Mechanisms of resistance and susceptibility to experimental visceral leishmaniosis: BALB/c mouse versus Syrian hamster model

Regulation of immunity during visceral Leishmania infection

Unicellular eukaryotes of the genus Leishmania are collectively responsible for a heterogeneous group of diseases known as leishmaniasis. The visceral form of leishmaniasis, caused by L. donovani or L. infantum, is a devastating condition, claiming 20,000 to 40,000 lives annually, with particular incidence in some of the poorest regions of the world. Immunity to Leishmania depends on the development of protective type I immune responses capable of activating infected phagocytes to kill intracellular amastigotes. However, despite the induction of protective responses, disease progresses due to a multitude of factors that impede an optimal response. These include the action of suppressive cytokines, exhaustion of specific T cells, loss of lymphoid tissue architecture and a defective humoral response. We will review how these responses are orchestrated during the course of infection, including both early and chronic stages, focusing on the spleen and the liver, which are the main target organs of visceral Leishmania in the host. A comprehensive understanding of the immune events that occur during visceral Leishmania infection is crucial for the implementation of immunotherapeutic approaches that complement the current anti-Leishmania chemotherapy and the development of effective vaccines to prevent disease.

Natural transmission of Leishmania infantum through experimentally infected Phlebotomus perniciosus highlights the virulence of Leishmania parasites circulating in the human visceral leishmaniasis outbreak in Madrid, Spain

A human leishmaniasis outbreak is occurring in the Madrid region, Spain, with the parasite and vector involved being Leishmania infantum and Phlebotomus perniciosus respectively. The aim of this study was to investigate the virulence of L. infantum isolates from the focus using a natural transmission model. Hamsters were infected by intraperitoneal inoculation (IP) or by bites of sand flies experimentally infected with L. infantum isolates obtained from P. perniciosus collected in the outbreak area (IPER/ES/2012/BOS1FL1 and IPER/ES/2012/POL2FL6) and a well characterized L. infantum strain JPCM5 (MCAN/ES/98/LLM-877). Hamster infections were monitored by clinical examination, serology, culture, parasite burden, Giemsa-stained imprints, PCR, histopathology and xenodiagnostic studies. Establishment of infection of L. infantum was achieved with the JPCM5 strain and outbreak isolates by both P. perniciosus infective bites or IP route. However, high virulence of BOS1FL1 and POL2FL6 isolates was highlighted by the clinical outcome of disease, high parasite detection in spleen and liver, high parasitic loads and positivity of Leishmania serology. Transmission by bite of POL2FL6 infected flies generated a slower progression of clinical disease than IP infection, but both groups were infective to P. perniciosus by xenodiagnosis at 2 months post-infection. Conversely, hamsters inoculated with JPCM5 were not infective to sand flies. Histopathology studies confirmed the wide spread of POL2FL6 parasites to several organs. A visceral leishmaniasis model that mimics the natural transmission in nature allowed us to highlight the high virulence of isolates that are circulating in the focus. These findings contribute to a better understanding of the outbreak epidemiology.

HisAK70: progress towards a vaccine against different forms of leishmaniosis

BACKGROUND

Leishmania major and Leishmania infantum are among the main species that are responsible for cutaneous leishmaniosis (CL) and visceral leishmaniosis (VL), respectively. The leishmanioses represent the second-largest parasitic killer in the world after malaria. Recently, we succeeded in generating a plasmid DNA (pCMV-HISA70m2A) and demonstrated that immunized mice were protected against L. major challenge. The efficacy of the DNA-vaccine was further enhanced by the inclusion of KMP-11 antigen into the antibiotic-free plasmid pVAX1-asd.

METHODS

Here, we describe the use of a HisAK70 DNA-vaccine encoding seven Leishmania genes (H2A, H2B, H3, H4, A2, KMP11 and HSP70) for vaccination of mice to assess the induction of a resistant phenotype against VL and CL.

