Immunopathogenesis of infection with the visceralizing Leishmania species

Accuracy evaluation of diagnostic methods for visceral leishmaniasis in adult patients with and without HIV infection: Clinical management implications

Visceral leishmaniasis (VL) poses a serious health threat, particularly when untreated, necessitating accurate diagnosis. While the gold-standard method involves identifying amastigotes in bone marrow aspirate (BMA), this procedure is invasive and occasionally contraindicated. Additionally, when VL is associated with HIV infection the serologies accuracies could be affected. This study aims to evaluate and compare diagnostic methods for VL in patients with and without HIV coinfection. We enrolled prospectively 127 consecutive adult VL patients, 48 (37.8%) of whom had HIV coinfection, in Brazil's Midwestern region, where VL is endemic. Parasitological examination served as the reference standard for accuracy analysis, with index tests including immunofluorescent antibody test (IFAT), immunochromatographic test with rK39 protein (rK39-ICT), and blood polymerase chain reaction (PCR). Specificity assessment involved 430 healthy blood donors from the same endemic area. Ninety-two patients had parasitologically confirmed VL. Among HIV-uninfected patients, rK39-ICT exhibited sensitivity comparable to PCR (93.6%; 95% CI: 83.6-100 vs. 97.8%; 95% CI: 93.6-99.2, respectively) and superior to IFAT (71.1%; 95% CI: 57.9-84.3). However, in HIV-infected patients, rK39-ICT sensitivity was notably lower than PCR (40.0%; 95% CI: 22.5-57.5 vs. 97.4%; 95% CI: 92.5-98.9) and similar to IFAT (67.5%; 95% CI: 52.9-82.0). Combining two serological tests in parallel identified 82.1% of parasitologically confirmed VL cases, with a negative likelihood ratio significantly lower than either test alone. No test achieved a specificity of 90%, and there were no significant differences in specificity observed among the index tests. The positivity rate of parasitological examination in the 127 VL patients was higher in HIV-infected compared to HIV-uninfected patients, 91.3% (95% CI: 83.2-99.4) versus 67.6% (95% CI: 56.9-78.3), respectively. These findings underscore the necessity of accounting for HIV infection when choosing VL diagnostic methods. Although rK39-ICT provides reliable results in HIV-uninfected patients, BMA examination remains crucial for accurate diagnosis in individuals with HIV/AIDS. In cases where bone marrow aspiration is contraindicated, employing IFAT and rK39-ICT in parallel could be considered, as the occurrence of both positive results is uncommon in healthy individuals from endemic areas.

Effects of Amphotericin B-Conjugated Functionalized Carbon Nanoparticles in the Treatment of Cutaneous Leishmaniasis

Leishmaniasis is a parasitic disease spread by the bite of an infected sandfly and caused by protozoan parasites of the genus Leishmania. Currently, there is no vaccine available for leishmaniasis in humans, and the existing chemotherapy methods face various clinical challenges. The majority of drugs are limited to a few toxic compounds, with some parasite strains developing resistance. Therefore, the discovery and development of a new anti-leishmanial compound is crucial. One promising strategy involves the use of nanoparticle delivery systems to accelerate the effectiveness of existing treatments. In this study, Amphotericin B (AmB) was incorporated into functionalized carbon nanotube (f-CNT) and evaluated for its efficacy against Leishmania major in vitro and in a BALB/c mice model. The increase in footpad thickness was measured, and real-time PCR was used to quantify the parasite load post-infection. Levels of nitric oxide and cytokines IL-4 and IFN-γ were also determined. We found that f-CNT-AmB significantly reduced the levels of promastigotes and amastigotes of the Leishmania parasite. The nanoparticle showed strong anti-leishmanial activity with an IC50 of 0.00494 ± 0.00095 mg/mL for promastigotes and EC50 of 0.00294 ± 0.00065 mg/mL for amastigotes at 72 h post-infection, without causing harm to mice macrophages. Treatment of infected BALB/c mice with f-CNT-AmB resulted in a significant decrease in cutaneous leishmania (CL) lesion size in the foot pad, as well as reduced Leishmania burden in both lymph nodes and spleen. The levels of nitric oxide and IFN-γ significantly increased in the f-CNT-AmB treated groups. Also, our results showed that the level of IL-4 significantly decreased after f-CNT-AmB treatment in comparison to other groups. In conclusion, our results demonstrate that AmB loaded into f-CNT is significantly more effective than AmB alone in inhibiting parasite propagation and promoting a shift towards a Th1 response.

Visceral Leishmaniasis Following A+AVD Treatment in a Patient with Classical Hodgkin's Lymphoma: A Case Report and Review of the Literature

We present the case of a 43-year-old Caucasian man who developed visceral leishmaniasis (VL) following treatment with a combination of brentuximab vedotin and doxorubicin, vinblastine, and dacarbazine (A+AVD) for advanced-stage classical Hodgkin's lymphoma (cHL). The patient initially showed a favorable response to the treatment, but shortly after completing six cycles, he experienced recurrent fever, splenomegaly, and severe anemia. Extensive infectious disease evaluations led to a diagnosis of VL, confirmed by PCR testing. The patient was treated with amphotericin B, resulting in full clinical recovery. In addition to presenting this rare case, we conducted a full review of the literature on VL in the context of hematological disorders, including non-Hodgkin's lymphoma, splenic marginal zone lymphoma, and other lymphoproliferative diseases. This review highlights the increasing prevalence of VL in immunocompromised individuals, particularly those undergoing treatments like chemotherapy or immunotherapy, and underscores the importance of considering VL in differential diagnoses when such patients present with persistent fever and splenomegaly.

Artemisinin: An Anti-Leishmania Drug that Targets the Leishmania Parasite and Activates Apoptosis of Infected Cells

Leishmaniasis is a relevant disease worldwide due to its presence in many countries and an estimated prevalence of 10 million people. The causative agent of this disease is the obligate intracellular parasite Leishmania which can infect different cell types. Part of its success depends on its ability to evade host defense mechanisms such as apoptosis. Apoptosis is a finely programmed process of cell death in which cells silently dismantle and actively participate in several processes such as immune response, differentiation, and cell growth. Leishmania has the ability to delay its initiation to persist in the cell. It has been well documented that different Leishmania species target different pathways that lead to apoptosis of cells such as macrophages, neutrophils, and dendritic cells. In many cases, the observed anti-apoptotic effect has been associated with a significant reduction in caspase-3 activity. Leishmania has also been shown to target several pathways involved in apoptosis such as MAPK, PI3K/Akt, and the antiapoptotic protein Bcl-xL. Understanding the strategies used by Leishmania to subvert the defense mechanisms of host cells, particularly apoptosis, is very relevant for the development of therapies and vaccines. In recent years, the drug artemisinin has been shown to be effective against several parasitic diseases. Its role against Leishmania may be promising. In this review, we provide important aspects of the disease, the strategies used by the parasite to suppress apoptosis, and the role of artemisinin in Leishmania infection.

