Canine visceral leishmaniasis: successful chemotherapy induces macrophage antileishmanial activity via the L-arginine nitric oxide pathway

MicroRNA-21 and microRNA-148a affects PTEN, NO and ROS in canine leishmaniasis

Canine Visceral leishmaniasis (CanL) poses a severe public health threat in several countries. Disease progression depends on the degree of immune response suppression. MicroRNAs (miRs) modulate mRNA translation into proteins and regulate various cellular functions and pathways associated with immune responses. MiR-21 and miR-148a can alter the parasite load and M1 macrophages are the principal cells in dogs' leishmanicidal activity. A previous study found increased miR-21 and miR-148a in splenic leukocytes (SL) of dogs with CanL using microarray analysis and in silico analysis identified PTEN pathway targets. PTEN is involved in the immune regulation of macrophages. We measured PTEN and the production of reactive oxygen species (ROS) and nitric oxide (NO) before and after transfection SLs of dogs with CanL with mimic and inhibition of miR-21 and miR-148a. PTEN levels increased, NO and ROS decreased in SLs from dogs with CanL. Inhibition of miRNA-21 resulted in PTEN increase; in contrast, PTEN decreased after miR-148a inhibition. Nitrite (NO₂) levels increased after transfection with miR-21 inhibitor but were decreased with miR-148a inhibitor. The increase in miR-21 promoted a reduction in ROS and NO levels, but miR-148a inhibition increased NO and reduced ROS. These findings suggest that miR-21 and miR-148a can participate in immune response in CanL, affecting PTEN, NO, and ROS levels.

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.

Neutrophil properties in healthy and Leishmania infantum-naturally infected dogs

Visceral leishmaniasis is a chronic disease that affects humans and dogs as well. Dogs, the domestic reservoir of Leishmania, play a central role in the transmission of visceral leishmaniasis, the most severe form of this disease. Neutrophils are the most abundant leukocytes in blood and interact with the parasite after infection. Here, we evaluate the effector properties of neutrophils from healthy and naturally Leishmania infantum-infected dogs. Our results showed that the parasite induced neutrophil extracellular trap (NET) release from neutrophils in both groups. Additionally, phagocytosis and NETs contributed differently to parasite killing by neutrophils from healthy and infected animals, and IFN-γ, IL-8, IL-4 and TNF-α production by neutrophils from both groups were differentially modulated by the parasite. Our results contribute to a better understanding of the complex role played by neutrophils in canine visceral leishmaniasis, which may favor the development of more effective therapies.

Biomarkers Associated With Leishmania infantum Exposure, Infection, and Disease in Dogs

Canine leishmaniosis (CanL) is a vector-borne disease caused by the protozoan Leishmania (Leishmania) infantum species [syn. L. (L.) infantum chagasi species in the Americas] which is transmitted by the bite of a female phlebotomine sand fly. This parasitosis is endemic and affect millions of dogs in Asia, the Americas and the Mediterranean basin. Domestic dogs are the main hosts and the main reservoir hosts for human zoonotic leishmaniosis. The outcome of infection is a consequence of intricate interactions between the protozoan and the immunological and genetic background of the host. Clinical manifestations can range from subclinical infection to very severe disease. Early detection of infected dogs, their close surveillance and treatment are essential to control the dissemination of the parasite among other dogs, being also a pivotal element for the control of human zoonotic leishmaniosis. Hence, the identification of biomarkers for the confirmation of Leishmania infection, disease and determination of an appropriate treatment would represent an important tool to assist clinicians in diagnosis, monitoring and in giving a realistic prognosis to subclinical infected and sick dogs. Here, we review the recent advances in the identification of Leishmania infantum biomarkers, focusing on those related to parasite exposure, susceptibility to infection and disease development. Markers related to the pathogenesis of the disease and to monitoring the evolution of leishmaniosis and treatment outcome are also summarized. Data emphasizes the complexity of parasite-host interactions and that a single biomarker cannot be used alone for CanL diagnosis or prognosis. Nevertheless, results are encouraging and future research to explore the potential clinical application of biomarkers is warranted.

Insights on adaptive and innate immunity in canine leishmaniosis

Canine leishmaniosis (CanL) is caused by the parasite Leishmania infantum and is a systemic disease, which can present with variable clinical signs, and clinicopathological abnormalities. Clinical manifestations can range from subclinical infection to very severe systemic disease. Leishmaniosis is categorized as a neglected tropical disease and the complex immune responses associated with Leishmania species makes therapeutic treatments and vaccine development challenging for both dogs and humans. In this review, we summarize innate and adaptive immune responses associated with L. infantum infection in dogs, and we discuss the problems associated with the disease as well as potential solutions and the future direction of required research to help control the parasite.

Metabolomic Analyses of Leishmania Reveal Multiple Species Differences and Large Differences in Amino Acid Metabolism

Comparative genomic analyses of Leishmania species have revealed relatively minor heterogeneity amongst recognised housekeeping genes and yet the species cause distinct infections and pathogenesis in their mammalian hosts. To gain greater information on the biochemical variation between species, and insights into possible metabolic mechanisms underpinning visceral and cutaneous leishmaniasis, we have undertaken in this study a comparative analysis of the metabolomes of promastigotes of L. donovani, L. major and L. mexicana. The analysis revealed 64 metabolites with confirmed identity differing 3-fold or more between the cell extracts of species, with 161 putatively identified metabolites differing similarly. Analysis of the media from cultures revealed an at least 3-fold difference in use or excretion of 43 metabolites of confirmed identity and 87 putatively identified metabolites that differed to a similar extent. Strikingly large differences were detected in their extent of amino acid use and metabolism, especially for tryptophan, aspartate, arginine and proline. Major pathways of tryptophan and arginine catabolism were shown to be to indole-3-lactate and arginic acid, respectively, which were excreted. The data presented provide clear evidence on the value of global metabolomic analyses in detecting species-specific metabolic features, thus application of this technology should be a major contributor to gaining greater understanding of how pathogens are adapted to infecting their hosts.

