Antigen-specific immunosuppression in visceral leishmaniasis is cell mediated

The role of CD4+ T cells in visceral leishmaniasis; new and emerging roles for NKG7 and TGFβ

Visceral leishmaniasis is a potentially devastating neglected tropical disease caused by the protozoan parasites Leishmania donovani and L. infantum (chagasi). These parasites reside in tissue macrophages and survive by deploying a number of mechanisms aimed at subverting the host immune response. CD4+ T cells play an important role in controlling Leishmania parasites by providing help in the form of pro-inflammatory cytokines to activate microbiocidal pathways in infected macrophages. However, because these cytokines can also cause tissue damage if over-produced, regulatory immune responses develop, and the balance between pro-inflammatory and regulatory CD4+ T cells responses determines the outcomes of infection. Past studies have identified important roles for pro-inflammatory cytokines such as IFNγ and TNF, as well as regulatory co-inhibitory receptors and the potent anti-inflammatory cytokine IL-10. More recently, other immunoregulatory molecules have been identified that play important roles in CD4+ T cell responses during VL. In this review, we will discuss recent findings about two of these molecules; the NK cell granule protein Nkg7 and the anti-inflammatory cytokine TGFβ, and describe how they impact CD4+ T cell functions and immune responses during visceral leishmaniasis.

Intramuscular Immunization with a Liposomal Multi-Epitope Chimeric Protein Induces Strong Cellular Immune Responses against Visceral Leishmaniasis

Control of the intracellular parasite Leishmania (L.) requires the activation of strong type 1 cellular immune responses. Towards this goal, in the present study, a multiepitope chimeric protein named LiChimera was encapsulated into cationic liposomes and its protective efficacy against experimental visceral leishmaniasis was investigated. Liposomal LiChimera conferred significant protection against L. infantum as evidenced by the significantly reduced parasite loads in the spleen and liver. Protection detected in Lipo:LiChimera-immunized mice was dependent on the differentiation of long-lasting cellular immune responses and particularly the induction of antigen-specific multifunctional memory CD4+ TH1 and CD8+ T cells that persisted during infection, as evidenced by the persistent high production of IFN-γ and IL-2 and proliferation activity. Notably, protected mice were also characterized by significantly low numbers of non-regulatory CD4+ T cells able to co-produce IFN-γ and IL-10, an important population for disease establishment, as compared to non-immunized control group. Collectively, these results demonstrate that cationic liposomes containing LiChimera can be considered an effective candidate vaccine against visceral leishmaniasis.

From Infection to Death: An Overview of the Pathogenesis of Visceral Leishmaniasis

Kala-azar, also known as visceral leishmaniasis (VL), is a disease caused by Leishmania infantum and L. donovani. Patients experience symptoms such as fever, weight loss, paleness, and enlarged liver and spleen. The disease also affects immunosuppressed individuals and has an overall mortality rate of up to 10%. This overview explores the literature on the pathogenesis of preclinical and clinical stages, including studies in vitro and in animal models, as well as complications and death. Asymptomatic infection can result in long-lasting immunity. VL develops in a minority of infected individuals when parasites overcome host defenses and multiply in tissues such as the spleen, liver, and bone marrow. Hepatosplenomegaly occurs due to hyperplasia, resulting from parasite proliferation. A systemic inflammation mediated by cytokines develops, triggering acute phase reactants from the liver. These cytokines can reach the brain, causing fever, cachexia and vomiting. Similar to sepsis, disseminated intravascular coagulation (DIC) occurs due to tissue factor overexpression. Anemia, hypergammaglobulinemia, and edema result from the acute phase response. A regulatory response and lymphocyte depletion increase the risk of bacterial superinfections, which, combined with DIC, are thought to cause death. Our understanding of VL's pathogenesis is limited, and further research is needed to elucidate the preclinical events and clinical manifestations in humans.

Potential Biomarkers for Asymptomatic Visceral Leishmaniasis among Iraq-Deployed U.S. Military Personnel

Visceral leishmaniasis (VL) is a chronic infection caused by Leishmania (L.) donovani or L. infantum parasites. Despite having the infection, most individuals never develop the clinical disease and are able to control the parasite and remain asymptomatic. However, some progress to symptomatic VL, leading to death if untreated. The host immune response has a major role in determining the progression and severity of the clinical manifestations in VL; several immune biomarkers of symptomatic VL have been described with interferon-gamma release as a surrogate biomarker of host cellular immunity. However, new biomarkers to identify asymptomatic VL (AVL) are needed for the identification of people at risk for VL activation. In our study, levels of chemokine/cytokine in the supernatants of peripheral mononuclear blood cells (PBMC) from 35 AVL⁺ Iraq-deployed participants, stimulated in vitro with soluble Leishmania antigen for 72 h, were assessed by a bead-based assay that allows the measurement of multiple analytes. PBMC of AVL-negative military beneficiaries were used as controls. Monocyte Chemoattractant Protein-1, Monokine Induced by Gamma Interferon and Interleukin-8, were detected at high levels in AVL⁺ stimulated cultures from Iraq deployers compared to uninfected controls. Measurement of chemokine/cytokine levels can identify cellular immune responses in AVL⁺ asymptomatic individuals.

Multifunctional, TNF-α and IFN-γ-Secreting CD4 and CD8 T Cells and CD8High T Cells Are Associated With the Cure of Human Visceral Leishmaniasis

Visceral leishmaniasis (VL) is a chronic and often fatal disease caused by protozoans of the genus Leishmania that affects millions of people worldwide. Patients with symptomatic VL have an impaired anti-Leishmania-specific CD4⁺ T-cell response, which is reversed after clinical cure. In contrast, the quality of the CD4⁺ and CD8⁺ T-cell responses involved in resistance and/or cure of VL relies on the capability of these cells to activate polyfunctional and memory responses, which are associated with the simultaneous production of three cytokines: IFN-γ, IL-2, and TNF-α. Models for the development of CD4 and CD8 T-cell quality in memory and protection to leishmaniasis have been described previously. We aimed to assess the functionality of the T cells involved in the recovery of the immune suppression throughout the VL treatment. Therefore, we cultured peripheral blood mononuclear cells (PBMCs) from VL patients and healthy controls in vitro with soluble Leishmania antigen (SLA). Cell surface markers and intracellular cytokine production were determined on days 7, 14, 21, 30, 60, 90, and 180 after the beginning of chemotherapy. We observed that the frequencies of CD4⁺TNF-α⁺IFN-γ⁺ and the multifunctional CD4⁺IL-2⁺TNF-α⁺IFN-γ⁺, together with CD4⁺TNF-α⁺ and CD4⁺IFN-γ⁺ T cells, increased throughout and at the end of the treatment, respectively. In addition, enhanced frequencies of CD8⁺IL-2⁺TNF-α⁺IFN-γ⁺ and CD8⁺TNF-α⁺IFN-γ T cells were also relevant in the healing process. Noteworthy, the frequencies of the CD4⁺ and CD8 central-memory T cells, which produce IL-2, TNF-α, and IFN-γ and ensure the memory response against parasite reinfection, are significantly enhanced in cured patients. In addition, the subset of the non-functional CD8^Low population is predominant in VL untreated patients and decreases along the chemotherapy treatment. In contrast, a CD8^High subset increased towards the cure. Furthermore, the cure due to treatment with meglumine antimoniate or with liposomal amphotericin B was associated with the recovery of the T-cell immune responses. We described the evolution and participation of functional T cells during the treatment of patients with VL. Our results disclosed that the clinical improvement of patients is significantly associated with the participation of the CD4⁺ and CD8⁺ cytokine-secreting T cells.