Steppe lemmings and Chinese hamsters as new potential animal models for the study of the Leishmania subgenus Mundinia (Kinetoplastida: Trypanosomatidae)

Leishmania, the dixenous trypanosomatid parasites, are the causative agents of leishmaniasis currently divided into four subgenera: Leishmania, Viannia, Sauroleishmania, and the recently described Mundinia, consisting of six species distributed sporadically all over the world infecting humans and/or animals. These parasites infect various mammalian species and also cause serious human diseases, but their reservoirs are unknown. Thus, adequate laboratory models are needed to enable proper research of Mundinia parasites. In this complex study, we compared experimental infections of five Mundinia species (L. enriettii, L. macropodum, L. chancei, L. orientalis, and four strains of L. martiniquensis) in three rodent species: BALB/c mouse, Chinese hamster (Cricetulus griseus) and steppe lemming (Lagurus lagurus). Culture-derived parasites were inoculated intradermally into the ear pinnae and progress of infection was monitored for 20 weeks, when the tissues and organs of animals were screened for the presence and quantity of Leishmania. Xenodiagnoses with Phlebotomus duboscqi were performed at weeks 5, 10, 15 and 20 post-infection to test the infectiousness of the animals throughout the experiment. BALB/c mice showed no signs of infection and were not infectious to sand flies, while Chinese hamsters and steppe lemmings proved susceptible to all five species of Mundinia tested, showing a wide spectrum of disease signs ranging from asymptomatic to visceral. Mundinia induced significantly higher infection rates in steppe lemmings compared to Chinese hamsters, and consequently steppe lemmings were more infectious to sand flies: In all groups tested, they were infectious from the 5th to the 20th week post infection. In conclusion, we identified two rodent species, Chinese hamster (Cricetulus griseus) and steppe lemming (Lagurus lagurus), as candidates for laboratory models for Mundinia allowing detailed studies of these enigmatic parasites. Furthermore, the long-term survival of all Mundinia species in steppe lemmings and their infectiousness to vectors support the hypothesis that some rodents have the potential to serve as reservoir hosts for Mundinia.

Phenotypic and functional characteristics of monocyte subsets in the blood and bone marrow of Indian subjects with Visceral Leishmaniasis

Visceral leishmaniasis (VL) is a potentially fatal parasitic infection caused by Leishmania donovani in India. L. donovani is an obligate intracellular protozoan residing mostly in macrophages of the reticuloendothelial system throughout chronic infection. Monocytic phagocytes are critical in the pathogenesis of different forms of leishmaniasis. Subsets of monocytes are distinguished by their surface markers into CD14+CD16- classical monocytes, CD14+CD16+ intermediate monocytes, and CD16++CD14low non-classical monocyte subsets. During cutaneous leishmaniasis (CL), intermediate monocyte are reported to be a source of inflammatory cytokines IL-1β and TNF, and they express CCR2 attracting them to sites of inflammatory pathology. We examined monocyte subsets in the blood and bone marrow of patients with VL from an endemic site in Bihar, India, and found these contrasted with the roles of monocytes in CL. During VL, intermediate and non-classical CD16+ monocyte subsets expressed instead a non-inflammatory phenotype with low CCR2, high CX3CR1 and low microbicidal oxidant generation, making them more similar to patrolling monocytes than inflammatory cells. Bone marrow CD16+ monocyte subsets expressed a phenotype that might be more similar to the inflammatory subsets of CL, although our inability to obtain bone marrow from healthy donors in the endemic region hampered this interpretation Overall the data suggest that CD16+ intermediate monocyte subsets in VL patients express a phenotypes that contributes to an immunosuppressed pathologic immune state, but in contrast to CL, these do not mediate localized inflammatory responses.

Comparative Analysis of Leishmania major Nucleoside Hydrolases Toward Selecting Multi-target Strategy

PURPOSE

Leishmania causes multiple types of leishmaniasis in different parts of the world. It has a lack of metabolic machine to produce purine bases. Therefore, the parasite produces purine bases through the breakdown of nutritional nucleotides and it makes the nucleoside hydrolases (NHs) good drug targets. They have different substrate-preferring (SP) types. Our objectives were modeling and comparative analysis of these protein structures for Leishmania major.

METHOD

In this work, available sequences for all SP types of L. major NH enzymes including inosine-uridine preferring NH (IUNH), inosine-guanosine preferring NH (IGNH), and inosine-adenosine-guanosine preferring NH (IAGNH) were used to make 24 structural models via SWISS-MODEL and LOMETS. After evaluating the structural models, three enzyme structures were finalized and used to analyze substrate-binding pockets.

RESULTS

The three SP types of L. major NH enzymes that can breakdown purine nucleosides were highly different in terms of sequence, structure, and profile of interacting residues within the substrate-binding pockets. In this study, new enzyme structures have been presented for three SP types and they have been compared in different aspects and it indicated that they were very different from each other.

CONCLUSION

Although, previously indicated that from these three SP types in genera other than Leishmania, the role of IGNH and IAGNH was greater than IUNH in supplying purine bases, till this work, just IUNH has been structurally studied and used in drug-design investigations for Leishmania. Therefore, we are offering to use all three SP types of NHs as multi-target strategy in anti-leishmaniosis drug-design studies.

Total serum N-glycans mark visceral leishmaniasis in human infections with Leishmania infantum

Visceral leishmaniasis (VL) is a clinical form of leishmaniasis with high mortality rates when not treated. Diagnosis suffers from invasive techniques and sub-optimal sensitivities. The current (affordable) treatment with pentavalent antimony as advised by the WHO is possibly harmful to the patient. There is need for an improved diagnosis to prevent possibly unnecessary treatment. N-glycan analysis may aid in diagnosis. We evaluated the N-glycan profiles from active VL, asymptomatic infections (ASYMP) and controls from non-endemic (NC) and endemic (EC) areas. Active VL has a distinct N-glycome profile that associates with disease severity. Our study suggests that the observed glycan signatures could be a valuable additive to diagnosis and assist in identifying possible markers of disease and understanding the pathogenesis of VL. Further studies are warranted to assess a possible future role of blood glycome analysis in active VL diagnosis and should aim at disease specificity.

The glycoprotein gp63- a potential pan drug target for developing new antileishmanial agents

Leishmaniasis is a tropical parasitic disease caused by Leishmania spp. They cause several presentations of illness ranging from cutaneous leishmaniasis to visceral leishmaniasis. The current arsenal of drugs to treat leishmaniasis is limited, and drug resistance further impedes the problem. Therefore, it is necessary to revisit the available information to identify an alternative or new target for treatment. The glycoprotein 63 (gp63), is a potential anti-leishmanial target that plays a significant role in host-pathogen interaction and virulence. Many studies are ongoing to develop gp63 inhibitors or use it as a vaccine target. In this review, we will discuss the potential of gp63 as a drug target. This review summarises the studies focusing on gp63 as a drug target and its inhibitors identified using in silico approaches.

NLRP12-expressing dendritic cells mediate both dissemination of infection and adaptive immune responses in visceral leishmaniasis

The NLR protein NLRP12 contributes to innate immunity, but the mechanism remains elusive. Infection of Nlrp12 -/- or wild-type mice with Leishmania infantum led to aberrant parasite tropism. Parasites replicated to higher levels in livers of Nlrp12 -/- mice than in the livers of WT mice and failed to disseminate to spleens. Most retained liver parasites resided in dendritic cells (DCs), with correspondingly fewer infected DCs in spleens. Furthermore, Nlrp12 -/- DCs expressed lower CCR7 than WT DCs, failed to migrate toward CCL19 or CCL21 in chemotaxis assays, and migrated poorly to draining lymph nodes after sterile inflammation. Leishmania-infected Nlpr12 -/- DCs were significantly less effective at transporting parasites to lymph nodes than WT DCs. Consistently, adaptive immune responses were also impaired in infected Nlrp12 -/- mice. We hypothesize that Nlrp12-expressing DCs are required for efficient dissemination and immune clearance of L. infantum from the site of initial infection. This is at least partly due to the defective expression of CCR7.

