₀ value against macrophages were 550 ± 29.21 μg mL^-1, while cytotoxicity for erythrocytes was around 20% at the highest concentration assessed, with HC₅₀ > 800 μg mL^-1. While MuEO-induced anti-Leishmania activity is not mediated by increases in both lysosomal activity and nitric oxide production in macrophages, the results suggest the antiamastigote activity is associated with an immunomodulatory activity of macrophages due to an increase of phagocytic capability induced by MuEO. Thus, MuEO presented significant activity against Leishmania amazonensis, probably modulating the activation of macrophages, with low cytotoxicity to murine macrophages and human erythrocytes.

Leishmania amazonensis fails to induce the release of reactive oxygen intermediates by CBA macrophages

CBA mouse macrophages effectively control Leishmania major infection, yet are permissive to Leishmania amazonensis. It has been established that some Leishmania species are destroyed by reactive oxygen species (ROS). However, other species of Leishmania exhibit resistance to ROS or even down-modulate ROS production. We hypothesized that L. amazonensis–infected macrophages reduce ROS production soon after parasite–cell interaction. Employing a highly sensitive analysis technique based on chemiluminescence, the production of superoxide () and hydrogen peroxide (H₂O₂) by L. major- or L. amazonensis-infected CBA macrophages were measured. L. major induces macrophages to release levels of 3·5 times higher than in uninfected cells. This production is partially dependent on NADPH oxidase (NOX) type 2. The level of accumulated H₂O₂ is 20 times higher in L. major-than in L. amazonensis-infected cells. Furthermore, macrophages stimulated with L. amazonensis release amounts of ROS similar to uninfected cells. These findings support previous studies showing that CBA macrophages are effective in controlling L. major infection by a mechanism dependent on both production and H₂O₂ generation. Furthermore, these data reinforce the notion that L. amazonensis survive inside CBA macrophages by reducing ROS production during the phagocytic process.

Arabinosylated lipoarabinomannan skews Th2 phenotype towards Th1 during Leishmania infection by chromatin modification: involvement of MAPK signaling

The parasitic protozoan Leishmania donovani is the causative organism for visceral leishmaniasis (VL) which persists in the host macrophages by deactivating its signaling machinery resulting in a critical shift from proinflammatory (Th1) to an anti-inflammatory (Th2) response. The severity of this disease is mainly determined by the production of IL-12 and IL-10 which could be reversed by use of effective immunoprophylactics. In this study we have evaluated the potential of Arabinosylated Lipoarabinomannan (Ara-LAM), a cell wall glycolipid isolated from non pathogenic Mycobacterium smegmatis, in regulating the host effector response via effective regulation of mitogen-activated protein kinases (MAPK) signaling cascades in Leishmania donovani infected macrophages isolated from BALB/C mice. Ara-LAM, a Toll-like receptor 2 (TLR2) specific ligand, was found to activate p38 MAPK signaling along with subsequent abrogation of extracellular signal-regulated kinase (ERKs) signaling. The use of pharmacological inhibitors of p38MAPK and ERK signaling showed the importance of these signaling pathways in the regulation of IL-10 and IL-12 in Ara-LAM pretreated parasitized macrophages. Molecular characterization of this regulation of IL-10 and IL-12 was revealed by chromatin immunoprecipitation assay (CHIP) which showed that in Ara-LAM pretreated parasitized murine macrophages there was a significant induction of IL-12 by selective phosphorylation and acetylation of histone H3 residues at its promoter region. While, IL-10 production was attenuated by Ara-LAM pretreatment via abrogation of histone H3 phosphorylation and acetylation at its promoter region. This Ara-LAM mediated antagonistic regulations in the induction of IL-10 and IL-12 genes were further correlated to changes in the transcriptional regulators Signal transducer and activator of transcription 3 (STAT3) and Suppressor of cytokine signaling 3 (SOCS3). These results demonstrate the crucial role played by Ara-LAM in regulating the MAPK signaling pathway along with subsequent changes in host effector response during VL which might provide crucial clues in understanding the Ara-LAM mediated protection during Leishmania induced pathogenesis.

Stage-specific pathways of Leishmania infantum chagasi entry and phagosome maturation in macrophages

The life stages of Leishmania spp. include the infectious promastigote and the replicative intracellular amastigote. Each stage is phagocytosed by macrophages during the parasite life cycle. We previously showed that caveolae, a subset of cholesterol-rich membrane lipid rafts, facilitate uptake and intracellular survival of virulent promastigotes by macrophages, at least in part, by delaying parasitophorous vacuole (PV)-lysosome fusion. We hypothesized that amastigotes and promastigotes would differ in their route of macrophage entry and mechanism of PV maturation. Indeed, transient disruption of macrophage lipid rafts decreased the entry of promastigotes, but not amastigotes, into macrophages (P<0.001). Promastigote-containing PVs were positive for caveolin-1, and co-localized transiently with EEA-1 and Rab5 at 5 minutes. Amastigote-generated PVs lacked caveolin-1 but retained Rab5 and EEA-1 for at least 30 minutes or 2 hours, respectively. Coinciding with their conversion into amastigotes, the number of promastigote PVs positive for LAMP-1 increased from 20% at 1 hour, to 46% by 24 hours, (P<0.001, Chi square). In contrast, more than 80% of amastigote-initiated PVs were LAMP-1+ at both 1 and 24 hours. Furthermore, lipid raft disruption increased LAMP-1 recruitment to promastigote, but not to amastigote-containing compartments. Overall, our data showed that promastigotes enter macrophages through cholesterol-rich domains like caveolae to delay fusion with lysosomes. In contrast, amastigotes enter through a non-caveolae pathway, and their PVs rapidly fuse with late endosomes but prolong their association with early endosome markers. These results suggest a model in which promastigotes and amastigotes use different mechanisms to enter macrophages, modulate the kinetics of phagosome maturation, and facilitate their intracellular survival.

