Immunopathogenesis of infection with the visceralizing Leishmania species

Changing demographics of visceral leishmaniasis in northeast Brazil: Lessons for the future

Background

Visceral leishmaniasis (VL) caused by Leishmania infantum became a disease of urban areas in Brazil in the last 30 years and there has been an increase in asymptomatic L. infantum infection with these areas.

Methodology/Principal findings

A retrospective study of human VL was performed in the state of Rio Grande do Norte, Brazil, for the period of 1990–2014. The data were divided into five-time periods. For all VL cases, data on sex, age, nutritional status and childhood vaccination were collected. Geographic information system tools and statistical models were used to analyze the dispersion of human VL. The mean annual incidence of VL was 4.6 cases/100,000 inhabitants, with total 3,252 cases reported. The lethality rate was 6.4%. Over time the annual incidence of VL decreased in the 0–4 years (p<0.0001) and 5–9 (p <0.0001) age groups, but increased in ages 20–39 (p<0.001) and >40 years (p<0.0001). VL occurred more often in males (β₂ = 2.5; p<0.0001). The decreased incidence of VL in children was associated with improved nutritional status and childhood immunizations including measles, poliomyelitis, BCG, and hepatitis B. Human VL correlated temporally and geographically with canine L. infantum infection (p = 0.002, R² = 0.438), with rainfall and with Lutzomyia longipalpis density (r = 0.762). Overall, the incidence of VL decreased, while VL-AIDS increased, especially between 2010–2014. VL was more frequently found in areas that lacked urban infrastructure, detected by lack of garbage collection and sewers, whereas HIV infection was associated with higher levels of schooling and evidence of higher socioeconomic status.

Conclusion/Significance

The demographics of VL in northeastern Brazil have changed. Disease incidence has decreased in children and increased in adults. They were associated with improvements in nutrition, socioeconomic status and immunization rates. Concurrent VL-AIDS poses a serious challenge for the future.

We studied factors associated with the changing demographics of visceral leishmaniasis (VL) in Northeast Brazil, including environmental and socioeconomic determinants of disease, during the period 1990 to 2014. The incidence of VL was higher in urban areas, and regions with higher levels of canine L. infantum infection. Human males were more commonly affected than females. The incidence of VL in children under age 10 decreased during the period of study, simultaneous with increased incidence in adults. Reduction in the VL incidence among children was associated with improved socioeconomic status, administration of childhood vaccines and better nutritional status. Geographic areas with higher rainfall had higher densities of Lu. longipalpis, the primary vector of L. infantum in Brazil. VL was more frequently found in areas with indicators of poverty including sparse garbage collection and lack of urban infrastructure. During the past 25 years, HIV/AIDS has spread to areas where VL is endemic and has contributed to an increased incidence of VL-AIDS co-infection in adults.

Cellular apoptosis and nitric oxide production in PBMC and spleen from dogs with visceral leishmaniasis

Nitric oxide (NO) is involved in the death of the Leishmania parasite and regulation of apoptosis. We quantified the frequency of cells producing NO and its levels in the peripheral blood mononuclear cells (PBMC), leukocytes from spleen in Visceral Leishmaniasis (VL) symptomatic dogs and correlated NO levels with apoptosis and parasite load in the spleen. The percentage of NO+ cells and CD14+/NO+ was higher in PBMC and spleen cells in infected dogs than in controls. The levels of NO+ and CD14+/NO+ cells was higher in PBMC, but lower spleen of dogs infected than compared to control. Late apoptosis rates increased in PBMC and spleen of infected dogs compared to controls, and the NO levels and apoptosis not showed correlation. There was a positive correlation between the percentage of cells producing NO in the spleen and parasite load. The NO participates in the immune response in the canine VL, but it is not apoptosis inducer.

Monocyte-Derived Signals Activate Human Natural Killer Cells in Response to Leishmania Parasites

Activated natural killer (NK) cells release interferon (IFN)-γ, which is crucial for the control of intracellular pathogens such as Leishmania. In contrast to experimental murine leishmaniasis, the human NK cell response to Leishmania is still poorly characterized. Here, we investigated the interaction of human blood NK cells with promastigotes of different Leishmania species (Leishmania major, Leishmania mexicana, Leishmania infantum, and Leishmania donovani). When peripheral blood mononuclear cells or purified NK cells and monocytes (all derived from healthy blood donors from Germany without a history of leishmaniasis) were exposed to promastigotes, NK cells showed increased surface expression of the activation marker CD69. The extent of this effect varied depending on the Leishmania species; differences between dermotropic and viscerotropic L. infantum strains were not observed. Upregulation of CD69 required direct contact between monocytes and Leishmania and was partly inhibitable by anti-interleukin (IL)-18. Unexpectedly, IL-18 was undetectable in most of the supernatants (SNs) of monocyte/parasite cocultures. Confocal fluorescence microscopy of non-permeabilized cells revealed that Leishmania-infected monocytes trans-presented IL-18 to NK cells. Native, but not heat-treated SNs of monocyte/Leishmania cocultures also induced CD69 on NK cells, indicating the involvement of a soluble heat-labile factor other than IL-18. A role for the NK cell-activating cytokines IL-1β, IL-2, IL-12, IL-15, IL-21, and IFN-α/β was excluded. The increase of CD69 was not paralleled by NK cell IFN-γ production or enhanced cytotoxicity. However, prior exposure of NK cells to Leishmania parasites synergistically increased their IFN-γ release in response to IL-12, which was dependent on endogenous IL-18. CD1c+ dendritic cells were identified as possible source of Leishmania-induced IL-12. Finally, we observed that direct contact between Leishmania and NK cells reduced the expression of CD56 mRNA and protein on NK cells. We conclude that Leishmania activate NK cells via trans-presentation of IL-18 by monocytes and by a monocyte-derived soluble factor. IL-12 is needed to elicit the IFN-γ-response of NK cells, which is likely to be an important component of the innate control of the parasite.

CD45RO+ T Cells and T Cell Activation in the Long-Lasting Immunity after Leishmania infantum Infection

Manifestations of Leishmania infantum infection range from asymptomatic to symptomatic visceral leishmaniasis (VL). People with symptomatic VL (sVL) have suppressed immune responses against Leishmania antigens that are reversed after clinical cure. The intradermal leishmanin skin test (LST) is negative during sVL, but it becomes positive after treatment. The aim of this study was to compare T cell responses in individuals with sVL, recovered VL (RecVL), and endemic controls. Endemic controls were household contacts of a VL case and they were grouped by their LST results, either positive (LST+) or negative (LST-). Mononuclear cells were studied ex vivo or after stimulation with soluble Leishmania antigens (SLA); cell surface markers and cytokines were determined. T cells, ex vivo, from individuals with sVL and from LST+ individuals presented a higher activation for CD4⁺ and CD8⁺ cells expressing CD69. However, lymphocytes from sVL stimulated with SLA had lower percentages of CD4⁺ and CD8⁺ cells expressing CD69 and CD8⁺ cells expressing CD25, with no release of interferon-γ or tumor necrosis factor. sVL subjects had lower percentage of memory cells (CD4⁺ CD45RO+), ex vivo, without SLA stimulation than RecVL, LST+, or LST- (P = 0.0022). However, individuals with sVL had fewer regulatory cells after SLA stimulation (CD4⁺ CD25^HIGH, P = 0.04 and CD4⁺ FOXP3+, P = 0.02) than RecVL. The decrease in specific memory and activated CD4⁺ and CD8⁺ cells, as in response to Leishmania antigens, could explain, in part, the immune impairment during sVL. Finally, protective T cell responses are long lasting because both RecVL or LST+ individuals maintain a specific protective response to Leishmania years after the primary infection.

Dermotropic Leishmania donovani in Sri Lanka: visceralizing potential in clinical and preclinical studies

The visceralizing potential of apparently dermotropic Leishmania donovani in Sri Lanka (L. donovani-SL) was investigated through long-term follow-up of cutaneous leishmaniasis (CL) patients and in vivo and in vitro experimental infection models. CL patients (n = 250) treated effectively with intra-lesional antimony therapy were followed-up six monthly for 4 years. There was no clinical evidence of visceralization of infection (VL) during this period. Infection of BALB/c mice with L. donovani-SL (test) through intra-dermal route led to the development of cutaneous lesions at the site of inoculation with no signs of systemic dissemination, in contrast to the observations made in animals similarly infected with a visceralizing strain of L. donovani-1S (control). Cytokine (IL-10, IFN-γ) release patterns of splenocytes and lymph node cell cultures derived from mice primed with experimental infections (with either test or control parasites) revealed significantly high IFN-γ response associated with test mice with CL, while prominent IL-10 levels were observed in association with control mice with VL. Furthermore, diminished infection efficiency, intracellular growth and survival of L. donovani-SL parasites compared with L. donovani-1S were evident through in vitro macrophage infection experiments. These studies confirm, for the first time, the essential dermotropic nature of L. donovani-SL suggesting natural attenuation of virulence of local parasite strains.

