Requirement for T cells and effect of lymphokines in successful chemotherapy for an intracellular infection. Experimental visceral leishmaniasis

Innate biosignature of treatment failure in human cutaneous leishmaniasis

The quality and magnitude of the immune and inflammatory responses determine the clinical outcome of Leishmania infection, and contribute to the efficacy of antileishmanial treatments. However, the precise immune mechanisms involved in healing or in chronic immunopathology of human cutaneous leishmaniasis (CL) are not completely understood. Through sequential transcriptomic profiling of blood monocytes (Mo), neutrophils (Nφ), and eosinophils (Eφ) over the course of systemic treatment with meglumine antimoniate, we discovered that a heightened and sustained Type I interferon (IFN) response signature is a hallmark of treatment failure (TF) in CL patients. The transcriptomes of pre-treatment, mid-treatment and end-of-treatment samples were interrogated to identify predictive and prognostic biomarkers of TF. A composite score derived from the expression of 9 differentially expressed genes (common between Mo, Nφ and Eφ) was predictive of TF in this patient cohort for biomarker discovery. Similarly, machine learning models constructed using data from pre-treatment as well as post-treatment samples, accurately classified treatment outcome between cure and TF. Results from this study instigate the evaluation of Type-I IFN responses as new immunological targets for host-directed therapies for treatment of CL, and highlight the feasibility of using transcriptional signatures as predictive biomarkers of outcome for therapeutic decision making.

Visceral Leishmaniasis in a Twin Pregnancy: A Case Report and Review of the Literature

Visceral leishmaniasis (VL), often referred to as kala-azar, is quite rare in developed countries during pregnancy. Only few studies have evaluated its impact on perinatal outcome. It is caused primarily by Leishmania donovani or Leishmania infantum and presents with a wide spectrum of clinical manifestations from cutaneous ulcers to multisystem disease. Differential diagnosis is challenging as symptoms and signs are insidious, mimicking other diseases. Misdiagnosis can result in severe adverse perinatal outcomes, even maternal/neonatal death. Early treatment with liposomal amphotericin-B (LAmB) is currently the first choice with adequate effectiveness. We report a rare case of VL in a twin pregnancy with onset at the second trimester, presenting with periodic fever with rigors, right flank pain, and gradual dysregulation of all three cell lines. The positive rK39 enzyme-linked immunosorbent assay test confirmed the diagnosis. Treatment with LAmB resulted in clinical improvement within 48 h and in the delivery of two late-preterm healthy neonates with no symptoms or signs of vertical transmission. The one-year follow-up, of the mother and the neonates, was negative for recurrence. To our knowledge, this is the first reported case of VL in a twin pregnancy, and consequently treatment and perinatal outcome are of great importance.

Pediatric lymphatic leishmaniasis: a case report

BACKGROUND

There are three main forms of leishmaniases: visceral (the most serious form because it is almost always fatal without treatment), cutaneous (the most common, usually causing skin ulcers), and mucocutaneous (affecting mouth, nose, and throat). Leishmaniasis is caused by protozoan parasites, which are transmitted by the bite of infected female phlebotomine sandflies. The disease affects some of the world's poorest people and is associated with malnutrition, population displacement, poor housing, a weak immune system, and lack of financial resources. An estimated 700,000 to 1 million new cases occur annually. Only a small fraction of those infected by parasites causing leishmaniasis will eventually develop the disease. We report a case of exclusive lymph node involvement in leishmaniasis, presenting as localized lymphadenopathies. The diagnosis of lymphatic leishmaniasis was confirmed by the presence of Leishmania donovani bodies in fine needle aspiration cytology, and positive anti-rK39 antibodies. The bone marrow aspiration was negative for Leishmania donovani bodies. Abdominal ultrasound was done and there was no organomegaly. Furthermore, localized lymphadenopathies may provide a diagnostic challenge by clinically mimicking a lymphoma or other causes of lymphadenopathy. Due to its rarity and its tendency to pose a clinical diagnostic challenge, we decided to report a case of lymphatic leishmaniasis.

CASE PRESENTATION

A 12-year-old Amara male patient presented to the University of Gondar comprehensive specialized hospital, Northwestern Ethiopia, with six discrete right lateral cervical lymphadenopathies, the largest measuring 3 × 2 cm², with no cutaneous lesion. Fine needle aspiration cytology confirmed the diagnosis of leishmaniasis in lymph node, and he was put on sodium stibogluconate (20 mg/kg body weight/day) and paromomycin (15 mg/kg body weight/day) injections, which are given intramuscularly for 17 days. Having completed his medication at the University of Gondar comprehensive specialized hospital, he had a smooth course and was discharged with appointment scheduled for follow-up after 3 months.

CONCLUSION

In the clinical evaluation of a patient with isolated lymphadenopathies, leishmaniasis must be considered as a differential diagnosis in immunocompetent subjects in endemic areas for early diagnostic workup and management.

Host-directed antileishmanial interventions: Harvesting unripe fruits to reach fruition

Leishmaniasis is an exemplary paradigm of immune evasion, fraught with the perils of limited clinical assistance, escalating costs of treatment and made worse with the lack of suitable vaccine. While drugs remain central to large-scale disease control, the growing emergence of parasite resistance necessitates the need for combination therapy involving host-directed immunological agents. Also, since prolonged disease progression is associated with strong immune suppression of the host, augmentation of host immunity via restoration of the immunoregulatory circuit involving antigen-presenting cells and T-cells, activation of macrophage function and/or CD4⁺ T helper 1 cell differentiation may serve as an ideal approach to resolve severe cases of leishmaniasis. As such, therapies that embody a synergistic approach that involve direct killing of the parasite in addition to elevating host immunity are likely to pave the way for widespread elimination of leishmaniasis in the future. With this review, we aim to recapitulate the various immunotherapeutic agents found to hold promise in antileishmanial treatment both in vitro and in vivo. These include parasite-specific antigens, dendritic cell-targeted therapy, recombinant inhibitors of various components intrinsic to immune cell signaling and agonists or antagonists to immune cells and cytokines. We also summarize their abilities to direct therapeutic skewing of the host cell-immune response and review their potential to combat the disease either alone, or as adjunct modalities.

Immunophenotyping of Peripheral Blood, Lymph Node, and Bone Marrow T Lymphocytes During Canine Leishmaniosis and the Impact of Antileishmanial Chemotherapy

Dogs are a major reservoir of Leishmania infantum, etiological agent of canine leishmaniosis (CanL) a zoonotic visceral disease of worldwide concern. Therapeutic protocols based on antileishmanial drugs are commonly used to treat sick dogs and improve their clinical condition. To better understand the impact of Leishmania infection and antileishmanial drugs on the dog's immune response, this study investigates the profile of CD4⁺ and CD8⁺ T cell subsets in peripheral blood, lymph node, and bone marrow of sick dogs and after two different CanL treatments. Two CanL groups of six dogs each were treated with either miltefosine or meglumine antimoniate combined with allopurinol. Another group of 10 clinically healthy dogs was used as control. Upon diagnosis and during the following 3 months of treatment, peripheral blood, popliteal lymph node, and bone marrow mononuclear cells were collected, labeled for surface markers CD45, CD3, CD4, CD8, CD25, and intracellular nuclear factor FoxP3, and T lymphocyte subpopulations were immunophenotyped by flow cytometry. CanL dogs presented an overall increased frequency of CD8⁺ and CD4⁺CD8⁺ double-positive T cells in all tissues and a decreased frequency of CD4⁺ T cells in the blood. Furthermore, there was a higher frequency of CD8⁺ T cells expressing CD25⁺FoxP3⁺ in the blood and bone marrow. During treatment, these subsets recovered to levels similar to those of healthy dogs. Nevertheless, antileishmanial therapy caused an increase of CD4⁺CD25⁺FoxP3⁺ T cells in all tissues, associated with the decrease of CD8⁺CD25⁻FoxP3⁻ T cell percentages. These findings may support previous studies that indicate that L. infantum manipulates the dog's immune system to avoid the development of a protective response, ensuring the parasite's survival and the conditions that allow the completion of Leishmania life cycle. Both treatments used appear to have an effect on the dog's immune response, proving to be effective in promoting the normalization of T cell subsets.

