Interleukin-12 restores interferon-gamma production and cytotoxic responses in visceral leishmaniasis

Efficacy of an Immunotherapy Combining Immunogenic Chimeric Protein Plus Adjuvant and Amphotericin B against Murine Visceral Leishmaniasis

Visceral leishmaniasis (VL) in the Americas is a chronic systemic disease caused by infection with Leishmania infantum parasites. The toxicity of antileishmanial drugs, long treatment course and limited efficacy are significant concerns that hamper adequate treatment against the disease. Studies have shown the promise of an immunotherapeutics approach, combining antileishmanial drugs to reduce the parasitism and vaccine immunogens to activate the host immune system. In the current study, we developed an immunotherapy using a recombinant T cell epitope-based chimeric protein, ChimT, previously shown to be protective against Leishmania infantum, with the adjuvant monophosphoryl lipid A (MPLA) and amphotericin B (AmpB) as the antileishmanial drug. BALB/c mice were infected with L. infantum stationary promastigotes and later they received saline or were treated with AmpB, MPLA, ChimT/Amp, ChimT/MPLA or ChimT/MPLA/AmpB. The combination of ChimT/MPLA/AmpB significantly reduced the parasite load in mouse organs (p < 0.05) and induced a Th1-type immune response, which was characterized by higher ratios of anti-ChimT and anti-parasite IgG2a:IgG1 antibodies, increased IFN-γ mRNA and IFN-γ and IL-12 cytokines and accompanied by lower levels of IL-4 and IL-10 cytokines, when compared to other treatments and controls (all p < 0.05). Organ toxicity was also lower with the ChimT/MPLA/AmpB immunotherapy, suggesting that the inclusion of the vaccine and adjuvant ameliorated the toxicity of AmpB to some degree. In addition, the ChimT vaccine alone stimulated in vitro murine macrophages to significantly kill three different internalized species of Leishmania parasites and to produce Th1-type cytokines into the culture supernatants. To conclude, our data suggest that the combination of ChimT/MPLA/AmpB could be considered for further studies as an immunotherapy for L. infantum infection.

Lymphatic filariasis and visceral leishmaniasis coinfection: A review on their epidemiology, therapeutic, and immune responses

Coinfection is less commonly observed in individuals around the world, yet it is more common than the single infection. Around 800 million people worldwide are infected with helminths as a result of various diseases. Lymphatic filariasis (LF) and visceral leishmaniasis (VL) are chronic, deadly, crippling, and debilitating neglected tropical diseases (NTDs) that are endemic in tropical and subtropical regions of the world. Due to poor hygienic conditions, poverty, and genetic predisposition, those living in endemic areas are more likely to develop both leishmaniasis and filariasis. One of the key challenges in the management of LF/VL coinfection is the development of an effective therapeutic strategy that not only treats the first episode of VL but also prevents LF. However, there is a scarcity of knowledge and data on the relationship between LF and VL coinfection. While reviewing it was apparent that only a few studies relevant to LF/VL coinfections have been reported from southeastern Spain, Sudan, and the Indian subcontinents, highlighting the need for greater research in the most affected areas. We also looked at LF and VL as a single disease and also as a coinfection. Some features of the immune response evolved in mammalian hosts against LF and VL alone or against coinfection are also discussed, including epidemiology, therapeutic regimens, and vaccines. In addition to being potentially useful in clinical research, our findings imply the need for improved diagnostic methodology and therapeutics, which could accelerate the deployment of more specific and effective diagnosis for treatments to lessen the impact of VL/LF coinfections in the population.

Evaluation of systemic immunity in atypical cutaneous leishmaniasis caused by Leishmania (L.) infantum chagasi

In some central-American countries, Leishmania (L.) infantum chagasi infection can cause non-ulcerated or atypical cutaneous leishmaniasis (NUCL) in addition to the classic clinical form, visceral leishmaniasis (VL). Little is known about the host-parasite relationship that can contribute to the determination of one or another clinical form. The present study had the objective to evaluate the humoral and cellular immunity in the sera of individuals affected by NUCL to improve the comprehension of this atypical host-parasite interaction. Based on clinical and laboratory diagnosis, serum of 80 individuals was collected to evaluate the cytokines and immunoglobulins profile of NUCL (n = 47), VL patients (n = 5), and negative controls (n = 28). Cytokines were detected using Cytokine Bead Array (CBA) Human Th1/Th2/Th17 kit according to the manufacturer's instructions; class (IgG and IgM), and subclass of (IgG1 and IgG2) immunoglobulins was evaluated by ELISA using specific antigens. The concentration of TNF-α, IFN-γ, IL-2 and IL-4 cytokines in NUCL, VL and control was present below the detection threshold of CBA kit. IL-6, IL-10 and IL-17A cytokines was lower in NUCL compared to LV patients. Regarding to immunoglobulins, NUCL patients produced 4.0 times more IgG than the control, while VL patients produced 6.6 times more; and IgM level was 1.6 times higher in NUCL and 2.6 times in VL patients compared to the control. Concerning the immunoglobulins subclass, only VL patients showed positive reaction for IgG1, and IgG2 did not show positive reaction among the groups. The results showed a weak cellular and humoral systemic immune response in NUCL patients.

Preclinical validation of a live attenuated dermotropic Leishmania vaccine against vector transmitted fatal visceral leishmaniasis

Visceral Leishmaniasis (VL), a potentially fatal disease is caused by Leishmania donovani parasites with no vaccine available. Here we produced a dermotropic live attenuated centrin gene deleted Leishmania major (LmCen^−/−) vaccine under Good Laboratory Practices and demonstrated that a single intradermal injection confers robust and durable protection against lethal VL transmitted naturally via bites of L. donovani-infected sand flies and prevents mortality. Surprisingly, immunogenicity characteristics of LmCen^−/− parasites revealed activation of common immune pathways like L. major wild type parasites. Spleen cells from LmCen^−/− immunized and L. donovani challenged hamsters produced significantly higher Th1-associated cytokines including IFN-γ, TNF-α, and reduced expression of the anti-inflammatory cytokines like IL-10, IL-21, compared to non-immunized challenged animals. PBMCs, isolated from healthy people from non-endemic region, upon LmCen^−/− infection also induced more IFN-γ compared to IL-10, consistent with our immunogenicity data in LmCen^−/− immunized hamsters. This study demonstrates that the LmCen^−/− parasites are safe and efficacious against VL and is a strong candidate vaccine to be tested in a human clinical trial.

Karmakar et al produced a dermotropic, live attenuated centrin gene-deleted Leishmania major (LmCen^−/−) vaccine against Visceral Leishmaniasis (VL). They demonstrated in hamsters that a single intradermal injection confers robust and durable protection against lethal VL that is transmitted naturally via bites of L. donovani-infected sand flies.

The Role of Sialic Acids in the Establishment of Infections by Pathogens, With Special Focus on Leishmania

Carbohydrates or glycans are ubiquitous components of the cell surface which play crucial biological and structural roles. Sialic acids (Sias) are nine-carbon atoms sugars usually present as terminal residues of glycoproteins and glycolipids on the cell surface or secreted. They have important roles in cellular communication and also in infection and survival of pathogens. More than 20 pathogens can synthesize or capture Sias from their hosts and incorporate them into their own glycoconjugates and derivatives. Sialylation of pathogens’ glycoconjugates may be crucial for survival inside the host for numerous reasons. The role of Sias in protozoa such as Trypanosoma and Leishmania was demonstrated in previous studies. This review highlights the importance of Sias in several pathogenic infections, focusing on Leishmania. We describe in detail the contributions of Sias, Siglecs (sialic acid binding Ig-like lectins) and Neuraminidase 1 (NEU 1) in the course of Leishmania infection. A detailed view on the structural and functional diversity of Leishmania-related Sias and host-cell receptors will be provided, as well as the results of functional studies performed with different Leishmania species.