Evaluation of Live Recombinant Nonpathogenic Leishmania tarentolae Expressing Cysteine Proteinase and A2 Genes as a Candidate Vaccine against Experimental Canine Visceral Leishmaniasis

Canine Visceral Leishmaniasis (CVL) is a major veterinary and public health problem caused by Leishmania infantum (L. infantum) in many endemic countries. It is a severe chronic disease with generalized parasite spread to the reticuloendothelial system, such as spleen, liver and bone marrow and is often fatal when left untreated. Control of VL in dogs would dramatically decrease infection pressure of L. infantum for humans, since dogs are the main domestic reservoir. In the past decade, various subunits and DNA antigens have been identified as potential vaccine candidates in experimental animal models, but none has been approved for human use so far. In this study, we vaccinated outbreed dogs with a prime-boost regimen based on recombinant L. tarentolae expressing the L. donovani A2 antigen along with cysteine proteinase genes (CPA and CPB without its unusual C-terminal extension (CPB^-CTE) and evaluated its immunogenicity and protective immunity against L. infantum infectious challenge. We showed that vaccinated animals produced significantly higher levels of IgG2, but not IgG1, and also IFN-γ and TNF-α, but low IL-10 levels, before and after challenge as compared to control animals. Protection in dogs was also correlated with a strong DTH response and low parasite burden in the vaccinated group. Altogether, immunization with recombinant L. tarentolae A2-CPA-CPB^-CTE was proven to be immunogenic and induced partial protection in dogs, hence representing a promising live vaccine candidate against CVL.

One-year timeline kinetics of cytokine-mediated cellular immunity in dogs vaccinated against visceral leishmaniasis

BACKGROUND

The main control strategy for visceral leishmaniasis in Brazil has been based on the elimination of seropositive dogs, although this is not widely accepted. In this context, the use of a long-lasting protective vaccine against canine visceral leishmaniasis (CVL) has been highly expected. The aim of this work was to determine the timeline kinetics of the cytokine microenvironment derived from circulating leukocytes as supportive immunological biomarkers triggered by Leishmune® vaccine. Cross-sectional kinetic analysis of cellular immunity cytokines was carried out at three times (1, 6 and 12 months) after primovaccination with Leishmune®. In vitro short-term whole blood cultures were stimulated with Leishmania infantum soluble antigen (SLAg). The secreted cytokine signatures and their major sources were determined.

RESULTS

At six months after vaccination, Leishmune® induced an increase in IL-8, IFN-γ, IL-17a and TNF-α levels and a decrease in IL-10. Cytokine signature analysis revealed a shift in the microenvironment towards a pro-inflammatory profile mediated by IL-8 and IFN-γ. Both, CD4(+) (↑TNF-α(+) and ↑IFN-γ (+)) and CD8(+) (↑IL-17a and ↓IL-4) T-cells contributed to the acquired immune responses observed after stimulation with SLAg.

CONCLUSIONS

The changes observed in the cytokine profile suggested that Leishmune® was able to induce an effective response at six months after primovaccination. After one year, it returned to baseline suggesting the need of additional boosting.

Cutaneous immune mechanisms in canine leishmaniosis due to Leishmania infantum

Canine leishmaniosis (CanL) caused by the parasite Leishmania infantum is a systemic disease with variable clinical signs. The disease is endemic in the Mediterranean countries and dogs are the main domestic reservoir of the parasite. The quite complicated immune response against the parasite is crucial for the evolution of CanL infection with the skin playing a major role in its immunopathogenesis. After the inoculation of Leishmania promastigotes into the dermis by sand fly bites, complement factors, Langerhan's cells, neutrophils, fibroblasts and keratinocytes are involved in the activation of the innate arm of the skin immune system, with the macrophages and dendritic cells to play a major key role. The effective activation of cellular immunity is the cornerstone of dog's resistance against the parasite. Promastigotes reaching the dermis are engulfed, processed and transferred by APCs to draining lymph nodes to stimulate naïve T-cells for proliferation and differentiation into armed effector T-cells. Th1 cells activate the infected macrophages to kill Leishmania, whereas Th2 cells divert the immune response to humoral immunity and down regulation of cellular immunity with Th1 cell anergy. Inhibition of co-stimulatory molecules expression by infected macrophages contributes to T-cell anergy. In canine subclinical infections cutaneous lymphocytic infiltrate and parasites are absent, as opposed to dogs with clinical leishmaniosis. CD8+ cells constitute a significant population of cellular immunity in CanL since they outnumber CD4+ cells in the dermis, producing IFN-γ in sub clinically infected dogs and high levels of IL-4 in dogs with clinical leishmaniosis. Numerous B-lymphocytes have been shown to heavily infiltrate the dermis at least in exfoliative dermatitis in CanL. A mixed Th1/Th2 cytokine profile has been found in the dermis of naturally infected with L. infantum dogs. In the skin of dogs with clinical leishmaniosis, where plasma cells outnumber T lymphocytes in the dermal infiltrate, there is an overproduction of IL-4, IL-13 and TNF-α leading to Th2-biased humoral immune response. The issue of humoral immunity polarization in CanL remains controversial. Much still needs to be learned about other mechanisms underlying the complex interaction between the skin immune system and the parasite.

The protective immune response produced in dogs after primary vaccination with the LiESP/QA-21 vaccine (CaniLeish®) remains effective against an experimental challenge one year later

Control of canine leishmaniasis is an important objective for the benefit of dogs living in or visiting endemic areas and for public health because of the zoonotic nature of this disease. Resistance or susceptibility to developing canine leishmaniasis after exposure to Leishmania infantum is primarily determined by the ability of the immune system to develop an appropriate Th1-dominated specific response to the parasite. For this reason there is a need for effective canine vaccines that can decrease the number of dogs developing progressive infections. In this study, we followed the impact of the LiESP/QA-21 canine vaccine (composed of excreted-secreted proteins of L. infantum and the QA-21 saponin adjuvant), recently launched commercially in Europe, on selected humoral and cellular immune parameters following an infectious intravenous challenge with L. infantum promastigotes administered one year after the primary vaccine course. We also followed parasitological parameters to determine the parasitological status of the challenged dogs. In contrast to controls, vaccinated dogs retained significantly stronger cell-mediated immune responses against the parasite despite a virulent challenge and had significantly lower mean parasite burdens at the end of the study, associated with a lower probability of developing active infections. These results confirm that the immune responses generated by vaccination with LiESP/QA-21 are still effective against an intravenous challenge one year after the primary vaccine course.