Protection mediated by chemokine CXCL10 in BALB/c mice infected by Leishmania infantum

BACKGROUND

Visceral leishmaniasis (VL) caused by Leishmania infantum is characterised by the loss of the ability of the host to generate an effective immune response. Chemokines have a direct involvement in the pathogenesis of leishmaniasis, causing a rapid change in the expression of these molecules during infection by Leishmania.

OBJECTIVES

Herein, it was investigated the role of CXCL10 in controlling infection by L. infantum.

METHODS

RAW 264.7 macrophages were infected with L. infantum in vitro and treated or not with CXCL10 (25, 50 and 100 ng/mL). Parasite load, as well as nitric oxide (NO), IL-4 and IL-10 production were assessed at 24 and 48 h after infection. In vivo, BALB/c mice were infected and treated or not with CXCL10 (5 μg/kg) at one, three and seven days of infection. Parasite load, IFN-g, IL-4, TGF-β and IL-10 were evaluated one, seven and 23 days post treatment.

FINDINGS

In vitro, CXCL10 reduced parasitic load, not dependent on NO, and inhibited IL-10 and IL-4 secretion. In vivo, CXCL10 was able to reduce the parasite load in both liver and spleen, four weeks after infection, representing a higher decrease in the number of parasites in these organs, also induced IFN-γ at day 23 after treatment, correlating with the decrease in parasite load, and reduced IL-10 and TGF-β.

MAIN CONCLUSIONS

This study suggests a partial protective role of CXCL10 against L. infantum, mediated by IFN-g, not dependent on NO, and with suppression of IL-10 and TGF-β. These data may provide information for the development of new approaches for future therapeutic interventions for VL.

Comparative analyses of whole genome sequences of Leishmania infantum isolates from humans and dogs in northeastern Brazil

The genomic sequences of 20 Leishmania infantum isolates collected in northeastern Brazil were compared with each other and with the available genomic sequences of 29 L. infantum/donovani isolates from Nepal and Turkey. The Brazilian isolates were obtained in the early 1990s or since 2009 from patients with visceral or non-ulcerating cutaneous leishmaniasis, asymptomatic humans, or dogs with visceral leishmaniasis. Two isolates were from the blood and bone marrow of the same visceral leishmaniasis patient. All 20 genomic sequences display 99.95% identity with each other and slightly less identity with a reference L. infantum genome from a Spanish isolate. Despite the high identity, analysis of individual differences among the 32 million base pair genomes showed sufficient variation to allow the isolates to be clustered based on the primary sequence. A major source of variation detected was in chromosome somy, with only four of the 36 chromosomes being predominantly disomic in all 49 isolates examined. In contrast, chromosome 31 was predominantly tetrasomic/pentasomic, consistent with its regions of synteny on two different disomic chromosomes of Trypanosoma brucei. In the Brazilian isolates, evidence for recombination was detected in 27 of the 36 chromosomes. Clustering analyses suggested two populations, in which two of the five older isolates from the 1990s clustered with a majority of recent isolates. Overall the analyses do not suggest individual sequence variants account for differences in clinical outcome or adaptation to different hosts. For the first known time, DNA of isolates from asymptomatic subjects were sequenced. Of interest, these displayed lower diversity than isolates from symptomatic subjects, an observation that deserves further investigation with additional isolates from asymptomatic subjects.

Probing the efficacy of a heterologous Leishmania/L. Viannia braziliensis recombinant enolase as a candidate vaccine to restrict the development of L. infantum in BALB/c mice

In the present study, the Leishmania braziliensis enolase protein was evaluated as a vaccine candidate against visceral leishmaniasis (VL). The DNA sequence was cloned and the recombinant protein (rEnolase) was evaluated as a vaccine, associated with saponin, as an immune adjuvant. The protective efficacy of the rEnolase plus saponin combination was investigated in BALB/c mice against Leishmania infantum infection. The results revealed that the vaccine induced higher levels of IFN-γ, IL-12, and GM-CSF when a capture ELISA and flow cytometry were performed, as well as an antileishmanial nitrite production after using in vitro stimulation with rEnolase and an antigenic Leishmania preparation. The vaccinated animals, when compared to the control groups, showed a lower parasite burden in the liver, spleen, bone marrow, and paws' draining lymph nodes when both a limiting dilution technique and RT-PCR assay were performed. In addition, these mice showed low levels of antileishmanial IL-4, IL-10, and anti-Leishmania IgG1 isotype antibodies. Partial protection was associated with IFN-γ production, which was mainly mediated by CD4⁺ T cells. In conclusion, the present study's data showed that the L. braziliensis enolase protein could be considered a vaccine candidate that offers heterologous protection against VL.

Cutaneous Manifestations of Human and Murine Leishmaniasis

The leishmaniases are diseases caused by pathogenic protozoan parasites of the genus Leishmania. Infections are initiated when a sand fly vector inoculates Leishmania parasites into the skin of a mammalian host. Leishmania causes a spectrum of inflammatory cutaneous disease manifestations. The type of cutaneous pathology is determined in part by the infecting Leishmania species, but also by a combination of inflammatory and anti-inflammatory host immune response factors resulting in different clinical outcomes. This review discusses the distinct cutaneous syndromes described in humans, and current knowledge of the inflammatory responses associated with divergent cutaneous pathologic responses to different Leishmania species. The contribution of key hematopoietic cells in experimental cutaneous leishmaniasis in mouse models are also reviewed and compared with those observed during human infection. We hypothesize that local skin events influence the ensuing adaptive immune response to Leishmania spp. infections, and that the balance between inflammatory and regulatory factors induced by infection are critical for determining cutaneous pathology and outcome of infection.

A vaccine composed of a hypothetical protein and the eukaryotic initiation factor 5a from Leishmania braziliensis cross-protection against Leishmania amazonensis infection

In the present study, two proteins cloned from Leishmania braziliensis species, a hypothetical protein (LbHyp) and the eukaryotic initiation factor 5a (EiF5a), were evaluated to protect BALB/c mice against L. amazonensis infection. The animals were immunized with the antigens, either separately or in combination, using saponin as an immune adjuvant in both cases. Spleen cells from vaccinated and later infected mice produced significantly higher levels of protein and parasite-specific IFN-γ, IL-12, and GM-CSF, in addition to low levels of IL-4 and IL-10. Evaluating the parasite load by means of a limiting dilution technique and quantitative Real-Time PCR, vaccinated animals presented significant reductions in the parasite load in both infected tissues and organs, as well as lower footpad swelling, when compared to the control (saline and saponin) groups. The best results regarding the protection of the animals were achieved when the combined vaccine was administered into the animals. Protection was associated with an IFN-γ production against parasite antigens, which was mediated by both CD4+ and CD8+ T cells and correlated with antileishmanial nitrite production. In conclusion, data from the present study show that this polyprotein vaccine, which combines two L. braziliensis proteins, can induce protection against L. amazonensis infection.

Comprehensive candidate gene analysis for symptomatic or asymptomatic outcomes of Leishmania infantum infection in Brazil

Genetic risk factors contribute to asymptomatic versus symptomatic visceral leishmaniasis (VL) outcomes following infection with Leishmania infantum. We therefore carried out a family-based (n = 918 post-quality control fully genotyped and phenotyped individuals) candidate gene study for symptomatic VL or asymptomatic delayed-type hypersensitivity (DTH) skin test phenotypes in highly endemic neighborhoods of northeast Brazil. A total of 248 SNPs were genotyped in 42 genes selected as candidates on the basis of prior genetic, immunological, and transcriptional profiling studies. The most significant association with the VL phenotype was with SNP rs6785358 (P = 5.7e-04; p_corrected = 0.026) 3.8 kb upstream of TGFBR2, the gene encoding the type 2 receptor for transforming growth factor beta (TGFβ). A second inhibitory member of the TGBβ superfamily signaling pathway, SMAD7, was associated with the DTH phenotype (SNP rs7238442: P = 0.001; p_corrected = 0.051). The most significant association for the DTH phenotype was with SNP rs10800309 (P = -8.4e-06; p_corrected = 3.9e-04) situated 3.1 kb upstream of FCGR2A, the gene encoding the low-affinity IIa receptor for the Fc fragment of IgG. Overall, our results imply a role for IgG-mediated inflammation in determining DTH associated with asymptomatic infection and contribute to growing evidence that the TGFβ pathway is important in the immunopathogenesis of VL.