Potential biomarkers of immune protection in human leishmaniasis

Leishmaniasis is a vector-borne neglected tropical disease endemic in over 100 countries around the world. Available control measures are not always successful, therapeutic options are limited, and there is no vaccine available against human leishmaniasis, although several candidate antigens have been evaluated over the last decades. Plenty of studies have aimed to evaluate the immune response development and a diverse range of host immune factors have been described to be associated with protection or disease progression in leishmaniasis; however, to date, no comprehensive biomarker(s) have been identified as surrogate marker of protection or exacerbation, and lack of enough information remains a barrier for vaccine development. Most of the current understanding of the role of different markers of immune response in leishmaniasis has been collected from experimental animal models. Although the data generated from the animal models are crucial, it might not always be extrapolated to humans. Here, we briefly review the events during Leishmania invasion of host cells and the immune responses induced against Leishmania in animal models and humans and their potential role as a biomarker of protection against human leishmaniasis.

Role of Cytokines in Experimental and Human Visceral Leishmaniasis

Visceral Leishmaniasis (VL) is the most fatal form of disease leishmaniasis. To date, there are no effective prophylactic measures and therapeutics available against VL. Recently, new immunotherapy-based approaches have been established for the management of VL. Cytokines, which are predominantly produced by helper T cells (Th) and macrophages, have received great attention that could be an effective immunotherapeutic approach for the treatment of human VL. Cytokines play a key role in forming the host immune response and in managing the formation of protective and non-protective immunities during infection. Furthermore, immune response mediated through different cytokines varies from different host or animal models. Various cytokines viz. IFN-γ, IL-2, IL-12, and TNF-α play an important role during protection, while some other cytokines viz. IL-10, IL-6, IL-17, TGF-β, and others are associated with disease progression. Therefore, comprehensive knowledge of cytokine response and their interaction with various immune cells is very crucial to determine appropriate immunotherapies for VL. Here, we have discussed the role of cytokines involved in VL disease progression or host protection in different animal models and humans that will determine the clinical outcome of VL and open the path for the development of rapid and accurate diagnostic tools as well as therapeutic interventions against VL.

Case Report: Severe Visceral Leishmaniasis in a Patient with HIV Coinfection Undergoing Treatment for Erythema Nodosum Leprosum

We report a case of visceral leishmaniasis (VL)/HIV coinfection in a patient undergoing regular antiretroviral therapy and treatment with thalidomide for erythema nodosum leprosum. He presented at a health service with high fever, chills, asthenia, pale skin, lower limb edema, hepatomegaly, and splenomegaly. Visceral leishmaniasis was confirmed by direct examination, and serological and molecular tests. Serum levels of Th1/Th2 cytokines were measured. The patient began treatment with liposomal amphotericin B, with good clinical response; however, VL recurred 6 months later. Treatment was reinitiated, maintaining secondary prophylaxis with liposomal amphotericin B. The patient showed clinical improvement with important recovery of CD4⁺ T-lymphocyte count.

A case of visceral leishmaniasis found by left oblique hernia: A case report

Visceral leishmaniasis (VL) is an infectious disease caused by Leishmania protozoa. Since sporadic cases of this disease are noted in non-endemic areas and are associated with a limited outbreak, the disease is easily overlooked. In addition, other illnesses exhibit similar symptoms. It is difficult for clinicians to establish an accurate diagnosis and develop effective treatments for this disease. The present study reported a case of a 25-year-old young man admitted to the hospital due to oblique hernia. The case was diagnosed as VL. The patient presented with persistent night sweats and fatigue as described in his admission history. However, the body temperature was normal. Routine examination revealed that the patient exhibited chronic hepatitis B infection, pancytopenia, hepatosplenomegaly, increased erythrocyte sedimentation rate, significant plasma cell infiltration in bone marrow aspirate and hypergammaglobulinemia. The retrospective analysis of the present case can improve the diagnostic accuracy and treatment rate of VL in non-epidemic areas.

Combined in vitro IL-12 and IL-15 stimulation promotes cellular immune response in dogs with visceral leishmaniasis

Domestic dogs are the main reservoir of Leishmania infantum, a causative agent of visceral leishmaniasis (VL). The number of human disease cases is associated with the rate of canine infection. Currently available drugs are not efficient at treating canine leishmaniasis (CanL) and months after the treatment most dogs show disease relapse, therefore the development of new drugs or new therapeutic strategies should be sought. In CanL, dogs lack the ability to mount a specific cellular immune response suitable for combating the parasite and manipulation of cytokine signaling pathway has the potential to form part of effective immunotherapeutic methods. In this study, recombinant canine cytokines (rcaIL-12, rcaIL-2, rcaIL-15 and rcaIL-7) and soluble receptor IL-10R1 (rcasIL-10R1), with antagonistic activity, were evaluated for the first time in combination (rcaIL-12/rcaIL-2, rcaIL-12/rcaIL-15, rcaIL-12/rcasIL-10R1, rcaIL-15/rcaIL-7) or alone (rcasIL-10R1) to evaluate their immunomodulatory capacity in peripheral blood mononuclear cells (PBMCs) from dogs with leishmaniasis. All the combinations of recombinant proteins tested were shown to improve lymphoproliferative response. Further, the combinations rcaIL-12/rcaIL-2 and rcaIL-12/rcaIL-15 promoted a decrease in programmed cell death protein 1 (PD-1) expression in lymphocytes. These same combinations of cytokines and rcaIL-12/rcasIL-10R1 induced IFN-γ and TNF-α production in PBMCs. Furthermore, the combination IL-12/IL-15 led to an increased in T-bet expression in lymphocytes. These findings are encouraging and indicate the use of rcaIL-12 and rcaIL-15 in future in vivo studies aimed at achieving polarization of cellular immune responses in dogs with leishmaniasis, which may contribute to the development of an effective treatment against CanL.

Dogs are the main reservoir of Leishmania infantum, a protozoan parasite that causes lethal systemic disease in human beings (Visceral Leishmaniasis, VL) and dogs (Canine Leishmaniasis, CanL). In dogs, the disease is often associated with extensive skin lesions. Curbing canine infection could help control human VL. Currently available drugs are not effective in treating CanL, and treated dogs frequently relapse, even when removed from an endemic area. Developing new drugs or alternative therapeutic strategies are essential for the proper treatment of CanL. Dogs that acquire the parasite can develop the disease or control the infection, depending on the body’s immune response. Cellular immune responses lead to infection control and prevent the disease from developing. Some proteins called cytokines, produced mainly by cells of the immune system, can favor the development of cellular immune responses. In this study, several recombinant cytokines and/or one cytokine blocking protein were tested, alone or in combination, for their ability to promote cellular immune response in dogs with leishmaniasis. One of the combinations of recombinant protein tested was the best at facilitating this cellular immune response. The findings reported here are encouraging and indicate the use of a combination of two recombinant cytokines (rcaIL-12/rcaIL-15) in future immunotherapeutic trials for CanL.

Oral treatment with T6-loaded yeast cell wall particles reduces the parasitemia in murine visceral leishmaniasis model

Yeast cell wall particles isolated from Saccharomyces cerevisiae (scYCWPs) have a rich constitution of β-glucan derived from the cell wall. After removing intracellular contents, β-glucan molecules are readily recognized by dectin-1 receptors, present on the cytoplasmic membrane surface of the mononuclear phagocytic cells and internalized. Leishmania spp. are obligate intracellular parasites; macrophages are its primary host cells. An experimental murine model of visceral leishmaniasis caused by L. infantum was used to evaluate the antileishmanial activity of oral administration of these particles. A low-water soluble thiophene previously studied in vitro against L. infantum was entrapped into scYCWPs to direct it into the host cell, in order to circumvent the typical pharmacokinetic problems of water-insoluble compounds. We found that scYCWPs + T6 reduced the parasitic burden in the liver and spleen. There was an increase in IFN-γ levels related to nitric oxide production, explaining the reduction of the L. infantum burden in the tissue. Histological analysis did not show signals of tissue inflammation and biochemical analysis from plasma did not indicate signals of cytotoxicity after scYCWPs + T6 treatment. These findings suggested that scYCWPs + T6 administered through oral route reduced the parasitic burden without causing toxic effects, satisfying requirements for development of new strategies to treat leishmaniasis.