In vitro sodium nitroprusside-mediated toxicity towards Leishmania amazonensis promastigotes and axenic amastigotes

Leishmania parasites survive despite exposure to the toxic nitrosative oxidants during phagocytosis by the host cell. In this work, the authors investigated comparatively the resistance of Leishmania amazonensis promastigotes and axenic amastigotes to a relatively strong nitrosating agent that acts as a nitric oxide (NO) donor, sodium nitroprusside (SNP). Results demonstrate that SNP is able to decrease, in vitro, the number of L. amazonensis promastigotes and axenic amastigotes in a dose-dependent maner. Promastigotes, cultured in the presence of 0.25, 0.5, and 1 mmol L(-1) SNP for 24 h showed about 75% growth inhibition, and 97-100% when the cultures were treated with >2 mmol L(-1) SNP. In contrast, when axenic amastigotes were growing in the presence of 0.25-8 mM SNP added to the culture medium, 50% was the maximum of growth inhibition observed. Treated promastigotes presented reduced motility and became round in shape further confirming the leishmanicidal activity of SNP. On the other hand, axenic amastigotes, besides being much more resistant to SNP-mediated cytotoxicity, did not show marked morphological alteration when incubated for 24 h, until 8 mM concentrations of this nitrosating agent were used. The cytotoxicity toward L. amazonensis was attenuated by reduced glutathione (GSH), supporting the view that SNP-mediated toxicity triggered multiple oxidative mechanisms, including oxidation of thiols groups and metal-independent oxidation of biomolecules to free radical intermediates.

Inhibition of IL-2 induced IL-10 production as a principle of phase-specific immunotherapy

Leishmania donovani, a protozoan parasite, inflicts a fatal disease, visceral leishmaniasis. The suppression of antileishmanial T cell responses that characterizes the disease was proposed to be due to deficiency of a T cell growth factor, IL-2. We demonstrate that during the first week after L. donovani infection, IL-2 induces IL-10 that suppresses the host-protective functions of T cells 14 days after infection. The observed suppression is concurrent with increased CD4+ glucocorticoid-induced TNF receptor+ T cells and Foxp3 expression in BALB/c mice, implicating IL-2-dependent regulatory T cell control of antileishmanial immune responses. Indeed, IL-2 and IL-10 neutralization at different time points after the infection demonstrates their distinct roles at the priming and effector phases, respectively, and establishes kinetic modulation of ongoing immune responses as a principle of a rational, phase-specific immunotherapy.

Role of the C-type lectins DC-SIGN and L-SIGN in Leishmania interaction with host phagocytes

Leishmaniasis is a parasitic disease that courses with cutaneous or visceral clinical manifestations. The amastigote stage of the parasite infects phagocytes and modulates the effector function of the host cells. Our group has described that the interaction between Leishmania and immature monocyte-derived dendritic cells (DCs) takes place through dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN), a C-type lectin that specifically recognizes fungal, viral and bacterial pathogens. The DC-SIGN-mediated recognition of Leishmania amastigotes does not induce DC maturation, and the DC-SIGN ligand/s on Leishmania parasites is/are still unknown. We have also found that the DC-SIGN-related molecule L-SIGN, specifically expressed in lymph node and liver sinusoidal endothelial cells, acts as a receptor for L. infantum, the parasite responsible for visceral leishmaniasis, but does not recognize L. pifanoi, which causes the cutaneous form of the disease. Therefore, DC-SIGN and L-SIGN differ in their ability to interact with Leishmania species responsible for either visceral or cutaneous leishmaniasis. A deeper knowledge of the parasite-C-type lectin interaction may be helpful for the design of new DC-based therapeutic vaccines against Leishmania infections.

A sensitive flow cytometric methodology for studying the binding of L. chagasi to canine peritoneal macrophages

BACKGROUND

The Leishmania promastigote-macrophage interaction occurs through the association of multiple receptors on the biological membrane surfaces. The success of the parasite infection is dramatically dependent on this early interaction in the vertebrate host, which permits or not the development of the disease. In this study we propose a novel methodology using flow cytometry to study this interaction, and compare it with a previously described "in vitro" binding assay.

METHODS

To study parasite-macrophage interaction, peritoneal macrophages were obtained from 4 dogs and adjusted to 3 x 10(6) cells/mL. Leishmania (Leishmania) chagasi parasites (stationary-phase) were adjusted to 5 x 10(7) cells/mL. The interaction between CFSE-stained Leishmania chagasi and canine peritoneal macrophages was performed in polypropylene tubes to avoid macrophage adhesion. We carried out assays in the presence or absence of normal serum or in the presence of a final concentration of 5% of C5 deficient (serum from AKR/J mice) mouse serum. Then, the number of infected macrophages was counted in an optical microscope, as well as by flow citometry. Macrophages obtained were stained with anti-CR3 (CD11b/CD18) antibodies and analyzed by flow citometry.

RESULTS

Our results have shown that the interaction between Leishmania and macrophages can be measured by flow cytometry using the fluorescent dye CFSE to identify the Leishmania, and measuring simultaneously the expression of an important integrin involved in this interaction: the CD11b/CD18 (CR3 or Mac-1) beta2 integrin.

CONCLUSION

Flow cytometry offers rapid, reliable and sensitive measurements of single cell interactions with Leishmania in unstained or phenotypically defined cell populations following staining with one or more fluorochromes.

Leishmania and the pathogenesis of HIV infection

Acquired immunodeficiency syndrome (AIDS) and leishmaniasis overlap in several parts of the world, and microorganisms responsible for these human diseases infect and replicate within the macrophage. Therefore, the opportunity that the pathogenesis of the human immunodeficiency virus (HIV) and Leishmania infections could be modulated within dually infected individual is optimized. The most prominent clinical feature of AIDS is the development of debilitating secondary infections induced by several opportunistic microorganisms, including protozoa. Michel Tremblay, Martin Olivier and Richard Bernier here focus on the recently reported information on the putative cofactor role that the intracellular pathogen of the genus Leishmania may play in the pathogenesis of HIV infection.

Modulation of host cell intracellular Ca2+

During the course of evolution, protozoan parasites have developed strategies to subvert the immune response of their host in order to multiply, reproduce and survive. One of these inherited strategies is their capacity to modulate the host cell transductional mechanisms in their favor. Alteration of host cells Ca(2-) homeostasis following interaction and/or invasion by protozoan parasites such as Leishmania donovani, Trypanosoma cruzi, Plasmodium falciparum or Entamoeba histolytica has been reported. There is direct evidence that such disturbances are responsible for pathogenesis observed during parasitic infections. This homeostatic imbalance of Ca(2+) in the host cell is an early inducible event whose underlying mechanisms needs further investigation, as discussed here by Martin Olivier.

Leishmaniasis and AIDS co-infection: the Spanish example

There are an estimated 300 instances of Leishmania/HIV co-infection, of which 200 have occurred in Spain. Jorge Alvar here asks: is there an epidemiological or immunological basis for this high proportion?