Recent updates and perspectives on approaches for the development of vaccines against visceral leishmaniasis

Visceral leishmaniasis (VL) is one of the most important tropical diseases worldwide. Although chemotherapy has been widely used to treat this disease, problems related to the development of parasite resistance and side effects associated with the compounds used have been noted. Hence, alternative approaches for VL control are desirable. Some methods, such as vector control and culling of infected dogs, are insufficiently effective, with the latter not ethically recommended. The development of vaccines to prevent VL is a feasible and desirable measure for disease control; for example, some vaccines designed to protect dogs against VL have recently been brought to market. These vaccines are based on the combination of parasite fractions or recombinant proteins with adjuvants that are able to induce cellular immune responses; however, their partial efficacy and the absence of a vaccine to protect against human leishmaniasis underline the need for characterization of new vaccine candidates. This review presents recent advances in control measures for VL based on vaccine development, describing extensively studied antigens, as well as new antigenic proteins recently identified using immuno-proteomic techniques.

Atypical Manifestations of Cutaneous Leishmaniasis in a Region Endemic for Leishmania braziliensis: Clinical, Immunological and Parasitological Aspects

BACKGROUND

Atypical cutaneous leishmaniasis (ACL) has become progressively more frequent in Corte de Pedra, Northeast Brazil. Herein we characterize clinical presentation, antimony response, cytokine production and parasite strains prevailing in ACL.

METHODOLOGY/PRINCIPAL FINDINGS

Between 2005 and 2012, 51 ACL (cases) and 51 temporally matched cutaneous leishmaniasis (CL) subjects (controls) were enrolled and followed over time in Corte de Pedra. Clinical and therapeutic data were recorded for all subjects. Cytokine secretion by patients' peripheral blood mononuclear cells (PBMC) stimulated with soluble parasite antigen in vitro, and genotypes in a 600 base-pair locus in chromosome 28 (CHR28/425451) of the infecting L. (V.) braziliensis were compared between the two groups. ACL presented significantly more lesions in head and neck, and higher rate of antimony failure than CL. Cytosine-Adenine substitutions at CHR28/425451 positions 254 and 321 were highly associated with ACL (p<0.0001). In vitro stimulated ACL PBMCs produced lower levels of IFN-γ (p = 0.0002) and TNF (p <0.0001), and higher levels of IL-10 (p = 0.0006) and IL-17 (p = 0.0008) than CL PBMCs.

CONCLUSIONS/SIGNIFICANCE

ACL found in Northeast Brazil is caused by distinct genotypes of L. (V.) braziliensis and presents a cytokine profile that departs from that in classical CL patients. We think that differences in antigenic contents among parasites may be in part responsible for the variation in cytokine responses and possibly immunopathology between CL and ACL.

Blood Transcriptional Profiling Reveals Immunological Signatures of Distinct States of Infection of Humans with Leishmania infantum

Visceral leishmaniasis (VL) can be lethal if untreated; however, the majority of human infections with the etiological agents are asymptomatic. Using Illumina Bead Chip microarray technology, we investigated the patterns of gene expression in blood of active VL patients, asymptomatic infected individuals, patients under remission of VL and controls. Computational analyses based on differential gene expression, gene set enrichment, weighted gene co-expression networks and cell deconvolution generated data demonstrating discriminative transcriptional signatures. VL patients exhibited transcriptional profiles associated with pathways and gene modules reflecting activation of T lymphocytes via MHC class I and type I interferon signaling, as well as an overall down regulation of pathways and gene modules related to myeloid cells, mainly due to differences in the relative proportions of monocytes and neutrophils. Patients under remission of VL presented heterogeneous transcriptional profiles associated with activation of T lymphocytes via MHC class I, type I interferon signaling and cell cycle and, importantly, transcriptional activity correlated with activation of Notch signaling pathway and gene modules that reflected increased proportions of B cells after treatment of disease. Asymptomatic and uninfected individuals presented similar gene expression profiles, nevertheless, asymptomatic individuals exhibited particularities which suggest an efficient regulation of lymphocyte activation and a strong association with a type I interferon response. Of note, we validated a set of target genes by RT-qPCR and demonstrate the robustness of expression data acquired by microarray analysis. In conclusion, this study profiles the immune response during distinct states of infection of humans with Leishmania infantum with a novel strategy that indicates the molecular pathways that contribute to the progression of the disease, while also providing insights into transcriptional activity that can drive protective mechanisms.

Infections of humans with the protozoan parasites L. donvani and L. infantum can lead to the development of the disease visceral leishmaniasis, but also to an asymptomatic status. However, the mechanisms that result in these clinical outcomes after infection are poorly understood. In this study, we applied a data-driven approach to obtain insights into the immunological processes linked to the progression of the disease or to protective mechanisms. For this purpose, we evaluated the patterns of expression for genes that code proteins from the entire human genome in the peripheral blood from patients with visceral leishmaniasis, from individuals who remained asymptomatic after infections with L. infantum, from patients who were recovering from disease after treatment and from uninfected individuals. By employing computational analysis to evaluate the blood transcriptional activity of each group, we identified transcriptional signatures that correlate with previous findings obtained through different analytical methods. Moreover, our analyses uncovered hitherto unidentified molecular pathways and gene networks associated with the transcriptional profiles of individuals recovering from disease or that did not develop symptoms after infection. This suggests that activation of protective responses can be useful targets for the development of new therapies for visceral leishmaniasis.

Immunotherapeutic Potential of Eugenol Emulsion in Experimental Visceral Leishmaniasis

BACKGROUND

The therapy of visceral leishmaniasis (VL) is limited by resistance, toxicity and decreased bioavailability of the existing drugs coupled with dramatic increase in HIV-co-infection, non-availability of vaccines and down regulation of cell-mediated immunity (CMI). Thus, we envisaged combating the problem with plant-derived antileishmanial drug that could concomitantly mitigate the immune suppression of the infected hosts. Several plant-derived compounds have been found to exert leishmanicidal activity via immunomodulation. In this direction, we investigated the antileishmanial activity of eugenol emulsion (EE), complemented with its immunomodulatory and therapeutic efficacy in murine model of VL.

METHODOLOGY/PRINCIPAL FINDINGS

Oil-in-water emulsion of eugenol (EE) was prepared and size measured by dynamic light scattering (DLS). EE exhibited significant leishmanicidal activity with 50% inhibitory concentration of 8.43±0.96 μg ml-1 and 5.05±1.72 μg ml─1, respectively against the promastigotes and intracellular amastigotes of Leishmania donovani. For in vivo effectiveness, EE was administered intraperitoneally (25, 50 and 75 mg/kg b.w./day for 10 days) to 8 week-infected BALB/c mice. The cytotoxicity of EE was assessed in RAW 264.7 macrophages as well as in naive mice. EE induced a significant drop in hepatic and splenic parasite burdens as well as diminution in spleen and liver weights 10 days post-treatment, with augmentation of 24h-delayed type hypersensitivity (DTH) response and high IgG2a:IgG1, mirroring induction of CMI. Enhanced IFN-γ and IL-2 levels, with fall in disease-associated Th2 cytokines (IL-4 and IL-10) detected by flow cytometric bead-based array, substantiated the Th1 immune signature. Lymphoproliferation and nitric oxide release were significantly elevated upon antigen revoke in vitro. The immune-stimulatory activity of EE was further corroborated by expansion of IFN-γ producing CD4+ and CD8+ splenic T lymphocytes and up-regulation of CD80 and CD86 on peritoneal macrophages. EE treated groups exhibited induction of CD8+ central memory T cells as evidenced from CD62L and CD44 expression. No biochemical alterations in hepatic and renal enzymes were observed.

CONCLUSIONS

Our results demonstrate antileishmanial activity of EE, potentiated by Th1 immunostimulation without adverse side effects. The Th1 immune polarizing effect may help to alleviate the depressed CMI and hence complement the leishmanicidal activity.

A Subset of Neutrophils Expressing Markers of Antigen-Presenting Cells in Human Visceral Leishmaniasis

BACKGROUND

Visceral leishmaniasis (VL) is a potentially fatal parasitic disease associated with fever, cachexia and impaired protective T-cell responses against the parasite.

METHODS

Peripheral blood leukocytes from 105 subjects with VL and healthy control subjects from the endemic region of Muzaffarpur, Bihar, India, were compared using flow cytometry and reverse-transcriptase quantitative polymerase chain reaction. Findings were correlated with clinical data.