Animal models for the study of leishmaniasis immunology

Leishmaniasis remains a major public health problem worldwide and is classified as Category I by the TDR/WHO, mainly due to the absence of control. Many experimental models like rodents, dogs and monkeys have been developed, each with specific features, in order to characterize the immune response to Leishmania species, but none reproduces the pathology observed in human disease. Conflicting data may arise in part because different parasite strains or species are being examined, different tissue targets (mice footpad, ear, or base of tail) are being infected, and different numbers (“low” 1×10² and “high” 1×10⁶) of metacyclic promastigotes have been inoculated. Recently, new approaches have been proposed to provide more meaningful data regarding the host response and pathogenesis that parallels human disease. The use of sand fly saliva and low numbers of parasites in experimental infections has led to mimic natural transmission and find new molecules and immune mechanisms which should be considered when designing vaccines and control strategies. Moreover, the use of wild rodents as experimental models has been proposed as a good alternative for studying the host-pathogen relationships and for testing candidate vaccines. To date, using natural reservoirs to study Leishmania infection has been challenging because immunologic reagents for use in wild rodents are lacking. This review discusses the principal immunological findings against Leishmania infection in different animal models highlighting the importance of using experimental conditions similar to natural transmission and reservoir species as experimental models to study the immunopathology of the disease.

Use of a recombinant cysteine proteinase from Leishmania (Leishmania) infantum chagasi for the Immunotherapy of canine visceral Leishmaniasis

BACKGROUND

A recombinant cysteine proteinase from Leishmania (Leishmania) infantum chagasi (rLdccys1) was previously shown to induce protective immune responses against murine and canine visceral leishmaniasis. These findings encouraged us to use rLdccys1 in the immunotherapy of naturally infected dogs from Teresina, Piauí, a region of high incidence of visceral leishmaniasis in Brazil.

METHODOLOGY/PRINCIPAL FINDINGS

Thirty naturally infected mongrel dogs displaying clinical signs of visceral leishmaniasis were randomly divided in three groups: one group received three doses of rLdccys1 in combination with the adjuvant Propionibacterium acnes at one month interval between each dose; a second group received three doses of P. acnes alone; a third group received saline. The main findings were: 1) dogs that received rLdccys1 with P. acnes did not display increase of the following clinical signs: weight loss, alopecia, onychogryphosis, cachexia, anorexia, apathy, skin lesions, hyperkeratosis, ocular secretion, and enlarged lymph nodes; they also exhibited a significant reduction in the spleen parasite load in comparison to the control dogs; 2) rLdccys1-treated dogs exhibited a significant delayed type cutaneous hypersensitivity elicited by the recombinant antigen, as well as high IgG2 serum titers and low IgG1 serum titers; sera from rLdccys1-treated dogs also contained high IFN-γ and low IL-10 concentrations; 3) control dogs exhibited all of the clinical signs of visceral leishmaniasis and had low serum IgG2 and IFN-γ levels and high concentrations of IgG1 and IL-10; 4) all of the dogs treated with rLdccys1 were alive 12 months after treatment, whereas dogs which received either saline or P. acnes alone died within 3 to 7 months.

CONCLUSIONS/SIGNIFICANCE

These findings illustrate the potential use of rLdccys1 as an additional tool for the immunotherapy of canine visceral leishmaniasis and support further studies designed to improve the efficacy of this recombinant antigen for the treatment of this neglected disease.

Primary vaccination with the LiESP/QA-21 vaccine (CaniLeish) produces a cell-mediated immune response which is still present 1 year later

Canine leishmaniasis, an important zoonotic disease of dogs, is the result of an ineffective and inappropriate immune response to infection with Leishmania infantum. It is widely accepted that the appropriate immune response is characterised by a T-helper (Th)1-dominated profile in an overall mixed Th1/Th2 response. The absence of a strong Th1 response is associated with progression to the clinical disease. Thus, there is a need for an effective vaccine that could modulate the immune response to a more appropriate profile against the parasite. In this study we measured the impact of the LiESP/QA-21 canine vaccine, recently launched commercially in Europe, on selected humoral and cellular immune markers for one year after a primary vaccination course. The humoral response to vaccination was characterised by a predominantly IgG2 profile. Vaccinated dogs developed long-lasting cell-mediated immune responses against L. infantum, specifically with a stronger ability of macrophages to reduce intracellular parasite burdens in co-culture with autologous lymphocytes compared to control dogs (p=0.0002), which was correlated with induction of inducible nitric oxide synthase (iNOS) and production of nitric oxide (NO) derivatives. These results confirm that vaccination with LiESP/QA-21 is capable of inducing an appropriate Th1-dominated immune profile which persists for a full year.

Dogs immunized with LBSap vaccine displayed high levels of IL-12 and IL-10 cytokines and CCL4, CCL5 and CXCL8 chemokines in the dermis

The complex interplay between cytokines and chemokines regulates innate and adaptive immune responses against pathogens; specifically, cytokine and chemokine expression drives activation of immune effector cells and their recruitment to tissue infection sites. Herein, we inoculated dogs with Leishmania braziliensis antigens plus saponin (the LBSap vaccine), as well as with the vaccine components, and then used real-time PCR to evaluate the kinetics of dermal expression of mRNAs of cytokines (IL-12, IFN-γ, TNF-α, IL-4, IL-13, TGF-β and IL-10) and chemokines (CCL2, CCL4, CCL5, CCL21 and CXCL8) 1, 12, 24 and 48 h after inoculation. We also evaluated the correlation between cytokine and chemokine expression and dermal cellularity. The LBSap vaccine induced high levels of IL-12 and IL-10 expression at 12 and 24 h, respectively. Furthermore, we observed positive correlations between IL-12 and IL-13 expression, IFN-γ and IL-13 expression, and IL-13 and TGF-β expression, suggesting that a mixed cytokine microenvironment developed after immunization with the vaccine. Inoculation with the saponin adjuvant alone induced a chemokine and cytokine expression profile similar to that observed in the LBSap group. CCL4 and CXCL8 chemokine expression was up regulated by the LBSap vaccine. CCL5 expression was initially highest in the LBSap group, but at 48 h, expression was highest in the LB group. Information about the kinetics of the immune response to this vaccine gained using this dog model will help to elucidate the mechanisms of and factors involved in a protective response against Leishmania infection and will aid in establishing rational approaches for the development of vaccines against canine visceral leishmaniasis.