RESULTS

HisAK70 was successful in vaccinated mice, resulting in a high amount of efficient sterile hepatic granulomas associated with a hepatic parasite burden fully resolved in the VL model; and resulting in 100% inhibition of parasite visceralization in the CL model.

CONCLUSIONS

The results suggest that immunization with the HisAK70 DNA-vaccine may provide a rapid, suitable, and efficient vaccination strategy to confer cross-protective immunity against VL and CL.

Immucillins ImmA and ImmH Are Effective and Non-toxic in the Treatment of Experimental Visceral Leishmaniasis

BACKGROUND

Immucillins ImmA (IA), ImmH (IH) and SerMe-ImmH (SMIH) are synthetic deazapurine nucleoside analogues that inhibit Leishmania (L.) infantum chagasi and Leishmania (L.) amazonensis multiplication in vitro without macrophage toxicity. Immucillins are compared to the Glucantime standard drug in the chemotherapy of Leishmania (L.) infantum chagasi infection in mice and hamsters. These agents are tested for toxicity and immune system response.

METHODOLOGY/PRINCIPAL FINDINGS

BALB/c mice were infected with 107 amastigotes, treated with IA, IH, SMIH or Glucantime (2.5mg/kg/day) and monitored for clinical variables, parasite load, antibody levels and splenocyte IFN-γ, TNF-α, and IL-10 expression. Cytokines and CD4+, CD8+ and CD19+ lymphocyte frequencies were assessed in uninfected controls and in response to immucillins. Urea, creatinine, GOT and GPT levels were monitored in sera. Anti-Leishmania-specific IgG1 antibodies (anti-NH36) increased in untreated animals. IgG2a response, high levels of IFN-γ, TNF-α and lower levels of IL-10 were detected in mice treated with the immucillins and Glucantime. Immucillins permitted normal weight gain, prevented hepato-splenomegaly and cleared the parasite infection (85-89%) without renal and hepatic toxicity. Immucillins promoted 35% lower secretion of IFN-γ in uninfected controls than in infected mice. IA and IH increased the CD4+ T and CD19+ B cell frequencies. SMIH increased only the proportion of CD-19 B cells. IA and IH also cured infected hamsters with lower toxicity than Glucantime.

CONCLUSIONS/SIGNIFICANCE

Immucillins IA, IH and SMIH were effective in treating leishmaniasis in mice. In hamsters, IA and IH were also effective. The highest therapeutic efficacy was obtained with IA, possibly due to its induction of a TH1 immune response. Low immucillin doses were required and showed no toxicity. Our results disclose the potential use of IA and IH in the therapy of visceral leishmaniasis.

Adaptation of Leishmania donovani to cutaneous and visceral environments: in vivo selection and proteomic analysis

Leishmaniasis is a neglected tropical disease caused by Leishmania protozoa. Two main forms are found in the Old World, self-limited cutaneous leishmaniasis and potentially fatal visceral leishmaniasis, with parasite dissemination to liver, bone marrow, and spleen. The Leishmania donovani species complex is the causative agent of visceral leishmaniasis worldwide, but atypical L. donovani strains can cause cutaneous leishmaniasis. We hypothesized that L. donovani can adapt to survive in response to restrictions imposed by the host environment. To assess this, we performed in vivo selection in BALB/c mice with a cutaneous L. donovani clinical isolate to select for parasites with increased capacity to survive in visceral organs. We then performed whole cell proteomic analysis and compared this visceral-selected strain to the original cutaneous clinical isolate and to a visceral leishmaniasis clinical isolate. Overall, there were no major shifts in proteomic profiles; however, translation, biosynthetic processes, antioxidant protection, and signaling were elevated in visceral strains. Conversely, transport and trafficking were elevated in the cutaneous strain. Overall, these results provide new insight into the adaptability of Leishmania parasites to the host environment and on the factors that mediate their ability to survive in different organs.

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.

Using humans to make a human leishmaniasis vaccine

The cellular immune response to peptide pools from conserved Leishmania antigens in leishmaniasis-immune individuals identified epitopes for a human DNA vaccine (Das et al., this issue).