RESULTS

An expanded population of low-density neutrophils that expressed HLA-DR, CD80 and CD86 was observed in subjects with VL. This neutrophil population contracted after successful treatment of disease. Plasma from patients with acute VL was able to induce similar high-level HLA-DR expression in neutrophils from healthy subjects. HLA-DR⁺ neutrophils from subjects with VL did not stimulate T-cell proliferation, but they did express higher programmed cell death ligand-1 (PDL1) than other neutrophils, and lymphocytes of the same subjects expressed high programmed cell death 1 (PD1).

CONCLUSIONS

Patients with acute VL have expanded circulating low-density neutrophils expressing markers of antigen presentation, which diminish after treatment. Development of HLA-DR⁺ neutrophils is stimulated, at least in part, by components of plasma from patients with acute disease. Although we found no evidence that they act as antigen-presenting cells, these neutrophils expressed markers implicating a role in T-cell exhaustion.

Leishmania, the phagosome, and host responses: The journey of a parasite

Leishmania is the eukaryotic parasite responsible for leishmaniases, a spectrum of diseases that puts at risk roughly 350millions of people in 98 countries according to the Drugs for Neglected Diseases initiative (DNDi). This parasite has a complex life cycle composed of two distinct stages, the promastigote form found in the female sand-fly vector and the amastigote form that replicates in the mammalian host (Teixeira et al., 2013) [1]. To survive, the parasite interacts with its host immune system at multiple levels. In this review, we discuss the nature of those interactions, how they affect the host immune system, and how they affect parasite survival from the very beginning of the life cycle in the vector to its dissemination within the mammalian host.

A vaccine combining two Leishmania braziliensis proteins offers heterologous protection against Leishmania infantum infection

In the present study, two Leishmania braziliensis proteins, one hypothetical and the eukaryotic initiation factor 5a (EiF5a), were cloned and used as a polyproteins vaccine for the heterologous protection of BALB/c mice against infantum infection. Animals were immunized with the antigens separately or in association, and in both cases saponin was used as an adjuvant. In the results, spleen cells from mice inoculated with the individual or polyproteins vaccine and lately challenged produced significantly higher levels of protein- and parasite-specific IFN-γ, IL-12, and GM-CSF, when both a capture ELISA and flow cytometry assays were performed. Evaluating the parasite load by a limiting dilution as well as by RT-PCR, these animals presented significant reductions in the parasite number in all evaluated organs, when compared to the control (saline and saponin) groups. The best protection was reached when the polyproteins vaccine was employed. Protection was associated with the IFN-γ production against parasite extracts, which was mediated by both CD4(+) and CD8(+) T cells and correlated with the antileishmanial nitrite production. In this context, this vaccine combining two L. braziliensis proteins was able to induce a heterologous protection against VL, and could be considered in future studies to be tested against other Leishmania species or in other mammalian hosts.

Compartmentalized Immune Response in Leishmaniasis: Changing Patterns throughout the Disease

Visceral leishmaniasis (VL) is characterized by loss of T-cell responsiveness and absence of Leishmania-specific IFN-γ production by peripheral blood mononuclear cells. However, the expressions of IFN-γ and TNF-α are up-regulated in the tissues and plasma of VL patients. There is a paucity of information regarding the cytokine profile expressed by different target tissues in the same individual and the changes it undergoes throughout the course of infection. In this work we evaluated IFN-γ, TNF-α, IL-10, and TGF-β mRNA expression using real-time RT-PCR in 5 target tissues at 6 months and 16 months post-infection (PI) in a canine experimental model which mimics many aspects of human VL. The spleen and liver of Leishmania infantum experimentally-infected dogs elicited a pro- and anti- inflammatory response and high parasite density at 6 and 16 months PI. The popliteal lymph node, however, showed an up-regulation of IFN-γ cytokin at commencement of the study and was at the chronic phase when the IL-10 and TGF-β expression appeared. In spite of skin parasite invasion, local cytokine response was absent at 6 months PI. Parasite growth and onset of clinical disease both correlated with dermal up-regulation of all the studied cytokines. Our VL model suggests that central target organs, such as the spleen and liver, present a mixed cytokine immune response early on infection. In contrast, an anti-inflammatory/regulatory immune response in peripheral tissues is activated in the later chronic-patent stages of the disease.

Infection and Activation of Human Neutrophils with Fluorescent Leishmania infantum

Neutrophils (PMNs) are recruited in high numbers to sites of host infection by the protozoan parasites of the genus Leishmania. Although PMNs are capable of phagocytizing Leishmania parasites and are potent producers of anti-microbial compounds including reactive oxygen species (ROS), they are unable to control the establishment of infection. Prior studies document production of ROS in isolated PMNs incubated with Leishmania under conditions allowing phagocytosis, but without a measure of single cells' responses it cannot be discerned whether PMN activation and ROS production is suppressed or ineffective in the cells that internalize the parasite. To address these interactions, we engineered a strain of fluorescent, mCherry-expressing Leishmania infantum (mCherry-Li). By infecting isolated human PMNs in vitro with mCherry-Li, we observed ready association of the parasites with PMNs in a time- and dose-dependent fashion. We also examined production of PMN ROS (using the fluorescent compound DHR123) and PMN activation (as evidence by loss of surface CD62L expression). Whereas many Li-associated (mCherry⁺) PMNs responded to parasite interactions and uptake with ROS production and/or activation, a proportion exhibited neither response. Furthermore, a large proportion of mCherry - "bystander" PMNs displayed both ROS production and activation. The heterogeneous response of PMNs to Leishmania exposure leads us to hypothesize, first, that some PMNs exhibit decreased activation upon phagocytosis of Leishmania, and could support their maintenance. Second, responses of bystander PMNs may contribute to a local inflammatory environment that is ineffective at parasite clearance.

Polymerase chain reaction detection and inducible nitric-oxide synthase expression of Leishmania major in mice inoculated by two different routes

Introduction:

Leishmania major needs a sensitive and specific method for proper diagnosis. This study aims to study the course and histopathology of L. major in certain tissues of experimentally infected BALB/c mice after subcutaneous (sc) and intraperitoneal (ip) inoculation.

Materials and Methods:

After infecting BALB/c mice using sc and ip inoculation, the histopathology was studied. The kinetoplastic DNA polymerase chain reaction (PCR) for its molecular detection and detect the inducible nitric-oxide synthase (iNOS) pattern during the first 3 months of infection.

Result:

PCR could detect the presence of L. major in all spleens, lymph nodes, and skin ulcers by both inoculation routes while (33%) and (42%) of livers were positive after sc and ip routes, respectively. Chronic inflammatory cell infiltrates with capsulitis was found in the spleen, lymph nodes, and liver. Granulomas were found in the spleen and liver. There was a statistically significant difference in iNOS expression along the experiment in the spleen and lymph nodes by both routes and in the liver by ip only. Apart from the liver, iNOS could not be detected on the 2^nd week postinfection and was high after 1 month for both routes in all samples; a moderate decrease at 2 months and the highest decrease were detected after 3 months.

Conclusions:

L. major inoculation by both routes produce visceral disease in mice, and kinetoplastic DNA PCR can detect its presence from the 2^nd week up to the 3^rd month postinfection. The iNOS expression was high at 1 and 2 months and remained throughout the 3 months of the experiment; which plays an important role in the disease course and control.

A new Leishmania-specific hypothetical protein, LiHyT, used as a vaccine antigen against visceral leishmaniasis

The present study aimed to evaluate a new Leishmania-specific hypothetical protein, LiHyT, as a vaccine candidate against VL. The immunogenicity of the recombinant protein (rLiHyT) plus saponin was evaluated in BALB/c mice. In the results, it is shown that rLiHyT plus saponin vaccinated mice produced high levels of IFN-γ, IL-12, and GM-CSF after in vitro stimulation of spleen cells using both rLiHyT and Leishmania infantum SLA. The protective efficacy was evaluated after subcutaneous challenge with stationary promastigotes of L. infantum. Immunized and infected mice, when compared to the controls, showed significant reductions in the number of parasites in the liver, spleen, bone marrow, and in the paws' draining lymph nodes. Protection was associated with an IL-12-dependent production of IFN-γ, mainly by CD4(+) T cells, with a minor contribution of CD8(+) T cells. In these mice, a decrease in the parasite-mediated IL-4 and IL-10 responses, as well as a predominance of LiHyT- and parasite-specific IgG2a isotype antibodies, were also observed. The present study showed that a new Leishmania-specific protein, when combined with a Th1-type adjuvant, presents potential to be used as a vaccine against VL.