Successful therapy of visceral leishmaniasis with curdlan involves T-helper 17 cytokines

The aim of this study was to evaluate and characterize the therapeutic potential of curdlan, a naturally occurring β-glucan immunomodulator, against visceral leishmaniasis, a fatal parasitic disease. Curdlan eliminated the liver and spleen parasite burden in a 45-day BALB/c mouse model of visceral leishmaniasis at a dosage of 10 mg/kg/day as determined by Giemsa-stained organ impression smears. Curdlan was associated with production of the disease-resolving T-helper (Th) 1 and Th17-inducing cytokines interleukin (IL)-6, IL-1β, and IL-23, as well as with production of Th17 cytokines IL-17 and IL-22, as determined by enzyme-linked immunosorbent assay (ELISA) and real time polymerase chain reaction (RT-PCR). Reversal of curdlan-mediated protection by anti-IL-17 and anti-IL-23 monoclonal antibodies showed the importance of Th17 cytokines. Significantly decreased production of both IL-17 and IL-22 by mice that received anti-IL-23 antibody suggested the essential role of IL-23 in Th17 differentiation. Although administration of recombinant IL-17 or IL-23 caused significant suppression of the organ parasite burden, with marked generation of interferon γ and nitric oxide (NO), effects were much faster for IL-17. These results documented that although both IL-23 and IL-17 play major roles in the antileishmanial effect of curdlan, the effect of IL-23 may occur indirectly, through the induction of IL-17 production.

Use of a LiESP/QA-21 vaccine (CaniLeish) stimulates an appropriate Th1-dominated cell-mediated immune response in dogs

Canine leishmaniasis is an important zoonotic disease of dogs. The clinical outcome of infection is variable, with the efficiency of the immune response being the key determining factor. There is now a general consensus that a predominant Th1 immune profile in an overall mixed Th1/Th2 response is associated with resistance in dogs, and the absence of a strong Th1 influence is associated with a progression to clinical disease. As a result, there has been a growing demand for vaccines that can induce a specific, strong Th1 response. In this study, we measured the impact of a primary course of a newly available LiESP/QA-21 vaccine on selected humoral and cellular markers of the canine immune response during the onset of immunity. All vaccinated dogs developed a humoral response characterised by IgG2 production. More importantly, vaccinated dogs developed significantly stronger cell-mediated immunity responses than did control dogs. Vaccination induced specific cellular reactivity to soluble Leishmania antigens, with a Leishmania-specific lymphoproliferation (p = 0.0072), characterised by an increased population of T lymphocytes producing IFN-γ (p = 0.0021) and a significant ability of macrophages to reduce intracellular parasite burdens in vitro after co-culture with autologous lymphocytes (p = 0.0014). These responses were correlated with induction of the NOS pathway and production of NO derivatives, which has been shown to be an important leishmanicidal mechanism. These results confirm that vaccination with LiESP/QA-21 induces an appropriate Th1-profile cell-mediated response within three weeks of completing the primary course, and that this response effectively reduces the parasite load in pre-infected macrophages in vitro.

The dog is the principle reservoir of Leishmania infantum, a parasite spread from dog to dog by a sandfly vector. The reduction of canine leishmaniasis is therefore a key factor in the overall management of the epidemiology of this parasite. There is also a need for effective prevention on welfare grounds because of the clinical severity of this potentially fatal disease in dogs. The key factor determining the outcome of infection in dogs is the ability to mount a Th1-dominated immune response, because this is more effective against intracellular pathogens such as L. infantum. Until now, in Europe, only measures to reduce sandfly bites have been available, and for many years there has been a strong demand for a vaccine that provides specific and effective immunity. The recent launch of the first European canine leishmaniasis vaccine (CaniLeish) has provided a means to achieve this, but data on its impact on the dog's immune system are required. The data presented here demonstrate the specific stimulation of an effective Th1-dominated anti-L. infantum response within three weeks of the administration of the vaccine, and provides a basis for the understanding of the mode of action of this new tool.

Vaccines for canine leishmaniasis

Leishmaniasis is the third most important vector-borne disease worldwide. Visceral leishmaniasis (VL) is a severe and frequently lethal protozoan disease of increasing incidence and severity due to infected human and dog migration, new geographical distribution of the insect due to global warming, coinfection with immunosuppressive diseases, and poverty. The disease is an anthroponosis in India and Central Africa and a canid zoonosis (ZVL) in the Americas, the Middle East, Central Asia, China, and the Mediterranean. The ZVL epidemic has been controlled by one or more measures including the culling of infected dogs, treatment of human cases, and insecticidal treatment of homes and dogs. However, the use of vaccines is considered the most cost-effective control tool for human and canine disease. Since the severity of the disease is related to the generation of T-cell immunosuppression, effective vaccines should be capable of sustaining or enhancing the T-cell immunity. In this review we summarize the clinical and parasitological characteristics of ZVL with special focus on the cellular and humoral canine immune response and review state-of-the-art vaccine development against human and canine VL. Experimental vaccination against leishmaniasis has evolved from the practice of leishmanization with living parasites to vaccination with crude lysates, native parasite extracts to recombinant and DNA vaccination. Although more than 30 defined vaccines have been studied in laboratory models no human formulation has been licensed so far; however three second-generation canine vaccines have already been registered. As expected for a zoonotic disease, the recent preventive vaccination of dogs in Brazil has led to a reduction in the incidence of canine and human disease. The recent identification of several Leishmania proteins with T-cell epitopes anticipates development of a multiprotein vaccine that will be capable of protecting both humans and dogs against VL.

Evaluation of TNF-α, IL-4, and IL-10 and parasite density in spleen and liver of L. (L.) chagasi naturally infected dogs

Dogs are the main domestic reservoirs of L. (L.) chagasi. Once in the vertebrate host, the parasite can cause visceral leishmaniasis, which can also be transmitted to humans. Cytokines are key elements of the host immune response against Leishmania spp. To investigate whether tumor necrosis factor (TNF)-α, interleukin (IL)-4 and IL-10 are associated with pattern infection in dogs, these cytokines were quantified in the spleen and liver of dogs naturally infected with L. (L.) chagasi, with or without clinical manifestations, and their levels were correlated with the parasite load verified in these organs. A total of 40 adult dogs naturally infected with L. (L.) chagasi were assessed, together with 12 uninfected control dogs. Samples from spleen and liver were used to determine the cytokine levels by capture ELISA and for quantifying parasite load by real-time PCR. Statistical analysis was performed using the minimum Chi square method and group means were compared using the Tukey test. TNF-α, IL-4 and IL-10 levels in infected dogs were higher than in control groups; the liver was the main cytokine-producing organ during infection. The level of splenic TNF-α showed correlation with parasite load and may represent an important marker for infection process evolution, with the participation of IL-10. These results may contribute to a clearer understanding of the immune response in dogs infected with L. (L.) chagasi, which may lead to the development of prophylactic or preventive measures for these animals.