Potential of TLR agonist as an adjuvant in Leishmania vaccine against visceral leishmaniasis in BALB/c mice

Morbid infection of leishmaniasis is posing threat to humankind due to its exacerbating prevalence in newer emerging areas. Moreover, the availability of limited drugs, their toxicity, limited efficacy, the emergence of drug resistance, and unavailability of vaccines are the major obstacles in its elimination. This implies the demand for a prophylactic vaccine candidate to prevent this infection and resulting fatal disease. We evaluated gardiquimod (a toll-like receptor-7 agonist) for its action as an adjuvant with the heat-killed antigen of Leishmania donovani. BALB/c mice were immunized with a vaccine either with or without adjuvant and given challenge infection. The results depicted the low parasite burden, higher delayed-type hypersensitivity response, and higher levels of IgG2a, Th1 cytokines, and NO in immunized mice in contrast to infected control mice. Low levels of Th2 cytokines and IgG1 were also noticed in the vaccinated mice than in infected mice. The mice immunized with a combination of gardiquimod and heat-killed antigen showed maximum efficacy. The results from the present study reflect the potential of tested vaccine candidate with gardiquimod as an adjuvant.

Adjuvant effects of TLR agonist gardiquimod admixed with Leishmania vaccine in mice model of visceral leishmaniasis

Tropical and subtropical areas of the world are affected by leishmaniasis, which is caused by Leishmania spp. It has been categorized as an NTD (neglected tropical disease) because of its negligence. The sand fly of genus Phlebotomus acts as the vector for the transmission of the promastigote form of this protozoan parasite to the mammalian host where it converts to amastigote form in the macrophages. Visceral form of leishmaniasis (VL) is a deadly infection in the endothelial system of the human and other mammals. Only a few chemotherapeutic agents are available for the treatment of this infectious disease whereas no vaccine is available for the control of leishmanial infection. Therefore in the current study, we have tested the effects of gardiquimod (a TLR agonist) as an adjuvant in combination with the formalin-killed antigen of L. donovani as a vaccine. The mice were vaccinated thrice at an interval of 2 weeks and challenged with L. donovani promastigotes after 2 weeks of the last vaccination. We assessed the parasite load, delayed-type hypersensitivity (DTH) responses, humoral and cell-mediated immune response in BALB/c mice before and after challenge infection with L. donovani. Immunized mice were found to have the least parasite load, high DTH response, elevated levels of Th1 cytokines, IgG2a, and nitric oxide than non-immunized and infected control mice. The efficacy of the vaccine was boosted with the use of adjuvant gardiquimod that depicts its potential as an adjuvant in this study. Our study is reporting the adjuvant effects of gardiquimod for the first time. Further studies using other Leishmania species can be performed to signify its role.

Immune induction by adjuvanted Leishmania donovani vaccines against the visceral leishmaniasis in BALB/c mice

Visceral leishmaniasis (VL) is a neglected tropical disease caused by Leishmania donovani or Leishmania infantum. Currently, the patients are treated with chemotherapeutic drugs; however, their toxicity limits their use. It would be desirable to develop a vaccine against this infection. In this study, we assessed the efficacy of different vaccine formulations at variable time points. Heat-killed (HK) antigen of Leishmania donovani was adjuvanted with two adjuvants (AddaVax and Montanide ISA 201) and three immunizations at a gap of 2 weeks (wk) were given to BALB/c mice. After 2 weeks of the last booster, mice were given challenge infection and sacrificed before challenge and after 4wk, 8wk, and 12 wk post-challenge. Significant protective immunity was observed in all the immunized animals and it was indicated by the notable rise in delayed-type hypersensitivity (DTH) response, remarkably declined parasite burden, a significant increase in the levels of interferon-gamma (IFN-γ), interleukin-12, interleukin-17 (Th1 cytokines), and IgG2a in contrast to infected control mice. Montanide ISA 201 with HK antigen provided maximum protection followed by AddaVax with HK and then HK alone. These findings elaborate on the importance of the tested adjuvants in the vaccine formulations against murine visceral leishmaniasis.

Adjuvanted vaccines driven protection against visceral infection in BALB/c mice by Leishmania donovani

Kinteoplastid protozoan parasite of genus Leishmania is the pathogen that causes leishmaniasis. Its prevalence is highest after malaria and visceral leishmaniasis is the most dreaded form of infection. No vaccine is available for the disease management and it relies wholly on a few chemotherapeutic agents which are toxic and besides drug resistance their costs are the limitations. Therefore, development of an effective vaccine is urgently required. In this study, Montanide ISA 201 and AddaVax were assessed for their adjuvant potential along with formalin-inactivated or killed vaccine for the immune induction. Immunological and parasitological studies were conducted to evaluate the efficacy of different vaccine formulations in BALB/c mice before challenge infection as well as 4, 8, and 12 weeks after challenge. The efficacy of vaccines was evidenced with reduced parasite burden, the higher DTH response, Th1 cytokines, and IgG2a isotype antibody in immunized mice. All the vaccines showed their potential against Leishmania donovani infection and vaccine formulated with Montanide ISA 201 exhibited maximum efficacy. Our results suggest the potential of these vaccine formulations in controlling Leishmania infection.

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.

Meglumine Antimoniate and Miltefosine Combined With Allopurinol Sustain Pro-inflammatory Immune Environments During Canine Leishmaniosis Treatment

Canine leishmaniosis (CanL) caused by Leishmania infantum is a zoonotic disease of global concern. Antileishmanial drug therapies commonly used to treat sick dogs improve their clinical condition, although when discontinued relapses can occur. Thus, the current study aims to evaluate the effect of CanL treatments in peripheral blood, lymph node, and bone marrow cytokine profile associated with clinical recovery. Two groups of six dogs diagnosed with CanL were treated with miltefosine combined with allopurinol and meglumine antimoniate combined with allopurinol (MT+A and MG+A), respectively. At diagnosis and after treatment, during a 3-month follow-up, clinical signs, hematological and biochemical parameters, urinalysis results and antileishmanial antibody titers were registered. Furthermore, peripheral blood, popliteal lymph node, and bone marrow samples were collected to assess the gene expression of IL-2, IL-4, IL-5, IL-10, IL-12, TNF-α, TGF-β, and IFN-γ by qPCR. In parallel, were also evaluated samples obtained from five healthy dogs. Both treatment protocols promoted the remission of clinical signs as well as normalization of hematological and biochemical parameters and urinalysis values. Antileishmanial antibodies returned to non-significant titers in all dogs. Sick dogs showed a generalized upregulation of IFN-γ and downregulation of IL-2, IL-4, and TGF-β, while gene expression of IL-12, TNF-α, IL-5, and IL-10 varied between groups and according to evaluated tissue. A trend to the normalization of cytokine gene expression was induced by both miltefosine and meglumine antimoniate combined therapies. However, IFN-γ gene expression was still up-regulated in the three evaluated tissues. Furthermore, the effect of treatment in the gene expression of cytokines that were not significantly changed by infection, indicates that miltefosine and meglumine antimoniate combined therapy directly affects cytokine generation. Both combined therapies are effective in CanL treatment, leading to sustained pro-inflammatory immune environments that can compromise parasite survival and favor dogs' clinical cure. In the current study, anti-inflammatory and regulatory cytokines do not seem to play a prominent role in CanL or during clinical recovery.