Propolis reduces Leishmania amazonensis-induced inflammation in the liver of BALB/c mice

Experimental models of mouse paw infection with L. amazonensis show an induction of a strong inflammatory response in the skin, and parasitic migration may occur to secondary organs with consequent tissue injury. There are few studies focusing on the resolution of damage in secondary organs caused by Leishmania species-related cutaneous leishmaniasis. We investigated the propolis treatment effect on liver inflammation induced by Leishmania amazonensis infection in the mouse paw. BALB/c mice were infected in the hind paw with L. amazonensis (10(7)) promastigote forms. After 15 days, animals were treated daily with propolis (5 mg/kg), Glucantime (10 mg/kg), or with propolis plus Glucantime combined. After 60 days, mice were euthanized and livers were collected for inflammatory process analysis. Liver microscopic analysis showed that propolis reduced the inflammatory process compared to untreated infected control. There was a decrease of liver myeloperoxidase and N-acetyl-β-glucosaminidase activity levels, collagen fiber deposition, pro-inflammatory cytokine production, and plasma aspartate transaminase and alanine transaminase levels. Furthermore, propolis treatment enhanced anti-inflammatory cytokine levels and reversed hepatosplenomegaly. Our data demonstrated that daily low doses of Brazilian propolis reduced the secondary chronic inflammatory process in the liver caused by L. amazonensis subcutaneous infection in a susceptible mice strain.

Studies in the mouse model identify strain variability as a major determinant of disease outcome in Leishmania infantum infection

Background

Visceral leishmaniasis is a severe and potentially fatal disease caused by protozoa of the genus Leishmania, transmitted by phlebotomine sandflies. In Europe and the Mediterranean region, L. infantum is the commonest agent of visceral leishmaniasis, causing a wide spectrum of clinical manifestations, including asymptomatic carriage, cutaneous lesions and severe visceral disease. Visceral leishmaniasis is more frequent in immunocompromised individuals and data obtained in experimental models of infection have highlighted the importance of the host immune response, namely the efficient activation of host’s macrophages, in determining infection outcome. Conversely, few studies have addressed a possible contribution of parasite variability to this outcome.

Methods

In this study, we compared three isolates of L. infantum regarding their capacity to grow in the organs of mice, the way they activate the host’s macrophages and other components of the immune response and also their capacity to cope with host’s antimicrobial mechanisms, namely reactive oxygen and nitrogen species.

Results

We found that the three parasite strains significantly differed regarding the degree to which they induced nitric oxide synthase (NOS2) and arginase expression in infected macrophages and the pattern of cytokine production they induced in the host, resulting in different degrees of inflammatory response in infected livers. Additionally, the three strains also significantly differed in their in vitro susceptibility to reactive oxygen and nitrogen species. This variability was reflected in the capacity of each strain to persist and proliferate in the organs of wild-type as well as NOS2- and phagocyte oxidase- deficient mice.

Conclusions

The results obtained in this study show that parasite strain variability is an important determinant of disease outcome in L. infantum visceral leishmaniasis, with relevant implications for studies on host-pathogen interaction and also for leishmanicidal drug development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1259-6) contains supplementary material, which is available to authorized users.

Metabolomic Analyses of Leishmania Reveal Multiple Species Differences and Large Differences in Amino Acid Metabolism

Comparative genomic analyses of Leishmania species have revealed relatively minor heterogeneity amongst recognised housekeeping genes and yet the species cause distinct infections and pathogenesis in their mammalian hosts. To gain greater information on the biochemical variation between species, and insights into possible metabolic mechanisms underpinning visceral and cutaneous leishmaniasis, we have undertaken in this study a comparative analysis of the metabolomes of promastigotes of L. donovani, L. major and L. mexicana. The analysis revealed 64 metabolites with confirmed identity differing 3-fold or more between the cell extracts of species, with 161 putatively identified metabolites differing similarly. Analysis of the media from cultures revealed an at least 3-fold difference in use or excretion of 43 metabolites of confirmed identity and 87 putatively identified metabolites that differed to a similar extent. Strikingly large differences were detected in their extent of amino acid use and metabolism, especially for tryptophan, aspartate, arginine and proline. Major pathways of tryptophan and arginine catabolism were shown to be to indole-3-lactate and arginic acid, respectively, which were excreted. The data presented provide clear evidence on the value of global metabolomic analyses in detecting species-specific metabolic features, thus application of this technology should be a major contributor to gaining greater understanding of how pathogens are adapted to infecting their hosts.

Antigenicity, Immunogenicity and Protective Efficacy of Three Proteins Expressed in the Promastigote and Amastigote Stages of Leishmania infantum against Visceral Leishmaniasis

In the present study, two Leishmania infantum hypothetical proteins present in the amastigote stage, LiHyp1 and LiHyp6, were combined with a promastigote protein, IgE-dependent histamine-releasing factor (HRF); to compose a polyproteins vaccine to be evaluated against L. infantum infection. Also, the antigenicity of the three proteins was analyzed, and their use for the serodiagnosis of canine visceral leishmaniasis (CVL) was evaluated. The LiHyp1, LiHyp6, and HRF DNA coding sequences were cloned in prokaryotic expression vectors and the recombinant proteins were purified. When employed in ELISA assays, all proteins were recognized by sera from visceral leishmaniasis (VL) dogs, and presented no cross-reactivity with either sera from dogs vaccinated with a Brazilian commercial vaccine, or sera of Trypanosoma cruzi-infected or Ehrlichia canis-infected animals. In addition, the antigens were not recognized by antibodies from non-infected animals living in endemic or non-endemic areas for leishmaniasis. The immunogenicity and protective efficacy of the three proteins administered in the presence of saponin, individually or in combination (composing a polyproteins vaccine), were evaluated in a VL murine model: BALB/c mice infected with L. infantum. Spleen cells from mice inoculated with the individual proteins or with the polyproteins vaccine plus saponin showed a protein-specific production of IFN-γ, IL-12, and GM-CSF after an in vitro stimulation, which was maintained after infection. These animals presented significant reductions in the parasite burden in different evaluated organs, when compared to mice inoculated with saline or saponin. The decrease in parasite burden was associated with an IL-12-dependent production of IFN-γ against parasite total extracts (produced mainly by CD4+ T cells), correlated to the induction of parasite proteins-driven NO production. Mice inoculated with the recombinant protein-based vaccines showed also high levels of parasite-specific IgG2a antibodies. The polyproteins vaccine administration induced a more pronounced Th1 response before and after challenge infection than individual vaccines, which was correlated to a higher control of parasite dissemination to internal organs.

A Leishmania-specific hypothetical protein expressed in both promastigote and amastigote stages of Leishmania infantum employed for the serodiagnosis of, and as a vaccine candidate against, visceral leishmaniasis

BACKGROUND

LiHyV is an antigenic hypothetical protein present in both promastigote and amastigote stages of Leishmania infantum, which was recently identified by an immunoproteomic approach. A recombinant version of this protein (rLiHyV) was evaluated as a diagnostic marker for canine VL (CVL). In addition, the prophylactic efficacy of the rLiHyV protein, and two of its CD8(+) T cell epitopes, has been analyzed in a murine model of visceral leishmaniasis (VL).

METHODS

Initially, the rLiHyV protein was evaluated by an ELISA technique for the serodiagnosis of CVL. Secondly, vaccines composed of the recombinant protein and both chemically synthesized peptides, combined with saponin as an adjuvant; were administered subcutaneously into BALB/c mice. The cellular and humoral responses generated by vaccination were evaluated. In addition, the parasite burden and immune response were studied 10 weeks after L. infantum infection.

RESULTS

The rLiHyV protein was recognized by antibodies of VL dogs. No cross-reactivity was obtained with sera from dogs vaccinated with a Brazilian commercial vaccine, with sera from animals infected with Trypanosoma cruzi, Babesia canis and Ehrlichia canis, or those from non-infected animals living in an endemic area for leishmaniasis. After challenge with L. infantum, spleen cells of BALB/c mice vaccinated with rLiHyV/saponin stimulated with parasite antigens showed a higher production of IFN-γ, IL-12 and GM-CSF, than the same cells obtained from mice vaccinated with the individual peptides, or mice from control (inoculated with saline or saponin) groups. This Th1-type cellular response observed in rLiHyV/saponin vaccinated mice was accompanied by the induction of parasite-specific IgG2a isotype antibodies. Animals immunized with rLiHyV/saponin showed significant reductions in the parasite burden in the liver, spleen, bone marrow and in the lymph nodes draining the paws relative to control mice.

CONCLUSIONS

The present study showed for the first time that the L. infantum LiHyV protein could be considered as a vaccine candidate against L. infantum infection, as well as a diagnostic marker for CVL.