Protective or Detrimental? Understanding the Role of Host Immunity in Leishmaniasis

The intracellular protozoan parasites of the genus Leishmania are the causative agents of leishmaniasis, a vector-borne disease of major public health concern, estimated to affect 12 million people worldwide. The clinical manifestations of leishmaniasis are highly variable and can range from self-healing localized cutaneous lesions to life-threatening disseminated visceral disease. Once introduced into the skin by infected sandflies, Leishmania parasites interact with a variety of immune cells, such as neutrophils, monocytes, dendritic cells (DCs), and macrophages. The resolution of infection requires a finely tuned interplay between innate and adaptive immune cells, culminating with the activation of microbicidal functions and parasite clearance within host cells. However, several factors derived from the host, insect vector, and Leishmania spp., including the presence of a double-stranded RNA virus (LRV), can modulate the host immunity and influence the disease outcome. In this review, we discuss the immune mechanisms underlying the main forms of leishmaniasis, some of the factors involved with the establishment of infection and disease severity, and potential approaches for vaccine and drug development focused on host immunity.

Cytokines: Key Determinants of Resistance or Disease Progression in Visceral Leishmaniasis: Opportunities for Novel Diagnostics and Immunotherapy

Leishmaniasis is a parasitic disease of humans, highly prevalent in parts of the tropics, subtropics, and southern Europe. The disease mainly occurs in three different clinical forms namely cutaneous, mucocutaneous, and visceral leishmaniasis (VL). The VL affects several internal organs and is the deadliest form of the disease. Epidemiology and clinical manifestations of VL are variable based on the vector, parasite (e.g., species, strains, and antigen diversity), host (e.g., genetic background, nutrition, diversity in antigen presentation and immunity) and the environment (e.g., temperature, humidity, and hygiene). Chemotherapy of VL is limited to a few drugs which is expensive and associated with profound toxicity, and could become ineffective due to the parasites developing resistance. Till date, there are no licensed vaccines for humans against leishmaniasis. Recently, immunotherapy has become an attractive strategy as it is cost-effective, causes limited side-effects and do not suffer from the downside of pathogens developing resistance. Among various immunotherapeutic approaches, cytokines (produced by helper T-lymphocytes) based immunotherapy has received great attention especially for drug refractive cases of human VL. Therefore, a comprehensive knowledge on the molecular interactions of immune cells or components and on cytokines interplay in the host defense or pathogenesis is important to determine appropriate immunotherapies for leishmaniasis. Here, we summarized the current understanding of a wide-spectrum of cytokines and their interaction with immune cells that determine the clinical outcome of leishmaniasis. We have also highlighted opportunities for the development of novel diagnostics and intervention therapies for VL.

Modulation of the immune response and infection pattern to Leishmania donovani in visceral leishmaniasis due to arsenic exposure: An in vitro study

The arsenic contamination of ground water in visceral leishmaniasis (VL) endemic areas in Bihar, India leads to human exposure through drinking water. Possibly, the consumed arsenic (As) accumulates in the tissues of VL patients, who subsequently internalize intracellular amastigotes to confer resistance against chemotherapy to the parasite, leading to modulation in the host’s immune response. This hypothesis appears to be consistent with the in vitro findings that in arsenic-exposed parasites, the mitochondrial membrane potential became depolarized, whereas the reduced thiol and lactate production was overexpressed with enhanced glucose consumption; therefore, the reduced thiol possibly supports an immunosuppressive state in the host cells. This observation was well supported by the down-regulated expression of pro-inflammatory cytokines (IL-2, IL-12, IFN-γ, and TNF-α) with a suppressed anti-leishmanial function of macrophage (NO, ROS). In contrast, the pathophysiological mechanism of VL has received ample support by the promotion of Th2 cytokines (IL-4 and IL-10) in the presence of arsenic-exposed Leishmania parasites (Ld^AS). Dysfunction of mitochondria and the overexpression of lactate production raise the possibility of the Warburg effect being operative through the up-regulation of glucose consumption by parasites to enhance the energy production, possibly augmenting virulence. Therefore, we surmise from our data that arsenic exposure to Leishmania donovani modulates the immune response and infection pattern by impairing parasite function, which may affect the anti-leishmanial effect in VL.

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.

Leptin regulates Granzyme-A, PD-1 and CTLA-4 expression in T cell to control visceral leishmaniasis in BALB/c Mice

Visceral leishmaniasis (VL) is responsible for several deaths in malnourished children accompanied by diminished circulating leptin and impaired cell-mediated immunity. Typically, leptin deficiency is associated with the Th2 polarization that markedly coincides with the pathogenesis of VL. The aim of the present study was to unravel the prophylactic role of leptin in malnutrition-coupled VL mice. Interestingly, we observed that L. donovani infection itself reduces the serum leptin levels in malnutrition. Exogenous leptin restored severe body weight loss and parasite load in the spleen and liver of malnourished infected mice compared to controls. Leptin increases functional CD8+ T-cell population, Granzyme-A expression down-regulates anergic T-cell markers such as PD-1 and CTLA-4. It was also noticed that, leptin suppresses GM-CSF mRNA expression in parasite favored monocytes and reduced arginase activity in bone marrow derived macrophage indicate macrophages dependent T-cell activation and proliferation. Leptin-induced IFN-γ, IL-2, and TNF-α cytokines in the culture supernatant of splenocytes upon soluble leishmanial antigen (SLA) stimulation and significantly up-regulates serum IgG2a titers, which help to generate Th1 immune response in VL. Furthermore, leptin induced a granulomatous response and restored L. donovani induced tissue degeneration in the liver. Altogether, our findings suggest the exogenous leptin can restore T cell mediated immunity in malnourished VL mice.

Causes and consequences of higher Leishmania infantum burden in patients with kala-azar: a study of 625 patients

BACKGROUND

An infected host's Leishmania infantum load in blood is considered to be an estimate of his or her total parasite burden. Therefore, the measurement of blood parasite burden is important in the identification of factors involved in parasite control.

METHODS

Quantitative polymerase chain reaction was performed on blood samples from 625 patients with kala-azar consecutively admitted to a reference hospital in Teresina, Brazil. Primers were used to amplify a segment of kDNA using the TaqMan system. Non-parametric statistical tests were applied.

RESULTS

The median blood parasite burden was 499.2 amastigote equivalents (AE)/ml. Children <1 year old (yo) had a high parasite burden, which dropped sharply after the first year of life (192.8, AE/ml at 1 < 2 yo) and remained lower until adolescence. Following adolescence, the parasite burden increased with age, peaking among elderly individuals. Men had a higher parasite burden than women. HIV-infected patients had a much higher parasite burden than non-infected patients. The parasite burden of children under 5 years with acute moderate to severe malnourishment (weight-for-age and body mass index z-scores <-2) was almost three times greater than that of better-nourished children. The parasite burden identified in deceased patients was more than twice that of surviving patients; those with a higher risk of death, sepsis, pneumonia and jaundice also had increased parasite burdens. All of these differences were statistically significant at P-values <0.05.

CONCLUSIONS

These data indicate that the parasite burden in patients with kala-azar was associated with age- and gender-associated factors and with HIV infection status. Acute malnutrition could be either a cause or a consequence of a higher parasite burden. An individual's parasite burden influences his or her clinical profile, disease severity and mortality risk. The best explanation for the presence of a higher parasite burden in individuals with these immunoregulatory conditions and severe disease is the occurrence of acquired immunosuppression followed by heightened innate immunity.