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.

Characterisation of the ex vivo virulence of Leishmania infantum isolates from Phlebotomus perniciosus from an outbreak of human leishmaniosis in Madrid, Spain

BACKGROUND

Since mid 2009, an outbreak of human leishmaniosis in Madrid, Spain, has involved more than 560 clinical cases. Many of the cases occurred in people who live in areas around a newly constructed green park (BosqueSur). This periurban park provides a suitable habitat for sand flies (the vectors of Leishmania infantum). Indeed, studies of blood meals from sand flies captured in the area showed a strong association between the insect vector, hares or rabbits, and humans in the area. Interestingly, up to 70% of cases have been found in immunocompetent patients (aged between 46-60 years). This study was designed to evaluate the ex vivo virulence of the L. infantum isolates from Phlebotomus perniciosus captured in this area of Madrid.

METHODS

Murine macrophages and dendritic cells were infected ex vivo with L. infantum strain BCN150, isolate BOS1FL1, or isolate POL2FL7. At different times after infection, the infection indices, cytokine production (IL-12p40 and IL-10), NO release and arginase activities were evaluated.

RESULTS

Using an ex vivo model of infection in murine bone marrow-derived cells, we found that infection with isolates BOS1FL1 and POL2FL7 undermined host immune defence mechanisms in multiple ways. The main factors identified were changes in both the balance of iNOS versus arginase activities and the equilibrium between the production of IL-12 and IL-10. Infection with isolates BOS1FL1 and POL2FL7 also resulted in higher infection rates compared to the BCN150 strain. Infection index values at 24 h were as follows: BCN150-infected cells, 110 for infected MØ and 115 for infected DC; BOS1FL1-infected cells, 300 for infected MØ and 247 for infected DC; and POL2FL7-infected cells, 275 for infected MØ and 292 for infected DC.

CONCLUSIONS

Our data indicate that L. infantum isolates captured from this endemic area exhibited high virulence in terms of infection index, cytokine production and enzymatic activities involved in the pathogenesis of visceral leishmaniosis. Altogether, these data provide a starting point for the study of the virulence behaviour of parasites (BOS1FL1 and POL2FL7) isolated from P. perniciosus during the outbreak of human leishmaniosis in Madrid, Spain, and their involvement in infecting immunocompetent hosts.

Combining cationic liposomal delivery with MPL-TDM for cysteine protease cocktail vaccination against Leishmania donovani: evidence for antigen synergy and protection

BACKGROUND

With the paucity of new drugs and HIV co-infection, vaccination remains an unmet research priority to combat visceral leishmaniasis (VL) requiring strong cellular immunity. Protein vaccination often suffers from low immunogenicity and poor generation of memory T cells for long-lasting protection. Cysteine proteases (CPs) are immunogenic proteins and key mediators of cellular functions in Leishmania. Here, we evaluated the vaccine efficacies of CPs against VL, using cationic liposomes with Toll like receptor agonists for stimulating host immunity against L. donovani in a hamster model.

METHODOLOGY/PRINCIPAL FINDINGS

Recombinant CPs type I (cpb), II (cpa) and III (cpc) of L. donovani were tested singly and in combination as a triple antigen cocktail for antileishmanial vaccination in hamsters. We found the antigens to be highly immunoreactive and persistent anti-CPA, anti-CPB and anti-CPC antibodies were detected in VL patients even after cure. The liposome-entrapped CPs with monophosphoryl lipid A-Trehalose dicorynomycolate (MPL-TDM) induced significantly high nitric oxide (up to 4 fold higher than controls) mediated antileishmanial activity in vitro, and resulted in strong in vivo protection. Among the three CPs, CPC emerged as the most potent vaccine candidate in combating the disease. Interestingly, a synergistic increase in protection was observed with liposomal CPA, CPB and CPC antigenic cocktail which reduced the organ parasite burden by 1013-1016 folds, and increased the disease-free survival of >80% animals at least up to 6 months post infection. Robust secretion of IFN-γ and IL-12, along with concomitant downregulation of Th2 cytokines, was observed in cocktail vaccinates, even after 3 months post infection.