Assessment of Vaccine-Induced Immunity Against Canine Visceral Leishmaniasis

Canine visceral leishmaniasis is an increasingly important public health problem. Dogs infected by Leishmania infantum are the main domestic reservoir of the parasite and play a key role in its transmission to humans. Recent findings have helped in the development of novel diagnostic methods, and of control measures such as vaccines, some of which are already commercially available. However, quantitative procedures should be followed to confirm whether these vaccines elicit a cell-mediated immune response. The present work describes the need for this evaluation, and the techniques available for confirming this type of immune response.

Leishmanicidal therapy targeted to parasite proteases

Leishmaniasis is considered a serious public health problem and the current available therapy has several disadvantages, which makes the search for new therapeutic targets and alternative treatments extremely necessary. In this context, this review focuses on the importance of parasite proteases as target drugs against Leishmania parasites, as a chemotherapy approach. Initially, we discuss about the current scenario for the treatment of leishmaniasis, highlighting the main drugs used and the problems related to their use. Subsequently, we describe the inhibitors of major proteases of Leishmania already discovered, such as Compound s9 (aziridine-2,3-dicarboxylate), Compound 1c (benzophenone derivative), Au2Phen (gold complex), AubipyC (gold complex), MDL 28170 (dipeptidyl aldehyde), K11777, Hirudin, diazo-acetyl norleucine methyl ester, Nelfinavir, Saquinavir, Nelfinavir, Saquinavir, Indinavir, Saquinavir, GNF5343 (azabenzoxazole), GNF6702 (azabenzoxazole), Benzamidine and TPCK. Next, we discuss the importance of the protease gene to parasite survival and the aspects of the validation of proteases as target drugs, with emphasis on gene disruption. Then, we describe novel important strategies that can be used to support the research of new antiparasitic drugs, such as molecular modeling and nanotechnology, whose main targets are parasitic proteases. And finally, we discuss possible perspectives to improve drug development. Based on all findings, proteases could be considered potential targets against leishmaniasis.

Immunomodulatory Therapy of Visceral Leishmaniasis in Human Immunodeficiency Virus-Coinfected Patients

Patients with visceral leishmaniasis (VL)–human immunodeficiency virus (HIV) coinfection experience increased drug toxicity and treatment failure rates compared to VL patients, with more frequent VL relapse and death. In the era of VL elimination strategies, HIV coinfection is progressively becoming a key challenge, because HIV-coinfected patients respond poorly to conventional VL treatment and play an important role in parasite transmission. With limited chemotherapeutic options and a paucity of novel anti-parasitic drugs, new interventions that target host immunity may offer an effective alternative. In this review, we first summarize current views on how VL immunopathology is significantly affected by HIV coinfection. We then review current clinical and promising preclinical immunomodulatory interventions in the field of VL and discuss how these may operate in the context of a concurrent HIV infection. Caveats are formulated as these interventions may unpredictably impact the delicate balance between boosting of beneficial VL-specific responses and deleterious immune activation/hyperinflammation, activation of latent provirus or increased HIV-susceptibility of target cells. Evidence is lacking to prioritize a target molecule and a more detailed account of the immunological status induced by the coinfection as well as surrogate markers of cure and protection are still required. We do, however, argue that virologically suppressed VL patients with a recovered immune system, in whom effective antiretroviral therapy alone is not able to restore protective immunity, can be considered a relevant target group for an immunomodulatory intervention. Finally, we provide perspectives on the translation of novel theories on synergistic immune cell cross-talk into an effective treatment strategy for VL–HIV-coinfected patients.

Gamma Interferon-Regulated Chemokines in Leishmania donovani Infection in the Liver

In the livers of C57BL/6 mice, gamma interferon (IFN-γ) controls intracellular Leishmania donovani infection and the efficacy of antimony (Sb) chemotherapy. Since both responses usually correlate with granulomatous inflammation, we tested six prominently expressed, IFN-γ-regulated chemokines-CXCL9, CXCL10, CXCL13, CXCL16, CCL2, and CCL5-for their roles in (i) mononuclear cell recruitment and granuloma assembly and maturation, (ii) initial control of infection and self-cure, and (iii) responsiveness to Sb treatment. Together, the results for the L. donovani-infected livers of chemokine-deficient mice (CXCR6^-/- mice were used as CXCL16-deficient surrogates) indicated that individual IFN-γ-induced chemokines have diverse affects and (i) may be entirely dispensable (CXCL13, CXCL16), (ii) may promote (CXCL10, CCL2, CCL5) or downregulate (CXCL9) initial granuloma assembly, (iii) may enhance (CCL2, CCL5) or hinder (CXCL10) early parasite control, (iv) may promote granuloma maturation (CCL2, CCL5), (v) may exert a granuloma-independent action that enables self-cure (CCL5), and (vi) may have no role in responsiveness to chemotherapy. Despite the near absence of tissue inflammation in early-stage infection, parasite replication could be controlled (in CXCL10^-/- mice) and Sb was fully active (in CXCL10^-/-, CCL2^-/-, and CCL5^-/- mice). These results characterize chemokine action in the response to L. donovani and also reemphasize that (i) recruited mononuclear cells and granulomas are not required to control infection or respond to Sb chemotherapy, (ii) granuloma assembly, control of infection, and Sb's efficacy are not invariably linked expressions of the same T cell-dependent, cytokine-mediated antileishmanial mechanism, and (iii) granulomas are not necessarily hallmarks of protective antileishmanial immunity.

In vivo/In vitro immune responses to L. major isolates from patients with no clinical response to Glucantime

BACKGROUND

Leishmaniasis is a major health problem in some endemic areas of tropical and subtropical areas of the world. Interleukin-12 (IL-12) and interferon gamma (IFN-γ) are essential cytokines associated with initiation of Th1 response. The main objective of this study was to evaluate of the type of immune response to L. major isolates from patients with no clinical response to antimonite (Glucantime).

MATERIALS AND METHODS

This experimental study was carried out during 2013-2014. In the current study Leishmania major were isolated from 10 CL patients with a history of at least one course of treatment with Meglumine antimonate (Sb5). The isolates were used to evaluate in vitro and in vivo response to Sb5. J774 murine macrophage cell line was used for in vitro tests and Balb/c mice was used for in vivo studies. IL-12 gene expression was evaluated using Real-time PCR and IFN-γ serum level was quantified using ELISA technique. SPSS (version: 20), analysis of Covariance (ANCOVA) was used for statistical analysis.

RESULTS

PCR results confirmed that all 10 isolates were L. major. The mean of IL-12 gene expression in vitro, in vivo and IFN-γ serum levels (pg/ml) after 2 and 3 weeks treatment in vivo, increased significantly following the treatment with Glucantime in the two groups of Balb/c mice infected either with patients' isolates or standard L. major. No significant difference was seen between the patients' isolates and standard species.

CONCLUSIONS

Although the L. major were isolated from patients with active lesion and no clinical response to Glucantime after at least one courses of Glucantime treatment but in vivo and in vitro immune response of L. major isolates showed no difference between the patients' isolates and standard L. major.

Current challenges in treatment options for visceral leishmaniasis in India: a public health perspective

Visceral leishmaniasis (VL) is a serious parasitic disease causing considerable mortality and major disability in the Indian subcontinent. It is most neglected tropical disease, particularly in terms of new drug development for the lack of financial returns. An elimination campaign has been running in India since 2005 that aim to reduce the incidence of VL to below 1 per 10,000 people at sub-district level. One of the major components in this endeavor is reducing transmission through early case detection followed by complete treatment. Substantial progress has been made during the recent years in the area of VL treatment, and the VL elimination initiatives have already saved many lives by deploying them effectively in the endemic areas. However, many challenges remain to be overcome including availability of drugs, cost of treatment (drugs and hospitalization), efficacy, adverse effects, and growing parasite resistance. Therefore, better emphasis on implementation research is urgently needed to determine how best to deliver existing interventions with available anti-leishmanial drugs. It is essential that the new treatment options become truly accessible, not simply available in endemic areas so that they may promote healing and save lives. In this review, we highlight the recent advancement and challenges in current treatment options for VL in disease endemic area, and discuss the possible strategies to improve the therapeutic outcome.