Transcriptional Profiling in Experimental Visceral Leishmaniasis Reveals a Broad Splenic Inflammatory Environment that Conditions Macrophages toward a Disease-Promoting Phenotype

Visceral Leishmaniasis (VL), caused by the intracellular protozoan Leishmania donovani, is characterized by relentlessly increasing visceral parasite replication, cachexia, massive splenomegaly, pancytopenia and ultimately death. Progressive disease is considered to be due to impaired effector T cell function and/or failure of macrophages to be activated to kill the intracellular parasite. In previous studies, we used the Syrian hamster (Mesocricetus auratus) as a model because it mimics the progressive nature of active human VL. We demonstrated previously that mixed expression of macrophage-activating (IFN-γ) and regulatory (IL-4, IL-10, IL-21) cytokines, parasite-induced expression of macrophage arginase 1 (Arg1), and decreased production of nitric oxide are key immunopathologic factors. Here we examined global changes in gene expression to define the splenic environment and phenotype of splenic macrophages during progressive VL. We used RNA sequencing coupled with de novo transcriptome assembly, because the Syrian hamster does not have a fully sequenced and annotated reference genome. Differentially expressed transcripts identified a highly inflammatory spleen environment with abundant expression of type I and type II interferon response genes. However, high IFN-γ expression was ineffective in directing exclusive M1 macrophage polarization, suppressing M2-associated gene expression, and restraining parasite replication and disease. While many IFN-inducible transcripts were upregulated in the infected spleen, fewer were induced in splenic macrophages in VL. Paradoxically, IFN-γ enhanced parasite growth and induced the counter-regulatory molecules Arg1, Ido1 and Irg1 in splenic macrophages. This was mediated, at least in part, through IFN-γ-induced activation of STAT3 and expression of IL-10, which suggests that splenic macrophages in VL are conditioned to respond to macrophage activation signals with a counter-regulatory response that is ineffective and even disease-promoting. Accordingly, inhibition of STAT3 activation led to a reduced parasite load in infected macrophages. Thus, the STAT3 pathway offers a rational target for adjunctive host-directed therapy to interrupt the pathogenesis of VL.

Visceral leishmaniasis (VL) is a neglected parasitic disease that is caused by the intracellular protozoan Leishmania donovani. Patients with this disease suffer from muscle wasting, enlargement of the spleen, reduced blood counts and ultimately will die without treatment. Progressive disease is considered to be due to impaired cellular immunity, with T cell or macrophage dysfunction, or both. We studied the Syrian hamster as an infection model because it mimics the progressive nature of human disease. We examined global changes in gene expression in the spleen and splenic macrophages during experimental VL and identified a highly inflammatory spleen environment with abundant expression of interferon and interferon-response genes that would be expected to control the infection. However, the high level of IFN-γ expression was ineffective in mediating a protective macrophage response, restraining parasite replication and halting progression of disease. We found that IFN-γ itself stimulated parasite growth in splenic macrophages and induced expression of counter-regulatory molecules, which may paradoxically make the host more susceptible. These data give insights into the nature of the immune response that promotes the infection, and identifies potential targets for therapeutic intervention.

Genome-Wide Association Study of Cell-Mediated Response in Dogs Naturally Infected by Leishmania infantum

A genome-wide association study (GWAS) could unravel the complexity of the cell-mediated immunity (CMI) to canine leishmaniasis (CanL). Therefore, we scanned 110,165 single-nucleotide polymorphisms (SNPs), aiming to identify chromosomal regions associated with the leishmanin skin test (LST), lymphocyte proliferation assay (LPA), and cytokine responses to further understand the role played by CMI in the outcome of natural Leishmania infantum infection in 189 dogs. Based on LST and LPA, four CMI profiles were identified (LST^-/LPA^-, LST⁺/LPA^-, LST^-/LPA⁺, and LST⁺/LPA⁺), which were not associated with subclinically infected or diseased dogs. LST⁺/LPA⁺ dogs showed increased interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) levels and mild parasitism in the lymph nodes, whereas LST^-/LPA⁺ dogs, in spite of increased IFN-γ, also showed increased interleukin-10 (IL-10) and transforming growth factor β (TGF-β) levels and the highest parasite load in lymph nodes. Low T cell proliferation under low parasite load suggested that L. infantum was not able to induce effective CMI in the early stage of infection. Altogether, genetic markers explained 87%, 16%, 15%, 11%, 0%, and 0% of phenotypic variance in TNF-α, TGF-β, LST, IL-10, IFN-γ, and LPA, respectively. GWAS showed that regions associated with TNF-α include the following genes: IL12RB1, JAK3, CCRL2, CCR2, CCR3, and CXCR6, involved in cytokine and chemokine signaling; regions associated with LST, including COMMD5 and SHARPIN, involved in regulation of NF-κB signaling; and regions associated with IL-10, including LTBP1 and RASGRP3, involved in T regulatory lymphocytes differentiation. These findings pinpoint chromosomic regions related to the cell-mediated response that potentially affect the clinical complexity and the parasite replication in canine L. infantum infection.

Immunoprotective responses of T helper type 1 stimulatory protein-S-adenosyl-L-homocysteine hydrolase against experimental visceral leishmaniasis

It is well known that a patient in clinical remission of visceral leishmaniasis (VL) remains immune to reinfection, which provides a rationale for the feasibility of a vaccine against this deadly disease. In earlier studies, observation of significant cellular responses in treated Leishmania patients as well as in hamsters against leishmanial antigens from different fractions led to its further proteomic characterization, wherein S-adenosyl-L-homocysteine hydrolase (AdoHcy) was identified as a helper type 1 (Th1) stimulatory protein. The present study includes immunological characterization of this protein, its cellular responses [lymphoproliferation, nitric oxide (NO) production and cytokine responses] in treated Leishmania-infected hamsters and patients as well as prophylactic efficacy against Leishmania challenge in hamsters and the immune responses generated thereof. Significantly higher cellular responses were noticed against recombinant L. donovani S-adenosyl-L-homocysteine hydrolase (rLdAdoHcy) compared to soluble L. donovani antigen in treated samples. Moreover, stimulation of peripheral blood mononuclear cells with rLdAdoHcy up-regulated the levels of interferon (IFN)-γ, interleukin (IL)-12 and down-regulated IL-10. Furthermore, vaccination with rLdAdoHcy generated perceptible delayed-type hypersensitivity response and exerted considerably good prophylactic efficacy (∼70% inhibition) against L. donovani challenge. The efficacy was confirmed by the increased expression levels of inducible NO synthase and Th1-type cytokines, IFN-γ and IL-12 and down-regulation of IL-4, IL-10 and transforming growth factor (TGF)-β. The results indicate the potentiality of rLdAdoHcy protein as a suitable vaccine candidate against VL.

Visceral leishmaniasis: Revisiting current treatments and approaches for future discoveries

The current treatments for visceral leishmaniasis are old and toxic with limited routes of administration. The emergence of drug-resistant Leishmania threatens the efficacy of the existing reservoir of antileishmanials, leading to an urgent need to develop new treatments. It is particularly important to review and understand how the current treatments act against Leishmania in order to identify valid drug targets or essential pathways for next-generation antileishmanials. It is equally important to adapt newly emerging biotechnologies to facilitate the current research on the development of novel antileishmanials in an efficient fashion. This review covers the basic background of the current visceral leishmaniasis treatments with an emphasis on the modes of action. It briefly discusses the role of the immune system in aiding the chemotherapy of leishmaniasis, describes potential new antileishmanial drug targets and pathways, and introduces recent progress on the utilization of high-throughput phenotypic screening assays to identify novel antileishmanial compounds.

The Severity of Visceral Leishmaniasis Correlates with Elevated Levels of Serum IL-6, IL-27 and sCD14

BACKGROUND

Visceral leishmaniasis (VL) is a severe disease caused by infection with protozoa of the genus Leishmania. Classic VL is characterized by a systemic infection of phagocytic cells and an intense activation of the inflammatory response. It is unclear why 90% of infected individuals do not develop the disease while a minority develop the classical form. Furthermore, among those that develop disease, a small group progresses to more severe form that is unresponsive to treatment. The presence of inflammatory mediators in serum could theoretically help to control the infection. However, there is also a release of anti-inflammatory mediators that could interfere with the control of parasite multiplication. In this study, we took advantage of the spectrum of outcomes to test the hypothesis that the immune profile of individuals infected with Leishmania (L.) infantum is associated with the development and severity of disease.

METHODOLOGY/PRINCIPAL FINDINGS

Sera from patients with confirmed diagnosis of VL were evaluated for the presence of numerous molecules, and levels compared with healthy control and asymptomatic infected individuals.