CONCLUSION/SIGNIFICANCE

The present study is the first report of a comparative efficacy of leishmanial CPs and their cocktail using liposomal formulation with MPL-TDM against L. donovani. The level of protection attained has not been reported for any other subcutaneous single or polyprotein vaccination against VL.

Abortive T follicular helper development is associated with a defective humoral response in Leishmania infantum-infected macaques

Leishmania infantum causes a chronic infectious disease named visceral leishmaniasis (VL). We employed a non-human primate model to monitor immune parameters over time and gain new insights into the disease. Rhesus macaques were infected with L. infantum and the T helper and B cell immunological profiles characterized during acute and chronic phases of infection. Parasite detection in visceral compartments during the acute phase was associated with differentiation of effector memory CD4 T cells and increased levels of Th1 transcripts. At the chronic phase, parasites colonized novel lymphoid niches concomitant with increased expression of IL10. Despite the occurrence of hypergammaglobulinemia, the production of parasite-specific IgG was poor, being confined to the acute phase and positively correlated with the frequency of an activated memory splenic B cell population. We noticed the expansion of a splenic CD4 T cell population expressing CXCR5 and Bcl-6 during acute infection that was associated with the differentiation of the activated memory B cell population. Moreover, the number of splenic germinal centers peaked at one month after infection, hence paralleling the production of specific IgG. However, at chronic infection these populations contracted impacting the production of parasite-specific IgG. Our study provides new insights into the immune events taking place in a physiologically relevant host and a mechanistic basis for the inefficient humoral response during VL.

Development of novel prime-boost strategies based on a tri-gene fusion recombinant L. tarentolae vaccine against experimental murine visceral leishmaniasis

Visceral leishmaniasis (VL) is a vector-borne disease affecting humans and domestic animals that constitutes a serious public health problem in many countries. Although many antigens have been examined so far as protein- or DNA-based vaccines, none of them conferred complete long-term protection. The use of the lizard non-pathogenic to humans Leishmania (L.) tarentolae species as a live vaccine vector to deliver specific Leishmania antigens is a recent approach that needs to be explored further. In this study, we evaluated the effectiveness of live vaccination in protecting BALB/c mice against L. infantum infection using prime-boost regimens, namely Live/Live and DNA/Live. As a live vaccine, we used recombinant L. tarentolae expressing the L. donovani A2 antigen along with cysteine proteinases (CPA and CPB without its unusual C-terminal extension (CPB^-CTE)) as a tri-fusion gene. For DNA priming, the tri-fusion gene was encoded in pcDNA formulated with cationic solid lipid nanoparticles (cSLN) acting as an adjuvant. At different time points post-challenge, parasite burden and histopathological changes as well as humoral and cellular immune responses were assessed. Our results showed that immunization with both prime-boost A2-CPA-CPB^-CTE-recombinant L. tarentolae protects BALB/c mice against L. infantum challenge. This protective immunity is associated with a Th1-type immune response due to high levels of IFN-γ production prior and after challenge and with lower levels of IL-10 production after challenge, leading to a significantly higher IFN-γ/IL-10 ratio compared to the control groups. Moreover, this immunization elicited high IgG1 and IgG2a humoral immune responses. Protection in mice was also correlated with a high nitric oxide production and low parasite burden. Altogether, these results indicate the promise of the A2-CPA-CPB^-CTE-recombinant L. tarentolae as a safe live vaccine candidate against VL.