The expression of mannose receptors in skin fibroblast and their involvement in Leishmania (L.) amazonensis invasion

Leishmania are protozoa that invade mononuclear phagocytes with the involvement of different ligand-receptor systems, including mannose receptors. Until now, scant data are available concerning the mechanisms that govern the infection of Leishmania in other host cell types such as fibroblasts. Our aim was to analyze the expression of mannose receptors in primary cultures of skin fibroblasts (SF) further characterizing their role during the invasion of promastigotes of Leishmania (L.) amazonensis. Both fluorescent, light, and electron microscopy assays revealed that SF have mannose receptors since they bound and internalized mannosylated ligands in addition to being positively labeled by fuc-BSA-FITC probes. d-mannose competition assays revealed the participation of mannose receptors during the parasite association with SF presenting upregulated receptor expression during the initial steps of the infection. After longer periods of Leishmania:fibroblasts contact, the modulation noted in the host mannose receptors was reverted concomitantly to the infection control, suggesting that the parasites were required for the alteration maintenance and providing evidences that the SF may display microbicidal mechanisms to control the Leishmania infection.

CD40 signaling is impaired in L. major-infected macrophages and is rescued by a p38MAPK activator establishing a host-protective memory T cell response

Leishmania, a protozoan parasite, lives and multiplies as amastigote within macrophages. It is proposed that the macrophage expressed CD40 interacts with CD40 ligand on T cells to induce IFN-gamma, a Th1-type cytokine that restricts the amastigote growth. Here, we demonstrate that CD40 cross-linking early after infection resulted in inducible nitric oxide synthetase type-2 (iNOS2) induction and iNOS2-dependent amastigote elimination. Although CD40 expression remained unaltered on L. major-infected macrophages, delay in the treatment of macrophages or of mice with anti-CD40 antibody resulted in significant reduction in iNOS2 expression and leishmanicidal function suggesting impaired CD40 signaling in Leishmania infection. The inhibition of CD40-induced iNOS2 expression by SB203580, a p38-mitogen activated protein kinase (p38MAPK)-specific inhibitor, and the reversal of the inhibition by anisomycin, a p38MAPK activator, suggested a crucial role of p38MAPK in CD40 signaling. Indeed, the CD40-induced p38MAPK phosphorylation, iNOS2 expression and anti-leishmanial function were impaired in Leishmania-infected macrophages but were restored by anisomycin. Anisomycin's effects were reversed by SB203580 emphasizing the role of p38MAPK in CD40-induced iNOS2-dependent leishmanicidal function. Anisomycin administration in L. major-infected BALB/c mice resulted in significant reduction in the parasite load and established a host-protective Th1-type memory response. Also implicated in these findings is a scientific rationale to define novel anti-parasite drug targets and to bypass the problem of drug resistance.

Leishmania pifanoi pathogenesis: selective lack of a local cutaneous response in the absence of circulating antibody

Recently, a role for B cells in the pathogenesis associated with infection by Leishmania (Leishmania mexicana complex and L. donovani) has been established. In the case of L. mexicana complex parasites (L. mexicana, L. pifanoi, and L. amazonensis), a critical role for immunoglobulin G-mediated mechanisms for the amastigote stage in the host is evident; however, the immunological mechanisms involved remain to be established. In vitro analysis of the kinetics of parasite uptake by macrophages failed to indicate a major effect of antibody opsonization. Given the importance of CD4(+) T cells in the development of disease caused by these parasites, the possibility that the lack of pathogenesis was due to the lack of development of an immune response at the local site (draining lymph node and/or cutaneous site) was explored. Interestingly, the level of CD4(+)-T-cell activation (proliferation and cytokine) in draining lymph nodes from mice lacking circulating antibody (resistant) was found to be comparable to that in nodes from wild-type mice (susceptible) at 2, 5, and 10 weeks postinfection. However, antibody-deficient animals had markedly reduced numbers of monocytes and lymphocytes recruited or retained at the site of cutaneous infection in comparison to wild-type mice, indicating a selective impairment in the local cutaneous immune response. In vitro antigen presentation studies employing tissue-derived (opsonized) amastigotes demonstrated that L. pifanoi-infected FcR(-/-) macrophages, in contrast to comparably infected wild-type cells, failed to activate Leishmania antigen-specific T lymphocytes. These data, taken together, suggest that one possible mechanism for the role of antibody in pathogenesis may be to mediate parasite uptake and regulate the immune response at the local cutaneous site of infection.

C-reactive protein-mediated phagocytosis of Leishmania donovani promastigotes does not alter parasite survival or macrophage responses

C-reactive protein (CRP) is an acute phase protein that binds to surface structures of a number of different organisms. Leishmania donovani express CRP ligand when first entering the mammalian host and CRP has been shown to alter macrophage function. The aim of this study was to investigate the functional significance of CRP-mediated uptake of L. donovani on survival of the parasite within human macrophages and macrophage cell responses to the infection. CRP opsonized L. donovani uptake was inhibitable by including excess CRP in the fluid phase, suggesting Fc receptor usage rather than indirect complement-mediated uptake. Comparing equivalent initial infection loads, parasite survival over 72 h within peripheral blood derived macrophages (PBMs) and differentiated U937 cells was unaltered by CRP. Whereas CRP increased macrophage responses to phosphorylcholine coated erythrocytes, no significant alteration in tumour necrosis factor-alpha, interleukin (IL)-10 or IL-12 production from PBMs was observed between CRP opsonized or unopsonized L. donovani promastigotes. Thus, in contrast to other systems, where CRP opsonization results in macrophage activation, Leishmania can use CRP to improve infection without inducing detrimental macrophage activation.

Correlation between in vitro and in vivo infectivity of Leishmania infantum clones

Eleven clones of a single strain of Leishmania infantum (MCAN/ES/88/ISS441, Doba) were analyzed for biological behavior in vivo and in vitro. Different clones showed differences in growth dependent upon the two culture media employed. All clones displayed only slight differences in H2O2 and NaNO2 sensitivity compared to the original strain, whereas in vitro infectivity for mouse peritoneal macrophages differed significantly among the clones. In vivo infections in hamsters correlated strongly with in vitro infectivity. The phenotypic differences found suggest a polyclonal structure for the Leishmania infantum strain studied.