Cryptococcemia presenting as an opportunistic infection due to chronic visceral leishmaniasis

We present a case of visceral leishmaniasis (VL) in a previously immunocompetent patient. At the time of presentation, he was co-infected with Cryptococcus neoformans. This case demonstrates how infectious diseases besides human immunodeficiency virus can lead to immunosuppression for patients, placing them at risk of opportunistic infections.

Biomarkers for Zoonotic Visceral Leishmaniasis in Latin America

In Latin America, zoonotic visceral leishmaniasis (ZVL) arising from infection by L. infantum is primarily transmitted by Lutzomyia longipalpis sand flies. Dogs, which are chronic reservoirs of L. infantum, are considered a significant risk factor for acquisition of ZVL due to their close proximity to humans. In addition, as a vector-borne disease the intensity of exposure to vector sand flies can also enhance the risk of developing ZVL. Traditionally, IFN-γ and IL-10 are considered as the two main cytokines which determine the outcome of visceral leishmaniasis. However, more recently, the literature has demonstrated that different mediators, such as lipid mediators (PGE-2, PGF-2 alfa, LTB-4, resolvins) and other important inflammatory and anti-inflammatory cytokines are also involved in the pathogenicity of ZVL. Analysis of a greater number of mediators allows for a more complete view of disease immunopathogenesis. Additionally, our knowledge has expanded to encompass different biomarkers associated to disease severity and healing after specific treatments. These parameters can also be used to better define new potential targets for vaccines and chemotherapy for ZVL. Here, we will provide an overview of ZVL biomarkers identified for both humans and dogs and discuss their merits and shortcomings. We will also discuss biomarkers of vector exposure as an additional tool in our arsenal to combat ZVL.

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

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

The Deadly Dance of B Cells with Trypanosomatids

B cells are notorious actors for the host's protection against several infectious diseases. So much so that early vaccinology seated its principles upon their long-term protective antibody secretion capabilities. Indeed, there are many examples of acute infectious diseases that are combated by functional humoral responses. However, some chronic infectious diseases actively induce immune deregulations that often lead to defective, if not deleterious, humoral immune responses. In this review we summarize how Leishmania and Trypanosoma spp. directly manipulate B cell responses to induce polyclonal B cell activation, hypergammaglobulinemia, low-specificity antibodies, limited B cell survival, and regulatory B cells, contributing therefore to immunopathology and the establishment of persistent infections.

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.

Splenic CD4+ T Cells in Progressive Visceral Leishmaniasis Show a Mixed Effector-Regulatory Phenotype and Impair Macrophage Effector Function through Inhibitory Receptor Expression

Visceral leishmaniasis (VL), caused by infection with the intracellular protozoan Leishmania donovani, is a chronic progressive disease with a relentlessly increasing parasite burden in the spleen, liver and bone marrow. The disease is characterized by fever, splenomegaly, cachexia, and pancytopenia, and progresses to death if not treated. Control of Leishmania infection is mediated by Th1 (IFNγ-producing) CD4+ T cells, which activate macrophages to produce nitric oxide and kill intracellular parasites. However, despite expansion of CD4+ T cells and increased IFNγ expression in the spleen, humans with active VL do not control the infection. We used an experimental model of chronic progressive VL in hamsters, which mimics clinical and pathological features seen in humans, to better understand the mechanisms that lead to progressive disease. Transcriptional profiling of the spleen during chronic infection revealed expression of markers of both T cell activation and inhibition. CD4+ T cells isolated from the spleen during chronic progressive VL showed mixed expression of Th1 and Th2 cytokines and chemokines, and were marginally effective in controlling infection in an ex vivo T cell-macrophage co-culture system. Splenic CD4+ T cells and macrophages from hamsters with VL showed increased expression of inhibitory receptors and their ligands, respectively. Blockade of the inhibitory receptor PD-L2 led to a significant decrease in parasite burden, revealing a pathogenic role for the PD-1 pathway in chronic VL. PD-L2 blockade was associated with a dramatic reduction in expression of host arginase 1, but no change in IFNγ and inducible nitric oxide synthase. Thus, the expression of counter-regulatory molecules on splenic CD4+ T cells and macrophages promotes a more permissive macrophage phenotype and attenuates intracellular parasite control in chronic progressive VL. Host-directed adjunctive therapy targeting the PD-1 regulatory pathway may be efficacious for VL.

Immunogenicity and protective efficacy of DNA vaccine against visceral leishmaniasis in BALB/c mice

The current study was designed to examine the protective efficacy of DNA vaccines based on gp63 and Hsp70 against murine visceral leishmaniasis. Inbred BALB/c mice were immunized subcutaneously twice at an interval of three weeks with pcDNA3.1(+) encoding T cell epitopes of gp63 and Hsp70 individually and in combination. Animals were challenged intracardially with 107 promastigotes of Leishmania donovani 10 days post immunization and sacrificed 1, 2 and 3 months post challenge. The immunized animals revealed a significant reduction (P < 0.05) in splenic and hepatic parasite burden as compared to the infected controls. Maximum reduction in parasite load (P < 0.05) was observed in animals treated with a combination of pcDNA/gp63 and pcDNA/Hsp70. These animals also showed heightened DTH response, increased IgG2a, elevated Th1 cytokines (IFN-γ and IL-2) and reduced IgG1 and IL-10 levels. Thus, mice immunized with the cocktail vaccine exhibited significantly greater protection in comparison to those immunized with individual antigens.