Visceral leishmaniasis (VL) is the most severe form of leishmaniasis and has emerged as an opportunistic infection in HIV-1 infected patients in many parts of the world. Drug-resistant forms have developed so emergence and increased the need for advanced preventive strategies. Using live avirulent organisms as a vaccine has been proven to be more effective than other regimens. The lizard protozoan parasite Leishmania tarentolae is considered as nonpathogenic to humans. In our previous work, a recombinant L. tarentolae strain expressing the amastigote-specific L. donovani A2 antigen as a vaccine candidate elicited protection against L. infantum challenge in mice. Furthermore, combinations of CPA/CPB cysteine proteinases were more protective against visceral and cutaneous Leishmania infections than the individual forms. Herein, we used DNA/Live and Live/Live prime-boost vaccination strategies against visceral leishmaniasis in BALB/c mice consisting of the A2-CPA-CPB^-CTE tri-fusion genes formulated with cationic solid lipid nanoparticles and a recombinant L. tarentolae expressing the tri-fusion. Assessments of cytokine production, humoral responses, parasite burden and histopathological studies support that the recombinant L. tarentolae A2-CPA-CPB^-CTE candidate vaccine elicits a protective response against visceral leishmaniasis in mice and represents an important step forward in the development of new vaccine combinations against Leishmania infections.

UCP2 deficiency helps to restrict the pathogenesis of experimental cutaneous and visceral leishmaniosis in mice

BACKGROUND

Uncoupling protein 2 (UCP2) is a mitochondrial transporter that has been shown to lower the production of reactive oxygen species (ROS). Intracellular pathogens such as Leishmania upregulate UCP2 and thereby suppress ROS production in infected host tissues, allowing the multiplication of parasites within murine phagocytes. This makes host UCP2 and ROS production potential targets in the development of antileishmanial therapies. Here we explore how UCP2 affects the outcome of cutaneous leishmaniosis (CL) and visceral leishmaniosis (VL) in wild-type (WT) C57BL/6 mice and in C57BL/6 mice lacking the UCP2 gene (UCP2KO).

METHODOLOGY AND FINDINGS

To investigate the effects of host UCP2 deficiency on Leishmania infection, we evaluated parasite loads and cytokine production in target organs. Parasite loads were significantly lower in infected UCP2KO mice than in infected WT mice. We also found that UCP2KO mice produced significantly more interferon-γ (IFN-γ), IL-17 and IL-13 than WT mice (P<0.05), suggesting that UCP2KO mice are resistant to Leishmania infection.

CONCLUSIONS

In this way, UCP2KO mice were better able than their WT counterparts to overcome L. major and L. infantum infections. These findings suggest that upregulating host ROS levels, perhaps by inhibiting UPC2, may be an effective approach to preventing leishmaniosis.

A simple immune complex dissociation ELISA for leishmaniasis: standardization of the assay in experimental models and preliminary results in canine and human samples

Visceral leishmaniasis, caused by Leishmania (Leishmania) chagasi, is a chronic parasitic disease of humans and dogs. Confirmation of the protozoal agent in bone marrow, lymph node or spleen aspirate is diagnostic, while specific-IgG serology is used mainly for epidemiology despite the general presence of high levels of serum immunoglobulin. Anecdotal reports of false-negative serology in active disease cases are known and are ascribed to the formation of immune complexes. Because dissociation of immune complexes can be accomplished by acid treatment, we devised a simple, routine enzyme immunoassay (ELISA) for the dissociation of immune complexes in serum samples using acid treatment in wells adsorbed with Leishmania antigen (dELISA). Confirmatory acid dot-blot was also developed for antigen detection by anti-Leishmania rabbit antiserum. In experimental L. chagasi hamster models, immune complexes interfered with ELISA mostly in the 30 and 60 days postinfection, according to both dELISA and antigen dot-blot results. In larger samples from endemic areas, dELISA was positive in 10% of seronegative dog samples (7/70) and 3.5% in negative human samples (3/88), showing that dELISA could be used in the serodiagnosis of visceral leishmaniasis. Moreover, dELISA could be used as an alternative approach to screening asymptomatic visceral leishmaniasis patients, instead of invasive confirmatory testing.