Neuropeptides modulate a murine monocyte/macrophage cell line capacity for phagocytosis and killing of Leishmania major parasites

Host-parasite interactions and their outcome constitute a critical and challenging step in disease establishment in cutaneous leishmaniasis. In the present in vitro study we investigated the possible modulating effects of both sensory and autonomic neuropeptides that normally exist in human and mouse skin, on the uptake and leishmanicidal capacity of macrophages on Leishmania (L.) major parasites, using a monocyte/macrophage murine cell line (Raw 264.7). The sensory neuropeptides somatostatin (SOM), calcitonin gene-related peptide (CGRP) and substance P (SP) suppressed the macrophage capacity for phagocytosing L. major promastigotes at different concentrations, 10(-10) - 10(-5) M, however, the suppressive effect of SP does not reach a significant level. CGRP and SP enhanced the leishmanicidal capacity of macrophages at 10(-7) M, and 10(-5) M, respectively, whereas SOM was without effect. The autonomic neuropeptides vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) both suppressed the phagocytic and leishmanicidal capacities of macrophages at various concentrations, 10(-10) - 10(-5) M. The findings indicate that neuropeptides have modulating effects on macrophage-L. major interactions. These effects might be exerted by a direct action on macrophages or indirectly through induction of other mediators.

Inhibition of HIV-1-mediated syncytium formation and virus replication by the lipophosphoglycan from Leishmania donovani is due to an effect on early events in the virus life cycle

Previous findings have indicated that the major surface molecule of Leishmania, lipophosphoglycan (LPG), could abrogate HIV-1-induced syncytium formation and virus replication. In the present work, we were interested in characterizing this inhibitory process. Data from a new luciferase-based semiquantitative assay for syncytium formation, relying on the coincubation of a T-cell line containing an HIV-1 LTR-driven luciferase construct with a cell line chronically infected with HIV-1, confirmed that LPG was indeed a strong inhibitor of HIV-1-dependent syncytium formation and that this inhibition was dose-dependent. As determined by flow cytometric analyses, this inhibition was not apparently due to downregulation of CD4, CXCR4 or LFA-1, three distinct surface glycoproteins known to be important in HIV-1 mediated syncytium formation. Furthermore, LPG did not seem to affect signal transduction pathways in T cells as judged by measurement of HIV-1 LTR-driven reporter gene activity upon treatment with different stimuli. However, pretreatment of either of the cell lines used in the assay with LPG led to a significant decrease of virus-mediated syncytium formation, which was further accentuated when both cell lines were pretreated. LPG inhibition of HIV-1 replication was next assessed. When measuring either infection with luciferase-encoding recombinant HIV-1 particles or multinucleated giant cell formation following an acute virus infection, we again observed that LPG was efficient at blocking HIV-1 replication. Specific assays probing different steps of viral entry demonstrated that attachment was not hindered by LPG but that viral entry was modulated, suggesting that LPG targets a postbinding step. Hence, incorporation of LPG into a target cell membrane could influence its fluidity and diminish both the virus-cell and cell-to-cell fusion processes initiated by HIV-1.

Leishmanicidal activity of stearylamine-bearing liposomes in vitro

Liposomes consisting of stearylamine (SA) and egg yolk phosphatidylcholine (PC) were studied for their cytotoxic activity against freshly transformed promastigotes and intracellular amastigotes of Leishmania donovani, the causative agent of visceral leishmaniasis. More than 99% of the parasites of strain AG83 were killed within 60 min by treatment with 22 mol% SA-PC liposomes (132 microg/ml total lipids). This was further confirmed by incubating the liposome-treated promastigotes at 22 C for 96 hr. The killing activity of the liposomes progressively decreased with lowering lipid concentration. However, weak cytotoxic activity was still detected at 6.6 microg/ml lipids. Leishmanicidal activity of the liposomes became stronger with increasing SA content but was reduced with the incorporation of cholesterol in the liposomes. A similar cytotoxic effect was observed on other Indian strains of L. donovani, for example PKDL and DD8, as well as on species such as Leishmania donovani S1, Leishmania donovani infantum, Leishmania tropica, Leishmania amazonensis, and Leishmania mexicana. However, freshly transformed promastigotes appeared to be more susceptible than the ones subcultured. The strong leishmanicidal activity of SA-PC liposomes was also demonstrated toward intracellular L. donovani amastigotes. The SA-bearing vesicles could effectively inhibit the growth and multiplication of the parasites within the macrophages. The cytolytic activity of these liposomes on leishmanial parasites and low toxicity on host macrophages may, thus, find application in the therapy of leishmaniasis.

The immunologically protective P-4 antigen of Leishmania amastigotes. A developmentally regulated single strand-specific nuclease associated with the endoplasmic reticulum

The purified membrane-associated Leishmania pifanoi amastigote protein P-4 has been shown to induce protective immunity against infection and to elicit preferentially a T helper 1-like response in peripheral blood mononuclear cells of patients with American cutaneous leishmaniasis. As this molecule is potentially important for future vaccine studies, the L. pifanoi gene encoding the P-4 membrane protein was cloned and sequenced. Southern blot analyses indicate the presence of six tandemly arrayed copies of the P-4 gene in L. pifanoi; homologues of the P-4 gene are found in all other species of the genus Leishmania examined. DNA-derived protein sequence data indicated an identity to the P1 zinc-dependent nuclease of Penicillium citrinum (20.8%) and the C-terminal domain of the 3' nucleotidase of Leishmania donovani (33.7%). Consistent with these sequence analyses, purified L. pifanoi P-4 protein possesses single strand nuclease (DNA and RNA) and phosphomonoesterase activity, with a preference for UMP > TMP > AMP >> CMP. Double-labeling immunofluorescence microscopic analyses employing anti-binding protein antibodies revealed that the P-4 protein is localized in the endoplasmic reticulum of the amastigote. Northern blot analyses indicated that the gene is selectively expressed in the intracellular amastigote stage (mammalian host) but not in the promastigote stage (insect) of the parasite. Based upon its subcellular localization and single-stranded specific nuclease activity, possible roles of the P-4 nuclease in the amastigote in RNA stability (gene expression) or DNA repair are discussed.

Leishmania sp: comparative study with Toxoplasma gondii and Trypanosoma cruzi in their ability to initialize IL-12 and IFN-gamma synthesis

We compared in vitro and in vivo induction of IL-12 (p40) and IFN-gamma by mouse cells stimulated with Toxoplasma gondii, Trypanosoma cruzi, and different species of Leishmania. Spleen cells cultured in vitro with T. cruzi or T. gondii, but not with Leishmania, produced IL-12 (p40) and IFN-gamma. Accordingly, IL-12 (p40) was produced by macrophages stimulated in vitro with live T. cruzi or T. gondii or membrane glycoconjugates obtained from trypomastigotes or tachyzoites. No IL-12 production was detected when macrophages were stimulated with live parasites or glycoconjugates from Leishmania, regardless of priming with IFN-gamma. In vivo, only T. cruzi and T. gondii induced the synthesis of IL-12 and IFN-gamma by mouse spleen cells after intraperitoneal injection of parasites. When injected subcutaneously, live Leishmania sp. induced IL-12 (p40) and IFN-gamma production by draining lymph node cells, albeit the levels were slightly lower than those induced by infection with T. gondii or T. cruzi using the same route. Together our results indicate that under different conditions, the intracellular protozoa T. gondii and T. cruzi are more potent stimulators of IL-12 and IFN-gamma synthesis by host immune cells than parasites of the genus Leishmania.