Evaluation of the immunoprophylactic potential of a killed vaccine candidate in combination with different adjuvants against murine visceral leishmaniasis

Despite a large number of field trials, till date no prophylactic antileishmanial vaccine exists for human use. Killed antigen formulations offer the advantage of being safe but they have limited immunogenicity. Recent research has documented that efforts to develop effective Leishmania vaccine have been limited due to the lack of an appropriate adjuvant. Addition of adjuvants to vaccines boosts and directs the immunogenicity of antigens. So, the present study was done to evaluate the effectiveness of four adjuvants i.e. alum, saponin, cationic liposomes and monophosphoryl lipid-A in combination with Autoclaved Leishmania donovani (ALD) antigen against murine visceral leishmaniasis (VL). BALB/c mice were immunized thrice with respective vaccine formulation. Two weeks after last booster, challenge infection was given. Mice were sacrificed 15 days after last immunization and on 30, 60 and 90 post infection/challenge days. A considerable protective efficacy was shown by all vaccine formulations. It was evident from significant reduction in parasite load, profound delayed type hypersensitivity responses (DTH), increased IgG2a titres and high levels of Th1 cytokines (IFN-γ, IL-12) as compared to the infected controls. However, level of protection varied with the type of adjuvant used. Maximum protection was achieved with the use of liposome encapsulated ALD antigen and it was closely followed by group immunized with ALD+MPL-A. Significant results were also obtained with ALD+saponin, ALD+alum and ALD antigen (alone) but the protective efficacy was reduced as compared to other immunized groups. The present study reveals greater efficacy of two vaccine formulations i.e. ALD+liposome and ALD+MPL-A against murine VL.

Plasmodium falciparum malaria and invasive bacterial co-infection in young African children: the dysfunctional spleen hypothesis

Children with recent or acute malaria episodes are at increased risk of invasive bacterial infections (IBI). However, the exact nature of the malaria-IBI association is still unclear. Young children have an age-related spleen immunologic immaturity, mainly due to the still ongoing development of the marginal zone (MZ) B cell subset. By mounting a rapid antibody response against encapsulated bacteria, these cells are critical for the defence against highly pathogenic microorganisms that do not elicit classical T cell-dependent responses. There is increasing evidence that the anatomy of the spleen becomes disorganized during malaria infection, with complete dissolution of the MZ and apoptosis of MZ B cells. Correspondingly, a reduction in the frequency of the peripheral equivalent of the MZ B cells has been found in malaria endemic areas. A remarkable similarity exists in IBI susceptibility between African children with malaria and hyposplenic or splenectomized patients. However, studies specifically assessing the immune function of the spleen in controlling bacterial infections in young children with malaria are scarce.

Here, it is hypothesized that Plasmodium falciparum malaria infection constitutes a detrimental factor in the still immature spleen function of young children, resulting in a factually hyposplenic state during malaria episodes, putting children with malaria at a high risk to develop life-threatening bacterial infections. Studies to confirm or reject this hypothesis are greatly needed, as well as the development of affordable and feasible tools to assess the immune spleen function against encapsulated bacteria in children with malaria.

Ultrastructural study on tissue alterations caused by trypanosomatids in experimental murine infections

The ultrastructural study in different tissues of mice experimentally infected with isolates of Trypanosoma evansi, Trypanosoma cruzi, and Leishmania mexicana reveals changes in cardiac myocytes, skeletal muscle fibers, and hepatic, adrenal, kidney, and spleen cells. Some of these changes were cytoarchitectural and others consisted of necrosis. Alterations in the microvasculature were also found. The mononuclear cell infiltrate included neutrophils, eosinophils, and macrophages. This work shows that diverse mice tissues are important target for trypanosomatids.

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.

Bone marrow parasite burden among patients with New World kala-azar is associated with disease severity

Kala-azar or visceral leishmaniasis, found mostly throughout the Indian Subcontinent, East Africa, and Brazil, kills 20,000-40,000 persons annually. The agents, Leishmania donovani and Leishmania infantum, are obligatory intracellular protozoa of mononuclear phagocytes found principally in the spleen and bone marrow. Protracted fever, anemia, wasting, hepatosplenomegaly, hemorrhages, and bacterial co-infections are typical features. One hundred and twenty-two (122) in-hospital patients were studied to verify if higher bone marrow parasite load estimated by quantitative polymerase chain reaction is associated with severe disease. The estimated median parasite load was 5.0 parasites/10(6) human nucleated cells. It is much higher in deceased than among survivors (median 75.0 versus 4.2). Patients who lost more weight had a higher parasite burden, as well as patients with epistaxis, abdominal pain, edema, and jaundice. This study suggests that higher parasite load is influenced by wasting, which may lead to more severe disease.

Protein malnutrition impairs the immune response and influences the severity of infection in a hamster model of chronic visceral leishmaniasis

Leishmaniasis remains one of the world's most devastating neglected tropical diseases. It mainly affects developing countries, where it often co-exists with chronic malnutrition, one of the main risk factors for developing the disease. Few studies have been published, however, on the relationship between leishmaniasis progression and malnutrition. The present paper reports the influence of protein malnutrition on the immune response and visceral disease development in adult hamsters infected with Leishmania infantum fed either standard or low protein diets. The low protein diet induced severe malnutrition in these animals, and upon infection with L. infantum 33% had severe visceral leishmaniasis compared to only 8% of animals fed the standard diet. The infected, malnourished animals showed notable leukocyte depletion, mild specific antibody responses, impairment of lymphoproliferation, presence of parasites in blood (16.67% of the hamsters) and significant increase of the splenic parasite burden. Animals fed standard diet suffered agranulocytosis and monocytopenia, but showed stronger specific immune responses and had lower parasite loads than their malnourished counterparts. The present results show that protein malnutrition promotes visceral leishmaniasis and provide clues regarding the mechanisms underlying the impairment of the immune system.

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.

The role of inflammatory and anti-inflammatory cytokines in the pathogenesis of human tegumentary leishmaniasis

In tegumentary leishmaniasis caused by Leishmania braziliensis, there is evidence that increased production of IFN-γ, TNF-α and absence of IL-10 is associated with strong inflammatory reaction and with tissue destruction and development of the lesions observed in cutaneous leishmaniasis (CL) and mucosal leishmaniasis (ML). We evaluate the role of regulatory cytokines and cytokine antagonists in the down-regulation of immune response in L. braziliensis infection. Peripheral blood mononuclear cells from CL and ML were stimulated with soluble Leishmania antigen in the presence or absence of regulatory cytokines (IL-10, IL-27 and TGF-β) or antagonists of cytokines (α-TNF-α and α-IFN-γ). Cytokines production (IL-10, IL-17, TNF-α and IFN-γ) was measured by ELISA. IL-10 and TGF-β downmodulate TNF-α and IL-17 production, whereas IL-27 had no effect in the production of TNF-α, IFN-γ and IL-17 in these patients. Neutralization of TNF-α decreased IFN-γ level and the neutralization of IFN-γ decreased TNF-α level and increased IL-10 production. This study demonstrate that IL-10 and TGF-β are cytokines that appear to be more involved in modulation of immune response in CL and ML patients. IL-10 might have a protective role, since the neutralization of IFN-γ decreases the production of TNF-α in an IL-10-dependent manner.

