Inbred mice as model hosts for cutaneous leishmaniasis. I. Resistance and susceptibility to infection with Leishmania braziliensis, L. mexicana, and L. aethiopica

Memory T cells: promising biomarkers for evaluating protection and vaccine efficacy against leishmaniasis

Understanding the immune response to Leishmania infection and identifying biomarkers that correlate with protection are crucial for developing effective vaccines. One intriguing aspect of Leishmania infection is the persistence of parasites, even after apparent lesion healing. Various host cells, including dendritic cells, fibroblasts, and Langerhans cells, may serve as safe sites for latent infection. Memory T cells, especially tissue-resident memory T cells (TRM), play a crucial role in concomitant immunity against cutaneous Leishmania infections. These TRM cells are long-lasting and can protect against reinfection in the absence of persistent parasites. CD4+ TRM cells, in particular, have been implicated in protection against Leishmania infections. These cells are characterized by their ability to reside in the skin and rapidly respond to secondary infections by producing cytokines such as IFN-γ, which activates macrophages to kill parasites. The induction of CD4+ TRM cells has shown promise in experimental immunization, leading to protection against Leishmania challenge infections. Identifying biomarkers of protection is a critical step in vaccine development and CD4+ TRM cells hold potential as biomarkers, as their presence and functions may correlate with protection. While recent studies have shown that Leishmania-specific memory CD4+ T-cell subsets are present in individuals with a history of cutaneous leishmaniasis, further studies are needed to characterize CD4+ TRM cell populations. Overall, this review highlights the importance of memory T cells, particularly skin-resident CD4+ TRM cells, as promising targets for developing effective vaccines against leishmaniasis and as biomarkers of immune protection to assess the efficacy of candidate vaccines against human leishmaniasis.

Murine macrophages do not support the proliferation of Leishmania (Viannia) braziliensis amastigotes even in absence of nitric oxide and presence of high arginase activity

Leishmania (Viannia) braziliensis is the main species responsible for American tegumentary leishmaniasis in Brazil. Nevertheless, the use of this parasite species to study Leishmania infection in the murine model has been less conducted when compared with other Leishmania species. The control of murine infection with Leishmania has been associated with nitric oxide (NO) produced by inducible NO synthase (iNOS) from M1 macrophages, while arginase expressed by M2 macrophages is related to Leishmania proliferation. Here we use three different strains of L. (V.) braziliensis and one strain of L. (L.) major to study a 9-day infection of macrophages in vitro. Wild-type bone marrow-derived macrophages (BMDM) supported the proliferation of L. (L) major amastigotes from the 3rd day after infection, while all strains of L. (V.) braziliensis did not proliferate even inside IL-4-treated or iNOS knockout (KO) macrophages. The arginase activity was higher in iNOS KO than IL-4-treated macrophage showing that the absence of proliferation is independent of arginase. Importantly, L. (V.) braziliensis was able to cause uncontrolled disease in iNOS KO mice in vivo demonstrating that murine macrophages present at the site of infection have additional changes beyond inhibition of NO production or stimulation of arginase activity to support parasite proliferation.

Enhanced production of pro-inflammatory cytokines and chemokines in Ethiopian cutaneous leishmaniasis upon exposure to Leishmania aethiopica

The clinical course and outcome of cutaneous leishmaniasis (CL) vary due to the infecting Leishmania species and host genetic makeup that result in different immune responses against the parasites. The host immune response to Leishmania aethiopica (L.aethiopica), the causative agent of CL in Ethiopia, is poorly understood. To contribute to the understanding of the protective immune response in CL due to L.aethiopica, we characterized the cytokine response to L. aethiopica in patients with the localized form of CL (LCL) and age-and sex-matched apparently healthy controls. By applying a whole blood based in vitro culture we found enhanced release of TNF, IL-6, MCP-1 or CCL2, IP-10 or CXCL10, MIP-1β or CCL4 and IL-8 or CXCL8- but not of IL-10CL patients in response to L. aethiopica compared to the controls. No difference was observed between LCL cases and controls in the secretion of these cytokines and chemokines in whole blood cultures treated with the TLR-ligands LPS, MALP-2 or polyI: C. The observed increased secretion of the pro-inflammatory cytokines/chemokines reflects an enhanced response against the parasites by LCL patients as compared to healthy controls rather than a generally enhanced ability of blood leukocytes from LCL patients to respond to microbial constituents. Our findings suggest that the enhanced production of pro-inflammatory cytokines/chemokines is associated with localized cutaneous leishmaniasis caused by L.aethiopica.