Natural products as inhibitors of recombinant cathepsin L of Leishmania mexicana

Cysteine proteinases (cathepsins) from Leishmania spp. are promising molecular targets against leishmaniasis. Leishmania mexicana cathepsin L is essential in the parasite life cycle and a pivotal in virulence factor in mammals. Natural products that have been shown to display antileishmanial activity were screened as part of our ongoing efforts to design inhibitors against the L. mexicana cathepsin L-like rCPB2.8. Among them, agathisflavone (1), tetrahydrorobustaflavone (2), 3-oxo-urs-12-en-28-oic acid (3), and quercetin (4) showed significant inhibitory activity on rCPB2.8 with IC50 values ranging from 0.43 to 18.03 µM. The mechanisms of inhibition for compounds 1-3, which showed Ki values in the low micromolar range (Ki = 0.14-1.26 µM), were determined. The biflavone 1 and the triterpene 3 are partially noncompetitive inhibitors, whereas biflavanone 2 is an uncompetitive inhibitor. The mechanism of action established for these leishmanicidal natural products provides a new outlook in the search for drugs against Leishmania.

Fitness of Leishmania donovani parasites resistant to drug combinations

Drug resistance represents one of the main problems for the use of chemotherapy to treat leishmaniasis. Additionally, it could provide some advantages to Leishmania parasites, such as a higher capacity to survive in stress conditions. In this work, in mixed populations of Leishmania donovani parasites, we have analyzed whether experimentally resistant lines to one or two combined anti-leishmanial drugs better support the stress conditions than a susceptible line expressing luciferase (Luc line). In the absence of stress, none of the Leishmania lines showed growth advantage relative to the other when mixed at a 1:1 parasite ratio. However, when promastigotes from resistant lines and the Luc line were mixed and exposed to different stresses, we observed that the resistant lines are more tolerant of different stress conditions: nutrient starvation and heat shock-pH stress. Further to this, we observed that intracellular amastigotes from resistant lines present a higher capacity to survive inside the macrophages than those of the control line. These results suggest that resistant parasites acquire an overall fitness increase and that resistance to drug combinations presents significant differences in their fitness capacity versus single-drug resistant parasites, particularly in intracellular amastigotes. These results contribute to the assessment of the possible impact of drug resistance on leishmaniasis control programs.

Chemotherapy is currently the only treatment option for leishmaniasis, a neglected tropical disease produced by the protozoan parasite Leishmania. However, first-line drugs have different types of limitations including toxicity, price, efficacy and mainly emerging resistance. The WHO has recently recommended a combined therapy in order to extend the life expectancy of these compounds. The emergence and spread of Leishmania antimonial-resistant parasites have led to a high rate of antimonial failure in India and have raised questions about the selection and propagation risk of drug resistant parasites. The spread of drug-resistant parasites in the field probably depends on their transmission potential, which is influenced by, among other factors, the relative fitness of drug-resistant versus drug-susceptible parasites. In light of this, we have designed experimental studies to determine whether Leishmania donovani parasites resistant to single and combinations of anti-leishmanial drugs present any advantages in their ability to bear the different stress conditions versus a susceptible L. donovani line. Our results suggest that resistant parasites acquire an overall fitness increase and that resistance to drug combinations presents significant differences in their fitness capacity, particularly in intracellular amastigotes.

NLR proteins and parasitic disease

Parasitic diseases are a serious global health concern. Many of the most common and most severe parasitic diseases, including Chagas' disease, leishmaniasis, and schistosomiasis, are also classified as neglected tropical diseases and are comparatively less studied than infectious diseases prevalent in high income nations. The NLRs (nucleotide-binding domain leucine-rich-repeat-containing proteins) are cytosolic proteins known to be involved in pathogen detection and host response. The role of NLRs in the host response to parasitic infection is just beginning to be understood. The NLR proteins NOD1 and NOD2 have been shown to contribute to immune responses during Trypanosoma cruzi infection, Toxoplasma gondii infection, and murine cerebral malaria. The NLRP3 inflammasome is activated by T. cruzi and Leishmania amazonensis but also induces pathology during infection with schistosomes or malaria. Both the NLRP1 and NLRP3 inflammasomes respond to T. gondii infection. The NLRs may play crucial roles in human immune responses during parasitic infection, usually acting as innate immune sensors and driving the inflammatory response against invading parasites. However, this inflammatory response can either kill the invading parasite or be responsible for destructive pathology. Therefore, understanding the role of the NLR proteins will be critical to understanding the host defense against parasites as well as the fine balance between homeostasis and parasitic disease.

Eosinophils and mast cells in leishmaniasis

Leishmania spp. are parasitic protozoa endemic in tropical and subtropical regions and the causative agent of leishmaniasis, a collection of syndromes whose clinical manifestations vary according to host and pathogen factors. Leishmania spp. are inoculated into the mammalian host by the bite of an infected sand fly, whereupon they are taken up by phagocytosis, convert into the replicative amastigote stage within macrophages, reproduce, spread to new macrophages and cause disease manifestations. A curative response against leishmaniasis depends in the classical activation of macrophages and the IL-12-dependent onset of an adaptive type 1 response characterized by the production of IFN-γ. Emerging evidence suggests that neutrophils, dendritic cells and other immune cells can serve as either temporary or stable hosts for Leishmania spp. Furthermore, it is becoming apparent that the initial interactions of the parasite with resident or early recruited immune cells can shape both the macrophage response and the type of adaptive immune response being induced. In this review, we compile a growing number of studies demonstrating how the earliest interactions of Leishmania spp. with eosinophils and mast cells influence the macrophage response to infection and the development of the adaptive immune response, hence, determining the ultimate outcome of infection.

Xenodiagnosis of Leishmania donovani in BALB/c mice using Phlebotomus orientalis: a new laboratory model

Background

In areas endemic for visceral leishmaniasis (VL), the majority of infected hosts remain asymptomatic but potentially infectious to biting sand flies. Their infectiousness for sand fly vectors is crucial for the transmission of the disease and can be quantified only by xenodiagnosis. However, in the case of human hosts, xenodiagnosis can be problematic for ethical and logistic reasons. The BALB/c mouse model described in this paper was designed to enable xenodiagnostic studies on VL hosts circumventing the need for human volunteers, it permits xenodiagnosis using the same individual host repeatedly, over several months.

Methods

BALB/c mice were intradermally inoculated in the ear pinnae with Leishmania donovani, primarily metacyclic stages isolated from the thoracic midguts of experimentally-infected Phlebotomus orientalis females. Naïve sand flies were allowed to feed on anaesthetized mice in 1-3-weeks- interval, firstly on the site of inoculation of L. donovani (weeks 2–8 post infection, p.i.), later on the whole body of mice (weeks 9 – 15 p.i.). Infections of sand flies were evaluated microscopically or by PCR analysis.

Results

Although infected mice did not show any signs of disease, 19% (N = 876) of the P. orientalis females that fed at the site of inoculation, became infected. The majority of L. donovani-positive females (76%) had heavy infections with their stomodeal valves colonized by attached parasites. Inoculated mouse ears remained infective for sand flies until week 15 p.i. Females feeding on other parts of the body remained negative with exception of two groups feeding on contralateral ears by week 12 p.i. On week 15, however, these two mice returned negative at xenodiagnosis of the contralateral ears. In sacrificed mice, the highest parasite numbers were found in inoculated ears and their draining lymph nodes. Infections were detected also in the spleen, liver, blood and rarely in the contralateral ear.

Conclusions

The study showed that BALB/c mice harbored parasites in sufficient numbers to promote heavy infections in P. orientalis and thus comprised a suitable laboratory model for xenodiagnoses of L. donovani. Parasites persisted in the inoculation site and were found transmissible for months to sand flies biting on the same site.

T-cell populations and cytokine expression are impaired in thymus and spleen of protein malnourished BALB/c mice infected with Leishmania infantum

Visceral leishmaniasis (VL) is a parasitic infectious disease that causes significant morbidity and mortality in the tropical and subtropical regions of the world. Although infections with visceralizing Leishmania may be asymptomatic, factors such as undernutrition increase the likelihood of progressing to clinical disease. Protein malnutrition, the most deleterious cause of malnutrition in developing countries, has been considered as a primary risk factor for the development of clinical VL. However, data regarding the immunological basis of this association are scarce. With the aim to analyze the effects of protein malnutrition on Leishmania infantum infection, we used BALB/c mice subjected to control or low protein isocaloric diets. Each animal group was divided into two subgroups and one was infected with L. infantum resulting in four study groups: animals fed 14% protein diet (CP), animals fed 4% protein diet (LP), animals fed 14% protein diet and infected (CPi), and animals fed 4% protein diet and infected (LPi).The susceptibility to L. infantum infection and immune responses were assessed in terms of body and lymphoid organ weight, parasite load, lymphocyte subpopulations, and cytokine expression. LPi mice had a significant reduction of body and lymphoid organ weight and exhibited a severe decrease of lymphoid follicles in the spleen. Moreover, LPi animals showed a significant decrease in CD4⁺CD8⁺ T cells in the thymus, whereas there was an increase of CD4⁺ and CD8⁺ T cells percentages in the spleen. Notably, the cytokine mRNA levels in the thymus and spleen of protein malnourished-infected animals were altered compared to the CP mice. Protein malnutrition results in a drastic dysregulation of T cells and cytokine expression in the thymus and spleen of L. infantum-infected BALB/c mice, which may lead to defective regulation of the thymocyte population and an impaired splenic immune response, accelerating the events of a normal course of infection.