Immunoprophylaxis using polypeptide chimera vaccines plus adjuvant system promote Th1 response controlling the spleen parasitism in hamster model of visceral leishmaniasis

In recent years, several advances have been observed in vaccinology especially for neglected tropical diseases (NTDs). One of the tools employed is epitope prediction by immunoinformatic approaches that reduce the time and cost to develop a vaccine. In this scenario, immunoinformatics is being more often used to develop vaccines for NTDs, in particular visceral leishmaniasis (VL) which is proven not to have an effective vaccine yet. Based on that, in a previous study, two predicted T-cell multi-epitope chimera vaccines were experimentally validated in BALB/c mice to evaluate the immunogenicity, central and effector memory and protection against VL. Considering the results obtained in the mouse model, we assessed the immune response of these chimeras inMesocricetus auratushamster, which displays, experimentally, similar pathological status to human and dog VL disease. Our findings indicate that both chimeras lead to a dominant Th1 response profile, inducing a strong cellular response by increasing the production of IFN-γ and TNF-α cytokines associated with a decrease in IL-10. Also, the chimeras reduced the spleen parasite load and the weight a correlation between protector immunological mechanisms and consistent reduction of the parasitic load was observed. Our results demonstrate that both chimeras were immunogenic and corroborate with findings in the mouse model. Therefore, we reinforce the use of the hamster as a pre-clinical model in vaccination trials for canine and human VL and the importance of immunoinformatic to identify epitopes to design vaccines for this important neglected disease.

Ageing impairs protective immunity and promotes susceptibility to murine visceral leishmaniasis

It is well accepted that the impact of diseases is generally more detrimental in elderly individuals than in younger ones. Changes in the immune system due to ageing can directly affect the ability to respond effectively to infections and may contribute to the higher morbidities and mortalities in the elderly population. Leishmaniasis is a complex of clinically unique diseases caused by obligate intracellular protozoa belonging to genus Leishmania, wherein visceral leishmaniasis (VL) is the most severe form and is fatal if left untreated. In this study, aged mice (72 weeks old) presented increased susceptibility to L. infantum infection compared to younger mice (4–6-week-old), with notable parasitism in both the spleen and liver, as well as exhibiting hepatosplenomegaly. A pronounced inflammatory profile was observed in the aged-infected mice, with excessive production of TNF-α and nitrite, along with diminished IFN-γ production and reduced proliferative capacity of T cells (assessed by expression of the Ki67 marker). Additionally, both CD4+ and CD8+ T cells from the aged-infected mice presented increased expression of the inhibitory receptors PD-1 and KLRG1 that strongly correlated with the parasitism found in the liver and spleen of this group. Overall, the data reported in this study suggests for the first time that ageing may negatively impact the VL outcome and provides a perspective for new therapeutic strategies involving manipulation of immunosenescence features against Leishmania infection.

Elevated baseline expression of seven virulence factor RNA transcripts in visceralizing species of Leishmania: a preliminary quantitative PCR study

Introduction:

Leishmaniasis is a neglected tropical disease that manifests as three major disease phenotypes: cutaneous, mucocutaneous, and visceral. In this preliminary study, we quantified virulence factor (VF) RNA transcript expression in Leishmania species, stratified by geographic origin and propensity for specific disease phenotypes.

Methods:

Cultured promastigotes of 19 Leishmania clinical and ATCC isolates were extracted for total cellular RNA, cDNA was reverse transcribed, and qPCR assays were performed to quantify VF RNA transcript expression for hsp23, hsp70, hsp83, hsp100, mpi, cpb, and gp63.

Results:

Comparison of visceralizing species (Leishmania donovani, Leishmania chagasi, and Leishmania infantum) versus non-visceralizing species [Leishmania (Viannia) spp., Leishmania tropica, Leishmania major, Leishmania mexicana, and Leishmania amazonensis] revealed a significantly greater pooled transcript expression for visceralizing species (p = 0.0032). Similarly, Old World species demonstrated significantly higher VF RNA transcript expression than New World species (p = 0.0015). On a per-gene basis, species with a propensity to visceralize ubiquitously expressed higher levels of gp63 (p = 0.005), cpb (p = 0.0032), mpi (p = 0.0032), hsp23 (p = 0.0039), hsp70 (p = 0.0032), hsp83 (p = 0.0032), and hsp100 (p = 0.0032).

Conclusion:

Here, we provide quantitative, preliminary evidence of elevated VF RNA transcript expression driven largely by the visceralizing causative species of Leishmania. This work highlights the extensive heterogeneity in pathogenicity mechanisms between Leishmania species, which may partly underpin the fatal progression of visceral leishmaniasis.

T Lymphocyte Exhaustion During Human and Experimental Visceral Leishmaniasis

A key point of immunity against protozoan Leishmania parasites is the development of an optimal T cell response, which includes a low apoptotic rate, high proliferative activity and polyfunctionality. During acute infection, antigen-specific T cells recognize the pathogen resulting in pathogen control but not elimination, promoting the development and the maintenance of a population of circulating effector cells that mount rapid response quickly after re-exposure to the parasite. However, in the case of visceral disease, the functionality of specific T cells is lost during chronic infection, resulting in inferior effector functions, poor response to specific restimulation, and suboptimal homeostatic proliferation, a term referred to as T cell exhaustion. Multiple factors, including parasite load, infection duration and host immunity, affect T lymphocyte exhaustion. These factors contribute to antigen persistence by promoting inhibitory receptor expression and sustained production of soluble mediators, influencing suppressive cell function and the release of endogenous molecules into chronically inflamed tissue. Together, these signals encourage several changes, reprogramming cells into a quiescent state, which reflects disease progression to more severe forms, and development of acquired resistance to conventional drugs to treat the disease. These points are discussed in this review.

Thymoquinone Induced Leishmanicidal Effect via Programmed Cell Death in Leishmania donovani

Visceral leishmaniasis (VL) or kala-azar is a vector-borne dreaded protozoal infection that is caused by the parasite Leishmania donovani. With increases in the dramatic infection rates, present drug toxicity, resistance, and the absence of an approved vaccine, the development of new antileishmanial compounds from plant sources remains the keystone for the control of visceral leishmaniasis. In this study, we evaluated the leishmanicidal effect of thymoquinone against L. donovani with an in vitro and ex vivo model. Thymoquinone exhibited potent antipromastigote activity with IC₅₀ and IC₉₀ concentrations achieved at 6.33 ± 1.21 and 20.71 ± 2.15 μM, respectively, whereas the IC₅₀ and IC₉₀ concentrations were found to be 7.83 ± 1.65 and 27.25 ± 2.20 μM against the intramacrophagic form of amastigotes, respectively. Morphological changes in promastigotes and growth reversibility study following treatment confirmed the leishmanicidal effect of thymoquinone. Further, thymoquinone exhibited leishmanicidal activities against L. donovani promastigote through cytoplasmic shrinkage, membrane blebbing, chromatin condensation, cellular and nuclear shrinkage, and DNA fragmentation, as observed under scanning and transmission electron microscopy analyses. The antileishmanial activity was exerted via programmed cell death as proved by exposure of phosphatidylserine, DNA nicking by TUNEL assay, and loss of mitochondrial membrane potential. Thymoquinone at a concentration of 200 μM was devoid of any cytotoxic effects against mammalian macrophage cells. Thymoquinone showed strong leishmanicidal activity against L. donovani, which is mediated via an apoptosis mode of parasitic cell death, and accordingly, thymoquinone may be the source of a new lead molecule for the cure of VL.