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.

IFN-γ-induced macrophage antileishmanial mechanisms in mice: A role for immunity-related GTPases, Irgm1 and Irgm3, in Leishmania donovani infection in the liver

In C57BL/6 mice, Leishmania donovani infection in the liver provoked IFN-γ-induced expression of the immunity-related GTPases (IRG), Irgm1 and Irgm3. To gauge the antileishmanial effects of these macrophage factors in the liver, intracellular infection was analyzed in IRG-deficient mice. In early- (but not late-) stage infection, Irgm3(-/-) mice failed to properly control parasite replication, generated little tissue inflammation and were hyporesponsive to pentavalent antimony (Sb) chemotherapy. Observations limited to early-stage infection in Irgm1(-/-) mice demonstrated increased susceptibility and virtually no inflammatory cell recruitment to heavily-parasitized parenchymal foci but an intact response to chemotherapy. In L. donovani infection in the liver, the absence of either Irgm1 or Irgm3 impairs early inflammation and initial resistance; the absence of Irgm3, but not Irgm1, also appears to impair the intracellular efficacy of Sb chemotherapy.

Antileishmanial Activity of Disulfiram and Thiuram Disulfide Analogs in an Ex Vivo Model System Is Selectively Enhanced by the Addition of Divalent Metal Ions

Current treatments for cutaneous and visceral leishmaniasis are toxic, expensive, difficult to administer, and limited in efficacy and availability. Disulfiram has primarily been used to treat alcoholism. More recently, it has shown some efficacy as therapy against protozoan pathogens and certain cancers, suggesting a wide range of biological activities. We used an ex vivo system to screen several thiuram disulfide compounds for antileishmanial activity. We found five compounds (compound identifier [CID] 7188, 5455, 95876, 12892, and 3117 [disulfiram]) with anti-Leishmania activity at nanomolar concentrations. We further evaluated these compounds with the addition of divalent metal salts based on studies that indicated these salts could potentiate the action of disulfiram. In addition, clinical studies suggested that zinc has some efficacy in treating cutaneous leishmaniasis. Several divalent metal salts were evaluated at 1 μM, which is lower than the normal levels of copper and zinc in plasma of healthy individuals. The leishmanicidal activity of disulfiram and CID 7188 were enhanced by several divalent metal salts at 1 μM. The in vitro therapeutic index (IVTI) of disulfiram and CID 7188 increased 12- and 2.3-fold, respectively, against L. major when combined with ZnCl2. The combination of disulfiram with ZnSO4 resulted in a 1.8-fold increase in IVTI against L. donovani. This novel combination of thiuram disulfides and divalent metal ions salts could have application as topical and/or oral therapies for treatment of cutaneous and visceral leishmaniasis.

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

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

Leishmania specific CD4 T cells release IFNγ that limits parasite replication in patients with visceral leishmaniasis

Visceral leishmaniasis (VL) is associated with increased circulating levels of multiple pro-inflammatory cytokines and chemokines, including IL-12, IFNγ, and TNFα, and elevated expression of IFNγ mRNA in lesional tissue such as the spleen and bone marrow. However, an immunological feature of VL patients is that their peripheral blood mononuclear cells (PBMCs) typically fail to respond to stimulation with leishmanial antigen. Unexpectedly, it was recently shown that Leishmania specific IFNγ, can readily be detected when a whole blood stimulation assay (WBA) is used. We sought to define the conditions that permit whole blood cells to respond to antigen stimulation, and clarify the biological role of the IFNγ found to be released by cells from VL patients. CD4+ T cells were found to be crucial for and the main source of the IFNγ production in Leishmania stimulated whole blood (WB) cultures. Complement, antibodies and red blood cells present in whole blood do not play a significant role in the IFNγ response. The IFNγ production was reduced by blockade of human leukocyte antigen (HLA)-DR, indicating that the response to leishmanial antigens observed in WB of active VL patients is a classical HLA- T cell receptor (TCR) driven reaction. Most importantly, blockade of IFNγ in ex-vivo splenic aspirate cultures demonstrated that despite the progressive nature of their disease, the endogenous IFNγ produced in patients with active VL serves to limit parasite growth.

Our research aims to understand the immune failure underlying progression of human visceral leishmaniasis (VL). A key immunological feature of VL patients is that their peripheral blood mononuclear cells (PBMCs) do not respond to stimulation with leishmanial antigen. Surprisingly, when employing a whole blood assay we discovered significant levels of IFNγ in response to soluble Leishmania donovani antigen (WBA) in VL patients. We were interested to understand the relevance of the IFNγ to the anti-parasitic response. Animal models and in vitro studies have shown that IFNγ is a key effector cytokine required for control of the infection, however, the role of endogenous IFNγ in control of parasites in VL patients, has not been demonstrated. Our results show that CD4 cells were required for and were the source of Leishmania specific IFNγ in WBA of VL patients. Optimal IFNγ response required interaction with HLA-DR, supporting that VL is not due to an intrinsic Th1 response defect per se. The Leishmania driven IFNγ appears to limit parasite growth in patients with active VL, since blockade of IFNγ ex-vivo in splenic aspirate cultures enhanced parasite survival. This suggests that IFNγ may have been prematurely dismissed as an adjunct therapy in treatment of VL.

Experimental Validation of Multi-Epitope Peptides Including Promising MHC Class I- and II-Restricted Epitopes of Four Known Leishmania infantum Proteins

Leishmaniasis is a significant worldwide health problem for which no vaccine exists. Activation of CD4(+) and CD8(+) T cells is crucial for the generation of protective immunity against parasite. Recent trend in vaccine design has been shifted to epitope-based vaccines that are more specific, safe, and easy to produce. In the present study, four known antigenic Leishmania infantum proteins, cysteine peptidase A (CPA), histone H1, KMP-11, and Leishmania eukaryotic initiation factor (LeIF) were analyzed for the prediction of binding epitopes to H2(d) MHC class I and II molecules, using online available algorithms. Based on in silico analysis, eight peptides including highly scored MHC class I- and II-restricted epitopes were synthesized. Peptide immunogenicity was validated in MHC compatible BALB/c mice immunized with each synthetic peptide emulsified in complete Freund's adjuvant/incomplete Freund's adjuvant. CPA_p2, CPA_p3, H1_p1, and LeIF_p6 induced strong spleen cell proliferation upon in vitro peptide re-stimulation. In addition, the majority of the peptides, except of LeIF_p1 and KMP-11_p1, induced IFN-γ secretion, while KMP-11_p1 indicated a suppressive effect on IL-10 production. CPA_p2, CPA_p3, LeIF_p3, and LeIF_p6 induced IFN-γ-producing CD4(+) T cells indicating a TH1-type response. In addition, CPA_p2, CPA_p3, and H1_p1 induced also the induction of CD8(+) T cells. The induction of peptide-specific IgG in immunized mice designated also the existence of B cell epitopes in peptide sequences. Combining immunoinformatic tools and experimental validation, we demonstrated that CPA_p2, CPA_p3, H1_p1, H1_p3, CPA_p2, LeIF_p3, and LeIF_p6 are likely to include potential epitopes for the induction of protective cytotoxic and/or TH1-type immune responses supporting the feasibility of peptide-based vaccine development for leishmaniasis.