Leishmania: fine mapping of the Leishmanolysin molecule's conserved core domains involved in binding and internalization

The Leishmanolysin molecule's role in the uptake of Leishmania parasites by the human U937 pro-myelocytic cell line was studied, using synthetic peptides representing the complete Leishmania (Viannia) guyanensis Leishmanolysin protein amino acid sequence. The particular peptides present in two protein's core domains efficiently impaired the internalization of promastigotes from four different Leishmania species and modified the kinetics of the binding of heterologous recombinant Leishmanolysin protein. The functional domains which exhibited this property represent a highly conserved portion of the sequence among different Leishmania species. The peptides' inhibitory activity correlated with their ability to bind molecules present on the surface of the human cell line. One of the two functional core domains identified involves the previously described adhesive sequence (SRYD) and the putative zinc-binding motif (HExxH). The second functional core domain includes a third histidine residue coordinated with zinc which determines the molecule's structural features. These findings indicate that the molecular interactions between Leishmanolysin's conserved domains and the macrophage surface molecules efficiently contribute to the parasite's internalization. Induction of neutralizing immune responses, which impair the early parasite-host interaction described here, may be an important alternative in designing synthetic subunit human leishmaniasis vaccines.

Leishmania major proteophosphoglycan is expressed by amastigotes and has an immunomodulatory effect on macrophage function

Proteophosphoglycan (PPG) is a newly described mucin-like glycoprotein found on the surface of Leishmania major promastigotes and secreted in the culture supernatant. We show here that antigenically similar PPGs are present in several Leishmania species. PPG could also be detected on the surface of amastigotes and in small, parasite-free vesicles in infected macrophages. Because of the similarity of its carbohydrate chains to lipophosphoglycan, a parasite receptor for host macrophages, PPG was tested for binding to macrophages. PPG bound to macrophages and was internalized in a time-dependent manner. PPG inhibited the production of tumor necrosis factor-alpha and synergized with interferon-gamma to stimulate the production of nitric oxide by macrophages. PPG may contribute to the binding of Leishmania to host cells and may play a role in modulating the biology of the infected macrophage at the early stage of infection.

Immunoprophylaxis and immunotherapy against experimental visceral leishmaniasis

The ability of the Leishmanial parasite, UR6 (MHOM/IN/1978/UR6) to act as a immunoprophylactic and immunotherapeutic agent against experimental visceral leishmaniasis in a hamster model was tested. The Leishmanial parasite, UR6, lacked LPG but possessed abundant message for kinetoplastid membrane protein-11 (KMP-11), and failed to induce visceral infection when given through the intracardiac route, unlike the virulent Leishmania donovani, AG83 (MHOM/IN/1983/AG83), the causative agent of Kala-azar. Priming of macrophage with UR6 in vitro, induced superoxide (O2-) generation whereas a similar experiment with virulent AG83 inhibited O2- generation. This observation prompted us to test the efficacy of UR6 as a immunoprophylactic and immunotherapeutic agent. It was observed that priming of hamsters with either live or sonicated UR6 in the absence of any adjuvant provided strong protection against subsequent virulent challenge. The UR6 mediated protection was also observed in hamsters having established infection. Furthermore, UR6 primed infected hamsters displayed a greatly extended life span as compared to infected hamsters. To our knowledge, this is the first report concerning the use of an atypical Leishmanial parasite, UR6 in immunoprophylaxis and immunotherapy in the absence of any adjuvant.

Regulatory sequences and a novel gene in the msp (GP63) gene cluster of Leishmania chagasi

The surface protease GP63 of Leishmania chagasi is encoded by a cluster of more than 18 tandem major surface protease (msp) genes belonging to three classes (mspL, mspS, mspC). mspL and mspS transcripts are differentially expressed during parasite growth. RNAs from mspS genes predominate during stationary phase, the time when parasite virulence and GP63 expression are maximal. We hypothesized that the unique regions downstream of mspS genes contain signals important for gene expression. The 2.8 kb region between tandem mspS genes was found to contain an 882 bp open reading frame designated mag. Copies of mag were found downstream of all mspS genes in the cluster. mag hybridized faintly to bands on Northern blots and a fully processed mag cDNA was identified in a promastigote cDNA library, providing evidence that mag genes are expressed at low levels. Similar to mspS RNAs, the abundance of mag RNAs was greater in stationary phase than logarithmic phase organisms, although mag RNAs were less abundant than mspS RNAs throughout growth. Northern blots and enzyme assays of promastigotes containing plasmid constructs in which the beta-galactosidase gene was followed by sequences between mspS coding regions, either with or without mag and its downstream sequences, suggest these regions have several regulatory effects accounting for the growth-associated changes in mspS expression.

In vitro Leishmania major promastigote-induced macrophage migration is modulated by sensory and autonomic neuropeptides

Recruitment, migration and adherence of macrophages and their interaction with inoculated promastigotes are key steps in the initiation of the inflammatory process in cutaneous leishmaniasis. Parasite- and nervous system-derived factors might be involved in this process. In the present study the chemotactic activities of live, killed and sonicated Leishmania major promastigotes and of the promastigote culture supernatant as well as the L. major surface protease gp63 towards a murine macrophage cell line, Raw 264.7, were investigated, using the Boyden technique. The sensory neuropeptides SOM, CGRP and SP, and the autonomic neuropeptides VIP and NPY, were also investigated for possible modulatory effects on this chemotaxis, using the living promastigotes. Living promastigotes were the most efficient attractants for macrophages compared with other forms of the parasites. Prior incubation of the macrophages with the parasites completely abolished the chemotactic activity. This might indicate that the living promastigote chemotaxis is a receptor-mediated process. On the other hand, paraformaldehyde-killed promastigotes not only failed to induce macrophage chemotaxis but also inhibited it in comparison with the control. The surface protease gp63 tended to inhibit the macrophage chemotactic activity and the sonicate tended to stimulate it compared with controls. The culture supernatant had no effect, indicating that the chemoattractive factors putatively synthesized by the living promastigotes are not released to the surrounding medium. Somatostatin inhibited L. major promastigote-induced macrophage migration at a high concentration, 10(-6) M, while substance P inhibited it at both low concentrations, 10(-10) and 10(-9) M, and a high one, 10(-6) M, the last-mentioned having the greatest inhibitory effect. A stimulatory effect of calcitonin gene-related peptide was found at high concentrations, 10(-5) and 10(-6) M. Vasoactive intestinal peptide stimulated macrophage chemotactic activity at both a high, 10(-5) M, and at a low, 10(-9) M, concentration, the same concentration at which neuropeptide Y exerted its maximum inhibitory effect.