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

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

Canine leishmaniasis in Southern Italy: a role for nitric oxide released from activated macrophages in asymptomatic infection?

Background

Human and canine leishmaniasis (CanL) by Leishmania infantum is endemic in Italy, with a high percentage of infected asymptomatic animals. However, the immune response mechanisms underlying the clinical presentation of CanL have not been fully investigated. Among leishmanicidal molecules produced by activated macrophages, nitric oxide (NO) produced by an inducible NO synthase seems to play an important protective role, but no conclusive data are available. Therefore, NO released by cultured macrophages from dogs with natural Leishmania infection living in an endemic area for CanL was evaluated.

Methods

On the basis of one year's clinical and laboratory follow-up, 22 dogs infected by Leishmania infantum were identified and grouped as: asymptomatic dogs (n = 13) and dogs with symptoms of leishmaniasis (n = 9). Each animal was bled twice at 4-month intervals and macrophage and lymphocyte cultures were obtained from peripheral blood mononuclear cells. Supernatants of L. infantum-infected macrophage cultures, with or without addition of autologous lymphocytes, were assayed for NO production by Griess reaction for nitrites.

Results

In the first months of the infection the levels of NO in supernatants of Leishmania-infected macrophages were higher in symptomatic than in asymptomatic dogs, but they were significantly increased in the latter group eight months after the diagnosis of infection. Furthermore, NO release significantly decreased in the presence of autologous lymphocytes in both groups of animals.

Conclusion

These results suggest that NO may be involved in the long-term protection of dogs against natural Leishmania infection and in the clinical presentation of canine leishmaniasis in the Mediterranean area.

Vaccines for leishmaniasis in the fore coming 25 years

Human vaccination against leishmaniasis using live Leishmania was used in Middle East and Russia (1941-1980). First-generation vaccines, composed by killed parasites induce low efficacies (54%) and were tested in humans and dogs Phase III trials in Asia and South America since 1940. Second-generation vaccines using live genetically modified parasites, or bacteria or viruses containing Leishmania genes, recombinant or native fractions are known since the 1990s. Due to the loss of PAMPs, the use of adjuvants increased vaccine efficacies of the purified antigens to 82%, in Phase III dog trials. Recombinant second-generation vaccines and third-generation DNA vaccines showed average values of parasite load reduction of 68% and 59% in laboratory animal models, respectively, but their success in field trials had not yet been reported. This review is focused on vaccine candidates that show any efficacy against leishmaniasis and that are already in different phase trials. A lot of interest though was generated in recent years, by the studies going on in experimental models. The promising candidates may find a place in the forth coming years. Among them most probably are the multiple-gene DNA vaccines that are stable and do not require cold-chain transportation. In the mean time, second-generation vaccines with native antigens and effective adjuvants are likely to be licensed and used in Public Health control programs in the fore coming 25 years. To date, only three vaccines have been licensed for use: one live vaccine for humans in Uzbekistan, one killed vaccine for human immunotherapy in Brazil and a second-generation vaccine for dog prophylaxis in Brazil.

Heterologous prime-boost vaccination with a non-replicative vaccinia recombinant vector expressing LACK confers protection against canine visceral leishmaniasis with a predominant Th1-specific immune response

Leishmaniasis caused by Leishmania infantum is a severe endemic disease in the Mediterranean basin, being domestic dogs the main reservoir of the disease that plays a key role in the transmission to humans. Studies on vaccines against canine leishmaniasis, aimed to modify the T cell repertoire, have advanced in recent years. LACK vaccination assays, using protein or DNA vectors, show protection against cutaneous L. major infections by redirecting the early IL-4 responses to a protective Th1 response. The aim of this study was to define the effectiveness and type of immune response in a canine visceral leishmaniasis model of two poxvirus vectors (Western reserve strain, WR and modified vaccinia virus Ankara, MVA) expressing the LACK protein of L. infantum in prime/boost vaccination protocols. The results obtained showed that dog vaccination priming with DNA-LACK followed by a booster with MVA-LACK or rVV-LACK triggered a Th1 type of immune response, leading to protection against canine visceral leishmaniasis. This protection correlated with absence of visceral leishmaniasis symptoms, lower Leishmania-specific antibodies, higher degree of T cell activation in Leishmania-target organs and higher synthesis of Th1 cytokines. In addition, we found that dogs boosted with the non-replicative virus show less VL symptoms and higher degree of T cell activation, providing evidences for a clear advantage of MVA-LACK as a vaccination vector against canine visceral leishmaniasis.

Phenotypical characteristics, biochemical pathways, molecular targets and putative role of nitric oxide-mediated programmed cell death in Leishmania

Nitric oxide (NO) has been demonstrated to be the principal effector molecule mediating intracellular killing of Leishmania, both in vitro and in vivo. We investigated the type of cell death process induced by NO for the intracellular amastigote stage of the protozoa Leishmania. Specific detection methods revealed a rapid and extensive cell death with morphological features of apoptosis in axenic amastigotes exposed to NO donors, in intracellular amastigotes inside in vitro - activated mouse macrophages and also in activated macrophages of regressive lesions in a leishmaniasis-resistant mouse model. We extended our investigations to the dog, a natural host-reservoir of Leishmania parasites, by demonstrating that co-incubation of infected macrophages with autologous lymphocytes derived from dogs immunised with purified excreted-secreted antigens of Leishmania resulted in a significant NO-mediated apoptotic cell death of intracellular amastigotes. From the biochemical point of view, NO-mediated Leishmania amastigotes apoptosis did not seem to be controlled by caspase activity as indicated by the lack of effect of cell permeable inhibitors of caspases and cysteine proteases, in contrast to specific proteasome inhibitors, such as lactacystin or calpain inhibitor I. Moreover, addition of the products of two NO molecular targets, cis-aconitase and glyceraldehyde-3-phosphate dehydrogenase, also had an inhibitory effect on the cell death induced by NO. Interestingly, activities of these two enzymes plus 6-phosphogluconate dehydrogenase, parasitic enzymes involved in both glycolysis and respiration processes, are overexpressed in amastigotes selected for their NO resistance. This review focuses on cell death of the intracellular stage of the pathogen Leishmania induced by nitrogen oxides and gives particular attention to the biochemical pathways and the molecular targets potentially involved. Questions about the role of Leishmania amastigotes NO-mediated apoptosis in the overall infection process are raised and discussed.