CONCLUSIONS/PRINCIPAL FINDINGS

Although differences were not observed in LPS levels, higher levels of sCD14 were detected in VL patients. Our data suggest that L. infantum may activate the inflammatory response via CD14, stimulating a generalized inflammatory response with production of several cytokines and soluble molecules, including IFN-γ, IL-27, IL-10, IL-6 and sCD14. These molecules were strongly associated with hepatosplenomegaly, neutropenia and thrombocytopenia. We also observed that IL-6 levels greater than 200 pg/ml were strongly associated with death. Together our data reinforce the close relationship of IFN-γ, IL-10, IL-6, TNF-α and IL-27 in the immune dynamics of VL and suggest the direct participation of sCD14 in the activation of the immune response against L. infantum.

Cross reactive molecules of human lymphatic filaria Brugia malayi inhibit Leishmania donovani infection in hamsters

Coinfections are common in natural populations and the outcome of their interactions depends on the immune responses of the host elicited by the parasites. Earlier we showed that immunization with BmAFII (Sephadex G-200 eluted) fraction of human lymphatic filaria Brugia malayi inhibited progression of Leishmania donovani infection in golden hamsters. In the present study we identified cross reactive molecules of B. malayi, and investigated their effect on L. donovani infection and associated immune responses in the host. The sequence alignment and sharing of linear T- and B-cell epitopes in protein molecules of B. malayi and L. donovani counterparts were studied in silico. Hamsters were immunized with robustly cross reactive SDS-PAGE resolved fractions F6 (54.2-67.8kDa) and F9 (41.3-45.0kDa) of B. malayi and subsequently inoculated with amastigotes of L. donovani intracardially. F6 inhibited (∼72%) L. donovani infection and upregulated Th1 cytokine expression, lymphoproliferation, IgG2, IgG2/3 levels and NO production, and downregulated Th2 cytokine expression. Sequences in HSP60 and EF-2 of F6 and L. donovani counterparts were conserved and B- and T-cell epitopes in the proteins shared antigenic regions. In conclusion, leishmania-cross reactive molecules of filarial parasite considerably inhibited leishmanial infection via Th1-mediated immune responses and NO production. Common B- and T-cell epitope regions in HSP60 and EF-2 of the parasites might have contributed to the inhibitory effect on the L. donovani infection. Thus, leishmania-cross reactive filarial parasite molecules may help in designing prophylactic(s) against L. donovani.

Soluble CD40 Ligand in Sera of Subjects Exposed to Leishmania infantum Infection Reduces the Parasite Load in Macrophages

BACKGROUND

While CD40L is typically a membrane glycoprotein expressed on activated T cells and platelets that binds and activates CD40 on the surface on antigen presenting cells, a soluble derivative (sCD40L) that appears to retain its biological activity after cleavage from cell membrane also exists. We recently reported that sCD40L is associated with clinical resolution of visceral leishmaniasis and protection against the disease. In the present study we investigated if this sCD40L is functional and exerts anti-parasitic effect in L. infantum-infected macrophages.

METHODOLOGY/PRINCIPAL FINDINGS

Macrophages from normal human donors were infected with L. infantum promastigotes and incubated with either sera from subjects exposed to L. infantum infection, monoclonal antibodies against human CD40L, or an isotype control antibody. We then evaluated infection by counting the number of infected cells and the number of parasites in each cell. We also measured a variety of immune modulatory cytokines in these macrophage culture supernatants by Luminex assay. The addition of sCD40L, either recombinant or from infected individuals' serum, decreased both the number of infected macrophages and number of intracellular parasites. Moreover, this treatment increased the production of IL-12, IL-23, IL-27, IL-15, and IL1β such that negative correlations between the levels of these cytokines with both the infection ratio and number of intracellular parasites were observed.

CONCLUSIONS/SIGNIFICANCE

sCD40L from sera of subjects exposed to L. infantum is functional and improves both the control of parasite and production of inflamatory cytokines of infected macrophages. Although the mechanisms involved in parasite killing are still unclear and require further exploration, these findings indicate a protective role of sCD40L in visceral leishmaniasis.

Impact of visceral leishmaniasis and curative chemotherapy on cytochrome P450 activity in Brazilian patients

AIMS

The aim of the present study was to investigate the impact of human visceral leishmaniasis (VL) and curative chemotherapy on the activity of cytochrome P450 (CYP) 3A, CYP2C9 and CYP2C19 in patients from an endemic region in Brazil.

METHODS

Adult patients with parasitologically confirmed VL were given a CYP phenotyping cocktail, comprising midazolam, omeprazole and losartan, immediately before (Study phase 1), 2-3 days (phase 2) and 3-6 months (phase 3) after curative VL chemotherapy. CYP activity was assessed by the apparent clearance of midazolam (CYP3A), omeprazole/5-hydroxyomeprazol ratio in plasma (CYP2C19) and losartan/E3174 ratio in urine (CYP2C9).

RESULTS

Mean values (95% confidence interval) in phases 1, 2 and 3 were, respectively: log apparent midazolam clearance, 1.21 (1.10-1.31), 1.45 (1.32-1.57) and 1.35 (1.26-1.44) ml min(-1)  kg(-1) ; omeprazole/5-hydroxyomeprazole ratio, 0.78 (0.61-0.94), 0.45 (0.27-0.63) and 0.37 (0.20-0.55); losartan/E3174 ratio, 0.66 (0.39-0.92), 0.35 (0.20-0.50) and 0.35 (0.16-0.53). Analysis of variance revealed significant differences in CYP3A (P = 0.018) and CYP2C19 (P = 0.008), but not CYP2C9 (P = 0.11) phenotypic activity, across the three study phases.

CONCLUSION

The phenotypic activities of CYP3A4 and CYP2C19 were significantly reduced during acute VL compared with post-chemotherapy. We propose that increased plasma concentrations of proinflammatory cytokines during active disease account for the suppression of CYP activity. The failure to detect significant changes in CYP2C9 activity in the overall cohort may reflect differential effects of the inflammatory process on the expression of CYP isoforms, although the possibility of insufficient statistical power cannot be dismissed.

Genetically Engineered Ascorbic acid-deficient Live Mutants of Leishmania donovani induce long lasting Protective Immunity against Visceral Leishmaniasis

Visceral leishmaniasis caused by Leishmania donovani is the most severe systemic form of the disease. There are still no vaccines available for humans and there are limitations associated with the current therapeutic regimens for leishmaniasis. Recently, we reported functional importance of Arabino-1, 4-lactone oxidase (ALO) enzyme from L. donovani involved in ascorbate biosynthesis pathway. In this study, we have shown that ΔALO parasites do not affect the ability of null mutants to invade visceral organs but severely impair parasite persistence beyond 16 week in BALB/c mice and hence are safe as an immunogen. Both short term (5 week) and long term (20 week) immunization with ΔALO parasites conferred sustained protection against virulent challenge in BALB/c mice, activated splenocytes and resulted in induction of pro-inflammatory cytokine response. Protection in immunized mice after challenge correlated with the stimulation of IFN-γ producing CD4⁺ and CD8⁺ T cells. Antigen-mediated cell immunity correlated with robust nitrite and superoxide generation, macrophage-derived oxidants critical in controlling Leishmania infection. Our data shows that live attenuated ΔALO parasites are safe, induce protective immunity and can provide sustained protection against Leishmania donovani. We further conclude that the parasites attenuated in their anti-oxidative defence mechanism can be exploited as vaccine candidates.