Recombinant guanosine-5'-triphosphate (GTP)-binding protein associated with Poloxamer 407-based polymeric micelles protects against Leishmania infantum infection

Leishmania virulence proteins should be considered as vaccine candidates against disease, since they are involved in developing infection in mammalian hosts. In a previous study, a Leishmania guanosine-5'-triphosphate (GTP)-binding protein was identified as a potential parasite virulence factor. In the present work, the gene encoding GTP was cloned and the recombinant protein (rGTP) was evaluated as a vaccine candidate against Leishmania infantum infection. The protein was associated with saponin (rGTP/Sap) or Poloxamer 407-based micelles (rGTP/Mic) as adjuvants, and protective efficacy was investigated in BALB/c mice after parasite challenge. Both rGTP/Sap and rGTP/Mic compositions induced a Th1-type immune response in vaccinated animals, with significantly higher levels of IFN-γ, IL-12, IL-2, TNF-α, GM-CSF, nitrite, specific IgG2a isotype antibody and positive lymphoproliferation, when compared to the control groups. This response was accompanied by significantly lower parasite load in the spleens, livers, bone marrows and draining lymph nodes of the animals. Immunological and parasitological evaluations indicated that rGTP/Mic induced a more polarized Th1-type response and higher reduction in the organ parasitism, and with lower hepatotoxicity, when compared to the use of rGTP/Sap. In conclusion, our preliminary data suggest that rGTP could be considered for further development as a vaccine candidate to protect against VL.

Nanoparticles Loaded with a New Thiourea Derivative: Development and In vitro Evaluation Against Leishmania amazonensis

BACKGROUND

Leishmaniasis is a neglected tropical disease caused by protozoa of the genus Leishmania. Current treatments are restricted to a small number of drugs that display both severe side effects and a potential for parasites to develop resistance. A new N-(3,4-methylenedioxyphenyl)-N'- (2-phenethyl) thiourea compound (thiourea 1) has shown promising in vitro activity against Leishmania amazonensis with an IC₅₀ of 54.14 μM for promastigotes and an IC₅₀ of 70 μM for amastigotes.

OBJECTIVE

To develop a formulation of thiourea 1 as an oral treatment for leishmaniasis, it was incorporated into Nanoparticles (NPs), a proven approach to provide long-acting drug delivery systems.

METHODS

Poly (D,L-Lactic-co-Glycolic Acid) (PLGA) polymeric NPs containing thiourea 1 were obtained through a nanoprecipitation methodology associated with solvent evaporation. The NPs containing thiourea 1 were characterized for Encapsulation Efficiency (EE%), reaction yield (% w/w), surface charge, particle size and morphology by Transmission Electron Microscopy (TEM).

RESULTS

NPs with thiourea 1 showed an improved in vitro leishmanicidal activity with a reduction in its cytotoxicity against macrophages (CC₅₀>100 μg/mL) while preserving its IC₅₀ against intracellular amastigotes (1.46 ± 0.09 μg/mL). This represents a parasite Selectivity Index (SI) of 68.49, which is a marked advancement from the reference drug pentamidine (SI = 30.14).

CONCLUSION

The results suggest that the incorporation into NPs potentiated the therapeutic effect of thiourea 1, most likely by improving the selective delivery of the drug to the phagocytic cells that are targeted for infection by L. amazonensis. This work reinforces the importance of nanotechnology in the acquisition of new therapeutic alternatives for oral treatments.

Influence of sex hormones on the immune response to leishmaniasis

The differences in morbidity and mortality patterns and life expectancy between the sexes are well established in different infectious and parasitic conditions, such as in leishmaniases, in which biological, genetic, sexual and hormonal variations can modulate the immune response indicating greater infectivity, prevalence and clinical severity in men. In this regard, in seeking the understanding of factors related to protection and susceptibility to infection, this review aimed to discuss the influence of sex hormones on the immune response to leishmaniases. In the literature, sex hormone variations promote differences in the innate, humoral and cell-mediated immune response, leading to greater susceptibility, mortality and complications in males. Epidemiological estimates confirm these results, showing a predominance of the disease, in its different clinical forms, in men and suggesting that sexual variations influence immunomodulatory mechanisms since the prevalence of cases comprises the post-puberty and adulthood period. In this perspective, the action of sex hormones has been investigated in different clinical models, highlighting the potential of testosterone in immunosuppression, given its association with greater susceptibility and poor control of parasite load and the induction of cell apoptosis and attenuation of pro-inflammatory signalling pathways. Therefore, hormonal variations influence the immune response among males and females against leishmaniases, in which androgens may present immunosuppressive potential, while steroids present immunomodulatory characteristics.

Leishmania spp. and leishmaniasis on the Caribbean islands

The kinetoplastid protozoan Leishmania spp. cause leishmaniasis, which clinically exhibit mainly as a cutaneous, mucocutanous or visceral form depending upon the parasite species in humans. The disease is widespread geographically, leading to 20 000 annual deaths. Here, leishmaniases in both humans and animals, reservoirs and sand fly vectors on the Caribbean islands are reviewed. Autochthonous human infections by Leishmania spp. were found in the Dominican Republic, Guadeloupe and Martinique as well as Trinidad and Tobago; canine infections were found in St. Kitts and Grenada; and equine infections were found in Puerto Rico. Imported human cases have been reported in Cuba. The parasites included Leishmania amazonensis, Le. martiniquensis and Le. waltoni. Possible sand fly vectors included Lutzomyia christophei, Lu. atroclavatus, Lu. cayennensis and Lu. flaviscutellata as well as Phlebotomus guadeloupensis. Reservoirs included rats, rice rats and mouse opossum. An updated study is warranted for the control and elimination of leishmaniasis in the region because some of the data are four decades old.

Host immune response against leishmaniasis and parasite persistence strategies: A review and assessment of recent research

Leishmaniasis, a neglected parasitic disease caused by a unicellular protozoan of the genus Leishmania, is transmitted through the bite of a female sandfly. The disease remains a major public health problem and is linked to tropical and subtropical regions, with an endemic picture in several regions, including East Africa, the Mediterranean basin and South America. The different causative species display a diversity of clinical presentations; therefore, the immunological data on leishmaniasis are both scarce and controversial for the different forms and infecting species of the parasite. The present review highlights the main immune parameters associated with leishmaniasis that might contribute to a better understanding of the pathogenicity of the parasite and the clinical outcomes of the disease. Our aim was to provide a concise overview of the immunobiology of the disease and the factors that influence it, as this knowledge may be helpful in developing novel chemotherapeutic and vaccine strategies.

Intravacuolar Pathogens Hijack Host Extracellular Vesicle Biogenesis to Secrete Virulence Factors

Extracellular vesicles (EVs) have garnered significant interest in recent years due to their contributions to cell-to-cell communication and disease processes. EVs are composed of a complex profile of bioactive molecules, which include lipids, nucleic acids, metabolites, and proteins. Although the biogenesis of EVs released by cells under various normal and abnormal conditions has been well-studied, there is incomplete knowledge about how infection influences EV biogenesis. EVs from infected cells contain specific molecules of both host and pathogen origin that may contribute to pathogenesis and the elicitation of the host immune response. Intracellular pathogens exhibit diverse lifestyles that undoubtedly dictate the mechanisms by which their molecules enter the cell’s exosome biogenesis schemes. We will discuss the current understanding of the mechanisms used during infection to traffic molecules from their vacuolar niche to host EVs by selected intravacuolar pathogens. We initially review general exosome biogenesis schemes and then discuss what is known about EV biogenesis in Mycobacterium, Plasmodium, Toxoplasma, and Leishmania infections, which are pathogens that reside within membrane delimited compartments in phagocytes at some time in their life cycle within mammalian hosts. The review includes discussion of the need for further studies into the biogenesis of EVs to better understand the contributions of these vesicles to host-pathogen interactions, and to uncover potential therapeutic targets to control these pathogens.