A comparative evaluation of efficacy of chemotherapy, immunotherapy and immunochemotherapy in visceral leishmaniasis-an experimental study

Visceral leishmaniasis (VL) represents the second most challenging infectious disease worldwide, leading to nearly 500,000 new cases and 60,000 deaths annually. Ninety per cent of VL cases occur in five countries namely Bangladesh, India, Nepal, Sudan and Brazil. 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. To combat this situation, immunochemotherapy can provide a solution. In the present study, an attempt has been made to assess the in vivo antileishmanial efficacy of chemotherapy, immunotherapy and immunochemotherapy with the use of a first generation antigen Killed Leishmania donovani (KLD) along with a standard drug sodium stibogluconate (SSG) and a newly tested antileishmanial cisplatin. Inbred BALB/c mice were infected with 10(7) promastigotes/0.1 ml of Leishmania donovani. A month after infection, these animals were given specific immunotherapy (KLD/KLD+MPL-A) or chemotherapy (SSG/cisplatin) or immunochemotherapy (SSG+KLD/SSG+KLD+MPL-A/cisplatin+KLD/cisplatin+KLD+MPL-A). Animals were sacrificed on 1, 15 and 30(th) day post treatment. The efficacy of these combinations was assessed in terms of parasite load and by immunological investigations. Infected mice and normal mice served as controls. Results showed that combination of drug and KLD significantly reduced the parasite burden, enhanced the DTH (Delayed Type Hypersensitivity) responses, showed increased levels of IgG2a and decreased levels of IgG1 as compared to mice given chemotherapy or immunotherapy alone. Further maximum protection was provided by SSG+KLD+MPL-A and it was most effective as depicted by 98.5% reduction in parasite load, a potent increase in IFN-γ levels and a significant decrease in IL-10 and IL-4 levels thus skewing the immune response towards Th1 type. Hence, immunochemotherapy is more effective in control of VL in comparison to chemotherapy or immunotherapy.

STAT4 is critical for immunity but not for antileishmanial activity of antimonials in experimental visceral leishmaniasis

We and others have previously shown that IL-12 is indispensable for immunity and is required for the optimal antiparasitic activity of antimonials in experimental visceral leishmaniasis caused by Leishmania donovani. Here we investigated the role of STAT4 in immunity against L. donovani using STAT4 knockout mice and also determined the effect of STAT4 deficiency in response to antimonial therapy. Upon infection with L. donovani, stat4⁻/⁻ BALB/c and C57BL/6 mice showed enhanced susceptibility to Leishmania during late time points of infection which was associated with a marked reduction in Th1 responses and hepatic immunopathology. Interestingly, these defects in Th1 responses in stat4⁻/⁻ did not impair the antimonial chemotherapy as both stat4⁻/⁻ and WT mice showed comparable levels of parasite clearance from the liver and spleen. These findings highlight the role of STAT4 in immunity to L. donovani infection and also provide evidence that STAT4 is dispensable for antimonial-based chemotherapy.

Development of an ex vivo lymph node explant model for identification of novel molecules active against Leishmania major

Leishmaniasis is a vector-borne zoonotic infection affecting people in tropical and subtropical regions of the world. Current treatments for cutaneous leishmaniasis are difficult to administer, toxic, expensive, and limited in effectiveness and availability. Here we describe the development and application of a medium-throughput screening approach to identify new drug candidates for cutaneous leishmaniasis using an ex vivo lymph node explant culture (ELEC) derived from the draining lymph nodes of Leishmania major-infected mice. The ELEC supported intracellular amastigote proliferation and contained lymph node cell populations (and their secreted products) that enabled the testing of compounds within a system that mimicked the immunopathological environment of the infected host, which is known to profoundly influence parasite replication, killing, and drug efficacy. The activity of known antileishmanial drugs in the ELEC system was similar to the activity measured in peritoneal macrophages infected in vitro with L. major. Using the ELEC system, we screened a collection of 334 compounds, some of which we had demonstrated previously to be active against L. donovani, and identified 119 hits, 85% of which were confirmed to be active by determination of the 50% effective concentration (EC50). We found 24 compounds (7%) that had an in vitro therapeutic index (IVTI; 50% cytotoxic/effective concentration [CC50]/EC50) > 100; 19 of the compounds had an EC50 below 1 μM. According to PubChem searchs, 17 of those compounds had not previously been reported to be active against Leishmania. We expect that this novel method will help to accelerate discovery of new drug candidates for treatment of cutaneous leishmaniasis.

Drug-resistant microorganisms with a higher fitness--can medicines boost pathogens?

Drug-resistant microorganisms (DRMs) are generally thought to suffer from a fitness cost associated with their drug-resistant trait, inflicting them a disadvantage when the drug pressure reduces. However, Leishmania resistant to pentavalent antimonies shows traits of a higher fitness compared to its sensitive counterparts. This is likely due the combination of an intracellular pathogen and a drug that targets the parasite's general defense mechanisms while at the same time stimulating the host's immune system, resulting in a DRM that is better adapted to withstand the host's immune response. This review aims to highlight how this fitter DRM has emerged and how it might affect the control of leishmaniasis. However, this unprecedented example of fitter antimony-resistant Leishmania donovani is also of significance for the control of other microorganisms, warranting more caution when applying or designing drugs that attack their general defense mechanisms or interact with the host's immune system.

Meglumine antimonate treatment enhances phagocytosis and TNF-α production by monocytes in human cutaneous leishmaniasis

This work evaluated phagocytic function, hydrogen peroxide (H(2)O(2)), TNF-α and IL-10 production by monocytes and serum INF-γ levels in New World human cutaneous leishmaniasis and the influence of meglumine antimonate treatment on these immune functions. The phagocytic capacity of monocytes in untreated Leishmania-infected individuals was significantly (2.5 times) lower than that of healthy controls, and antimonial treatment increased the phagocytosis by monocytes by about five times at the end of therapy. The leishmaniasis patients showed 3.9 times higher H(2)O(2) production than controls and treatment with meglumine antimonate did not influence the production of H(2)O(2), which remained enhanced until the end of treatment. Individuals with leishmaniasis showed 6.3 times lower TNF-α production than healthy individuals and meglumine antimonate treatment caused a significant increment (11.9 times) in its production. INF-γ serum levels were higher in Leishmania-infected individuals than healthy controls, and the production of IL-10 by monocytes was not influenced by infection or antimonial treatment. Enhancement of monocyte functions by the antimonial treatment suggests that the immunomodulatory effects of the drug may also play a part in the way meglumine antimonate acts against the parasite in human leishmaniasis, by directly increasing phagocytosis and TNF-α production.

Novel immunomodulatory function of 1,3,4-thiadiazole derivatives with leishmanicidal activity

OBJECTIVES

Previously, some nitroheteroaryl-1,3,4-thiadiazole derivatives were identified to have potent activity against Leishmania sp. The present aim was to complete the in vitro analysis, thereby investigating the in vivo efficiency of the analogues 15a, 21a and 21b against infected BALB/c mice.

METHODS

Following parasite inoculation and intraperitoneal drug administration (5 and 20 mg/kg/day) for 5 days, the course and size of cutaneous lesions, histopathology of the liver, parasite loads in the spleen through limiting dilution assay as well as spleen cell activation assays through cytokine secretion profiles were studied in BALB/c mice, over a period of 23 and 30 days post-drug injections.

RESULTS

The analogues significantly decreased lesion size and progression of infection in the liver and spleen, and were associated with granuloma formation, which correlates with disease regression in the liver of murine hosts. Moreover, the analogues had immunomodulatory effects, stimulating interferon-γ expression and suppressing interleukin-10 and interleukin-5 production, favouring type-1 immune responses and resolution of the parasitic infection.

CONCLUSIONS

Our results highlight marked differences between the responses of key anatomical organs to the thiadiazole derivatives in comparison with the current antileishmanial drug, meglumine antimoniate. The in vivo observations provide further evidence on the efficiency of the compounds for Leishmania treatment. The immunomodulatory function plays an essential role in enhancing cell-mediated immunity for complete clearance of the pathogen.