A new model of progressive visceral leishmaniasis in hamsters by natural transmission via bites of vector sand flies

BACKGROUND

Visceral leishmaniasis (VL) is transmitted by sand flies. Protection of needle-challenged vaccinated mice was abrogated in vector-initiated cutaneous leishmaniasis, highlighting the importance of developing natural transmission models for VL.

METHODS

We used Lutzomyia longipalpis to transmit Leishmania infantum or Leishmania donovani to hamsters. Vector-initiated infections were monitored and compared with intracardiac infections. Body weights were recorded weekly. Organ parasite loads and parasite pick-up by flies were assessed in sick hamsters.

RESULTS

Vector-transmitted L. infantum and L. donovani caused ≥5-fold increase in spleen weight compared with uninfected organs and had geometric mean parasite loads (GMPL) comparable to intracardiac inoculation of 10(7)-10(8) parasites, although vector-initiated disease progression was slower and weight loss was greater. Only vector-initiated L. infantum infections caused cutaneous lesions at transmission and distal sites. Importantly, 45.6%, 50.0%, and 33.3% of sand flies feeding on ear, mouth, and testicular lesions, respectively, were parasite-positive. Successful transmission was associated with a high mean percent of metacyclics (66%-82%) rather than total GMPL (2.0 × 10(4)-8.0 × 10(4)) per midgut.

CONCLUSIONS

This model provides an improved platform to study initial immune events at the bite site, parasite tropism, and pathogenesis and to test drugs and vaccines against naturally acquired VL.

Determinants for the development of visceral leishmaniasis disease

Leishmaniasis is a vector-borne neglected tropical disease associated with a spectrum of clinical manifestations, ranging from self-healing cutaneous lesions to fatal visceral infections. Among the most important questions in Leishmania research is why some species like L. donovani infect visceral organs, whereas other species like L. major remain in the skin. The determinants of visceral leishmaniasis are still poorly understood, although genomic, immunologic, and animal models are beginning to provide important insight into this disease. In this review, we discuss the vector, host, and pathogen factors that mediate the development of visceral leishmaniasis. We examine the progression of the parasite from the initial site of sand fly bite to the visceral organs and its ability to survive there. The identification of visceral disease determinants is required to understand disease evolution, to understand visceral organ survival mechanisms, and potentially to develop better interventions for this largely neglected disease.

Immunopathogenesis of non-healing American cutaneous leishmaniasis and progressive visceral leishmaniasis

The outcomes of Leishmania infection are determined by host immune and nutrition status, parasite species, and co-infection with other pathogens. While subclinical infection and self-healing cutaneous leishmaniasis (CL) are common, uncontrolled parasite replication can lead to non-healing local lesions or visceral leishmaniasis (VL). It is known that infection control requires Th1-differentiation cytokines (IL-12, IL-18, and IL-27) and Th1 cell and macrophage activation. However, there is no generalized consensus for the mechanisms of host susceptibility. The recent studies on regulatory T cells and IL-17-producing cells help explain the effector T cell responses that occur independently of the known Th1/Th2 cell signaling pathways. This review focuses on the immunopathogenesis of non-healing American CL and progressive VL. We summarize recent evidence from human and animal studies that reveals the mechanisms of dysregulated, hyper-responses to Leishmania braziliensis, as well as the presence of disease-promoting or the absence of protective responses to Leishmania amazonensis and Leishmania donovani. We highlight immune-mediated parasite growth and immunopathogenesis, with an emphasis on the putative roles of IL-17 and its related cytokines as well as arginase. A better understanding of the quality and regulation of innate immunity and T cell responses triggered by Leishmania will aid in the rational control of pathology and the infection.