Immunology of canine leishmaniasis

The role of dogs as the main reservoir of visceral leishmaniasis has led to an increased interest in the immune responses and in Leishmania antigens implicated in protective cellular immunity in canine visceral leishmaniasis. The primary goal is to control the prevalence of human disease. Immune responses in canine visceral leishmaniasis are reviewed. Cellular immune responses toward a Th1 subset mediated by IFN-gamma and TNF-alpha predominate in asymptomatic dogs exhibiting apparent resistance to visceral leishmaniasis. On the other hand, while the role of Th2 cytokines, such as IL-4 and IL-10, in symptomatic animals is still controversial, there is increasing evidence for a correlation of these cytokines with progressive disease. CD8+ cytotoxic T cells seem also likely to be involved in resistance to visceral leishmaniasis. Several Leishmania antigens implicated in protective immune responses are described and some pivotal points for development of an effective vaccine against canine visceral leishmaniasis are discussed.

Immunogenicity of a multicomponent DNA vaccine against visceral leishmaniasis in dogs

Vaccination of dogs, the domestic reservoir of Leishmania chagasi, could not only decrease the burden of canine visceral leishmaniasis (VL), but could also indirectly reduce the incidence of human VL. Intramuscular vaccination of foxhounds with a Leishmania multicomponent (10 antigen) DNA vaccine resulted in antigen-induced lymphoproliferative and IFN-gamma (but not IL-4) responses. This response was not augmented by co-administration of canine IL-12 or GM-CSF DNA adjuvants. The multicomponent DNA vaccine also induced a delayed type hypersensitivity (DTH) response to viable L. donovani promastigotes and led to a reduction of parasite burden in an in vitro intracellular infection model, and in the draining lymph node of dogs early after cutaneous challenge. Thus, the multicomponent DNA vaccine was effective in priming dogs for a parasite-specific type 1 cellular immune response, which was able to restrict parasite growth.

Lower nitric oxide susceptibility of trivalent antimony-resistant amastigotes of Leishmania infantum

We previously documented the induction of Leishmania amastigote apoptosis by trivalent antimony (SbIII) and nitric oxide (NO). We demonstrate here that SbIII-resistant amastigotes were resistant to NO toxicity when delivered extracellularly by NO donors or intracellularly via macrophage activation. Shared biochemical targets for SbIII and NO resistance in Leishmania are discussed.

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

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

Treatment of canine Old World visceral leishmaniasis: a systematic review

Canine visceral leishmaniasis is a systemic disease caused by Leishmania infantum. The aim of this systematic review was to identify and evaluate the evidence of efficacy of interventions for treatment or prevention of canine visceral leishmaniasis, and to propose recommendations for or against their use. Forty-seven articles describing clinical trials published between 1980 and 2004 fulfilled selection criteria. The evaluation of clinical trials provided good evidence for recommending the use of meglumine antimoniate at a minimum dosage of 100 mg kg(-1) daily for at least 3-4 weeks, combined with allopurinol in order to obtain a good clinical efficacy and a reduced relapse rate. The evaluation of the articles also provided fair evidence for recommending the use of pentamidine (4 mg kg(-1) twice weekly) and aminosidine (5 mg kg(-1) twice daily) for 3-4 weeks. There was insufficient evidence for recommending the use of allopurinol alone, amphotericin B, buparvaquone, ketoconazole, enrofloxacin, and the combinations of metronidazole with spiramicyn or metronidazole with enrofloxacin. Fair evidence against the use of aminosidine at high dosages (20-80 mg kg(-1) per day) was proposed due to its side effects. Evaluation of articles on repellent measures against sand fly vectors of leishmaniasis provided good evidence for recommending deltamethrin collars and fair evidence for recommending spot-on permethrin.

Lymphocytes of dogs immunised with purified excreted-secreted antigens of Leishmania infantum co-incubated with Leishmania infected macrophages produce IFN gamma resulting in nitric oxide-mediated amastigote apoptosis

The role of nitric oxide (NO) in the anti-leishmanial activity has been confirmed both in vitro and in vivo. Recently, we demonstrated that NO-mediated apoptosis-like amastigote death pathway is an important and highly regulated mechanism used for the clearance of Leishmania within infected murine macrophages stimulated to produce NO endogenously. To further characterize these important effector mechanisms in dog, a natural host-reservoir of L. infantum/L. chagasi, we have developed an ex vivo infection model of canine macrophages. Exposure of L. infantum-infected macrophages to autologous peripheral lymphocytes derived from dogs immunised with purified excreted-secreted antigens of L. infantum promastigotes (LiESAp) formulated with muramyl dipeptide (MDP) as adjuvant resulted in a significant leishmanicidal effect due to interferon (IFN)-gamma dependent macrophage activation. Concomitant accumulation of NO(3)(-)/NO(2)(-) in supernatants of co-cultured cells and in situ staining of parasites with terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling (TUNEL) and YOPRO-1 showed that NO-mediated apoptosis of intracellular L. infantum amastigotes is occurring in canine macrophages as previously observed in mouse models. Monitoring these parameters in dogs after immunisation and before experimental challenge can represent a useful and easy way to rapidly evaluate vaccine candidates against canine visceral leishmaniasis.

Recombinant cysteine proteinase from Leishmania (Leishmania) chagasi implicated in human and dog T-cell responses

High in vitro lymphoproliferative responses were induced in humans and dogs by a recombinant Leishmania (Leishmania) chagasi cysteine proteinase, with secretion of IFN-gamma in asymptomatic subjects or of IFN-gamma, interleukin 4 (IL-4), and IL-10 in oligosymptomatic subjects. In contrast, responses of symptomatic patients and dogs were lower, with production of IL-4 and IL-10.