The involvement of TLR2 and TLR4 in cytokine and nitric oxide production in visceral leishmaniasis patients before and after treatment with anti-leishmanial drugs

Toll-like receptors (TLRs) have significant involvement in Leishmania infection, although little is known about the relationship between these receptors, cytokines and nitric oxide (NO) in patients with visceral leishmaniasis (VL) before or after treatment with anti-leishmanial drugs. The goal of this study was to evaluate the expression of TLR2 and TLR4 in CD3+ and CD14+ cells and the production of TNF-α, IFN-γ, IL-17, IL-10, TGF-β and NO in peripheral blood mononuclear cells (PBMCs) from VL patients pre- and post-treatment with anti-leishmanial drugs. In addition, we investigated whether these receptors were involved in the production of these cytokines and NO. In the active VL patients, increased TLR2 and TLR4 expression in lymphocytes and monocytes, increased production of TNF-α, IL-10 and TGF-β and decreased production of IFN-γ, IL-17 and NO were observed. After treatment, TLR2 and TLR4 were still expressed in lymphocytes and monocytes, the TNF-α and IL-10 levels were lower, the production of IFN-γ, IL-17 and NO was higher, and the TGF-β level remained high. Before treatment, the production of TNF-α and NO was associated with TLR2 and TLR4 expression, while IL-10 production was only associated with TLR2 expression. After treatment, both receptors were associated with the production of TNF-α, IFN-γ, IL-10 and NO, while the production of IL-17 was associated only with TLR4 expression. The results presented in this study suggest that both TLR2 and TLR4 participate in the modulation of cytokine and NO production in VL patients, contributing to the pathogenesis of VL prior to treatment and the protective immune response after treatment.

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.

Imipramine exploits histone deacetylase 11 to increase the IL-12/IL-10 ratio in macrophages infected with antimony-resistant Leishmania donovani and clears organ parasites in experimental infection

The efflux of antimony through multidrug resistance protein (MDR)-1 is the key factor in the failure of metalloid treatment in kala-azar patients infected with antimony-resistant Leishmania donovani (Sb(R)LD). Previously we showed that MDR-1 upregulation in Sb(R)LD infection is IL-10-dependent. Imipramine, a drug in use for the treatment of depression and nocturnal enuresis in children, inhibits IL-10 production from Sb(R)LD-infected macrophages (Sb(R)LD-Mϕs) and favors accumulation of surrogates of antimonials. It inhibits IL-10-driven nuclear translocation of c-Fos/c-Jun, critical for enhanced MDR-1 expression. The drug upregulates histone deacetylase 11, which inhibits acetylation of IL-10 promoter, leading to a decrease in IL-10 production from Sb(R)LD-Mϕs. It abrogates Sb(R)LD-mediated p50/c-Rel binding to IL-10 promoter and preferentially recruits p65/RelB to IL-12 p35 and p40 promoters, causing a decrease in IL-10 and overproduction of IL-12 in Sb(R)LD-Mϕs. Histone deacetylase 11 per se does not influence IL-12 promoter activity. Instead, a imipramine-mediated decreased IL-10 level allows optimal IL-12 production in Sb(R)LD-Mϕs. Furthermore, exogenous rIL-12 inhibits intracellular Sb(R)LD replication, which can be mimicked by the presence of Ab to IL-10. This observation indicated that reciprocity exists between IL-10 and IL-12 and that imipramine tips the balance toward an increased IL-12/IL-10 ratio in Sb(R)LD-Mϕs. Oral treatment of infected BALB/c mice with imipramine in combination with sodium stibogluconate cleared organ Sb(R)LD parasites and caused an expansion of the antileishmanial T cell repertoire where sodium stibogluconate alone had no effect. Our study deciphers a detailed molecular mechanism of imipramine-mediated regulation of IL-10/IL-12 reciprocity and its impact on Sb(R)LD clearance from infected hosts.

Immunotherapy and targeted therapies in treatment of visceral leishmaniasis: current status and future prospects

Visceral leishmaniasis (VL) is a vector-borne chronic infectious disease caused by the protozoan parasite Leishmania donovani or Leishmania infantum. VL is a serious public health problem, causing high morbidity and mortality in the developing world with an estimated 0.2-0.4 million new cases each year. In the absence of a vaccine, chemotherapy remains the favored option for disease control, but is limited by a narrow therapeutic index, significant toxicities, and frequently acquired resistance. Improved understanding of VL pathogenesis offers the development and deployment of immune based treatment options either alone or in combination with chemotherapy. Modulations of host immune response include the inhibition of molecular pathways that are crucial for parasite growth and maintenance; and stimulation of host effectors immune responses that restore the impaired effector functions. In this review, we highlight the challenges in treatment of VL with a particular emphasis on immunotherapy and targeted therapies to improve clinical outcomes.

Immunotherapy and Immunochemotherapy in Visceral Leishmaniasis: Promising Treatments for this Neglected Disease

Leishmaniasis has several clinical forms: self-healing or chronic cutaneous leishmaniasis or post-kala-azar dermal leishmaniasis; mucosal leishmaniasis; visceral leishmaniasis (VL), which is fatal if left untreated. The epidemiology and clinical features of VL vary greatly due to the interaction of multiple factors including parasite strains, vectors, host genetics, and the environment. Human immunodeficiency virus infection augments the severity of VL increasing the risk of developing active disease by 100–2320 times. An effective vaccine for humans is not yet available. Resistance to chemotherapy is a growing problem in many regions, and the costs associated with drug identification and development, make commercial production for leishmaniasis, unattractive. The toxicity of currently drugs, their long treatment course, and limited efficacy are significant concerns. For cutaneous disease, many studies have shown promising results with immunotherapy/immunochemotherapy, aimed to modulate and activate the immune response to obtain a therapeutic cure. Nowadays, the focus of many groups centers on treating canine VL by using vaccines and immunomodulators with or without chemotherapy. In human disease, the use of cytokines like interferon-γ associated with pentavalent antimonials demonstrated promising results in patients that did not respond to conventional treatment. In mice, immunomodulation based on monoclonal antibodies to remove endogenous immunosuppressive cytokines (interleukin-10) or block their receptors, antigen-pulsed syngeneic dendritic cells, or biological products like Pam3Cys (TLR ligand) has already been shown as a prospective treatment of the disease. This review addresses VL treatment, particularly immunotherapy and/or immunochemotherapy as an alternative to conventional drug treatment in experimental models, canine VL, and human disease.

Cytokine profiles amongst Sudanese patients with visceral leishmaniasis and malaria co-infections

BACKGROUND

The immune system plays a critical role in the development of co-infections, promoting or preventing establishment of multiple infections and shaping the outcome of pathogen-host interactions. Its ability to mediate the interplay between visceral leishmaniasis (VL) and malaria has been suggested, but poorly documented. The present study investigated whether concomitant infection with Leishmania donovani complex and Plasmodium falciparum in naturally co-infected patients altered the immunological response elicited by the two pathogens individually.

RESULTS

Circulating levels of interferon (IFN)-γ, interleukin (IL)-2, IL-4, IL-6, IL-10, IL-12p70, IL-13, IL-17A and tumor necrosis factor (TNF) were assessed in sera of patients infected with active VL and/or malaria and healthy individuals from Gedarif State, Sudan. Comparative analysis of cytokine profiles from co- and mono-infected patients highlighted significant differences in the immune response mounted upon co-infection, confirming the ability of L. donovani and P. falciparum to mutually interact at the immunological level. Progressive polarization towards type-1 and pro-inflammatory cytokine patterns characterized the co-infected patients, whose response partly reflected the effect elicited by VL (IFN-γ, TNF) and malaria (IL-2, IL-13), and partly resulted from a synergistic interaction of the two diseases upon each other (IL-17A). Significantly reduced levels of P. falciparum parasitaemia (P <0.01) were detected in the co-infected group as opposed to the malaria-only patients, suggesting either a protective or a non-detrimental effect of the co-infection against P. falciparum infection.

CONCLUSIONS

These findings suggest that a new immunological scenario may occur when L. donovani and P. falciparum co-infect the same patient, with potential implications on the course and resolution of these diseases.

Whole blood assay and visceral leishmaniasis: Challenges and promises

For years, the ability to study immune responses in patients with active visceral leishmaniasis (VL) has been hampered by the absence of detectable antigen-specific Th1 responses using cells from peripheral blood mononuclear cells (PBMCs). Employing whole blood assay (WBA), we recently reported that whole blood cells of active VL patients maintain the capacity to secrete significant levels of antigen driven IFN-γ and IL-10. Furthermore, WBA that uses soluble leishmania antigen (SLA) have advantages over the leishmanin skin test (LST), in terms of higher specificity and better correlation with surrogate markers of exposures to Leishmania donovani. These findings open the door to a series of immunological and epidemiological studies not previously possible for VL. In the present review, we discuss current status, future perspectives as well as obstacles in the research on WBA. Research in this area is essential for development of potential immunological and epidemiological tools for VL.