Parasite burden in hamsters infected with two different strains of leishmania (Leishmania) infantum: "Leishman Donovan units" versus real-time PCR

To develop and test new therapeutics and immune prophylaxis strategies for visceral leishmaniasis (VL), understanding tissue parasitism evolution after experimental infection with Leishmania infantum is important. Experimental infection in a hamster model (Mesocricetus auratus) reproduces several typical aspects of canine and human VL that are closely related to the inoculum’s route. We quantified the parasitism in the liver and spleen of hamsters experimentally infected by various routes (intradermal, intraperitoneal, and intracardiac [IC]) and different strains of L. infantum (MHOM/BR/74/PP75 and Wild) and compared two different methodologies to evaluate tissue parasitism (Leishman Donovan units [LDU] and real-time qPCR). In addition, the quantification of specific total-IgG in the serum of uninfected and infected hamsters was determined by ELISA. The animals were followed for 1, 3, 6 and 9 months post-infection for survival analysis. We found that infection with the Wild strain by the IC route resulted in higher mortality. Positive antibody (IgG) responses were detected with higher peaks at 6 and 9 months in the IC group inoculated with PP75 strain. However, in animals infected with the Wild strain the IgG levels were elevated in all infected groups during all the time evaluated. We also observed by LDU analysis that the IC route lead to higher parasitism in the liver and spleen with both strains. Furthermore, qPCR showed higher sensitivity for identifying animals with low parasitic burden. In conclusion, qPCR can be useful for assessing parasitism in the spleen and liver of a hamster model infected with L. infantum independent of the route of infection, and this technique may become an essential tool for assessing parasite density in the hamster model after experimental treatment or immunization with potential vaccine candidates.

Conserved and quickly evolving immunome genes have different evolutionary paths

Genetic, transcript, and protein level variations have important functional and evolutionary consequences. We performed systematic data collection and analysis of copy-number variations, single-nucleotide polymorphisms, disease-causing variations, messenger RNA splicing variants, and protein posttranslational modifications for the genes and proteins essential for human immune system. Information about polymorphic and evolutionarily fixed genetic variations was used to group immunome genes to the most conserved and the most quickly changing ones under directed selection during the recent immunome evolution. Gene Ontology terms related to adaptive immunity are associated with gene groups subject to recent directing selection. In addition, several other characteristics of the immunome genes and proteins in these two categories have statistically significant differences. The presented findings question the usability of directed mouse genes as models for human diseases and conditions and shed light on the fine tuning of human immunity and its diverse functions.

Vaccine Development Against Leishmania donovani

Visceral leishmaniasis (VL) caused by Leishmania donovani and Leishmania infantum/chagasi represents the second most challenging infectious disease worldwide, leading to nearly 500,000 new cases and 60,000 deaths annually. Zoonotic VL caused by L. infantum is a re-emergent canid zoonoses which represents a complex epidemiological cycle in the New world where domestic dogs serve as a reservoir host responsible for potentially fatal human infection and where dog culling is the only measure for reservoir control. Life-long immunity to VL has motivated development of prophylactic vaccines against the disease but very few have progressed beyond the experimental stage. No licensed vaccine is available till date against any form of leishmaniasis. High toxicity and increasing resistance to the current chemotherapeutic regimens have further complicated the situation in VL endemic regions of the world. Advances in vaccinology, including recombinant proteins, novel antigen-delivery systems/adjuvants, heterologous prime-boost regimens and strategies for intracellular antigen presentation, have contributed to recent advances in vaccine development against VL. Attempts to develop an effective vaccine for use in domestic dogs in areas of canine VL should be pursued for preventing human infection. Studies in animal models and human patients have revealed the pathogenic mechanisms of disease progression and features of protective immunity. This review will summarize the accumulated knowledge of pathogenesis, immune response, and prerequisites for protective immunity against human VL. Authors will discuss promising vaccine candidates, their developmental status and future prospects in a quest for rational vaccine development against the disease. In addition, several challenges such as safety issues, renewed and coordinated commitment to basic research, preclinical studies and trial design will be addressed to overcome the problems faced in developing prophylactic strategies for protection against this lethal infection.