Leishmania tropica: What we know from its experimental models

Leishmania tropica causes different forms of leishmaniasis in many parts of the world. Animal models can help to clarify the issues of pathology and immune response in L. tropica infections and can be applied to the control, prevention and treatment of the disease. The aim of this article is to summarize published data related to experimental models of this parasite, presenting an overview of the subject. We also present in brief the epidemiology, transmission and human manifestation of L. tropica infection. Mice, rats and hamsters have been used for experimental models of L. tropica infection. Main findings of the published studies show that: (1) Hamsters are the best animal model for L. tropica infection, with the drawback of being outbred hence not suitable for many studies. (2) L. tropica infection causes a non-ulcerative and chronic pathology as cutaneous form in mice and usually visceral form in hamsters. (3) L. tropica infection in mice results in a weaker immune response in comparison to Leishmania major. (4) While the Th1 responses are evoked against L. tropica, Th2 responses do not explain the outcomes of this infection, and IL-10 and TGF-β are two main suppressive cytokines. (5) The host genotype affects the immune response and disease outcome of L. tropica infection and the dose, strain, routes of inoculation, and sex of the host are among the factors affecting disease outcome of this species.

The role of monocytes in models of infection by protozoan parasites

The confirmation of developmental differences between tissue macrophages and peripheral monocytes has changed our view of the functions and dynamics of these two important components of the innate immune system. It has been demonstrated conclusively that homeostasis of tissue resident macrophages is maintained by a low proliferative turn over. During an inflammatory response, bone marrow derived monocytes enter the tissue in large numbers and take part in the defense against the pathogens. After the destruction of invading pathogens, these cells disappear and tissue resident macrophages can be detected again. This new appreciation of the innate immune response has not only answered many outstanding questions regarding the role of the different myeloid cell types in inflammation, but also opened up new areas of research relating to the tissue- and pathogen-specific fate of the inflammatory macrophages or dendritic cells (DCs), and the transfer of this knowledge from mouse models to the human immune system. Nevertheless, there is still confusion in infection models, and especially in studies of human infections, as to what extent these recent observations and findings influence previous interpretations of data. This review will focus on insights from mouse models, summarize the literature on the ontogeny of macrophages and monocytes, explain the role of frequently used monocyte markers and effector molecules, and finally, discuss the role of inflammatory monocytes/macrophages/DCs in two experimental parasitic diseases.

Cross-protective efficacy of Leishmania infantum LiHyD protein against tegumentary leishmaniasis caused by Leishmania major and Leishmania braziliensis species

Vaccination can be considered the most cost-effective strategy to control neglected diseases, but nowadays there is not an effective vaccine available against leishmaniasis. In the present study, a vaccine based on the combination of the Leishmania-specific hypothetical protein (LiHyD) with saponin was tested in BALB/c mice against infection caused by Leishmania major and Leishmania braziliensis species. This antigen was firstly identified in Leishmania infantum and showed to be protective against infection of BALB/c mice using this parasite species. The immunogenicity of rLiHyD/saponin vaccine was evaluated, and the results showed that immunized mice produced high levels of IFN-γ, IL-12 and GM-CSF after in vitro stimulation with rLiHyD, as well as by using L. major or L. braziliensis protein extracts. After challenge, vaccinated animals showed significant reductions in the infected footpad swellings, as well as in the parasite burden in the infection site, liver, spleen, and infected paws draining lymph nodes, when compared to those that were inoculated with the vaccine diluent (saline) or immunized with saponin. The immunization of rLiHyD without adjuvant was not protective against both challenges. The partial protection obtained by the rLiHyD/saponin vaccine was associated with a parasite-specific IL-12-dependent IFN-γ secretion, which was produced mainly by CD4(+) T cells. In these animals, a decrease in the parasite-mediated IL-4 and IL-10 responses, associated with the presence of high levels of LiHyD- and parasite-specific IgG2a isotype antibodies, were also observed. The present study showed that a hypothetical protein that was firstly identified in L. infantum, when combined to a Th1 adjuvant, was able to confer a cross-protection against highly infective stationary-phase promastigotes of two Leishmania species causing tegumentary leishmaniasis.