Implications of Calreticulin Function in Parasite Biology

Calreticulin (CR) is a Ca(2+)-binding, multifunctional protein. The amazing array of CR-associated functions range from intracellular activities in secondary messenger release, protein folding and the modulation of gene expression to potential interactions with host receptors and signaling machinery and recognition by the host immune system. The multifunctional nature of CR may impact upon the ability of cells to recognize extracellular stimuli and coordinate appropriate responses. Identification of CR isolated from parasites and the conservation of its functions suggests that investigations into the contributions of CR to various aspects of parasite biology should be undertaken because it may reveal information regarding parasite interaction with the host and how the parasite may modulate its response to the host.

Tremblay M, Olivier M. The Lipophosphoglycan of Leishmania donovani Up-Regulates HIV-1 Transcription in T Cells Through the Nuclear Factor-κB Elements

We have recently demonstrated that the parasite Leishmania donovani and its surface molecule, lipophosphoglycan (LPG), can activate HIV-1 replication in monocytoid cells. Our present interest was to determine whether LPG could also up-regulate HIV-1 transcription in T cells. Using a CD4-positive human lymphoid T cell line (1G5) containing a stably integrated HIV-1 long terminal repeat (LTR)-luciferase construct, we found that LPG is a potent inducer of HIV-1 LTR activity. Treatment of 1G5 cells with signaling antagonists revealed that protein tyrosine kinase- and protein kinase A-dependent pathways were actively participating in the LPG-induced enhancement of HIV-1 LTR-driven activity. Transfection of Jurkat E6.1 cells with plasmids containing wild-type and nuclear factor-κB (NF-κB)-mutated HIV-1 LTR-luciferase constructs has suggested a role for NF-κB binding sites in the LPG-mediated induction of HIV-1 LTR activity. An LPG-induced binding factor specific to the NF-κB consensus sequences could be observed using electrophoretic mobility shift assay. Finally, transfection experiments performed with a vector containing HIV-1 κB binding sites only showed similar LPG-mediated induction, which was abrogated by sodium salicylate, a known NF-κB inhibitor. We thus demonstrate that the LPG-mediated induction of HIV-1 LTR activity in T cells involves several second messengers culminating in activation of HIV-1 LTR-driven transcription via NF-κB-binding consensus sequences. In conclusion, these results reinforce the idea that L. donovani is a putative cofactor in HIV-1 pathogenesis.

Leishmania mexicana amazonensis: differential display analysis and cloning of mRNAs from attenuated and infective forms

The virulence of Leishmania mexicana is determined by the concerted action of several parasite molecules. These cells lose their infectivity to host macrophages after prolonged cultivation in axenic growth media. Both virulent and attenuated variants of the parasite cells were cloned. The differential display reverse transcription-polymerase chain reaction technique was employed to understand whether this natural attenuation of the parasite cells is accompanied by differential expression of selected genes in those cells. Twelve different dinucleotide-anchored oligo(dT) antisense primers were used to make cDNAs from poly(A)+ mRNAs isolated from a clonal population of virulent and avirulent cells following a protocol optimized for Leishmania mRNAs. Those cDNAs were subjected to amplifications using each of the three different arbitrary decanucleotide primers and the corresponding anchored oligo(dT) primer. This procedure revealed four virulent-specific cDNA probes and one avirulent-specific cDNA probe. Differential expressions of these genes were confirmed by northern hybridization using the cloned cDNA probes. These results indicate that differential expression of genes may be the key in determining the molecular basis of leishmanial virulence.

Leishmania donovani attachment stimulates PKC-mediated oxidative events in bone marrow-derived macrophages

We investigated activation signaling events in bone marrow-derived macrophages after infection with Leishmania donovani, an intracellular parasite of macrophages. Leishmania donovani infection caused a general suppression of activation parameters like O2- and NO production. However, conditions which allow parasite attachment and prevent entry resulted in triggering of O2- and NO production and stimulation of O2 consumption. Optimal NO and O2- production occurred when bone marrow-derived macrophages and Leishmania ratio was 1:100. The activation signal for O2- production was initiated 15 min after parasite attachment, whereas augmentation of NO production started 6 h after attachment Activation of O2- and NO generation by L. donovani attachment was inhibited by staurosporine as well as by prolonged treatment of phorbol myristate acetate suggesting a protein kinase C-dependent mechanism. Translocation studies showed that protein kinase C activity in cell membrane fraction rapidly and transiently increased following parasite attachment. No such protein kinase C translocation event occurred in L. donovani infected bone marrow-derived macrophages. Phorbol myristate acetate was found to stimulate membrane translocation of protein kinase C in parasite attached cells whereas it was impaired in infected cells. However, both attachment and infection induced a similar shift of phorbol receptors from cytosolic to membrane fraction indicating that in infected cells the translocation of protein kinase C protein was not impaired but the activity of the membrane associated enzyme was somehow inhibited. These results suggest that although internalization of intracellular parasites like L. donovani caused inhibition of nitrite and superoxide release, mere attachment on macrophage surface resulted in an activation of protein kinase C-mediated downstream oxidative events.

The expression of biologically active human p53 in Leishmania cells: a novel eukaryotic system to produce recombinant proteins

We have investigated the use of Leishmania cells as a novel eukaryotic expression system for the production of recombinant protein. These cells are easy to maintain, requiring no CO2 incubator or shaker, and can be grown in standard tissue culture media. Leishmania cells can be readily transfected with plasmid DNA by electroporation and transformants selected with antibiotic resistance. Recent studies have shown that it is possible to express foreign genes in Leishmania for the purpose of understanding the biology of this protozoan cell. In the present study we report the use of this system as a means of producing a biologically functional human p53 protein. The conformation of the p53 protein is critical for its ability to bind specific DNA sequences. It is demonstrated that Leishmania-synthesized human p53 is phosphorylated and can bind specifically to its enhancer DNA sequence. These data demonstrate that Leishmania may represent a simple eukaryotic expression system for the production of biologically active recombinant proteins.