Role of Cytokines in Experimental and Human Visceral Leishmaniasis

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

Heterologous vaccine therapy associated with half course of Miltefosine promote activation of the proinflammatory response with control of splenic parasitism in a hamster model of visceral leishmaniasis

Visceral leishmaniasis (VL) is a serious and neglected disease present worldwide. Chemotherapy using pentavalent antimony (Sb^V) is the most practical and inexpensive strategy available for the VL treatment today, however, it has high toxicity. Alternatively, other drugs are used as viable leishmanicidal therapeutic options. Miltefosine is the only anti-leishmanial agent administered orally, however, it has been reducing its effectiveness. In this sense, there is no ideal therapy for VL since the drugs currently used trigger severe side effects causing discontinuation of treatment, which carries an imminent risk for the emergence of parasite resistance. With that, other therapeutic strategies are gaining prominence. Among them, immunotherapy and/or immunochemotherapy, which the activation/modulation of the immune system can redirect the host's immune response to an effective therapeutic result. Therefore, this work was designed to assess an immunochemotherapy protocol composed of half course of Miltefosine associated with LBSap vaccine (Milt+LBSap) using the hamster Mesocricetus auratus as an experimental model for VL treatment. When evaluating the main hematobiochemical, immunological and therapeutic efficacy parameters, it was demonstrated that the treatment with Milt+LBSap showed restoration of hematobiochemical condition and reduced serum levels of IgG-anti-Leishmania compared to animals infected non treated (INT). Beyond that, an increase in the number of CD4⁺ lymphocytes producers of IFN-γ in relation to INT or to animals treated with miltefosine during 28 days, and TNF-α increased compared to INT were observed. Also, it was found a reduction of IL-10-production in relation to INT, or animals that received LBSap vaccine only, or miltefosine, following by a reduction in the splenic parasitic burden. These results demonstrate that the immunochemotherapy protocol used can stimulate the immune response, inducing an expressive cellular response sufficient to control spleen parasitism, standing out as a promising proposal for the VL treatment.

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New therapy protocols for treatment of visceral leishmaniasis are requested.

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Immunochemotherapy can strengthen the immune response concomitant with a direct action of the drug against L.infantum.

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Immunochemotherapy with miltefosine plus LBSap vaccine against VL induces activation of cellular response immune.

Resistance to Experimental Visceral Leishmaniasis in Mice Infected With Leishmania infantum Requires Batf3

Unveiling the protective immune response to visceral leishmaniasis is critical for a rational design of vaccines aimed at reducing the impact caused by this fatal, if left untreated, vector-borne disease. In this study we sought to determine the role of the basic leucine zipper transcription factor ATF-like 3 (Batf3) in the evolution of infection with Leishmania infantum, the causative agent of human visceral leishmaniasis in the Mediterranean Basin and Latin America. For that, Batf3-deficient mice in C57BL/6 background were infected with an L. infantum strain expressing the luciferase gene. Bioluminescent imaging, as well as in vitro parasite titration, demonstrated that Batf3-deficient mice were unable to control hepatic parasitosis as opposed to wild-type C57BL/6 mice. The impaired microbicide capacities of L. infantum-infected macrophages from Batf3-deficient mice mainly correlated with a reduction of parasite-specific IFN-γ production. Our results reinforce the implication of Batf3 in the generation of type 1 immunity against infectious diseases.

In vitro Infectivity of Strains Isolated From Dogs Naturally Infected With Leishmania infantum Present a Distinct Pathogenic Profile in Hamsters

Visceral leishmaniasis (VL) is a severe disease caused by Leishmania infantum. Dogs are the parasite's main reservoir, favoring its transmission in the urban environment. The analysis of L. infantum from infected dogs contributes to the identification of more virulent parasites, thereby supporting basic and applied studies such as vaccinal and therapeutic strategies. We proposed the in vitro and in vivo characterization of L. infantum strains from naturally infected dogs from a VL endemic area based on an infectivity and pathogenicity analysis. DH82 canine macrophages were infected in vitro with different strains for infectivity analysis, showing distinct infectivity profiles. The strains that showed greater and lesser infectivity using in vitro analyses (616 and 614, respectively) were used to infect hamsters for pathogenicity analysis. The group infected with strain 616 showed 100% survival while the group infected with strain 614 showed 50% after seven months of follow up. Furthermore, the 614 strain induced more noticeable clinicopathological changes and biochemical abnormalities in liver function, along with high inflammation and parasite load in the liver and spleen. We confirmed high variability of infectivity and pathogenicity in L. infantum strains from infected dogs. The results support the belief that screening for L. infantum infectivity using in vitro experiments is inadequate when it comes to selecting the most pathogenic strain.

Central Asian Rodents as Model Animals for Leishmania major and Leishmania donovani Research

The clinical manifestation of leishmaniases depends on parasite species, host genetic background, and immune response. Manifestations of human leishmaniases are highly variable, ranging from self-healing skin lesions to fatal visceral disease. The scope of standard model hosts is insufficient to mimic well the wide disease spectrum, which compels the introduction of new model animals for leishmaniasis research. In this article, we study the susceptibility of three Asian rodent species (Cricetulus griseus, Lagurus lagurus, and Phodopus sungorus) to Leishmania major and L. donovani. The external manifestation of the disease, distribution, as well as load of parasites and infectiousness to natural sand fly vectors, were compared with standard models, BALB/c mice and Mesocricetus auratus. No significant differences were found in disease outcomes in animals inoculated with sand fly- or culture-derived parasites. All Asian rodent species were highly susceptible to L. major. Phodopus sungorus showed the non-healing phenotype with the progressive growth of ulcerative lesions and massive parasite loads. Lagurus lagurus and C. griseus represented the healing phenotype, the latter with high infectiousness to vectors, mimicking best the character of natural reservoir hosts. Both, L. lagurus and C. griseus were also highly susceptible to L. donovani, having wider parasite distribution and higher parasite loads and infectiousness than standard model animals.

Arginase and its mechanisms in Leishmania persistence

Leishmaniasis is a neglected infectious disease with clinical presentations ranging from asymptomatic or mild symptoms to chronic infection and eventual death. The mechanisms of disease susceptibility and pathology have been extensively studied, but there are no steadfast rules regarding leishmaniasis. A Th1 response is usually associated with infection control, while a predominant Th2 response is detrimental to the patient. In this scenario, the enzymes arginase and inducible nitric oxide synthase represent two possible pathways of immune response. While the former contributes to parasite replication, the latter is crucial for its control. In the present review, we collected study results that associate arginase expression in patients and in experimental models with disease susceptibility/chronicity and show some proposed mechanisms that explain the role of arginase in maintaining Leishmania infection, including polyamine and thiol synthesis, tissue-resident macrophage (TRM) proliferation and activation and T-cell suppression and exhaustion.