CD95 (FAS) and CD178 (FASL) induce the apoptosis of CD4+ and CD8+ cells isolated from the peripheral blood and spleen of dogs naturally infected with Leishmania spp

Infected dogs are urban reservoirs of Leishmania chagasi, which is a causative agent of visceral leishmaniasis (VL). Dogs exhibit immune suppression during the course of this disease, and lymphocyte apoptosis is involved in this process. To investigate apoptosis and the expression levels of FAS-FAS-associated death domain protein (CD95 or APO-1), FASL-FAS ligand protein (CD178), and TRAIL-TNF-related apoptosis-inducing ligand (CD253) receptors in peripheral blood mononuclear cells and spleen leukocytes from 38 symptomatic dogs with moderate VL and 25 healthy dogs were evaluated by flow cytometry. The apoptosis rate of blood and splenic CD4+ and CD8+ cells was higher in infected dogs than in healthy dogs. The expression levels of FAS and FASL in blood and splenic CD4+ cells were lower in infected dogs than in healthy dogs. FAS expression in CD8+ cells was higher in infected dogs than in healthy dogs; in contrast, FASL expression was lower in infected dogs. The expression of the TRAIL receptor increased only in splenic CD8+ cells from infected dogs. The FAS and FAS-L blocking antibodies confirmed the importance of these receptors in apoptosis. Our results enhance the current understanding of the immune response in dogs infected with L. chagasi, facilitating the future development of therapeutic interventions to reduce lymphocyte depletion.

Protective immunity using MPL-A and autoclaved Leishmania donovani as adjuvants along with a cocktail vaccine in murine model of visceral leishmaniasis

The current study is an extension of our previous study where we tested the protective efficacy of gp63 and Hsp70 against murine visceral leishmaniasis. The cocktail vaccine was combined with MPL-A and ALD adjuvants and the protection afforded by the three vaccines was compared. Inbred BALB/c mice were immunized twice at an interval of two weeks with the vaccine formulations. Two weeks after the booster, they were challenged with 10(7) promastigotes of Leishmania donovani and sacrificed on 30, 60 and 90 days post infection/challenge. The protective efficacy of vaccines was analyzed by assessment of the hepatic and splenic parasite burden and generation of cellular and humoral immune responses. The immunized animals revealed a significant reduction in parasite burden as compared to the infected controls. These animals also showed heightened DTH response, increased generation of IgG2a, IFN-γ and IL-2 by spleen cells. This was also accompanied by a decrease in the levels of IgG1 and IL-10. Mice immunized with gp63+Hsp70+MPL-A exhibited significantly greater protection in comparison to those immunized with gp63+Hsp70+ALD.

Lipopolysaccharide-Induced Cellular Activation May Participate in the Immunopathogenesis of Visceral Leishmaniasis Alone or in HIV Coinfection

Visceral Leishmaniasis (VL) is an infectious disease which constitutes a serious public health problem, integrating the list of neglected tropical diseases. The disease is characterized by a Leishmania-specific immune suppression T-cell depletion and a decrease of other hematopoietic cells. In parallel, an immunostimulatory response also occurs, represented by polyclonal B lymphocytes, T-cell activation, and systemic proinflammatory responses. Parasite antigens were believed to mediate both suppression and activation mechanisms, but these concepts are constantly being revised. Similar to reports on HIV/AIDS, we have proposed that gut parasitation by amastigotes and lymphocyte depletion could also affect gut-associated lymphoid tissue, leading to mucosal barrier breach and predisposing to microbial translocation. An increment of plasmatic lipopolysaccharide (LPS) levels observed in Brazilian VL patients was implicated in the reduced blood CD4⁺ and CD8⁺ T cell counts, systemic T-cell activation, pro-inflammatory cytokines and MIF plasma levels, suggesting that a bacterial molecule not associated with Leishmania infection can exert deleterious effects on immune system. Recent results also pointed that the proinflammatory response was potentiated in VL/HIV-AIDS coinfected patients. The LPS-mediated cell activation adds another concept to the immunopathogenesis of VL and can bring a rational for new therapeutic interventions that could ameliorate the management of these patients.

Immunobiology of visceral leishmaniasis

Visceral leishmaniasis (VL), commonly known as kala-azar, is caused by Leishmania donovani and Leishmania infantum (Leishmania chagasi in the Americas). These Leishmania species infect macrophages throughout the viscera, and parasites are typically found in the spleen, liver, and bone marrow. Patients with active disease typically exhibit marked immunosuppression, lack reactivity to the Leishmania skin test (LST), a delayed type hypersensitivity test, and their peripheral blood mononuclear cells (PBMC) fail to respond when stimulated with leishmanial antigens in vitro. However, most people infected with visceralizing species of Leishmania never develop disease. Understanding immune failure and the underlying immune mechanism that lead to disease as well as control of infection are key questions for research in this field. In this review, we discuss immunological events described in human and experimental VL and how these can affect the outcome of infection.

Leishmania chagasi naturally resistant to nitric oxide isolated from humans and dogs with visceral leishmaniasis in Brazil

Nitric oxide (NO) plays an important role as a leishmanicidal agent in murine macrophages. NO resistant Escherichia coli and Mycobacterium tuberculosis have been associated with poor outcomes of their resulting diseases. NO resistant Leishmania braziliensis has also been identified and exacerbates the clinical course of human leishmaniasis. We report, for the first time, natural resistance of Leishmania chagasi promastigotes to NO. These parasites were isolated from humans and dogs with visceral leishmaniasis. We also demonstrate that this resistance profile was associated with a greater survival capacity and a greater parasite burden in murine macrophages, independent of activation and after activation by IFN-γ and LPS.

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.

Regulatory T cells suppress T cell activation at the pathologic site of human visceral leishmaniasis

Suppression of T cell response is thought to be involved in the pathogenesis of visceral leishmaniasis (VL). Regulatory T cell (Treg) mediated immune-suppression is reported in animal models of Leishmania infection. However, their precise role among human patients still requires pathologic validation. The present study is aimed at understanding the frequency dynamics and function of Treg cells in the blood and bone marrow (BM) of VL patients. The study included 42 parasitologically confirmed patients, 17 healthy contact and 9 normal bone marrow specimens (NBM). We show i) the selective accumulation of Treg cells at one of the disease inflicted site(s), the BM, ii) their in vitro expansion in response to LD antigen and iii) persistence after successful chemotherapy. Results indicate that the Treg cells isolated from BM produces IL-10 and may inhibit T cell activation in IL-10 dependent manner. Moreover, we observed significantly higher levels of IL-10 among drug unresponsive patients, suggesting their critical role in suppression of immunity among VL patients. Our results suggest that IL-10 plays an important role in suppression of host immunity in human VL and possibly determines the efficacy of chemotherapy.

Importance of worldwide asymptomatic carriers of Leishmania infantum (L. chagasi) in human

Leishmaniasis due to Leishmania infantum (syn. L. chagasi) infection is a zoonotic disease present mainly in Mediterranean basin, central Asia and Brazil. Besides a limited number of human cases of clinical visceral leishmaniasis, a great number of infections remains asymptomatic. In this review, the prevalence of asymptomatic carriers of L. infantum was evaluated worldwide using parasitological methods or indirect testing such as a skin test or serology. The consequences of the presence of asymptomatic carriers on parasite transmission by blood donation or the development of clinical visceral leishmaniasis in immunocompromised individuals and its possible role as reservoir are discussed.