Leishmania major infection: the overture

Local infection of mice with Leishmania major results in either healing or death depending on the preferential action of Th1 or Th2 T helper cells, respectively. Although the parasite-induced T-cell responses and their consequences for the disease are well understood, relatively little is known about the initial events that kindle the adaptive immune response. Werner Salbach and Tamás Laskay here discuss how differences in parasites spreading from the site of infection to different immune organs during the first 10-24 hours and, in consequence, the 'where and when' of the first encounter of Leishmania with the cells of the immune system may well be the starting point for the development of resistance or susceptibility.

Leishmania pifanoi amastigote antigens protect mice against cutaneous leishmaniasis

In the search for a leishmaniasis vaccine, extensive studies have been carried out with promastigote (insect stage) molecules. Information in this regard on amastigote (mammalian host stage) molecules is limited. To investigate host immune responses to Leishmania amastigote antigens, we purified three stage-specific antigens (A2, P4, and P8) from in vitro-cultivated amastigotes of Leishmania pifanoi by using immunoaffinity chromatography. We found that with Corynebacterium parvum as an adjuvant, three intraperitoneal injections of 5 micrograms of P4 or P8 antigen provided partial to complete protection of BALB/c mice challenged with 10(5) to 10(7) L. pifanoi promastigotes. These immunized mice developed significantly smaller or no lesions and exhibited a 39- to 1.6 x 10(5)-fold reduction of lesion parasite burden after 15 to 20 weeks of infection. In addition, P8 immunization resulted in complete protection against L. amazonensis infection of CBA/J mice and partial protection of BALB/c mice, suggesting that this antigen provided cross-species protection of mice with different H-2 haplotypes. At different stages during infection, vaccinated mice exhibited profound proliferative responses to parasite antigens and increased levels of gamma interferon production, suggesting that a Th1 cell-mediated immune response is associated with the resistance in these mice. Taken together, the data in this report indicate the vaccine potential of amastigote-derived antigens.

Intergenic regions between tandem gp63 genes influence the differential expression of gp63 RNAs in Leishmania chagasi promastigotes

The major surface protease, gp63, of Leishmania chagasi is encoded by 18 or more tandem msp genes that can be grouped into three classes on the basis of their unique 3'-untranslated sequences (3'-UTRs) and their differential expression. RNAs from the mspLs occur predominantly during the logarithmic phase of promastigote growth in vitro, RNAs from the mspSs are present mainly in stationary phase, and RNAs from mspCs occur throughout growth in culture. All three classes of gp63 genes are constitutively transcribed during all growth phases, indicating that their expression is post-transcriptionally regulated. Chimeric plasmids containing the three different 3'-UTRs and downstream intergenic regions (IRs) fused downstream of the beta-galactosidase (beta-gal) coding region were transfected into L. chagasi, and their effects on beta-gal RNA processing and enzymatic activity were examined. The presence of the 3'-UTRs by themselves had no substantive effect on beta-gal expression. However, the 3'-UTR from a mspS plus its IR resulted in about 20-fold more beta-gal activity and RNA in stationary phase relative to logarithmic phase cells. In contrast, the 3'-UTRs plus IRs of mspL and mspC had either no or little effect, respectively, on beta-gal expression. Thus, differential expression of the mspLs and mspSs is post-transcriptionally controlled by different mechanisms.

Developmentally regulated expression of a novel 59-kDa product of the major surface protease (Msp or gp63) gene family of Leishmania chagasi

All species of Leishmania express a major surface protease (Msp or gp63) that facilitates the interactions of the parasite with its environment at several steps in its life cycle. The msp gene family in Leishmania chagasi contains three classes of genes whose mRNAs are differentially expressed during parasite growth. Logarithmic phase (low infectivity) promastigotes express only 63-kDa versions of Msp, whereas stationary phase (high infectivity) promastigotes express both 63- and 59-kDa Msps. The different migrations of the 59- and 63-kDa proteins on acrylamide gels are not due to differences in N-linked glycosylation or the membrane anchor. Plasmid transfections of Leishmania demonstrate that mspS2 of the stationary gene class encodes a 59-kDa protein. Expression of the 59-kDa protein in stationary phase promastigotes ceases after about 12 weeks of in vitro cultivation when the parasites become attenuated. Attenuated parasites can be stimulated to re-express the 59-kDa Msp by passage through mice followed by several in vitro passages of recovered promastigotes. Amastigotes express yet another subset of Msp proteins. Thus, the 59-kDa product of mspS2 is expressed only in stationary phase promastigotes and only after recent exposure to environmental changes encountered in the mammalian host cell.

Suppression of chemiluminescence of eastern oyster (Crassostrea virginica) hemocytes by the protozoan parasite Perkinsus marinus

Experiments were conducted to determine the ability of the protistan parasite, Perkinsus marinus, to inhibit chemiluminescence of hemocytes from the eastern oyster, Crassostrea virginica. Luminol-enhanced chemiluminescence (CL) was used to measure the production of reactive oxygen intermediates (ROI) generated by oyster hemocytes using zymosan as a stimulant. To determine whether P. marinus suppresses ROI evoked from zymosan-stimulated hemocytes, live or heat killed P. marinus in filtered estuarine water (YRW) (salinity = 20 ppt) were added to (1) zymosan-stimulated hemocytes after CL reached its peak, or (2) hemocytes at the same time as zymosan, and reduction of CL responses were recorded. In both tests, controls received only estuarine water. Live P. marinus meronts significantly suppressed ROI production by zymosan-stimulated hemocytes. The suppression of ROI production was dose dependent. Suppression of ROI production from zymosan-stimulated hemocytes by heat killed P. marinus was significantly less than by live P. marinus. Similarly, CL of hemocytes was reduced, though not significantly when hemocytes were exposed to YRW preincubated with P. marinus. When P. marinus meronts were used as a stimulant, no CL response was elicited. Results of this study suggest that P. marinus cells are able to suppress ROI release from oyster hemocytes, thus evading this component of the host's defense.