Leishmania donovani: CD2 biased immune response skews the SAG mediated therapy for a predominant Th1 response in experimental infection

We have evaluated the effect of combining CD2 with conventional antimonial (sb) therapy in protection in BALB/c mice infected with either drug sensitive or resistant strain of Leishmania donovani with 3×10(7) parasites via-intra-cardiac route. Mice were treated with anti CD2 adjunct SAG sub-cutaneously twice a week for 4 weeks. Assessment for measurement of weight, spleen size, anti-Leishmania antibody titer, T cell and anti-leishmanial macrophage function was carried out day 0, 10, 22 and 34 post treatments. The combination therapy was shown boosting significant proportion of T cells to express CD25 compared to SAG monotherapy. Although, the level of IFN-γ was not statistically different between combination vs monotherapy (p=0.298) but CD2 treatment even alone significantly influenced IFN-γ production than either SAG treatment (p=0.045) or with CD2 adjunct SAG treatment (p=0.005) in Ld-S strain as well as in Ld-R strain. The influence of CD2 adjunct treatment was also documented in anti-leishmanial functions in macrophages. As shown, the super-oxide generation began enhancing very early on day 10 after SAG treatment with CD2 during which SAG action was at minimum. Interestingly, the super-oxide generation ability remained intact in macrophage after treatment with immuno-chemotherapy even in mice infected with Leishmania resistant strain. Unlike SAG treatment, treatment of SAG with CD2 also led to production of nitric oxide and TNF-α, resulting in resulting in most effective clearance of L. donovani from infected macrophages. Our results indicate that CD2, which can boost up a protective Th1 response, might also be beneficial to enable SAG to induce Macrophages to produce Leishmanicidal molecules and hence control the infection in clinical situation like Kala-azar. Drug resistance is the major impedance for disease control but the encouraging results obtained after infecting mice with resistant strain of the parasite strongly imply that this drug can be effective even in treating resistant cases of Kala-azar.

T helper1/t helper2 cells and resistance/susceptibility to leishmania infection: is this paradigm still relevant?

Work in large part on Leishmania major in the 1980s identified two distinct apparently counter-regulatory CD4⁺ T cell populations, T helper (h)1 and Th2, that controlled resistance/susceptibility to infection respectively. However, the generation of IL-4^−/− mice in the 1990s questioned the paramount role of this Th2 archetypal cytokine in the non-healing response to Leishmania infection. The more recent characterization of CD4⁺ T cell regulatory populations and further effector CD4⁺ T helper populations, Th17, Th9, and T follicular (f)h cells as well as the acknowledged plasticity in T helper cell function has further added to the complexity of host pathogen interactions. These interactions are complicated by the multiplicity of cells that respond to CD4⁺ T cell subset signatory cytokines, as well as the diversity of Leishmania species that are often subject to significantly different immune-regulatory controls. In this article we review current knowledge with regard to the role of CD4⁺ T cells and their products during Leishmania infection. In particular we update on our studies using conditional IL-4Rα gene-deficient mice that have allowed dissection of the cell interplay dictating the disease outcomes of the major Leishmania species infecting humans.

Endogenous IL-13 plays a crucial role in liver granuloma maturation during Leishmania donovani infection, independent of IL-4Rα-responsive macrophages and neutrophils

Previous studies comparing interleukin 4 receptor α (IL-4Rα)^-/- and interleukin 4 (IL-4)^-/- BALB/c mice have indicated that interleukin 13 (IL-13), whose receptor shares the IL-4Rα subunit with IL-4, plays a protective role during visceral leishmaniasis. We demonstrate that IL-13^-/- BALB/c mice were less able to control hepatic growth of Leishmania donovani compared with wild-type mice. This correlated with significantly retarded granuloma maturation in IL-13^-/- mice, defective interferon γ (IFN-γ) production, and elevated IL-4 and interleukin 10 (IL-10) levels. L.donovani–infected IL-13^-/- mice also responded poorly to sodium stibogluconate-mediated chemotherapy compared with wild-type BALB/c mice. Because murine lymphocytes do not have IL-13 receptors, we examined the ability of macrophage/neutrophil-specific IL-4Rα^-/- mice to control primary infection with L. donovani and to respond to chemotherapy. Macrophage/neutrophil-specific IL-4Rα^-/- mice were as resistant to leishmaniasis as wild-type mice, and chemotherapy retained its efficacy. Consequently, in L. donovani infected BALB/c mice, IL-13 promotes hepatic granuloma formation and controls parasite burdens independently of direct effects on macrophages/neutrophils.

Use of antimony in the treatment of leishmaniasis: current status and future directions

In the recent past the standard treatment of kala-azar involved the use of pentavalent antimonials Sb(V). Because of progressive rise in treatment failure to Sb(V) was limited its use in the treatment program in the Indian subcontinent. Until now the mechanism of action of Sb(V) is not very clear. Recent studies indicated that both parasite and hosts contribute to the antimony efflux mechanism. Interestingly, antimonials show strong immunostimulatory abilities as evident from the upregulation of transplantation antigens and enhanced T cell stimulating ability of normal antigen presenting cells when treated with Sb(V) in vitro. Recently, it has been shown that some of the peroxovanadium compounds have Sb(V)-resistance modifying ability in experimental infection with Sb(V) resistant Leishmania donovani isolates in murine model. Thus, vanadium compounds may be used in combination with Sb(V) in the treatment of Sb(V) resistance cases of kala-azar.

Therapy with sodium stibogluconate in stearylamine-bearing liposomes confers cure against SSG-resistant Leishmania donovani in BALB/c mice

Background

Resistance of Leishmania donovani to pentavalent antimonials, the first-line treatment of visceral leishmaniasis (VL), has become a critical issue worldwide. Second-line and new drugs are also not devoid of limitations. Suitable drug-delivery systems can improve the mode of administration and action of the existing antimonials, thus increasing their clinical life.

Methodology/Principal Findings

We investigated the efficacy of sodium stibogluconate (SSG) in phosphatidylcholine (PC)–stearylamine-bearing liposomes (PC-SA-SSG), PC-cholesterol liposomes (PC-Chol-SSG) and free amphotericin B (AmB) against SSG-resistant L. donovani strains in 8-wk infected BALB/c mice. Animals were sacrificed and parasites in liver, spleen and bone marrow were estimated 4-wk post-treatment by microscopic examination of stamp smears and limiting dilution assay. A set of PC-SA-SSG and AmB treated mice were further studied for protection against reinfection. Serum antibodies and cytokine profiles of ex-vivo cultured splenocytes were determined by ELISA. Uptake of free and liposomal SSG in intracellular amastigotes was determined by atomic absorption spectroscopy. Rhodamine 123 and 5-carboxyfluorescein, known substrates of Pgp and MRP transporter proteins, respectively, were used in free and liposomal forms for efflux studies to estimate intracellular drug retention. Unlike free and PC-Chol-SSG, PC-SA-SSG was effective in curing mice infected with two differentially originated SSG-unresponsive parasite strains at significantly higher levels than AmB. Successful therapy correlated with complete suppression of disease-promoting IL-10 and TGF-β, upregulation of Th1 cytokines and expression of macrophage microbicidal NO. Cure due to elevated accumulation of SSG in intracellular parasites, irrespective of SSG-resistance, occurs as a result of increased drug retention and improved therapy when administered as PC-SA-SSG versus free SSG.

Conclusions/Significance

The design of this single-dose combination therapy with PC-SA-SSG for VL, having reduced toxicity and long-term efficacy, irrespective of SSG-sensitivity may prove promising, not only to overcome SSG-resistance in Leishmania, but also for drugs with similar resistance-related problems in other diseases.

Identification of small molecule lead compounds for visceral leishmaniasis using a novel ex vivo splenic explant model system

BACKGROUND

New drugs are needed to treat visceral leishmaniasis (VL) because the current therapies are toxic, expensive, and parasite resistance may weaken drug efficacy. We established a novel ex vivo splenic explant culture system from hamsters infected with luciferase-transfected Leishmania donovani to screen chemical compounds for anti-leishmanial activity.