Modulation of Cytokines and Extracellular Matrix Proteins Expression by Leishmania amazonensis in Susceptible and Resistant Mice

Leishmaniases are a complex of diseases with a broad spectrum of clinical forms, which depend on the parasite species, immunological status, and genetic background of the host. In the Leishmania major model, susceptibility is associated with the Th2 pattern of cytokines production, while resistance is associated with Th1 response. However, the same dichotomy does not occur in L. amazonensis-infected mice. Cytokines are key players in these diseases progression, while the extracellular matrix (ECM) components participate in the process of parasite invasion as well as lesion healing. In this article, we analyzed the influence of host genetics on the expression of cytokines, inducible nitric oxide synthase (iNOS), and ECM proteins, as well as the parasite load in mice with different genetic backgrounds infected by L. amazonensis. C57BL/10 and C3H/He mice were subcutaneously infected with 10⁶L. amazonensis promastigotes. Lesion kinetics, parasite load, cytokines, iNOS, and ECM proteins expression were measured by quantitative PCR (qPCR) in the footpad, draining lymph nodes, liver, and spleen at early (24 h and 30 days) and late phase (120 and 180 days) of infection. Analysis of lesion kinetics showed that C57BL/10 mice developed ulcerative lesions at the inoculation site after L. amazonensis infection, while C3H/He showed slight swelling in the footpad 180 days after infection. C57BL/10 showed progressive enhancement of parasite load in all analyzed organs, while C3H/He mice showed extremely low parasite loads. Susceptible C57BL/10 mice showed high levels of TGF-β mRNA in the footpad early in infection and high levels of proinflammatory cytokines mRNA (IL-12, TNF-α, and IFN-γ) and iNOS in the late phase of the infection. There is an association between increased expression of fibronectin, laminin, collagen III and IV, and TGF-β. On the other hand, resistant C3H/He mice presented a lower repertory of cytokines mRNA expression when compared with susceptible C57BL/10 mice, basically producing TNF-α, collagen IV, and laminin early in infection. The findings of our study indicate that L. amazonensis infection induces different cytokine expression in resistant and susceptible mice but not like the L. major model. An organ-compartmentalized cytokine response was observed in our model. Host genetics determine this response, which modulates ECM proteins expression.

Assessing the composition of the plasma membrane of Leishmania (Leishmania) infantum and L. (L.) amazonensis using label-free proteomics

Protozoan parasites of the genus Leishmania are causative agents of leishmaniasis, a wide range of diseases affecting 12 million people worldwide. The species L. infantum and L. amazonensis are etiologic agents of visceral and cutaneous leishmaniasis, respectively. Most proteome analyses of Leishmania have been carried out on whole-cell extracts, but such an approach tends to underrepresent membrane-associated proteins due to their high hydrophobicity and low solubility. Considering the relevance of this category of proteins in virulence, invasiveness and the host-parasite interface, this study applied label-free proteomics to assess the plasma membrane sub-proteome of L. infantum and L. amazonensis. The number of proteins identified in L. infantum and L. amazonensis promastigotes was 1168 and 1455, respectively. After rigorous data processing and mining, 157 proteins were classified as putative plasma membrane-associated proteins, of which 56 proteins were detected in both species, six proteins were detected only in L. infantum and 39 proteins were exclusive to L. amazonensis. The quantitative analysis revealed that two proteins were more abundant in L. infantum, including the glucose transporter 2, and five proteins were more abundant in L. amazonensis. The identified proteins associated with distinct processes and functions. In this regard, proteins of L. infantum were linked to metabolic processes whereas L. amazonensis proteins were involved in signal transduction. Moreover, transmembrane transport was a significant process among the group of proteins detected in both species and members of the superfamily of ABC transporters were highly represented. Interestingly, some proteins of this family were solely detected in L. amazonensis, such as ABCA9. GP63, a well-known virulence factor, was the only GPI-anchored protein identified in the membrane preparations of both species. Finally, we found several proteins with uncharacterized functions, including differentially abundant ones, highlighting a gap in the study of Leishmania proteins. Proteins characterization could provide a better biological understanding of these parasites and deliver new possibilities regarding the discovery of therapeutic targets, drug resistance and vaccine candidates.

Hemophagocytic lymphohistiocytosis secondary to visceral leishmaniasis in an endemic area in the north of Minas Gerais, Brazil

INTRODUCTION

Visceral leishmaniasis (VL) is an ill-studied disease that is endemic to several regions of Brazil. It is often complicated by hemophagocytic lymphohistiocytosis (HLH), a potentially fatal disorder resulting from excessive non-malignant activation/proliferation of T lymphocytes and macrophages. Considering the overlapping clinical and laboratory characteristics of these diseases, diagnosing HLH is a challenge. Therefore, tracking the association between VL and HLH is necessary in endemic areas. Although HLH can be inapparent and resolve with antileishmanicides, this may not always occur. HLH causes high lethality; therefore, immunosuppressive therapy should be instituted immediately in order to avoid a fatal outcome.

METHODS:

We described the epidemiological, clinical, laboratory, and therapeutic profile of this association in a region of Brazil endemic for VL.

RESULTS

We presented 39 patients with this association in a retrospective cohort of 258 children who were admitted from January 2012 to June 2017. Of the 39 patients, 31 were from urban areas (79.5%), and 21 (53%) were males. The mean age and weight were 2.86 (2.08) years and 14.03 (5.96) kg, respectively. The main symptoms were fever (100%), hepatosplenomegaly (100%), pallor of the skin and mucosa (82.5%), edema (38.5%), bleeding (25%), and jaundice (7.5%). Hemophagocytosis was identified in 16/37 (43.24%) patients, and direct examination revealed that 26/37 (70.27%) patients were positive for VL. The patients were treated as recommended by the Ministry of Health.

CONCLUSIONS

It was observed that HLH is a common complication in endemic areas, and its diagnosis must consider the overlapping of clinical characteristics and pancytopenia.

Sirolimus enhances the protection achieved by a DNA vaccine against Leishmania infantum

Background

Leishmaniases are a group of neglected tropical parasitic diseases, mainly affecting vulnerable populations of countries with poor socioeconomic status. Development of efficient vaccines is a priority due to the increasing incidence of drug resistance and toxicity to current treatments. In the search for a safe and efficient protective vaccine for human and dog visceral leishmaniases, we analyzed the suitability of the immunomodulatory drug sirolimus (SIR) to boost a preventive DNA vaccine against leishmaniasis. SIR is an already marketed drug that has been described to boost immune protection against different disease models and has also emerged as a promising therapeutic drug against L. major.

Methods

Syrian hamsters were treated with SIR concomitantly with the administration of a DNA vaccine formulation consisting in four plasmids carrying the Leishmania genes LACK, TRYP, PAPLE22 and KMPII, respectively. Two weeks after the last vaccination, the animals were infected intraperitoneally with L. infantum parasites. Five weeks post-infection the parasite load was measured by real-time PCR in target tissues and immune response was evaluated by determining anti-Leishmania specific antibodies in combination with cytokine expression in the spleen.

Results

Our results show that the DNA vaccine itself efficiently reduced the burden of parasites in the skin (P = 0.0004) and lymph nodes (P = 0.0452). SIR administration also enhanced the protection by reducing the parasite load in the spleen (P = 0.0004). Vaccinated animals with or without SIR co-treatment showed lower IFN-γ expression levels than those found in the spleen of control animals. mRNA expression levels of NOS2 and IL-10 were found to be significantly higher in the vaccinated plus SIR treated group.