Granzyme-mediated regulation of host defense in the liver in experimental Leishmania donovani infection

In the livers of susceptible C57BL/6 (B6) mice infected with Leishmania donovani, CD8(+) T cell mechanisms are required for granuloma assembly, macrophage activation, intracellular parasite killing, and self-cure. Since gene expression of perforin and granzymes A and B (GzmA and GzmB), cytolytic proteins linked to CD8(+) cell effector function, was enhanced in infected liver tissue, B6 mice deficient in these granular proteins were used to gauge host defense roles. Neither perforin nor GzmA was required; however, mice deficient in GzmB (GzmB(-/-), GzmB cluster(-/-), and GzmA×B cluster double knockout [DKO] mice) showed both delayed granuloma assembly and initially impaired control of parasite replication. Since these two defects in B6 mice were limited to early-stage infection, innately resistant 129/Sv mice were also tested. In this genetic setting, expression of both innate and subsequent T (Th1) cell-dependent acquired resistance, including the self-cure phenotype, was entirely derailed in GzmA×B cluster DKO mice. These results, in susceptible B6 mice for GzmB and in resistant 129/Sv mice for GzmA and/or the GzmB cluster, point to granzyme-mediated host defense regulation in the liver in experimental visceral leishmaniasis.

Nitroimidazo-oxazole compound DNDI-VL-2098: an orally effective preclinical drug candidate for the treatment of visceral leishmaniasis

OBJECTIVES

The objective of this study was to identify a nitroimidazo-oxazole lead molecule for the treatment of visceral leishmaniasis (VL).

METHODS

A library of 72 nitroimidazo-oxazoles was evaluated in vitro for their antileishmanial activity against luciferase-transfected DD8 amastigotes of Leishmania donovani. On the basis of their in vitro potency and pharmacokinetic properties, the promising compounds were tested in acute BALB/c mouse and chronic hamster models of VL via oral administration and efficacy was evaluated by microscopic counting of amastigotes after Giemsa staining. The best antileishmanial candidates (racemate DNDI-VL-2001) and its R enantiomer (DNDI-VL-2098) were evaluated in vitro against a range of Leishmania strains. These candidates were further studied in a hamster model using various dose regimens. Cytokine and inducible nitric oxide synthase estimations by real-time PCR and nitric oxide generation by Griess assay were also carried out for DNDI-VL-2098.

RESULTS

In vitro screening of nitroimidazo-oxazole compounds identified the racemate DNDI-VL-2001 (6-nitroimidazo-oxazole derivative) and its enantiomers as candidates for further evaluation in in vivo models of VL. DNDI-VL-2098 (IC50 of 0.03 μM for the DD8 strain) showed excellent in vivo activity in both mouse and hamster models, with an ED90 value of 3.7 and <25 mg/kg, respectively, and was also found to be very effective against high-grade infection in the hamster model. Our studies revealed that, along with leishmanicidal activity, DNDI-VL-2098 was also capable of inducing host-protective immune cells to suppress Leishmania parasites in hamsters.

CONCLUSIONS

These studies led to the identification of compound DNDI-VL-2098 as a preclinical candidate for further drug development as an oral treatment for VL.

The Cytotoxic T Lymphocyte Antigen-4 +49A/G Single Nucleotide Polymorphism Association With Visceral Leishmaniasis

Background:

Several lines of evidence approve that innate and adaptive immunity play key roles in the defense against visceral leishmaniasis (VL). The polymorphism within the cytotoxic T lymphocyte antigen 4 (CTLA-4) gene alters its expression.

Objectives:

The main aim of this study was to evaluate the polymorphism within the +49 position of the CTLA-4 gene of Iranian patients with VL in comparison with healthy controls.

Materials and Methods:

In this cross-sectional study, 88 patients with clinical presentations of VL, who were seropositive for Leishmania (group 1), 86 patients without clinical presentations but seropositive (group 2), and 115 healthy controls (group 3) were assessed with respect to the CTLA-4 +49A/G polymorphism, using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The anti-Leishmania antibody titration was evaluated using an immunofluorescence method.

Results:

Our results indicated that both CTLA-4 +49A/G polymorphisms were significantly associated with VL.

Conclusions:

According to the results, the polymorphisms within the +49 position of CTLA-4 can be associated with VL and may be considered as risk factors for the disease.

Dual immune modulatory effect of vitamin A in human visceral leishmaniasis

Vitamin A supplementation has shown to prevent mortality by diarrheal and respiratory diseases in several countries. Nevertheless, there are few studies investigating the effect of vitamin A in visceral leishmaniasis (VL), although there are reports of its deficiency in children with symptomatic VL in Brazil and Bangladesh. This study analyzed the effect of vitamin A on a subset of Treg cells and monocytes isolated from symptomatic VL and from healthy children residing in an endemic area for VL in Northeast Brazil. Serum retinol concentrations correlated inversely with IL-10 and TGF-β productions in CD4(+)CD25(high)Foxp3(+) T cells isolated from children with VL stimulated with leishmanial antigens. All-trans retinoic acid in vitro induced IL-10 in CD4(+)CD25(high)Foxp3(+) T cells; IL-10 and TGF-β production in CD4(+)CD25-Foxp3- T cells, and IL-10 in monocytes isolated from healthy children. However, the use of all-trans retinoic acid together with leishmanial antigens in vitro prevented increases in IL-10 production in Treg cells and monocytes isolated from VL children. Strikingly, those results show a potential dual role of vitamin A in the immune system: improvement of a regulatory profile in cells from healthy children after leishmanial stimulation and down modulation of IL-10 in Treg cells and monocytes during symptomatic VL. Therefore, the use of vitamin A concomitant to VL therapy might be useful in improving recovery from disease status caused by Leishmania infantum infection and warrants additional study.

Is the IL-10 -819 polymorphism associated with visceral leishmaniasis?

Previous investigations demonstrated that immune responses play critical roles in the defense against visceral leishmaniasis (VL). A key regulator of immune responses is the cytokine, IL-10 and polymorphisms within its promoter which could alter its expression. Thus, the aim of this study was to examine the correlation between polymorphism at the -819 position of the IL-10 gene and VL in a selected Iranian population. This cross-sectional study was performed on 100 patients with clinical presentation of VL and seropositive for the leishmania (group 1), 62 patients without clinical presentation but seropositive (group 2), and 128 healthy controls (group 3). The IL-10 -819 polymorphism was evaluated using the PCR-RFLP technique. The anti-leishmania antibody titration was assessed using an immunofluorescence assay. Our results showed that the polymorphism at IL-10 -819 (C/T) position was significantly associated with VL, and C/T genotype was significantly higher in VL patients when compared to groups 2 and 3 (p < 0.001). However, the results demonstrated that the C and T alleles were not associated with VL (p = 0.855). The data presented here confirm the results of previous reports that polymorphisms at the -819 position of the IL-10 gene can influence susceptibility to VL suggesting that the C/T genotype may be considered as a risk factor for the disease.

Immune regulation during chronic visceral leishmaniasis

Visceral leishmaniasis is a chronic parasitic disease associated with severe immune dysfunction. Treatment options are limited to relatively toxic drugs, and there is no vaccine for humans available. Hence, there is an urgent need to better understand immune responses following infection with Leishmania species by studying animal models of disease and clinical samples from patients. Here, we review recent discoveries in these areas and highlight shortcomings in our knowledge that need to be addressed if better treatment options are to be developed and effective vaccines designed.