Characterization of glycolytic enzymes--rAldolase and rEnolase of Leishmania donovani, identified as Th1 stimulatory proteins, for their immunogenicity and immunoprophylactic efficacies against experimental visceral leishmaniasis

Th1 immune responses play an important role in controlling Visceral Leishmaniasis (VL) hence, Leishmania proteins stimulating T-cell responses in host, are thought to be good vaccine targets. Search of such antigens eliciting cellular responses in Peripheral blood mononuclear cells (PBMCs) from cured/exposed/Leishmania patients and hamsters led to the identification of two enzymes of glycolytic pathway in the soluble lysate of a clinical isolate of Leishmania donovani--Enolase (LdEno) and aldolase (LdAld) as potential Th1 stimulatory proteins. The present study deals with the molecular and immunological characterizations of LdEno and LdAld. The successfully cloned and purified recombinant proteins displayed strong ability to proliferate lymphocytes of cured hamsters' along with significant nitric-oxide production and generation of Th1-type cytokines (IFN-γ and IL-12) from stimulated PBMCs of cured/endemic VL patients. Assessment of their prophylactic potentials revealed ∼ 90% decrease in parasitic burden in rLdEno vaccinated hamsters against Leishmania challenge, strongly supported by an increase in mRNA expression levels of iNOS, IFN-γ, TNF-α and IL-12 transcripts along with extreme down-regulation of TGF-β, IL-4 and IL-10. However, animals vaccinated with rLdAld showed comparatively lesser prophylactic efficacy (∼ 65%) with inferior immunological response. Further, with a possible implication in vaccine design against VL, identification of potential T-cell epitopes of both the proteins was done using computational approach. Additionally, in-silico 3-D modelling of the proteins was done in order to explore the possibility of exploiting them as potential drug targets. The comparative molecular and immunological characterizations strongly suggest rLdEno as potential vaccine candidate against VL and supports the notion of its being effective T-cell stimulatory protein.

Alteration of the serum biomarker profiles of visceral leishmaniasis during treatment

Until recently, chemotherapy for visceral leishmaniasis (VL; also known as kala-azar) was severely limited by factors such as high cost, route of administration, generation of side effects and potential for resistance. Although largely effective, chemotherapies have become available with the introduction of new drugs and multi-drug regimens for VL. These could be further improved by the identification of biomarkers that are altered during effective treatment. The identification of such biomarkers in the circulation would also simplify efficacy trials. In this study, we determined immunological signatures within the serum of ethnically and geographically distinct VL patients (from Bangladesh and Brazil). Our results indicate that inflammatory and regulatory cytokines (IFNγ, TNFα, IL-10, IL-17), as well as levels of growth factors (FGF, VEGF), are elevated within the serum of VL patients from these sites. The examination of samples from Brazilian VL patients during and beyond standard treatment with meglumine antimoniate identified multiple parameters that revert to levels comparable to those of healthy endemic control individuals. The consolidation of these results provides a 'response to treatment' signature that could be used within efficacy trials to rapidly and simply determine successful interruption of VL.

The IL-33/ST2 axis is associated with human visceral leishmaniasis and suppresses Th1 responses in the livers of BALB/c mice infected with Leishmania donovani

During visceral leishmaniasis, the control of hepatic parasite burden is mainly due to granuloma assembly in a microenvironment consisting of both Th1 and Th2 components. Using enzyme-linked immunosorbent assay (ELISA) dosages, quantitative PCR (qPCR), immunohistochemistry, and flow cytometry, we studied the role of interleukin-33 (IL-33), a recently described cytokine signaling through the ST2 receptor, during visceral leishmaniasis. We showed that a higher level of IL-33 was detected in the serum of patients with visceral leishmaniasis than in that from healthy donors and demonstrated the presence of IL-33(+) cells in a liver biopsy specimen from a patient. Similarly, in BALB/c mice experimentally infected with L. donovani, a higher level of IL-33 was detected in the serum, as well as the presence of IL-33(+) cells and ST2(+) cells in the mouse liver. In ST2(-/-) BALB/c mice, better control of the hepatic parasite burden and reduced hepatomegaly were observed. This was associated with strong induction of Th1 cytokines (gamma interferon [IFN-γ] and IL-12) compared to the level in wild-type (WT) mice and better recruitment of myeloid cells associated with strongly induced chemokines (CCL2 and CXCL2) and receptors (CCR2 and CXCR2). Conversely, BALB/c mice treated twice weekly with recombinant IL-33 showed a dramatically reduced induction of Th1 cytokines and delayed inhibition of monocyte and neutrophil recruitment in the liver, which was associated with reduced KC/CXCL1 and CXCR2 expression. Taken together, our results suggest that IL-33 could be a new deleterious regulator of the hepatic immune response against Leishmania donovani, via the repression of the Th1 response and myeloid cell recruitment.

IMPORTANCE

Visceral leishmaniasis is a life-threatening systemic disease due to the Leishmania protozoa L. infantum and L. donovani and is ranked by the World Health Organization as the second most important protozoan parasitic disease after malaria for its grave morbidity, high mortality, and global distribution. Leishmania parasites subvert the host's immune response to propagate to target organs, including the spleen, the bone marrow, and the liver. Control of hepatic parasite burdens depends on a delicate and poorly understood Th1/Th2 immune balance. To better understand this complex immune response, new cytokines are interesting targets for research studies. IL-33 is a newly described cytokine usually associated with Th2 response and involved in different diseases, including infectious diseases and hepatitis. Our results suggest that IL-33 could be a new factor of susceptibility and a potential prognostic marker during visceral leishmaniasis.

Live attenuated Leishmania donovani p27 gene knockout parasites are nonpathogenic and elicit long-term protective immunity in BALB/c mice

Leishmaniasis causes significant morbidity and mortality worldwide, and no vaccines against this disease are available. Previously, we had shown that the amastigote-specific protein p27 (Ldp27) is a component of an active cytochrome c oxidase complex in Leishmania donovani and that upon deletion of its gene the parasite had reduced virulence in vivo. In this study, we have shown that Ldp27(-/-) parasites do not survive beyond 20 wk in BALB/c mice and hence are safe as an immunogen. Upon virulent challenge, mice 12 wk postimmunization showed significantly lower parasite burden in the liver and spleen. When mice were challenged 20 wk postimmunization, a significant reduction in parasite burden was still noted, suggesting long-term protection by Ldp27(-/-) immunization. Immunization with Ldp27(-/-) induced both pro- and anti-inflammatory cytokine responses and activated splenocytes for enhanced leishmanicidal activity in association with NO production. Protection in both short- and long-term immunized mice after challenge with the wild-type parasite correlated with the stimulation of multifunctional Th1-type CD4 and CD8 T cells. Adoptive transfer of T cells from long-term immunized mice conferred protection against virulent challenge in naive recipient mice, suggesting involvement of memory T cell response in protection against Leishmania infection. Immunization of mice with Ldp27(-/-)also demonstrated cross-protection against Leishmania major and Leishmania braziliensis infection. Our data show that genetically modified live attenuated Ldp27(-/-) parasites are safe, induce protective immunity even in the absence of parasites, and can provide protection against homologous and heterologous Leishmania species.