Evidence that lipopolisaccharide may contribute to the cytokine storm and cellular activation in patients with visceral leishmaniasis

Background

Visceral leishmaniasis (VL) is characterized by parasite-specific immunosuppression besides an intense pro-inflammatory response. Lipopolisaccharide (LPS) has been implicated in the immune activation of T-cell deficient diseases such as HIV/AIDS and idiopathic lymphocytopenia. The source of LPS is gram-negative bacteria that enter the circulation because of immunological mucosal barrier breakdown. As gut parasitization also occurs in VL, it was hypothesized that LPS may be elevated in leishmaniasis, contributing to cell activation.

Methodology/Principal Findings

Flow cytometry analysis and immunoassays (ELISA and luminex micro-beads system) were used to quantify T-cells and soluble factors. Higher LPS and soluble CD14 levels were observed in active VL in comparison to healthy subjects, indicating that LPS was bioactive; there was a positive correlation between these molecules (r = 0.61;p<0.05). Interestingly, LPS was negatively correlated with CD4⁺ (r = −0.71;p<0.01) and CD8⁺ T-cells (r = −0.65;p<0.05). Moreover, higher levels of activation-associated molecules (HLA-DR, CD38, CD25) were seen on T lymphocytes, which were positively associated with LPS levels. Pro-inflammatory cytokines and macrophage migration inhibitory factor (MIF) were also augmented in VL patients. Consistent with the higher immune activation status, LPS levels were positively correlated with the inflammatory cytokines IL-6 (r = 0.63;p<0.05), IL-8 (r = 0.89;p<0.05), and MIF (r = 0.64;p<0.05). Also, higher plasma intestinal fatty acid binding protein (IFABP) levels were observed in VL patients, which correlated with LPS levels (r = 0.57;p<0.05).

Conclusions/Significance

Elevated levels of LPS in VL, in correlation with T-cell activation and elevated pro-inflammatory cytokines and MIF indicate that this bacterial product may contribute to the impairment in immune effector function. The cytokine storm and chronic immune hyperactivation status may contribute to the observed T-cell depletion. LPS probably originates from microbial translocation as suggested by IFABP levels and, along with Leishmania antigen-mediated immune suppression, may play a role in the immunopathogenesis of VL. These findings point to possible benefits of antimicrobial prophylaxis in conjunction with anti-Leishmania therapy.

Visceral leishmaniasis (VL) affects organs rich in lymphocytes, being characterized by intense Leishmania-induced T-cell depletion and reduction in other hematopoietic cells. In other infectious and non-infectious diseases in which the immune system is affected, such as HIV-AIDS and inflammatory bowel disease, damage to gut-associated lymphocyte tissues occurs, enabling luminal bacteria to enter into the circulation. Lipopolisaccharide (LPS) is a bacterial product that stimulates macrophages, leading to the production of pro-inflammatory cytokines and other soluble factors such as MIF, which in turn activate lymphocytes. Continuous and exaggerated stimulation causes exhaustion of the T-cell compartment, contributing to immunosuppression.

Herein, we show that an increment in LPS plasma levels also occurs in VL; the higher the LPS levels, the lower the TCD4⁺ and TCD8⁺ cell count in the blood. This T-cell depletion may affect the mucosal immune system, which, along with intestinal parasitization by amastigotes, may contribute to gut barrier damage and consequent microbial translocation. LPS levels were correlated with T-cell activation, pro-inflammatory cytokine plasma levels, MIF, and IFABP, showing that a bacterial molecule, probably from luminal origin, not associated with Leishmania infection can negatively affect the immune system. These findings points to possible benefits of antimicrobial prophylaxis in conjunction with anti-Leishmania therapy.

High levels of T lymphocyte activation in Leishmania-HIV-1 co-infected individuals despite low HIV viral load

BACKGROUND

Concomitant infections may influence HIV progression by causing chronic activation leading to decline in T-cell function. In the Americas, visceral (AVL) and tegumentary leishmaniasis (ATL) have emerged as important opportunistic infections in HIV-AIDS patients and both of those diseases have been implicated as potentially important co-factors in disease progression. We investigated whether leishmaniasis increases lymphocyte activation in HIV-1 co-infected patients. This might contribute to impaired cellular immune function.

METHODS

To address this issue we analyzed CD4+ T absolute counts and the proportion of CD8+ T cells expressing CD38 in Leishmania/HIV co-infected patients that recovered after anti-leishmanial therapy.

RESULTS

We found that, despite clinical remission of leishmaniasis, AVL co-infected patients presented a more severe immunossupression as suggested by CD4+ T cell counts under 200 cells/mm3, differing from ATL/HIV-AIDS cases that tends to show higher lymphocytes levels (over 350 cells/mm3). Furthermore, five out of nine, AVL/HIV-AIDS presented low CD4+ T cell counts in spite of low or undetectable viral load. Expression of CD38 on CD8+ T lymphocytes was significantly higher in AVL or ATL/HIV-AIDS cases compared to HIV/AIDS patients without leishmaniasis or healthy subjects.

CONCLUSIONS

Leishmania infection can increase the degree of immune system activation in individuals concomitantly infected with HIV. In addition, AVL/HIV-AIDS patients can present low CD4+ T cell counts and higher proportion of activated T lymphocytes even when HIV viral load is suppressed under HAART. This fact can cause a misinterpretation of these laboratorial markers in co-infected patients.

Enhanced efficacy and immunogenicity of 78kDa antigen formulated in various adjuvants against murine visceral leishmaniasis

Leishmania infection causes localized cutaneous to severe visceral disease in humans and animals. Current control measures, based on antimonial compounds, are not effective because of resistance in Leishmania. Vaccination would be a feasible alternative, but as yet no vaccine to protect humans against infection has been commercialized. Parasite antigens that preferentially stimulate the induction of significant protection through Th1 response presents a rational approach for a vaccine against leishmaniasis. With this view in mind, we investigated the potential of 78kDa antigen of Leishmania donovani alone and along with different adjuvants against murine visceral leishmaniasis. Various adjuvants used along with 78kDa antigen include monophosphoryl lipid A (MPL-A), liposomal encapsulation, recombinant IL-12, autoclaved Leishmania antigen (ALD) and Freund's adjuvant (FCA). BALB/c mice were immunized subcutaneously thrice with respective vaccine formulation. Challenge infection was given intracardially after 2 weeks of second booster. A significant decrease in parasite burden was seen in vaccinees over the infected controls on all post challenge days and was found that maximum protection was provided by 78kDa+rIL-12 vaccine and it was highly immunogenic as depicted by the reduction in parasite load (71-94.8%), reduction in infection rate of peritoneal macrophages (92.9-98%), enhanced DTH response (6.5-10.5 fold), increase in IgG2a anti-leishmanial antibody production (3-3.7 fold) and up-regulation of IFN-gamma (3.7-6.5 fold) and IL-2 levels (7.7-12.3 fold), which demonstrate the generation of protective Th1 type of immune response. Comparable results were also observed in 78kDa+MPL-A and liposome-encapsulated 78kDa vaccines with 56.5-92% and 62.9-93.4% reduction in parasite load respectively. Significant results have also been obtained with 78kDa antigen+ALD, 78kDa antigen+FCA and 78kDa antigen alone group but the protective efficacy was reduced as compared to the other vaccine groups. The present study indicates that the three vaccine formulations i.e. 78kDa antigen+rIL-12, liposome-encapsulated 78kDa antigen and 78kDa antigen+MPL-A, are highly efficacious and effective vaccine candidates against visceral leishmaniasis.