METHODOLOGY/PRINCIPAL FINDINGS

THIS MODEL HAS ADVANTAGES OVER IN VITRO SYSTEMS IN THAT IT: 1) includes the whole cellular population involved in the host-parasite interaction; 2) is initiated at a stage of infection when the immunosuppressive mechanisms that lead to progressive VL are evident; 3) involves the intracellular form of Leishmania; 4) supports parasite replication that can be easily quantified by detection of parasite-expressed luciferase; 5) is adaptable to a high-throughput screening format; and 6) can be used to identify compounds that have both direct and indirect anti-parasitic activity. The assay showed excellent discrimination between positive (amphotericin B) and negative (vehicle) controls with a Z' Factor >0.8. A duplicate screen of 4 chemical libraries containing 4,035 compounds identified 202 hits (5.0%) with a Z score of <-1.96 (p<0.05). Eighty-four (2.1%) of the hits were classified as lead compounds based on the in vitro therapeutic index (ratio of the compound concentration causing 50% cytotoxicity in the HepG(2) cell line to the concentration that caused 50% reduction in the parasite load). Sixty-nine (82%) of the lead compounds were previously unknown to have anti-leishmanial activity. The most frequently identified lead compounds were classified as quinoline-containing compounds (14%), alkaloids (10%), aromatics (11%), terpenes (8%), phenothiazines (7%) and furans (5%).

CONCLUSIONS/SIGNIFICANCE

The ex vivo splenic explant model provides a powerful approach to identify new compounds active against L. donovani within the pathophysiologic environment of the infected spleen. Further in vivo evaluation and chemical optimization of these lead compounds may generate new candidates for preclinical studies of treatment for VL.

Combination therapy with paromomycin-associated stearylamine-bearing liposomes cures experimental visceral leishmaniasis through Th1-biased immunomodulation

Visceral leishmaniasis (VL) caused by the parasite Leishmania donovani is a potentially fatal disease. Available limited drugs are toxic, require prolonged treatment duration, and are costly. A low-cost parenteral formulation of paromomycin sulfate (PM) has recently been approved for the treatment of VL. Monotherapy with PM runs the risk of development of resistance. Hence, efforts are needed to develop a combination therapy of PM with other drugs to shorten the duration of treatment and prolong the effective life of the drug. PM was formulated with leishmanicidal stearylamine (SA)-bearing phosphatidylcholine (PC) liposomes for low-dose therapy. In vitro and in vivo antileishmanial effects of the combination drug were determined. The immunomodulatory role of PC-SA-PM was determined using enzyme-linked immunosorbent assay (ELISA) and flow cytometry. Excluding the spleen, for which the therapeutic effect was additive, a remarkable synergistic activity toward cure and prophylaxis with a single-shot low-dose treatment with PC-SA-associated PM was achieved with BALB/c mice. PC-SA-PM showed an immunomodulatory effect on CD4(+) and CD8(+) T cells for gamma interferon (IFN-γ) production and downregulated disease-associated interleukin-10 (IL-10) and transforming growth factor β (TGF-β) to almost negligible levels. Such combination chemotherapy may provide a promising alternative for the cure of leishmaniasis, with a plausible conversion of the host immune response from a disease-promoting pattern to a Th1-biased response indicative of long-term resistance.

Immunomodulatory effect of picroliv on the efficacy of paromomycin and miltefosine in combination in experimental visceral leishmaniasis

Combination therapy for the treatment of visceral leishmaniasis has increasingly been advocated as a way to increase treatment efficacy and tolerance, to reduce treatment duration and cost, and to limit the emergence of drug resistance. In the present work, we have adopted a rational approach, which can modulate the immune response to overcome the negative control systems and to boost the positive killing responses. This study was designed to investigate the immunomodulatory effect of picroliv (standardized fraction from the alcoholic extract of root and rhizome of Picrorhiza kurroa) on a combination of paromomycin and miltefosine using Leishmania donovani/hamster model. Picroliv has significantly enhanced antileishmanial efficacy and lymphocyte proliferation when given in combination with paromomycin and miltefosine. Increased toxic oxygen metabolite generation and phagocytosis were also witnessed. Present study thus establishes the possible use of picroliv as adjunct to antileishmanial chemotherapy.

Therapeutic glucocorticoid-induced TNF receptor-mediated amplification of CD4+ T cell responses enhances antiparasitic immunity

Chronic infectious diseases and cancers are often associated with suboptimal effector T cell responses. Enhancement of T cell costimulatory signals has been extensively studied for cancer immunotherapy but not so for the treatment of infectious disease. The few previous attempts at this strategy using infection models have lacked cellular specificity, with major immunoregulatory mechanisms or innate immune cells also being targeted. In this study, we examined the potential of promoting T cell responses via the glucocorticoid-induced TNF receptor (GITR) family-related protein in a murine model of visceral leishmaniasis. GITR stimulation during established infection markedly improved antiparasitic immunity. This required CD4(+) T cells, TNF, and IFN-gamma, but crucially, was independent of regulatory T (Treg) cells. GITR stimulation enhanced CD4(+) T cell expansion without modulating Treg cell function or protecting conventional CD4(+) T cells from Treg cell suppression. GITR stimulation substantially improved the efficacy of a first-line visceral leishmaniasis drug against both acute hepatic infection and chronic infection in the spleen, demonstrating its potential to improve clinical outcomes. This study identifies a novel strategy to therapeutically enhance CD4(+) T cell-mediated antiparasitic immunity and, importantly, achieves this goal without impairment of Treg cell function.

Miltefosine promotes IFN-gamma-dominated anti-leishmanial immune response

Leishmania donovani, a protozoan parasite, resides and replicates as amastigotes within macrophages. The parasite inflicts the disease visceral leishmaniasis by suppressing host cell function. Neither a therapeutic vaccine nor an effective anti-leishmanial drug to reverse the immunosuppression is available. Although miltefosine (hexadecylphosphocholine or HPC) is a promising orally bioavailable anti-leishmanial drug, its efficacy is seriously compromised by contra-indications in pregnant women. Further rational redesigning of the drug requires studies on its mechanism of action, which is unknown at present. Because miltefosine is proposed to have immunomodulatory functions, we examined whether miltefosine exerts its anti-leishmanial functions by activating macrophages. We observed that miltefosine's anti-leishmanial function was significantly compromised in IFN-gamma-deficient macrophages suggesting the importance of endogenous IFN-gamma in miltefosine-induced anti-leishmanial functions of macrophages. Miltefosine induced IFN-gamma, neutralization of which reduced the anti-leishmanial functions of macrophages. IFN-gamma responsiveness is reduced in L. donovani-infected macrophages but is significantly restored by miltefosine, as it enhances IFN-gamma receptors and IFN-gamma induced STAT-1 phosphorylation but reduced activation of SHP-1, the phosphatase implicated in the down-regulation of STAT-1 phosphorylation. Miltefosine induced protein kinase C-dependent and PI3K-dependent p38MAP kinase phosphorylation and anti-leishmanial function. Miltefosine promotes p38MAP kinase-dependent anti-leishmanial functions and IL-12-dependent Th1 response. Leishmania donovani-infected macrophages induced Th2 response but miltefosine treatment reversed the response to Th1-type. Thus, our data define for the first time the mechanistic basis of host cell-dependent anti-leishmanial function of miltefosine.

In leishmaniasis due to Leishmania guyanensis infection, distinct intralesional interleukin-10 and Foxp3 mRNA expression are associated with unresponsiveness to treatment

The presence of intralesional natural regulatory T cells, characterized by the expression of Foxp3 mRNA, was analyzed in patients with localized leishmaniasis due to Leishmania guyanensis infection that was unresponsive to treatment with pentamidine isethionate. Foxp3 mRNA levels were associated with unresponsiveness to treatment among patients with a lesion duration of 1 month, but this association was not observed among patients with a lesion duration of <1 month. In conclusion, high intralesional expression of Foxp3 might be an indicator of poor response to treatment, depending on the duration of lesions.