Periodic administration of allopurinol is not effective for the prevention of canine leishmaniosis (Leishmania infantum) in the endemic areas

A total of 95 clinically healthy and seronegative for Leishmania infantum dogs, residing an area highly endemic for canine leishmaniosis (CL) and living an outdoor life-style, were split into positive and negative groups, and then were randomly assigned to receive allopurinol (n=51; 20 mg/kg once daily), or placebo (n=44) for 1 week per month, from April to November. Forty per cent (38/95) of these dogs were not reexamined and retested at the end of the trial for reasons unrelated to CL. None of the remaining 57 dogs exhibited the symptomatic form of the disease at the end of the 1-year follow-up period. Of the 15 allopurinol-treated dogs that were non-infected (negative PCR and tissue smear microscopy) at the beginning of the trial, 6 (40% P=0.03) became PCR-positive, of which 3 became also seropositive, at the end of the observation period. In contrast, only 1 of 7 (14.3%) placebo-treated non-infected dogs became PCR positive at the same time point. Of the 19 allopurinol-treated dogs that were infected (PCR-positive) at the beginning of the trial, 18 (94.7%) remained PCR-positive and one (5.3%) seroconverted, at the end of the observation period. Of the 16 initially infected and placebo-treated dogs, 14 (87.5%) remained PCR positive, of which one (6.7%) also turned positive by tissue smear microscopy. Therefore, it is concluded that the use of allopurinol, at the daily dose of 20mg/kg, for 1 week per month, during the period of sandfly activity, does not prevent the infection of non-infected dogs by L. infantum, and, also, does not help in the elimination of the parasite from dogs with asymptomatic infections.

Canine Leishmaniasis

Canine leishmaniasis is caused by Leishmania infantum (syn. L. chagasi, in America) and is transmitted by the bite of phlebotomine sand flies. Infected dogs constitute the main domestic reservoir of the parasite and play a key role in transmission to humans, in which the parasite produces visceral leishmaniasis. The increasing awareness that control of the human disease depends on effective control of canine leishmaniasis has promoted, in the last few years, research into leishmanial infection in dogs. Newly available specific reagents and molecular tools have been applied to the detailed investigation of canine leishmaniasis and important advances have been made in elucidating the epidemiology and pathology of the disease. These new findings have led to better understanding of the disease, and have also helped in the development of new diagnostic methods and control measures against the infection, such as insecticide-impregnated collars for dogs, new drugs and treatment protocols, and second generation vaccines, with the hope of not only reducing the heavy burden of the disease among dogs but also reducing the incidence of human visceral leishmaniasis.

Chemotherapy of canine leishmaniosis

Visceral leishmaniosis is a widespread and potentially fatal disease of dogs and humans common in the Mediterranean region, the Middle East, and South America. Canine leishmaniosis is most frequently treated with the drugs meglumine antimoniate, allopurinol, amphotericin B, or a combination of meglumine antimoniate and allopurinol. Therapy with the currently used drugs often achieves temporary clinical improvement and changes in immunologic parameters with restoration of the ability to mount parasite-specific cell mediated responses and decrease in anti-leishmanial antibody titers. However, treatment usually does not prevent relapse of disease or eliminate parasite carriage. Due to the current lack of an ultimate and effective therapy for canine leishmaniosis, new drugs, delivery systems and treatment strategies are necessary to achieve a consistent parasitological cure in infected dogs.

Nitric oxide-mediated proteasome-dependent oligonucleosomal DNA fragmentation in Leishmania amazonensis amastigotes

Resistance to leishmanial infections depends on intracellular parasite killing by activated host macrophages through the L-arginine-nitric oxide (NO) metabolic pathway. Here we investigate the cell death process induced by NO for the intracellular protozoan Leishmania amazonensis. Exposure of amastigotes to moderate concentrations of NO-donating compounds (acidified sodium nitrite NaNO(2) or nitrosylated albumin) or to endogenous NO produced by lipopolysaccharide or gamma interferon treatment of infected macrophages resulted in a dramatic time-dependent cell death. The combined use of several standard DNA status analysis techniques (including electrophoresis ladder banding patterns, YOPRO-1 staining in flow cytofluorometry, and in situ recognition of DNA strand breaks by TUNEL [terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling] assay) revealed a rapid and extensive fragmentation of nuclear DNA in both axenic and intracellular NO-treated amastigotes of L. amazonensis. Despite some similarities to apoptosis, the nuclease activation responsible for characteristic DNA degradation was not under the control of caspase activity as indicated by the lack of involvement of cell-permeable inhibitors of caspases and cysteine proteases. In contrast, exposure of NO-treated amastigotes with specific proteasome inhibitors, such as lactacystin or calpain inhibitor I, markedly reduced the induction of the NO-mediated apoptosis-like process. These data strongly suggest that NO-induced oligonucleosomal DNA fragmentation in Leishmania amastigotes is, at least in part, regulated by noncaspase proteases of the proteasome. The determination of biochemical pathways leading up to cell death might ultimately allow the identification of new therapeutic targets.

Inducible nitric oxide synthase expression in Leishmania-infected dog macrophages

Nitric oxide (NO) production by the inducible NO synthase (iNOS or NOS2) represents one of the main microbicidal mechanisms of murine macrophages, but its role in other animal models is poorly investigated. Therefore, the aim of this work was to evaluate NOS2 expression in dog macrophages infected with Leishmania infantum. Macrophages obtained from peripheral blood of healthy dogs were activated with recombinant human interferon (rhIFN)-gamma and bacterial lipopolysaccharide (LPS) and then infected with L. infantum promastigotes. zymodeme MONI. For the immunofluorescence assay fixed macrophages were incubated with polyclonal rabbit anti-NOS2 and then with rhodamine F(ab')2 goat anti-rabbit IgG. For immunoblotting, cell lysates were submitted to SDS-PAGE and blots were incubated with polyclonal rabbit anti-NOS2 and then with horseradish peroxidase-conjugated goat anti-rabbit IgG. Results demonstrated that L. infantum-infected cells, after stimulation with rhIFN-gamma and LPS, displayed high levels of fluorescence for the NOS2 in their cytoplasm, unlike unstimulated uninfected macrophages. In western blotting, polyclonal anti-NOS2 reacted specifically with a protein band corresponding to 130 kDa. The signal produced in Leishmania-infected cells stimulated with rhIFN-gamma and LPS was higher than that produced in Leishmania-infected unstimulated cells. No band was detected in cellular lysates from uninfected unstimulated cells. These results indicate that dog macrophages can express NOS2, and suggest a role for IFN-gamma and LPS in NOS2 induction also in this animal model.