Conclusions

Co-administration of SIR enhances a DNA vaccination regimen against L. infantum, improving the reduction of parasite load in skin, lymph node and spleen. The analysis of immune markers in the spleen after challenge suggests that the trend to recover naïve levels of IFN-γ and IL-10, and the concurrent higher expression of NOS2, may be responsible for the protection induced by our vaccine co-administered with SIR.

An immunoinformatic approach driven by experimental proteomics: in silico design of a subunit candidate vaccine targeting secretory proteins of Leishmania donovani amastigotes

Background

Visceral leishmaniasis (VL) caused by dimorphic Leishmania species is a parasitic disease with high socioeconomic burden in endemic areas worldwide. Sustaining control of VL in terms of proper and prevailing immunity development is a global necessity amid unavailability of a prophylactic vaccine. Screening of experimental proteome of the human disease propagating form of Leishmania donovani (amastigote) can be more pragmatic for in silico mining of novel vaccine candidates.

Methods

By using an immunoinformatic approach, CD4+ and CD8+ T cell-specific epitopes from experimentally reported L. donovani proteins having secretory potential and increased abundance in amastigotes were screened. A chimera linked with a Toll-like receptor 4 (TLR4) peptide adjuvant was constructed and evaluated for physicochemical characteristics, binding interaction with TLR4 in simulated physiological condition and the trend of immune response following hypothetical immunization.

Results

Selected epitopes from physiologically important L. donovani proteins were found mostly conserved in L. infantum, covering theoretically more than 98% of the global population. The multi-epitope chimeric vaccine was predicted as stable, antigenic and non-allergenic. Structural analysis of vaccine-TLR4 receptor docked complex and its molecular dynamics simulation suggest sufficiently stable binding interface along with prospect of non-canonical receptor activation. Simulation dynamics of immune response following hypothetical immunization indicate active and memory B as well as CD4+ T cell generation potential, and likely chance of a more Th1 polarized response.

Conclusions

The methodological approach and results from this study could facilitate more informed screening and selection of candidate antigenic proteins for entry into vaccine production pipeline in future to control human VL.

TLR4 abrogates the Th1 immune response through IRF1 and IFN-β to prevent immunopathology during L. infantum infection

A striking feature of human visceral leishmaniasis (VL) is chronic inflammation in the spleen and liver, and VL patients present increased production levels of multiple inflammatory mediators, which contribute to tissue damage and disease severity. Here, we combined an experimental model with the transcriptional profile of human VL to demonstrate that the TLR4-IFN-β pathway regulates the chronic inflammatory process and is associated with the asymptomatic form of the disease. Tlr4-deficient mice harbored fewer parasites in their spleen and liver than wild-type mice. TLR4 deficiency enhanced the Th1 immune response against the parasite, which was correlated with an increased activation of dendritic cells (DCs). Gene expression analyses demonstrated that IRF1 and IFN-β were expressed downstream of TLR4 after infection. Accordingly, IRF1- and IFNAR-deficient mice harbored fewer parasites in the target organs than wild-type mice due to having an increased Th1 immune response. However, the absence of TLR4 or IFNAR increased the serum transaminase levels in infected mice, indicating the presence of liver damage in these animals. In addition, IFN-β limits IFN-γ production by acting directly on Th1 cells. Using RNA sequencing analysis of human samples, we demonstrated that the transcriptional signature for the TLR4 and type I IFN (IFN-I) pathways was positively modulated in asymptomatic subjects compared with VL patients and thus provide direct evidence demonstrating that the TLR4-IFN-I pathway is related to the nondevelopment of the disease. In conclusion, our results demonstrate that the TLR4-IRF1 pathway culminates in IFN-β production as a mechanism for dampening the chronic inflammatory process and preventing immunopathology development.

Visceral leishmaniasis (VL) is one of the most lethal neglected tropical diseases and is caused by Leishmania parasites. Most subjects infected with Leishmania present subclinical VL symptoms, and their immune response is mediated by Th1 cells and immunoregulatory mechanisms. However, when infection progresses to disease, VL patients present increased levels of inflammatory mediators in the serum which are related to the severity of disease. During infection, Toll-like receptors (TLRs) interact with Leishmania parasites and contribute to the outcome of the disease. Herein, we report that TLR4 signaling hampers the chronic immune response during VL to prevent immunopathology. TLR4 triggers the activation of IRF1 and thus induces the transcription of IFN-β, which in turn acts directly on Th1 cells to limit the production of IFN-γ. In addition, a transcription analysis of human VL samples provides direct evidence demonstrating that the TLR4-IFN-I pathway is related to the asymptomatic form of the disease. Collectively, our findings reveal that TLR4 hampers the Th1 immune response through IRF1 and IFN-β to prevent immunopathology during VL.

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

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

Intracellular anti-leishmanial effect of Spergulin-A, a triterpenoid saponin of Glinus oppositifolius

Background

Many of present chemotherapeutics are inadequate and also resistant against visceral leishmaniasis (VL), an immunosuppressive ailment caused by Leishmania donovani. Despite the interest in plant-based drug development, no antileishmanial drugs from plant source are currently available. Glinus oppositifolius had been reported in favor of being immune modulators along with other traditional uses. Novel anti-VL therapies can rely on host immune-modulation with associated leishmanicidal action.

Objective

Discovery of novel plant-based antileishmanial compound from G. oppositifolius having permissible side effects.

Methods

With this rationale, an n-BuOH fraction of the methanolic extract of the plant and obtained triterpenoid saponin Spergulin-A were evaluated against acellular and intracellular L. donovani. Immunostimulatory activity of them was confirmed by elevated TNF-α and extracellular NO production from treated MФs and was found nontoxic to the host cells. Identification and structure confirmation for isolated Spergulin-A was performed by ESI-MS,¹³C, and ¹H NMR.

Results

Spergulin-A was found ineffective against the acellular forms while, against the intracellular parasites at 30 μg/mL, the reduction was 92.6% after 72 hrs. Spergulin-A enhanced ROS and nitric oxide (NO) release and changes in Gp91-phox, i-NOS, and pro and anti-inflammatory cytokines elaborated its intracellular anti-leishmanial activity.

Conclusion

The results supported that G. oppositifolius and Spergulin-A can potentiate new lead molecules for the development of alternative drugs against VL.

Prevalence of Leishmania species among patients with cutaneous leishmaniasis in Qassim province of Saudi Arabia

Background

Leishmaniasis is a parasitic infection endemic in more than ninety countries of the world. The cutaneous leishmaniasis (CL) is a most common form of leishmaniasis and it remains to be a major public health issue in Saudi Arabia. This study was undertaken to investigate the Leishmania species responsible for CL infection in different provinces of Qassim, Saudi Arabia.

Methods

Skin biopsies were obtained from CL patients and DNA was extracted using the Magna pure system. Leishmania species were identified by highly specific/sensitive quantitative and qualitative PCR.

Results

Out of total 206 CL biopsies, 49.5% biopsies were found to be positive for Leishmania major (L. major), 28.6% biopsies were positive for Leishmania tropica (L. tropica), 3.9% were found to be positive for Leishmania infantum/donovani (L. infantum/donovani). Not only have these, all tested CL biopsies showed negative test for Leishmania mexicana (L. mexicana) and Leishmania viannia (L. viannia).