Innate immune defense in visceral leishmaniasis: cytokine mediated protective role by allogeneic effector cell

Antileishmanial role of mouse splenic natural killer (NK) cell was studied in allogeneic condition. In vitro data indicates that NK cells of allogeneic (C57BL/6, H2(b)) non-leishmania exposed mouse have strong antileishmanial effect against Leishmania donovani infected BALB/c (H2(d)) macrophages. Physical contact between the effector (NK cell) and the target cells (infected macrophages) is essential in this system since; cell free supernatant generated after coculturing of effector cells with infected target cells fails to elicit any antileishmanial effect. Although NK cells from allogeneic mouse are strongly attached to the infected macrophages but unable to kill it in such interaction. The antileishmanial effect of allogeneic NK cells is mediated by TNF-alpha and not by IFN-gamma. In vivo cellular therapy of established infection with NK cells from non-leishmania exposed allogeneic mouse significantly reduces the total parasite burden in the spleen of infected animal.

Immunoactivation and immunopathogeny during active visceral leishmaniasis

Visceral leishmaniasis is caused by protozoan parasites of the Leishmania donovani complex. During active disease in humans, high levels of IFN-γ and TNF-α detected in blood serum, and high expression of IFN-γ mRNA in samples of the lymphoid organs suggest that the immune system is highly activated. However, studies using peripheral blood mononuclear cells have found immunosuppression specific to Leishmania antigens; this poor immune response probably results from Leishmania antigen-engaged lymphocytes being trapped in the lymphoid organs. To allow the parasites to multiply, deactivating cytokines IL-10 and TGF-β may be acting on macrophages as well as anti-Leishmania antibodies that opsonize amastigotes and induce IL-10 production in macrophages. These high activation and deactivation processes are likely to occur mainly in the spleen and liver and can be confirmed through the examination of organ samples. However, an analysis of sequential data from studies of visceral leishmaniasis in hamsters suggests that factors outside of the immune system are responsible for the early inactivation of inducible nitric oxide synthase, which occurs before the expression of deactivating cytokines. In active visceral leishmaniasis, the immune system actively participates in non-lymphoid organ lesioning. While current views only consider immunocomplex deposition, macrophages, T cells, cytokines, and immunoglobulins by diverse mechanism also play important roles in the pathogenesis.

Macrophage and T-cell gene expression in a model of early infection with the protozoan Leishmania chagasi

Visceral leishmaniasis is a potentially fatal infectious disease caused by the protozoan parasite Leishmania infantum/chagasi in the New World, or by L. donovani or L. infantum/chagasi in the Old World. Infection leads to a variety of outcomes ranging from asymptomatic infection to active disease, characterized by fevers, cachexia, hepatosplenomegaly and suppressed immune responses. We reasoned that events occurring during the initial few hours when the parasite encounters cells of the innate and adaptive immune systems are likely to influence the eventual immune response that develops. Therefore, we performed gene expression analysis using Affymetrix U133Plus2 microarray chips to investigate a model of early infection with human monocyte-derived macrophages (MDMs) challenged with wild-type L. chagasi parasites, with or without subsequent co-culture with Leishmania-naïve, autologous T-cells. Microarray data generated from total RNA were analyzed with software from the Bioconductor Project and functional clustering and pathway analysis were performed with DAVID and Gene Set Enrichment Analysis (GSEA), respectively. Many transcripts were down-regulated by infection in cultures containing macrophages alone, and the pattern indicated a lack of a classically activated phenotype. By contrast, the addition of autologous Leishmania-naïve T cells to infected macrophages resulted in a pattern of gene expression including many markers of type 1 immune cytokine activation (IFN-γ, IL-6, IL-1α, IL-1β). There was simultaneous up-regulation of a few markers of immune modulation (IL-10 cytokine accumulation; TGF-β Signaling Pathway). We suggest that the initial encounter between L. chagasi and cells of the innate and adaptive immune system stimulates primarily type 1 immune cytokine responses, despite a lack of classical macrophage activation. This local microenvironment at the site of parasite inoculation may determine the initial course of immune T-cell development.

Visceral leishmaniasis (VL) is a potentially fatal vector-borne infectious disease that leads to a variety of outcomes ranging from asymptomatic infection to symptomatic disease. In northeast Brazil, the etiological agent of VL is the protozoan Leishmania chagasi/infantum. Active VL is characterized by fevers, weight loss, hepatosplenomegaly and eventually immune suppression. Without treatment, most symptomatic patients die from secondary bacterial or viral super-infection. We hypothesized that a unique immune response to L. chagasi is initiated early during the initial interactions between the immune system cells that first encounter the parasite. These include macrophages and T-cells, elements of the innate and adaptive immune systems, respectively. We studied an in vitro model of these interactions in which human monocyte-derived macrophages were challenged with L. chagasi, and subsequently cultured with Leishmania-naïve, autologous T cells. Using microarray chips, we examined changes in global gene expression induced by these early interactions. Infection did not elicit a classical inflammatory program in macrophages. However, co-culture of infected macrophages and autologous T cells exhibited a pattern of gene expression, including many markers of acute inflammation or a type 1 immune response. These data suggest that early changes at the site of parasite infection would be conducive to the development of a protective type 1 response, followed by modulation of this same response.

Immune response to leishmania: paradox rather than paradigm

The leishmaniases are a group of diseases caused by protozoan parasites of the genus Leishmania. Various Leishmania species can cause human infection, producing a spectrum of clinical manifestations. It is estimated that 350 million people are at risk, with a global yearly incidence of 1-1.5 million for cutaneous and 500,000 for visceral leishmaniasis (VL). VL is a major cause of morbidity and mortality in East Africa and the Indian subcontinent. Coinfection with HIV enhances the risk of the disease. The only control measure currently available in India is case detection and treatment with antimonial drugs, which are expensive, not always available and cannot be self-administered. Newer drugs like oral miltefosine have not become widely available. Vector and reservoir control is difficult due to the elusive nature of the vector and the diversity of the animal reservoir. A detailed knowledge of immune response to the parasite would help in designing prophylactic and therapeutic strategies against this infection.