Growth factor and Th2 cytokine signaling pathways converge at STAT6 to promote arginase expression in progressive experimental visceral leishmaniasis

Host arginase 1 (arg1) expression is a significant contributor to the pathogenesis of progressive visceral leishmaniasis (VL), a neglected tropical disease caused by the intracellular protozoan Leishmania donovani. Previously we found that parasite-induced arg1 expression in macrophages was dependent on STAT6 activation. Arg1 expression was amplified by, but did not require, IL-4, and required de novo synthesis of unknown protein(s). To further explore the mechanisms involved in arg1 regulation in VL, we screened a panel of kinase inhibitors and found that inhibitors of growth factor signaling reduced arg1 expression in splenic macrophages from hamsters with VL. Analysis of growth factors and their signaling pathways revealed that the Fibroblast Growth Factor Receptor 1 (FGFR-1) and Insulin-like Growth Factor 1 Receptor (IGF-1R) and a number of downstream signaling proteins were activated in splenic macrophages isolated from hamsters infected with L. donovani. Recombinant FGF-2 and IGF-1 increased the expression of arg1 in L. donovani infected hamster macrophages, and this induction was augmented by IL-4. Inhibition of FGFR-1 and IGF-1R decreased arg1 expression and restricted L. donovani replication in both in vitro and ex vivo models of infection. Inhibition of the downstream signaling molecules JAK and AKT also reduced the expression of arg1 in infected macrophages. STAT6 was activated in infected macrophages exposed to either FGF-2 or IGF-1, and STAT6 was critical to the FGFR-1- and IGF-1R-mediated expression of arg1. The converse was also true as inhibition of FGFR-1 and IGF-1R reduced the activation of STAT6 in infected macrophages. Collectively, these data indicate that the FGFR/IGF-1R and IL-4 signaling pathways converge at STAT6 to promote pathologic arg1 expression and intracellular parasite survival in VL. Targeted interruption of these pathological processes offers an approach to restrain this relentlessly progressive disease.

Visceral leishmaniasis (VL), caused by the intracellular protozoan Leishmania donovani, is a progressive infection that is particularly common in impoverished populations of the world. People die from this disease unless it is treated. We used an experimental infection model that mimics the clinical and pathological features of human VL to study how the parasite causes this severe disease. We found that host macrophages infected with Leishmania donovani are activated in a way that leads to the expression of arginase, an enzyme that counteracts the cell's mechanisms that control the infection. This disease-promoting activation pathway was driven by the convergence of growth factor and cytokine signaling pathways and activation of the transcription factor STAT6. Chemical inhibition of signaling through the fibroblast growth factor receptor-1 (FGFR-1) or insulin-like growth factor-1 receptor (IGF-IR), or genetic knockdown of STAT6 led to reduced expression of arginase and enhanced control of the infection by macrophages. This indicates that the growth factor signaling pathways together with the cytokine pathways promote this disease. Interventions designed to disrupt this signaling could help in the treatment of VL.

Clinical and parasitological protection in a Leishmania infantum-macaque model vaccinated with adenovirus and the recombinant A2 antigen

BACKGROUND

Visceral leishmaniasis (VL) is a severe vector-born disease of humans and dogs caused by Leishmania donovani complex parasites. Approximately 0.2 to 0.4 million new human VL cases occur annually worldwide. In the new world, these alarming numbers are primarily due to the impracticality of current control methods based on vector reduction and dog euthanasia. Thus, a prophylactic vaccine appears to be essential for VL control. The current efforts to develop an efficacious vaccine include the use of animal models that are as close to human VL. We have previously reported a L. infantum-macaque infection model that is reliable to determine which vaccine candidates are most worthy for further development. Among the few amastigote antigens tested so far, one of specific interest is the recombinant A2 (rA2) protein that protects against experimental L. infantum infections in mice and dogs.

METHODOLOGY/PRINCIPAL FINDINGS

Primates were vaccinated using three rA2-based prime-boost immunization regimes: three doses of rA2 plus recombinant human interleukin-12 (rhIL-12) adsorbed in alum (rA2/rhIL-12/alum); two doses of non-replicative adenovirus recombinant vector encoding A2 (Ad5-A2) followed by two boosts with rA2/rhIL-12/alum (Ad5-A2+rA2/rhIL12/alum); and plasmid DNA encoding A2 gene (DNA-A2) boosted with two doses of Ad5-A2 (DNA-A2+Ad5-A2). Primates received a subsequent infectious challenge with L. infantum. Vaccines, apart from being safe, were immunogenic as animals responded with increased pre-challenge production of anti-A2-specific IgG antibodies, though with some variability in the response, depending on the vaccine formulation/protocol. The relative parasite load in the liver was significantly lower in immunized macaques as compared to controls. Protection correlated with hepatic granuloma resolution, and reduction of clinical symptoms, particularly when primates were vaccinated with the Ad5-A2+rA2/rhIL12/alum protocol.

CONCLUSIONS/SIGNIFICANCE

The remarkable clinical protection induced by A2 in an animal model that is evolutionary close to humans qualifies this antigen as a suitable vaccine candidate against human VL.

Treatment failure in leishmaniasis: drug-resistance or another (epi-) phenotype?

Two major leishmaniasis treatments have shown a significant decrease in effectiveness in the last few decades, mostly in the Indian subcontinent but also in other endemic areas. Drug resistance of Leishmania correlated only partially to treatment failure (TF) of pentavalent antimonials, and has so far proved not to be important for the increased miltefosine relapse rates observed in the Indian subcontinent. While other patient- or drug-related factors could also have played a role, recent studies identified several parasite features such as infectivity and host manipulation skills that might contribute to TF. This perspective aims to discuss how different parasitic features other than drug resistance can contribute to TF of leishmaniasis and how this may vary between different epidemiological contexts.

Animal models for the study of leishmaniasis immunology

Leishmaniasis remains a major public health problem worldwide and is classified as Category I by the TDR/WHO, mainly due to the absence of control. Many experimental models like rodents, dogs and monkeys have been developed, each with specific features, in order to characterize the immune response to Leishmania species, but none reproduces the pathology observed in human disease. Conflicting data may arise in part because different parasite strains or species are being examined, different tissue targets (mice footpad, ear, or base of tail) are being infected, and different numbers (“low” 1×10² and “high” 1×10⁶) of metacyclic promastigotes have been inoculated. Recently, new approaches have been proposed to provide more meaningful data regarding the host response and pathogenesis that parallels human disease. The use of sand fly saliva and low numbers of parasites in experimental infections has led to mimic natural transmission and find new molecules and immune mechanisms which should be considered when designing vaccines and control strategies. Moreover, the use of wild rodents as experimental models has been proposed as a good alternative for studying the host-pathogen relationships and for testing candidate vaccines. To date, using natural reservoirs to study Leishmania infection has been challenging because immunologic reagents for use in wild rodents are lacking. This review discusses the principal immunological findings against Leishmania infection in different animal models highlighting the importance of using experimental conditions similar to natural transmission and reservoir species as experimental models to study the immunopathology of the disease.

Combination of liposomal CpG oligodeoxynucleotide 2006 and miltefosine induces strong cell-mediated immunity during experimental visceral leishmaniasis

Immuno-modulators in combination with antileishmanial drug miltefosine is a better therapeutic approach for treatment of Visceral Leishmaniasis (VL) as it not only reduces the dose of miltefosine but also shortens the treatment regimen. However, immunological mechanisms behind the perceived benefits of this combination therapy have not been investigated in detail. In the present study, we hypothesized that potential use of drugs that target the host in addition to the parasite might represent an alternative strategy for combination therapy. We investigated immune responses generated in Leishmania donovani infected animals (hamsters and mice) treated with combination of CpG-ODN-2006 and miltefosine at short dose regimen. Infected animals were administered CpG-ODN-2006 (0.4 mg/kg, single dose), as free and liposomal form, either alone or in combination with miltefosine for 5 consecutive days and parasite clearance was evaluated at day 4 and 7 post treatment. Animals that received liposomal CpG-ODN-2006 (lipo-CpG-ODN-2006) and sub-curative miltefosine (5 mg/kg) showed the best inhibition of parasite multiplication (∼97%) which was associated with a biased Th1 immune response in. Moreover, compared to all the other treated groups, we observed increased mRNA expression levels of pro-inflammatory cytokines (IFN-γ, TNF-α and IL-12) and significantly suppressed levels of Th2 cytokines (IL-10 and TGF-β) on day 4 post treatment in animals that underwent combination therapy with lipo-CpG-ODN-2006 and sub-curative miltefosine. Additionally, same therapy also induced heightened iNOS mRNA levels and NO generation, increased IgG2 antibody level and strong T-cell response in these hamsters compared with all the other treated groups. Collectively, our results suggest that combination of lipo-CpG-ODN-2006 and sub-curative miltefosine generates protective T-cell response in an animal model of visceral leishmaniasis which is characterized by strong Th1 biased immune response thereby underlining our hypothesis that combination therapy, at short dose regimen can be used as a novel way of treating visceral leishmaniasis.