Conclusions

This is the first comprehensive study that shows the majority of CL in Qassim was caused by L. major and L. tropica. To the best of our knowledge, this is the very first report that shows the occurrence of L. infantum/donovani in Saudi Arabia. This requires higher alert to the Ministry of Health of Saudi Arabia to take proactive actions in preventing the onset of L. major, L. tropica, L. infantum and L. donovani infections.

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

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

Understanding Resistance vs. Susceptibility in Visceral Leishmaniasis Using Mouse Models of Leishmania infantum Infection

Every year, up to 90,000 new cases of Visceral Leishmaniasis and 30,000 resultant deaths are estimated to occur worldwide. Such numbers give relevance to the continuous study of this complex form of the disease: a zoonosis and an anthroponosis; two known etiological agents (Leishmania infantum and L. donovani, respectively); with an estimated average ratio of 1 symptomatic per 10 asymptomatic individuals; and sometimes associated with atypical clinical presentations. This complexity, which results from a long co-evolutionary process involving vector-host, host-pathogen, and pathogen-vector interactions, is still not completely understood. The determinants of visceralization are not fully defined and the dichotomy resistance vs. susceptibility remains unsolved, translating into obstacles that delay the progress of global disease control. Inbred mouse models, with different susceptibility patterns to Leishmania infection, have been very useful in exploring this dichotomy. BALB/c and C57BL/6 mice were described as susceptible strains to L. donovani visceral infection, while SV/129 was considered resistant. Here, we used these three mouse models, but in the context of L. infantum infection, the other Leishmania species that cause visceral disease in humans, and dynamically compared their local and systemic infection-induced immune responses in order to establish a parallel and to ultimately better understand susceptibility vs. resistance in visceral leishmaniasis. Overall, our results suggest that C57BL/6 mice develop an intermediate “infection-phenotype” in comparison to BALB/c and SV/129 mouse strains, considering both the splenic parasite burden and the determined target organs weights. However, the immune mechanisms associated with the control of infection seem to be different in each mouse strain. We observed that both BALB/c and SV/129, but not C57BL/6 mice, show an infection-induced increase of splenic T follicular helper cells. On the other hand, differences detected in terms of CD21 expression by B cells early after infection, together with the quantified anti-Leishmania specific antibodies, suggest that SV/129 are faster than BALB/c and C57BL/6 mice in the assembly of an efficient B-cell response. Additionally, we observed an infection-induced increase in polyfunctional CD4+ T cells in the resistant SV/129 model, opposing an infection-induced increase in CD4+IL-10+ cells in susceptible BALB/c mice. Our data aligns with the observations reported for L. donovani infection and suggest that not only a single mechanism, but an interaction of several could be necessary for the control of this parasitic disease.

Fatal Visceral Leishmaniasis Caused by Leishmania infantum, Lebanon

Visceral leishmaniasis, a fatal disease if not treated, is caused by Leishmania parasites. This disease might be overlooked in the Middle East because of limited awareness and low incidence. We report 5 patients who died of visceral leishmaniasis in Lebanon and make recommendations to improve faster diagnosis and treatment.

Sex-Related Differences in Immune Response and Symptomatic Manifestations to Infection with Leishmania Species

Worldwide, an estimated 12 million people are infected with Leishmania spp. and an additional 350 million are at risk of infection. Leishmania are intracellular parasites that cause disease by suppressing macrophage microbicidal responses. Infection can remain asymptomatic or lead to a spectrum of diseases including cutaneous, mucocutaneous, and visceral leishmaniasis. Ultimately, the combination of both pathogen and host factors determines the outcome of infection. Leishmaniasis, as well as numerous other infectious diseases, exhibits sex-related differences that cannot be explained solely in terms of environmental exposure or healthcare access. Furthermore, transcriptomic evidence is revealing that biological sex is a variable impacting physiology, immune response, drug metabolism, and consequently, the progression of disease. Herein, we review the distribution, morbidity, and mortality among male and female leishmaniasis patients. Additionally, we discuss experimental findings and new avenues of research concerning sex-specific responses in cutaneous and visceral leishmaniasis. The limitations of current therapies and the emergence of drug-resistant parasites underscore the need for new treatments that could harness the host immune response. As such, understanding the mechanisms driving the differential immune response and disease outcome of males versus females is a necessary step in the development of safer and more effective treatments against leishmaniasis.

Epidemiological and Experimental Evidence for Sex-Dependent Differences in the Outcome of Leishmania infantum Infection

Leishmania infantum causes visceral leishmaniasis (VL) in Brazil. We previously observed that VL is more common in males than females living in endemic neighborhoods, despite similar exposure. Using a larger sample, we document that VL is more common in males than females, but only after puberty. BALB/c and C57BL/6 mouse models confirmed that there is a biological basis for male susceptibility to symptomatic VL, showing higher parasite burdens in males than females. Female C57BL/6 mice generated more antigen-induced cytokines associated with curative responses (interferon-γ, interleukin [IL]-1β). Males expressed higher levels of IL-10 and tumor necrosis factor, which are linked to exacerbated disease. Different parasite lines entered or survived at a higher rate in macrophages of male- than female-origin. These results suggest that males are inherently more susceptible to L. infantum than females and that mice are a valid model to study this sex-dependent difference.

Bayesian compartmental model for an infectious disease with dynamic states of infection

Population-level proportions of individuals that fall at different points in the spectrum [of disease severity], from asymptomatic infection to severe disease, are often difficult to observe, but estimating these quantities can provide information about the nature and severity of the disease in a particular population. Logistic and multinomial regression techniques are often applied to infectious disease modeling of large populations and are suited to identifying variables associated with a particular disease or disease state. However, they are less appropriate for estimating infection state prevalence over time because they do not naturally accommodate known disease dynamics like duration of time an individual is infectious, heterogeneity in the risk of acquiring infection, and patterns of seasonality. We propose a Bayesian compartmental model to estimate latent infection state prevalence over time that easily incorporates known disease dynamics. We demonstrate how and why a stochastic compartmental model is a better approach for determining infection state proportions than multinomial regression is by using a novel method for estimating Bayes factors for models with high-dimensional parameter spaces. We provide an example using visceral leishmaniasis in Brazil and present an empirically-adjusted reproductive number for the infection.

MALDI MS imaging investigation of the host response to visceral leishmaniasis

Mass spectrometry imaging (MSI) of animal tissues has become an important tool for in situ molecular analyses and biomarker studies in several clinical areas, but there are few applications in parasitological studies. Leishmaniasis is a neglected tropical disease, and experimental mouse models have been essential to evaluate pathological and immunological processes and to develop diagnostic methods. Herein we have employed MALDI MSI to examine peptides and low molecular weight proteins (2 to 20 kDa) differentially expressed in the liver during visceral leishmaniasis in mice models. We analyzed liver sections of Balb/c mice infected with Leishmania infantum using the SCiLS Lab software for statistical analysis, which facilitated data interpretation and thus highlighted several key proteins and/or peptides. We proposed a decision tree classification for visceral leishmaniasis with distinct phases of the disease, which are named here as healthy, acute infection and chronic infection. Among others, the ion of m/z 4963 was the most important to identify acute infection and was tentatively identified as Thymosin β4. This peptide was previously established as a recovery factor in the human liver and might participate in the response of mice to Leishmania infection. This preliminary investigation shows the potential of MALDI MSI to complement classical compound selective imaging techniques and to explore new features not yet recognized by these approaches.

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

Background

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

Methodology/Principal findings

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

Conclusion/Significance

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

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

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

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