Leishmania donovani triose phosphate isomerase: a potential vaccine target against visceral leishmaniasis

Visceral leishmaniasis (VL) is one of the most important parasitic diseases with approximately 350 million people at risk. Due to the non availability of an ideal drug, development of a safe, effective, and affordable vaccine could be a solution for control and prevention of this disease. In this study, a potential Th1 stimulatory protein- Triose phosphate isomerase (TPI), a glycolytic enzyme, identified through proteomics from a fraction of Leishmania donovani soluble antigen ranging from 89.9–97.1 kDa, was assessed for its potential as a suitable vaccine candidate. The protein- L. donovani TPI (LdTPI) was cloned, expressed and purified which exhibited the homology of 99% with L. infantum TPI. The rLdTPI was further evaluated for its immunogenicity by lymphoproliferative response (LTT), nitric oxide (NO) production and estimation of cytokines in cured Leishmania patients/hamster. It elicited strong LTT response in cured patients as well as NO production in cured hamsters and stimulated remarkable Th1-type cellular responses including IFN-ã and IL-12 with extremely lower level of IL-10 in Leishmania-infected cured/exposed patients PBMCs in vitro. Vaccination with LdTPI-DNA construct protected naive golden hamsters from virulent L. donovani challenge unambiguously (∼90%). The vaccinated hamsters demonstrated a surge in IFN-ã, TNF-á and IL-12 levels but extreme down-regulation of IL-10 and IL-4 along with profound delayed type hypersensitivity and increased levels of Leishmania-specific IgG2 antibody. Thus, the results are suggestive of the protein having the potential of a strong candidate vaccine.

Immune response regulation by leishmania secreted and nonsecreted antigens

Leishmania infection consists in two sequential events, the host cell colonization followed by the proliferation/dissemination of the parasite. In this review, we discuss the importance of two distinct sets of molecules, the secreted and/or surface and the nonsecreted antigens. The importance of the immune response against secreted and surface antigens is noted in the establishment of the infection and we dissect the contribution of the nonsecreted antigens in the immunopathology associated with leishmaniasis, showing the importance of these panantigens during the course of the infection. As a further example of proteins belonging to these two different groups, we include several laboratorial observations on Leishmania Sir2 and LicTXNPx as excreted/secreted proteins and LmS3arp and LimTXNPx as nonsecreted/panantigens. The role of these two groups of antigens in the immune response observed during the infection is discussed.

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.

Reassessment of immune correlates in human visceral leishmaniasis as defined by cytokine release in whole blood

Depressed cell-mediated immunity in human visceral leishmaniasis (VL) (also known as kala-azar), revealed as the inability of peripheral blood mononuclear cells (PBMCs) to respond to Leishmania antigen, remains a hallmark of and is thought to underlie the progressive nature of this disease. We recently reported the ability of a whole-blood, gamma interferon (IFN-γ) release assay to detect subclinical infections among healthy individuals living in an area where kala-azar is endemic (Bihar, India) and the surprising result that patients with active VL also secreted significant levels of antigen-specific IFN-γ in this assay. We were interested in ascertaining whether these findings would be true for a larger cohort of subjects and in employing the whole-blood assay to detect additional cytokines that might better correlate with the disease status of infected individuals. We evaluated IFN-γ, tumor necrosis factor alpha (TNF-α), and interleukin-10 (IL-10) release in 35 patients with active VL, 54 patients with VL who were cured, 27 patients with other diseases, 52 healthy controls who lived in regions where VL or kala-azar is not endemic (NEHCs [for nonendemic healthy controls]), and 147 healthy controls who lived in regions where kala-azar is endemic (EHCs [for endemic healthy controls]). The cellular responses of the EHCs were correlated with their serological antibody titers against Leishmania donovani and Phlebotomus argentipes saliva. The whole-blood cells from the majority of both active (80%) and cured (85%) VL patients, as well as 24% of EHCs with presumed subclinical infections, produced significantly elevated levels of IFN-γ. The findings do not support a severe Th1 response defect in kala-azar. Importantly, only the patients with active VL also produced IL-10, which in conjunction with IFN-γ better reflects the immune responses that distinguish individuals with active disease from cured or subclinically infected, immune individuals.

Evaluation of Leishmania donovani protein disulfide isomerase as a potential immunogenic protein/vaccine candidate against visceral Leishmaniasis

In Leishmania species, Protein disulfide isomerase (PDI) - a redox chaperone, is reported to be involved in its virulence and survival. This protein has also been identified, through proteomics, as a Th1 stimulatory protein in the soluble lysate of a clinical isolate of Leishmania donovani (LdPDI). In the present study, the molecular characterization of LdPDI was carried out and the immunogenicity of recombinant LdPDI (rLdPDI) was assessed by lymphocyte proliferation assay (LTT), nitric oxide (NO) production, estimation of Th1 cytokines (IFN-γ and IL-12) as well as IL-10 in PBMCs of cured/endemic/infected Leishmania patients and cured L. donovani infected hamsters. A significantly higher proliferative response against rLdPDI as well as elevated levels of IFN-γ and IL-12 were observed. The level of IL-10 was found to be highly down regulated in response to rLdPDI. A significant increase in the level of NO production in stimulated hamster macrophages as well as IgG2 antibody and a low level of IgG1 in cured patient's serum was observed. Higher level of IgG2 antibody indicated its Th1 stimulatory potential. The efficacy of pcDNA-LdPDI construct was further evaluated for its prophylactic potential. Vaccination with this construct conferred remarkably good prophylactic efficacy (∼90%) and generated a robust cellular immune response with significant increases in the levels of iNOS transcript as well as TNF-α, IFN-γ and IL-12 cytokines. This was further supported by the high level of IgG2 antibody in vaccinated animals. The in vitro as well as in vivo results thus indicate that LdPDI may be exploited as a potential vaccine candidate against visceral Leishmaniasis (VL).

Analysis of the expression of toll-like receptors 2 and 4 and cytokine production during experimental Leishmania chagasi infection

Toll-like receptors (TLRs) recognise pathogen-derived molecules and influence immunity to control parasite infections. This study aimed to evaluate the mRNA expression of TLRs 2 and 4, the expression and production of the cytokines interleukin (IL)-12, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, IL-17, IL-10 and transforming growth factor (TGF)-β and the production of nitric oxide (NO) in the spleen of mice infected with Leishmania chagasi. It also aimed to evaluate any correlations between mRNA expression TLR2 and 4 and cytokines and NO production. Infection resulted in increased TLR2-4, IL-17, TNF-α and TGF-β mRNA expression during early infection, with decreased expression during late infection correlating with parasite load. IFN-γ and IL-12 mRNA expression decreased at the peak of parasitism. IL-10 mRNA expression increased throughout the entire time period analysed. Although TGF-β, TNF-α and IL-17 were highly produced during the initial phase of infection, IFN-γ and IL-12 exhibited high production during the final phase of infection. IL-10 and NO showed increased production throughout the evaluated time period. In the acute phase of infection, there was a positive correlation between TLR2-4, TNF-α, IL-17, NO, IL-10 and TGF-β expression and parasite load. During the chronic phase of infection, there was a positive correlation between TLR2-4, TNF-α, IL-17 and TGF-β expression and parasite load. Our data suggest that infection by L. chagasi resulted in modulation of TLRs 2 and 4 and cytokines.

Adenosine and immune imbalance in visceral leishmaniasis: the possible role of ectonucleotidases

Visceral leishmaniasis (VL) is the most severe form of leishmaniasis and is responsible for most Leishmania-associated deaths. VL represents a serious public health problem that affects many countries. The immune response in leishmaniasis is very complex and is poorly understood. The Th1 versus Th2 paradigm does not appear to be so clear in visceral leishmaniasis, suggesting that other immunosuppressive or immune-evasion mechanisms contribute to the pathogenesis of VL. It has been demonstrated that generation of adenosine, a potent endogenous immunosuppressant, by extracellular enzymes capable to hydrolyze adenosine tri-nucleotide (ATP) at the site of infection, can lead to immune impairment and contribute to leishmaniasis progression. In this regard, this paper discusses the unique features in VL immunopathogenesis, including a possible role for ectonucleotidases in leishmaniasis.

New challenges in the epidemiology and treatment of visceral leishmaniasis in periurban areas

Visceral leishmaniasis [VL] represents a major public health problem in many areas of the world. This review focuses on the impact of periurbanization on the epidemiology and treatment of VL, using Brazil as an example. VL continues to be mostly a disease of poverty with impact on families. However, the disease has expanded in Latin America, with foci reported as far south as Argentina. There is an increasing overlap of Leishmania infantum chagasi and HIV infections and other immunosuppressive conditions, resulting in VL emerging as an opportunistic infection. This new setting poses new challenges for VL disease control and patient management.

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.