TLR4 and NKT cell synergy in immunotherapy against visceral leishmaniasis

NKT cells play an important role in autoimmune diseases, tumor surveillance, and infectious diseases, providing in most cases protection against infection. NKT cells are reactive to CD1d presented glycolipid antigens. They can modulate immune responses by promoting the secretion of type 1, type 2, or immune regulatory cytokines. Pathogen-derived signals to dendritic cells mediated via Toll like Receptors (TLR) can be modulated by activated invariant Natural Killer T (iNKT) cells. The terminal β-(1–4)-galactose residues of glycans can modulate host responsiveness in a T helper type-1 direction via IFN-γ and TLRs. We have attempted to develop a defined immunotherapeutic, based on the cooperative action of a TLR ligand and iNKT cell using a mouse model of visceral leishmaniasis. We evaluated the anti-Leishmania immune responses and the protective efficacy of the β-(1–4)-galactose terminal NKT cell ligand glycosphingophospholipid (GSPL) antigen of L. donovani parasites. Our results suggest that TLR4 can function as an upstream sensor for GSPL and provoke intracellular inflammatory signaling necessary for parasite killing. Treatment with GSPL was able to induce a strong effective T cell response that contributed to effective control of acute parasite burden and led to undetectable parasite persistence in the infected animals. These studies for the first time demonstrate the interactions between a TLR ligand and iNKT cell activation in visceral leishmaniasis immunotherapeutic.

Kala azar (visceral leishmaniasis) is a deadly disease caused by the parasitic protozoa Leishmania donovani. In absence of a suitable vaccine, the incidence of leishmaniasis has increased. The World Health Organization observes that, if the disease is not treated, the fatality rate in developing countries can be as high as 100% within 2 years. Therapy of visceral leishmaniasis can be complicated by toxic side effects, drug resistance, and the need for prolonged treatment regimens. Therefore, improved therapy for leishmaniasis remains desirable. Immunotherapy to selectively induce type 1 immune responses considered essential for resistance to leishmaniasis has shown great promise. CD1d-binding glycolipids stimulate TCR signaling and activation of invariant natural killer T (iNKT) cells. Terminal β-(1–4)-galactose residues in glycoconjugates have been identified as the TLR ligand that induces IFN-γ via TLR signaling. We have used the β-(1–4)-galactose terminal glycosphingophospholipid (GSPL) antigen from L. donovani parasites to treat infected BALB/c mice. We report that immunotherapy with GSPL induced IFN-γ, a type 1 cytokine, through the cooperative action of TLR4 and NKT-cells that contributed to effective control of acute parasite burden in the infected animals.

Visceral leishmaniasis treatment: What do we have, what do we need and how to deliver it?

Leishmaniasis is one of the most neglected tropical disease in terms of drug discovery and development. Most antileishmanial drugs are highly toxic, present resistance issues or require hospitalization, being therefore not adequate to the field. Recently improvements have been achieved by combination therapy, reducing the time and cost of treatment. Nonetheless, new drugs are still urgently needed. In this review, we describe the current visceral leishmaniasis (VL) treatments and their limitations. We also discuss the new strategies in the drug discovery field including the development and implementation of high-throughput screening (HTS) assays and the joint efforts of international teams to deliver clinical candidates.

Immunity to visceral leishmaniasis using genetically defined live-attenuated parasites

Leishmaniasis is a protozoan parasitic disease endemic to the tropical and subtropical regions of the world, with three major clinical forms, self-healing cutaneous leishmaniasis (CL), mucocutaneous leishmaniasis (MCL), and visceral leishmaniasis (VL). Drug treatments are expensive and often result in the development of drug resistance. No vaccine is available against leishmaniasis. Subunit Leishmania vaccine immunization in animal models has shown some efficacy but little or none in humans. However, individuals who recover from natural infection are protected from reinfection and develop life-long protection, suggesting that infection may be a prerequisite for immunological memory. Thus, genetically altered live-attenuated parasites with controlled infectivity could achieve such memory. In this paper, we discuss development and characteristics of genetically altered, live-attenuated Leishmania donovani parasites and their possible use as vaccine candidates against VL. In addition, we discuss the challenges and other considerations in the use of live-attenuated parasites.