Lymph node cells from BALB/c mice with chronic visceral leishmaniasis exhibiting cellular anergy and apoptosis: involvement of Ser/Thr phosphatase

Visceral leishmaniasis (VL) produced in BALB/c mice through intracardial administration of Leishmania donovani amastigotes was accompanied by hepatosplenomegaly with high organ parasite load and lymphadenopathy when followed up to 4-months or so. To elucidate the mechanism of immunosuppression associated with VL, we report here progressive impairment of the proliferative response of lymph node cells (lymphocytes) from infected animals (I-LNC) to in vitro stimulation with the combination of phorbol 12-myristate 13-acetate (PMA) and ionomycin (Io) that could be related to the downregulation of PKC and MAP kinase (ERK 1/2) activation process. Further, pretreatment of I-LNC with the protein phosphatase inhibitor okadaic acid (OA), but not with calyculin A or sodium orthovanadate, significantly restored their proliferative response as well as PMA-induced activation of PKC. A population of LNC (primarily T-lymphocytes) from chronically infected animals was shown to undergo apoptosis, the number of which increased considerably following PMA+ Io stimulation. The apoptotic pathway, which was followed through binding of cells to Annexin V, activation of caspase-3 and fragmentation of DNA, involved destabilization of mitochondria, probably as a result of downregulation of PKC and Bcl-2. Interestingly, prior incubation of I-LNC with OA reversed the state of cell cycle arrest (anergy) and apoptosis through progression of cells from G0/G1 to S and G2/M phases with transcriptional activation of IL-2 and IL-2R genes. Our results suggest that the cellular (immune) dysfunction in VL could be attributed to dephosphorylation of key molecules in the T-lymphocyte signaling pathway by Ser/Thr phosphatase leading to their inactivation.

Visceral leishmaniasis complicated by fungal pulmonary valve endocarditis

We present a rare neglected case of fungal pulmonary valve endocarditis which presented with typical extra cardiac manifestations after repeated injections for treatment of visceral leishmaniasis. Surgical intervention to replace the pulmonary valve was the only option to manage the patient in spite of extensive medical treatment.

Balance of IL-10 and interferon-gamma plasma levels in human visceral leishmaniasis: implications in the pathogenesis

BACKGROUND

Leishmaniasis remains a serious public health problem in several parts of the developing world. Effective prophylactic measurements are hampered by imprecise comprehension of different aspects of the disease, including its immunoregulation. A better comprehension of immunoregulation in human VL may be useful both for designing and evaluating immunoprophylaxis.

METHODS

To explore immunoregulatory mechanisms, 20 visceral leishmaniasis (VL) patients were evaluated during active disease and at different periods up to one year after treatment determining their plasma cytokine levels, clinical parameters (palpable spleen and liver) and antibody levels.

RESULTS

Elevated plasma levels of IFN-gamma and of IL-12 p40 were observed during active disease, significantly decreasing after treatment whereas in vitro Leishmania antigen-stimulated IFN-gamma production by PBMC exhibited an inverse pattern being low during disease and increasing steadily thereafter. Absence of IFN-gamma activity is a hallmark of VL. The main candidate for blunting IFN-gamma activity is IL-10, a cytokine highly elevated in plasma with sharp decrease after treatment. Activity of IL-10 is inferred by high levels of anti-Leishmania specific IgG1 and IgG3. TGF-beta had elevated total, but not of active, levels lessening the likelihood of being the IFN-gamma counterpart. Spleen or liver size presented a steady decrease but return to normal values at only 120 days after treatment. Anti-Leishmania IgG (total and subclasses) levels and DTH or Leishmania-stimulated lymphocyte proliferation conversion to positive also present a slow decrease after treatment. IL-6 plasma levels were elevated in only a few patients.

CONCLUSION

Taken together our results suggest that IFN-gamma and IL-10 are the molecules most likely involved in determining fate of disease. After treatment, there is a long delay before the immune profile returns to normal what precludes using plasma cytokine levels as criteria of cure as simpler clinical evaluations, as a palpable spleen or liver, can be used.

Immunopathogenesis of infection with the visceralizing Leishmania species

Human leishmaniasis is a spectral disease that includes asymptomatic self-resolving infection, localized skin lesions, and progressive visceral leishmaniasis. With some overlap, visceral and cutaneous leishmaniasis are usually caused by different species of Leishmania. This review focuses on host responses to infection with the species that cause visceral leishmaniasis, as they contrast with species causing localized cutaneous leishmaniasis. Data from experimental models document significant differences between host responses to organisms causing these diverse syndromes. The visceralizing Leishmania spp. cause localized organ-specific immune responses that are important determinants of disease outcome. Both the Leishmania species causing cutaneous and those causing visceral leishmaniasis require a Type 1 immune response to undergo cure in mouse models. However, during progressive murine infection with the visceralizing Leishmania sp., the Type 1 response is suppressed at least in part by TGF-beta and IL-10 without type 2 cytokine production. This contrasts with the cutaneous species L. major, in which a Type 2 response suppresses type 1 cytokines and leads to murine disease progression. Population and family studies are beginning to elucidate human genetic determinants predisposing to different outcomes of Leishmania infection. These studies should eventually result in a better understanding of the immunopathogenesis and the spectrum of human leishmaniasis.

Pulcherrimasaponin, from the leaves of Calliandra pulcherrima, as adjuvant for immunization in the murine model of visceral leishmaniasis

A novel triterpenoidal saponin, called pulcherrimasaponin (CP05), isolated from the leaves of Calliandra pulcherrima Benth. shows remarkable similarities to the previously described potent adjuvant, QS21 saponin (Quillaja saponaria Molina). On the basis of chemical and physicochemical evidence, its structure was established as [3beta,16alpha,28[2E,6S[2E,6S(2E,6S)]]]-olean-12-en-28-oic acid 3-[[O-alpha-l-arabinopyranosyl-(1-->2)-O-alpha-l-arabinopyranosyl-(1-->6)-2-(acetylamino)-2-deoxy-beta-d-glucopyranosyl]oxy]-16-hydroxy-O-beta-d-glucopyranosyl-(1-->3)-O-[O-beta-d-xylopyranosyl-(1-->3)-beta-d-xylopyranosyl-(1-->4)-O-6-deoxy-alpha-l-mannopyranosyl-(1-->2)-6-O-[6-[[2-O-2,6-dimethyl-1-oxo-6-(beta-d-xylopyranosyloxy)-2,7-octadienyl]-[(6-deoxy-beta-d-glucopyranosyl)oxy]-2,6-dimethyl-1-oxo-2,7-octadienyl]-beta-d-xylopyranosyl]oxy]-2,6-dimethyl-1-oxo-2,7-octadienyl]-beta-d-glucopyranosyl ester. In vivo toxicity assays disclosed similar and transitory local swelling and loss of hair but no lethality for mice. The haemolytic index was higher for QS21 (5 microg/ml) than for CP05 (13 microg/ml). Mouse vaccination with either CP05 or QS21 in combination with the fucose-mannose ligand (FML) antigen of Leishmania donovani showed anti-FML responses, significantly enhanced over the saponin and saline controls, in IgM, IgG, IgG1, IgG2a, IgG2b and IgG3. Antibody levels were similar for both vaccines in most subtypes. However, QS21-FML vaccine showed a 1.5 to 2.1 proportional increase over the CP05-FML vaccine in IgG, IgG2a and IgG3 responses. The delayed type of hypersensitivity against leishmanial antigen was impressively increased for CP05-FML and for QS21-FML-treated animals over controls (p<0.005). Enhancement was similar for both vaccines (p<0.05). The safety analysis and the effect on humoral and cellular immune responses demonstrated that the novel Calliandra pulcherrima Benth. CP05 saponin is a potential candidate for a vaccine adjuvant.