Induction of interleukin 1 alpha in murine macrophages infected in vitro with different species and strains of Leishmania

It is now generally agreed that several cytokines released by immunocompetent cells such as macrophages play a crucial role in the outcome of infections caused by protozoa belonging to the genus Leishmania. In particular, tumor necrosis factor (TNF) induction during the course of cutaneous leishmaniasis has been related to resistance to L. major infection in mice. However, the role played by interleukin 1 (IL-1) in the host response to leishmaniasis has yet to be completely elucidated. The aim of this work was to study whether different species and strains of Leishmania could induce IL-1 alpha in murine macrophages in vitro. Resident peritoneal macrophages of BALB/c and C3H/HeN mice were infected with L. donovani, L. major, or different strains of L. infantum. It was found that L. donovani did not induce IL-1 alpha in macrophages from either mice strain. Infection with L. major or with three out of six strains of L. infantum induced consistent amounts of IL-1 alpha, but only in macrophages from genetically resistant C3H/HeN mice. No relationship was found between the rate of infection of macrophages and the amount of IL-1 alpha detected in the supernatants of infected macrophages. Data obtained confirm that the release of IL-1 alpha by murine macrophages infected in vitro with Leishmania is influenced by the genetic background of the cells as well as by the parasite species.

Lipophosphoglycan blocks attachment of Leishmania major amastigotes to macrophages

Promastigotes of the intracellular protozoan parasite Leishmania major invade mononuclear phagocytes by a direct interaction between the cell surface lipophosphoglycan found on all Leishmania species and macrophage receptors. This interaction is mediated by phosphoglycan repeats containing oligomers of beta (1-3)Gal residues specific to L. major. We show here that although amastigotes also use lipophosphoglycan to bind to both primary macrophages and a cell line, this interaction is independent of the beta (1-3)Gal residues employed by promastigotes. Binding of amastigotes to macrophages could be blocked by intact lipophosphoglycan from L. major amastigotes as well as by lipophosphoglycan from promastigotes of several other Leishmania species, suggesting involvement of a conserved domain. Binding of amastigotes to macrophages could be blocked significantly by the monoclonal antibody WIC 108.3, directed to the lipophosphoglycan backbone. The glycan core of lipophosphoglycan could also inhibit attachment of amastigotes, but to a considerably lesser extent. The glycan core structure is also present in the type 2 glycoinositolphospholipids which are expressed on the surface of amastigotes at 100-fold-higher levels than lipophosphoglycan. However, their inhibitory effect could not be increased even when they were used at a 300-fold-higher concentration than lipophosphoglycan, indicating that lipophosphoglycan is the major macrophage-binding molecule on amastigotes of L. major. In the presence of complement, the attachment of amastigotes to macrophages was not altered, suggesting that lipophosphoglycan interacts directly with macrophage receptors.

In vitro study of the anti-leishmanial activity of biodegradable nanoparticles

Leishmania are obligate intracellular parasites, responsible for leishmaniasis. Leishmaniasis are transmitted via insect vector to vertebrate hosts including humans. The infection was reproduced in vitro with promastigotes which can infect murine resident peritoneal cells. Amphotericin B was incorporated into poly(D, L-lactide-co-glycolide) nanoparticles, biodegradable drug carriers, to allow specific targeting inside the cell. The interaction of the drug with infected cells was determined by exposing macrophage cultures to drug carriers. The toxic effects of polymeric drug carriers were defined prior to exposing cells to drug-loaded nanoparticles. For contact times up to 4h, cells tolerated polymer concentrations of 0.01%. The viability of parasites after treatment was determined. Infected macrophages were incubated at 26 degrees C (which allows the transformation of amastigote to promastigote) along with loaded and unloaded nanoparticles, as well as the free drug alone, and a count of the parasites in the medium was recorded. Anti-leishmanial activity was observed with drug-free nanoparticles. This activity may arise through the release of hydrogen peroxide following the activation of macrophages. The incorporation of amphotericin B did not enhance this effect. Interestingly, trehalose, a cryoprotector of the freeze-dried nanoparticles, altered parasite growth and activated macrophages.

Response of Leishmania chagasi promastigotes to oxidant stress

At the onset of infection, Leishmania promastigotes are phagocytized by mammalian macrophages. They must survive despite exposure to toxic oxidants such as hydrogen peroxide (H2O2) and superoxide (.O2-) generated during phagocytosis. We investigated the effects of these oxidants on Leishmania chagasi promastigotes and promastigote mechanisms for oxidant resistance. According to spin trapping and electron paramagnetic resonance spectrometry, .O2- could be generated by exposure of promastigotes to the redox-cycling compound menadione. Incubation in either menadione or H2O2 caused a concentration-dependent loss of promastigote viability. However, incubation in sublethal concentrations of H2O2 or menadione caused a stress response in promastigotes. This oxidant-induced response was associated with an increase in the amount of heat shock protein hsp70. Induction of a stress response by exposure of promastigotes either to heat shock or to sublethal oxidants (H2O2 or menadione) caused promastigotes to become more resistant to H2O2 toxicity. Sublethal menadione also caused promastigotes to become more virulent in a BALB/c mouse model of leishmaniasis. We previously correlated H2O2 cytotoxicity for promastigotes with the formation of hydroxyl radical (.OH) from H2O2. However, according to electron paramagnetic resonance spectrometry, the increase in H2O2 resistance after exposure to sublethal oxidants was not associated with diminished generation (i.e., scavenging) of .OH. These data suggest that there is a cross-protective stress response that occurs after exposure of L. chagasi promastigotes to heat shock or to sublethal H2O2 or .O2-, exposures that also occur during natural infection. This response results in increased resistance to H2O2 toxicity and increased virulence for a mammalian host.

Ricin-resistant mutants of Leishmania major which express modified lipophosphoglycan remain infective for mice

Glycosylation variants of the virulent Leishmania major clone V121 were generated by mutagenesis with N-methyl-N-nitroso-N-nitroguanidine and selected using the galactose-specific lectin Ricinus communis II (RCA II). Three mutants, 4B9, 1D1 and 1C12, which failed to bind RCA II, were found to have an altered expression of lipophosphoglycan (LPG), a molecule implicated in the attachment to host macrophages and survival within the phagolysosome. There were differences in the antigenicity, molecular weight and localization of LPG from mutant parasites as compared to V121. Expression of gp63, a surface molecule also implicated in attachment to macrophages, was unaltered. All 3 mutants caused disease when injected into genetically susceptible BALB/c mice but lesions developed at a much slower rate than those caused by the virulent V121 clone. This slow rate of lesion development did not correlate with promastigotes' ability to invade macrophages in vitro. Karyotype analysis showed that there was a reduction in the size of chromosome band number 2 in all 3 mutants. The differences in LPG and chromosome band 2 were retained by mutant clones following passage through mice, suggesting that these phenotypes are stable. Although the mutant parasites were infective and caused lesions, the changed structure of the LPG appeared to influence the virulence of the parasites.