Can type-1 responses against intracellular pathogens be T helper 2 cytokine dependent?

While control of intracellular pathogens, such as the protozoan Leishmania, is dependent on the generation of type-1 immune responses, the role of T helper 2 cytokines in the disease process is more controversial. Traditionally these cytokines were perceived as counter-regulating type-1 responses and promoting disease exacerbation. Nevertheless a substantial body of evidence now exists suggesting that the development of effective type-1 immunity can involve the significant involvement of the Th2 cytokines IL-4 and IL-13. This article reviews, using Leishmania species in particular, the circumstances under which these cytokines can promote protective type-1 immunity.

Meglumine antimonate directly increases phagocytosis, superoxide anion and TNF-alpha production, but only via TNF-alpha it indirectly increases nitric oxide production by phagocytes of healthy individuals, in vitro

Leishmania has developed mechanisms to escape from immune defense of phagocytes by inhibiting microbicidal oxygen and nitrogen radicals. This work evaluated the influence of meglumine antimonate (Sb(V)) on the phagocyte functions involved in the defense against leishmania, through phagocytosis, reactive oxygen, nitrogen and TNF-alpha production in the absence or presence of the drug, in vitro. Meglumine antimonate increased the number of Saccharomyces cerevisiae ingested by monocyte and the percentage of these cells engaged in phagocytosis, which resulted in an increase of the monocyte phagocytic index by 158%. Meglumine antimonate also increased the number of S. cerevisiae ingested by neutrophil and the percentage of these cells engaged in phagocytosis, increasing the neutrophil phagocytic index by 219%. The median of percent reduction of NBT was significantly increased after treatment with this pentavalent antimony from 89.5% to 96.5%. Meglumine antimonate had no influence on nitric oxide production, but it significantly increased the mean+/-SEM production of tumor necrosis factor by 230%. However, monocytes incubated with TNF significantly increased NO production. This antimonial increased the phagocytic capacity of monocytes and neutrophils and enhanced superoxide anion production by phagocytes, which represent the first line of defense against the parasite. Furthermore, meglumine antimonate increased TNF, and via this cytokine, it may also indirectly increase NO production. Our data suggest that these immunomodulatory effects of meglumine antimonate may play a role in fighting leishmania and that meglumine antimonate provides the phagocytes with a mechanism that prevents leishmania from escaping immune defense.

Efficacy of different treatment regimens of marbofloxacin in canine visceral leishmaniosis: a pilot study

This phase II, randomized, open-label field trial was designed to evaluate and compare the safety and efficacy of four treatment durations (10, 20, 28 or 40 days) with marbofloxacin administered orally at the dosage of 2mg/kg once a day for canine visceral leishmaniosis. Twenty-four dogs naturally infected with visceral leishmaniosis and without biochemical disorder evidences of renal insufficiency, were recruited by two Greek veterinarian clinics. They were also randomly assigned to one of the four treatment duration groups, and have been clinically, haematologically, biochemically and parasitologically followed-up regularly for 9 months. Efficacy was achieved for 5/6 dogs treated for 28 days, 4/6 dogs treated for 10 or 20 days and for 3/6 dogs treated for 40 days. Moreover, efficacy was reached more quickly (58.4 days) in dogs treated for 28 days. Improvement of clinical signs tended to be better and faster in the 28 days treatment group too. After 9 months of follow-up, a total of three cases could be considered as relapsing (two dogs treated for 40 days and one dog treated for 28 days). There was a significant reduction in amastigotes density in macrophages after 3 months in the four groups when compared with the parasite density at inclusion. No adverse effects were noticed during this 9 months study. Results obtained with marbofloxacin at the dosage of 2mg/kg once a day for 28 days seem encouraging and may offer a safe alternative for treating canine visceral leishmaniosis.

Inhibition of ABC transporters abolishes antimony resistance in Leishmania Infection

The emergence of antimony (Sb) resistance has jeopardized the treatment of visceral leishmaniasis in various countries. Previous studies have considered the part played by leishmanial parasites in antimony resistance, but the involvement of host factors in the clinical scenario remained to be investigated. Here we show that unlike infection with Sb-sensitive (Sbs) Leishmania donovani, infection with Sb-resistant (Sb r) L. donovani induces the upregulation of multidrug resistance-associated protein 1 (MRP1) and permeability glycoprotein (P-gp) in host cells, resulting in a nonaccumulation of intracellular Sb following treatment with sodium antimony gluconate (SAG) favoring parasite replication. The inhibition of MRP1 and P-gp with resistance-modifying agents such as lovastatin allows Sb accumulation and parasite killing within macrophages and offers protection in an animal model in which infection with Sb r L. donovani is otherwise lethal. The occurrence of a similar scenario in clinical cases is supported by the findings that unlike monocytes from SAG-sensitive kala-azar (KA) patients, monocytes from SAG-unresponsive KA patients overexpress P-gp and MRP1 and fail to accumulate Sb following in vitro SAG treatment unless pretreated with inhibitors of ABC transporters. Thus, the expression status of MRP1 and P-gp in blood monocytes may be used as a diagnostic marker for Sb resistance and the treatment strategy can be designed accordingly. Our results also indicate that lovastatin, which can inhibit both P-gp and MRP1, might be beneficial for reverting Sb resistance in leishmaniasis as well as drug resistance in other clinical situations, including cancer.

Antimonial treatment of visceral leishmaniasis: are current in vitro susceptibility assays adequate for prognosis of in vivo therapy outcome?

In most of the Indian subcontinent, the first line treatment for visceral leishmaniasis (VL) is sodium stibogluconate (SSG), an antimonial drug, but the efficacy of the drug varies according to region. We aimed to characterize the in vitro antimony susceptibility of clinical isolates of Nepalese VL patients, and to correlate this in vitro parasite phenotype to clinical therapy outcome. Thirty-three clinical isolates of L. donovani were taken from patients with known disease history. These isolates were typed and the susceptibility of intracellular amastigotes to pentavalent (SbV) and trivalent (SbIII) antimonials was determined. We observed (i) 22 SbV-resistant isolates out of 33 tested and (ii) 3 SbIII-resistant isolates out of 12 tested. Amongst the latter, there were three combinations of in vitro phenotypes: (i) parasites sensitive (n=4) or (ii) resistant to both drugs (n=3) and (iii) resistant to SbV only (n=5). There was no geographical clustering in terms of in vitro susceptibility. The relation between the in vitro susceptibility to antimonials and the corresponding in vivo treatment outcome was ambiguous. Our results highlight the need to adjust the currently used Leishmania drug susceptibility assays if they are to be used for prognosis of in vivo SSG treatment outcome.

The immunology of parasite infections in immunocompromised hosts

Immune compromise can modify the severity and manifestation of some parasitic infections. More widespread use of newer immnosuppressive therapies, the growing population of individuals with immunocompromised states as well as the prolonged survival of these patients have altered the pattern of parasitic infection. This review article discusses the burden and immunology of parasitic infections in patients who are immunocompromised secondary to congenital immunodeficiency, malnutrition, malignancy, and immunosuppressive medications. This review does not address the literature on parasitic infections in the setting of HIV-1 infection.

Endogenous interleukin-18 is involved in immunity to Leishmania donovani but its absence does not adversely influence the therapeutic activity of sodium stibogluconate

Immunity to Leishmania donovani is associated with an interleukin (IL)-12 driven T helper 1 (Th1) response. In addition, the ability to respond to chemotherapy with sodium stibogluconate (SSG) requires a fully competent immune response and both Th1 and Th2 responses have been shown to positively influence the outcome of drug treatment. In the present study, the influence of IL-18, which can modulate both interferon (IFN)-gamma and IL-4 production, on the outcome of primary L. donovani infection and SSG therapy following infection was assessed using BALB/c IL-18-deficient and wild type mice. IL-18 deficiency was associated with an increased susceptibility to L. donovani infection, evident by day 40 post infection, resulting in higher parasite burdens in the spleen, liver, and bone marrow compared with wild type control animals. Infected IL-18-deficient mice had significantly lower splenocyte concanavalin A (ConA) induced IFN-gamma production as well as lower serum IL-12 and IFN-gamma levels, indicating a reduced Th1 response. However, drug treatment was equally effective in both mouse strains and restored serum IL-12 and IFN-gamma levels, and IFN-gamma production by ConA stimulated splenocytes of IL-18-deficient mice, to levels equivalent to similarly treated wild type mice.