Leishmaniasis phytotherapy. Nature's leadership against an ancient disease

The use of phytotherapy to treat human diseases has its roots in pre-historical times. Despite the modern advances achieved in the field of synthetic chemistry, the most efficient drugs available have their genesis directly or indirectly related with the vegetal kingdom. Indigenous communities have long used plant extracts to treat illnesses. Many of these extracts have shown effective action, with new bioactive compounds being extracted and screened every year. These extracts have also proven to be good sources of therapeutic agents to the treatment of Leishmaniasis. This work highlights some of these agents, while trying to emphasize the importance of plants as a source of new and powerful drugs against this widespread disease.

Nitric oxide production by macrophages of dogs vaccinated with killed Leishmania infantum promastigotes

Human visceral leishmaniosis is endemic in Southern Italy, where the dog is the main reservoir of viscerotropic strains of Leishmania infantum. The release of nitric oxide (NO) by interferon (IFN)-gamma-activated macrophages is an important leishmanicidal mechanism in several animal species. In this work NO production, phagocytosis and killing capacity of monocyte-derived dog macrophages were evaluated in vitro before and after administration of a vaccine composed of killed Leishmania infantum promastigotes. Moreover, IFN-gamma content was measured in concanavalin A-activated dog peripheral blood mononuclear cell (PBMC) supernatants employed for macrophage stimulation. Phagocytosis, killing capacity and NO production by canine macrophages increased significantly 1 month after vaccine administration, and the increase also persisted 5 months later. In addition, the amount of IFN-gamma in PBMC supernatants was significantly higher after vaccination. Overall, our results suggest the usefulness of evaluating the in vivo protective role of this promastigote preparation in dogs.

Infection of a canine macrophage cell line with leishmania infantum: determination of nitric oxide production and anti-leishmanial activity

We have previously shown that resistance to Leishmania infantum in dogs is associated with a Th1 type of immune response. In this study, we use a canine macrophage cell line (030-D) that can readily be infected with this protozoan parasite. Our aim is to further characterize the effector mechanisms involved in killing of Leishmania parasite in dogs. We observed that activation of 030-D cells by incubation with a supernatant derived from a Leishmania-specific T cell line containing IFN-gamma, TNF-alpha and interleukin-2 (IL-2) resulted in enhanced nitric oxide (NO) production by these cells. In addition, we observed enhanced anti-leishmanial activity of infected 030-cells after activation. Both, NO production and anti-leishmanial activity were abrogated by addition of L-N(G)-nitroargininemethyl ester (L-NAME), an analogue of L-arginine. Thus, NO play an important role in the anti-leishmanial activity of these canine macrophages. We propose the infection of the 030-D cell line as a good in vitro model to further investigate parasite-host cell interactions in dogs, a natural host of Leishmania parasites.

Bacterial adaptation to host innate immunity responses

Several recent reports show that different bacterial components trigger innate and inflammatory responses in host organisms. In parallel, selected bacterial virulence factors have been identified that interfere with corresponding responses. In many cases, this involves interference with host proinflammatory signal transduction pathways, whereas in selected cases bacterial virulence factors interfere with host antibacterial mechanisms. This indicates that bacteria, besides activating cellular responses, also have the capacity to directly interact with branches of the innate defence.

Evaluation of nitric oxide production by Leishmania infantum-infected dog macrophages

Protozoa of the genus Leishmania (L.) infect reticuloendothelial cells of several mammalian species, including dogs, in which they often give rise to a chronic, not self-healing visceral disease. Since the parasitocidal mechanism of macrophages towards Leishmania in dog has not yet been well investigated, in this work we have evaluated in Leishmania infantum-infected macrophage cultures from 10 healthy dogs, killing capacity and nitric oxide (NO) production, in terms of nitrite (NO2) levels. Parallel experiments were performed on macrophages stimulated with both Concanavalin A (ConA)-activated PBMC supernatants and Salmonella typhimurium lipopolysaccharide (LPS), and in the same conditions, but in the presence of the NO synthase inhibitor L-N monomethylarginine (L-NMMA). In L. infantum-infected macrophages, nitric oxide production was observed at a concentration significantly higher after stimulation with both Con A-activated PBMC supernatants and LPS than that observed in uninfected cells cultured in medium alone, or infected cells unstimulated or stimulated by PBMC supernatants or LPS alone, respectively. Moreover, NO production was abolished in the presence of the NO synthase inhibitor L-NMMA. Finally, killing of Leishmania by macrophages was significantly reduced in the presence of L-NMMA.

Improved methods to measure end products of nitric oxide in biological fluids: nitrite, nitrate, and S-nitrosothiols

The aim of this study was to compare and improve standard methods to determine nitrite (NO2-), nitrate (NO3-) and S-nitrosothiol (RSNO) levels in cell culture supernatants, sera, and urine. We modified the conventional Griess reaction by replacing sulfanilamide with dapsone (4,4'-diamino-diphenylsulfone) and compared the NO2- levels in our study samples with a commercially available NO2- assay kit. Our modification, along with ultrafiltration of the samples, resulted in an enhanced sensitivity to measure NO2- down to 0.2 microM. The detection limit was further improved to 0.02 microM when NO2- was identified by the fluorochrome 2,3-diaminonaphthalene (DAN). To measure the stable end product NO3- by the Griess reaction or the DAN method, this anion must be reduced to NO2-. We compared the capacity of bacterial nitrate reductase with the reducing metal cadmium to convert NO3- to NO2-. After reduction, NO2- levels were determined either by the DAN method or by our modified Griess reaction. We found that there was a high correlation (r2 = 0.998) in total NO2- concentrations in the study samples using both methods for reducing NO3- to NO2-. The simultaneous determination of NO2- and NO3- was achieved by using anion-exchange chromatography (HPLC; Polyspher IC AN-1 column). The detection limit of this assay for each anion is 0.5 microM, and it can be applied equally well to sera, urine, and culture media. We also adapted the DAN method to determine RSNO levels in our study samples. Using this approach, we were able to measure RSNO levels down to 0.15 microM. As result we discovered that RSNO levels were markedly increased in urine from septic patients and in supernatants from cytokine-stimulated human tumor cell lines. L-Citrulline, a coproduct of NO biosynthesis, was measured using a colorimetric assay with a sensitivity limit of 3.0 microM. Increased L-citrulline levels in media from cultured cells, but not in sera or urine, correlated with increased NO production. Although all methods studied were suitable for quantifying end products of NO in biological fluids and media, the use of bacterial reductase and the modified Griess reaction proved successful to provide the greatest sensitivity and linear range for routine measurements of NO2- and NO3-.