Sodium antimony gluconate induces generation of reactive oxygen species and nitric oxide via phosphoinositide 3-kinase and mitogen-activated protein kinase activation in Leishmania donovani-infected macrophages

Pentavalent antimony complexes, such as sodium stibogluconate and sodium antimony gluconate (SAG), are still the first choice for chemotherapy against various forms of leishmaniasis, including visceral leishmaniasis, or kala-azar. Although the requirement of a somewhat functional immune system for the antileishmanial action of antimony was reported previously, the cellular and molecular mechanism of action of SAG was not clear. Herein, we show that SAG induces extracellular signal-regulated kinase 1 (ERK-1) and ERK-2 phosphorylation through phosphoinositide 3-kinase (PI3K), protein kinase C, and Ras activation and p38 mitogen-activated protein kinase (MAPK) phosphorylation through PI3K and Akt activation. ERK-1 and ERK-2 activation results in an increase in the production of reactive oxygen species (ROS) 3 to 6 h after SAG treatment, while p38 MAPK activation and subsequent tumor necrosis factor alpha release result in the production of nitric oxide (NO) 24 h after SAG treatment. Thus, this study has provided the first evidence that SAG treatment induces activation of some important components of the intracellular signaling pathway, which results in an early wave of ROS-dependent parasite killing and a stronger late wave of NO-dependent parasite killing. This opens up the possibility of this metalloid chelate being used in the treatment of various diseases either alone or in combination with other drugs and vaccines.

Drug resistance in leishmaniasis

Leishmaniasis is a complex disease, with visceral and cutaneous manifestations, and is caused by over 15 different species of the protozoan parasite genus Leishmania. There are significant differences in the sensitivity of these species both to the standard drugs, for example, pentavalent antimonials and miltefosine, and those on clinical trial, for example, paromomycin. Over 60% of patients with visceral leishmaniasis in Bihar State, India, do not respond to treatment with pentavalent antimonials. This is now considered to be due to acquired resistance. Although this class of drugs has been used for over 60 years for leishmaniasis treatment, it is only in the past 2 years that the mechanisms of action and resistance have been identified, related to drug metabolism, thiol metabolism, and drug efflux. With the introduction of new therapies, including miltefosine in 2002 and paromomycin in 2005-2006, it is essential that there be a strategy to prevent the emergence of resistance to new drugs; combination therapy, monitoring of therapy, and improved diagnostics could play an essential role in this strategy.

Canine visceral leishmaniasis: Comparison of in vitro leishmanicidal activity of marbofloxacin, meglumine antimoniate and sodium stibogluconate

The control of canine leishmaniasis largely depends on the success of treatment. Drugs currently available to treat this disease are toxic and partially effective. The curative effect of marbofloxacin, a third-generation fluoroquinolone developed for veterinarian individual treatment, was evaluated in vitro in the presence of Leishmania infantum promastigotes and dog-monocyte-derived macrophages; meglumine antimoniate and sodium stibogluconate were used as comparative treatments. We observed that the killing of Leishmania promastigotes and intracellular amastigotes by marbofloxacin was dose-dependent. We demonstrated that successful treatment of canine infected macrophages for 48 h was possible with 500 microg/ml of marbofloxacin. Leishmanicidal activity acted through a TNF-alpha and nitric oxide pathway and correlated with the generation of nitric oxide (NO(2)) production by monocytes derived macrophages from infected (23+/-5 microM) or healthy (21+/-6 microM) dogs, in comparison with NO(2) concentration in infected/non-treated macrophages (< 3 microM, P<0.01). This significant induced parasiticidal effect correlated with extensive elimination of amastigotes by macrophages derived from infected (11+/-5) and healthy dogs (6+/-2), when compared to infected/non-treated macrophages (530+/-105 and 472+/-86 amastigotes, respectively, P< 0.01). Marbofloxacin was shown to be non-toxic at 500 microg/ml in vitro and no cell apoptosis was observed. The molecule was able to induce a parasitic process after significant elimination of amastigotes in leishmania-infected dog macrophages. We propose that marbofloxacin, compared to standard chemotherapeutic agents (meglumine antimoniate and sodium stibogluconate), could be an effective and pragmatic oral route alternative to treat canine leishmaniasis.

Sodium Stibogluconate Interacts with IL-2 in Anti-Renca Tumor Action via a T Cell-Dependent Mechanism in Connection with Induction of Tumor-Infiltrating Macrophages

IL-2 therapy results in 10-20% response rates in advanced renal cell carcinoma (RCC) via activating immune cells, in which the protein tyrosine phosphatase Src homology 2 domain-containing phosphatase 1 (SHP-1) is a key negative regulator. Based on finding that sodium stibogluconate (SSG) inhibited SHP-1, the anti-RCC potential and action mechanism of SSG and SSG/IL-2 in combination were investigated in a murine renal cancer model (Renca). Despite its failure to inhibit Renca cell proliferation in cultures, SSG induced 61% growth inhibition of Renca tumors in BALB/c mice coincident with an increase (2-fold) in tumor-infiltrating macrophages (Mphi). A combination of SSG and IL-2 was more effective in inhibiting tumor growth (91%) and inducing tumor-infiltrating Mphi (4-fold), whereas IL-2 alone had little effect. Mphi increases were also detected in the spleens of mice treated with SSG (3-fold) or SSG/IL-2 in combination (6-fold), suggesting a systemic Mphi expansion similar to those in SHP-deficient mice. T cell involvement in the anti-Renca tumor action of the combination was suggested by the observations that the treatment induced spleen IFN-gamma T cells in BALB/c mice, but failed to inhibit Renca tumor growth in athymic nude mice and that SSG treatment of T cells in vitro increased production of IFN-gamma capable of activating tumoricidal Mphi. The SSG and SSG/IL-2 combination treatments were tolerated in the mice. These results together demonstrate an anti-Renca tumor activity of SSG that was enhanced in combination with IL-2 and functions via a T cell-dependent mechanism with increased IFN-gamma production and expansion/activation of Mphi. Our findings suggest that SSG might improve anti-RCC efficacy of IL-2 therapy by enhancing antitumor immunity.

Antagonizing deactivating cytokines to enhance host defense and chemotherapy in experimental visceral leishmaniasis

In experimental visceral leishmaniasis, inhibition of interleukin 10 (IL-10) signaling enhances Th1-cell-associated responses, promoting gamma interferon (IFN-gamma) secretion, granuloma assembly, macrophage activation with substantial liver parasite killing, and synergy with pentavalent antimony (Sb) chemotherapy. To determine if inhibiting other suppressive cytokines has similar therapeutic potential, Leishmania donovani-infected BALB/c mice were injected with anti-IL-4 monoclonal antibody or receptor fusion antagonists of IL-13 or transforming growth factor beta (TGF-beta). Targeting IL-13 or TGF-beta enabled inhibition of L. donovani replication but little parasite killing; anti-IL-4 had no effect. None of the three antagonists promoted IFN-gamma production, granuloma maturation, or Sb efficacy. Excess IL-13 and TGF-beta exacerbated liver infection; however, effects were transient. Among IL-10, IL-4, IL-13, and TGF-beta, cytokines capable of disabling Th1-cell mechanisms (including those which support chemotherapy), IL-10 appears to be the appropriate target for therapeutic inhibition in visceral L. donovani infection.