A Luciferase-Expressing Leishmania braziliensis Line That Leads to Sustained Skin Lesions in BALB/c Mice and Allows Monitoring of Miltefosine Treatment Outcome

Background

Leishmania braziliensis is the most prevalent species isolated from patients displaying cutaneous and muco-cutaneous leishmaniasis in South America. However, there are difficulties for studying L. braziliensis pathogenesis or response to chemotherapy in vivo due to the natural resistance of most mouse strains to infection with these parasites. The aim of this work was to develop an experimental set up that could be used to assess drug efficacy against L. braziliensis. The model was tested using miltefosine.

Methodology/Principal Findings

A L. braziliensis line, originally isolated from a cutaneous leishmaniasis patient, was passaged repeatedly in laboratory rodents and further genetically manipulated to express luciferase. Once collected from a culture of parasites freshly transformed from amastigotes, 10⁶ wild type or luciferase-expressing stationary phase promastigotes were inoculated subcutaneously in young BALB/c mice or golden hamsters. In both groups, sustained cutaneous lesions developed at the site of inoculation, no spontaneous self- healing being observed 4 months post-inoculation, if left untreated. Compared to the wild type line features, no difference was noted for the luciferase-transgenic line. Infected animals were treated with 5 or 15 mg/kg/day miltefosine orally for 15 days. At the end of treatment, lesions had regressed and parasites were not detected. However, relapses were observed in animals treated with both doses of miltefosine.

Conclusions/Significance

Here we described experimental settings for a late-healing model of cutaneous leishmaniasis upon inoculation of a luciferase-expressing L. braziliensis line that can be applied to drug development projects. These settings allowed the monitoring of the transient efficacy of a short-term miltefosine administration.

Leishmania braziliensis is the most prevalent species isolated from patients displaying either cutaneous or mucocutaneous leishmaniasis in South America. In this study, we developed a transgenic luciferase-expressing L. braziliensis line. These parasites were passaged in hamsters and mice and then transformed back into promastigotes. Once inoculated subcutaneously in the footpad of young laboratory animals—BALB/c mice or golden hamsters, rapid and sustained footpad thickness increase developed. This experimental model was used to monitor the parasite load fluctuations and the response to miltefosine treatment. Mice were treated orally over a two-week period, starting at week 4 post-inoculation. Though such a regimen was shown to display efficacy, the effect was not sustained and both parasite re-expansion and delayed footpad thickness increase were noticed.

CCR2 signaling contributes to the differentiation of protective inflammatory dendritic cells in Leishmania braziliensis infection

In vertebrate hosts, Leishmania braziliensis parasites infect mainly mononuclear phagocytic system cells, which when activated by T helper cell type 1 cytokines produce nitric oxide and kill the pathogens. Chemokine (C-C motif) receptor 2 is a chemokine receptor that binds primarily chemokine (C-C motif) ligand 2 and has an important role in the recruitment of monocytic phagocytes. Although it has been reported that Leishmania braziliensis infection induces CCR2 expression in the lesions, the role of CCR2 during Leishmania braziliensis infection remains unknown. Here, we showed that CCR2 has a role in mediating protection against Leishmania braziliensis infection in mice. The absence of CCR2 resulted in increased susceptibility to infection and was associated with low amounts of Ly6C(+) inflammatory dendritic cells in the lesions, which we found to be the major sources of tumor necrosis factor production and induced nitric oxide synthase expression in C57BL/6 mice lesions. Consequently, CCR2(-/-) mice showed decreased tumor necrosis factor production and induced nitric oxide synthase expression, resulting in impaired parasite elimination. We also demonstrated that CCR2 has a role in directly mediating the differentiation of monocytes into inflammatory dendritic cells at the infection sites, contributing to the accumulation of inflammatory dendritic cells in Leishmania braziliensis lesions and subsequent control of parasite replication. Therefore, these data provide new information on the role of chemokines during the immune response to infections and identify a potential target for therapeutic interventions in cutaneous leishmaniasis.

A Review: The Current In Vivo Models for the Discovery and Utility of New Anti-leishmanial Drugs Targeting Cutaneous Leishmaniasis

The current in vivo models for the utility and discovery of new potential anti-leishmanial drugs targeting Cutaneous Leishmaniasis (CL) differ vastly in their immunological responses to the disease and clinical presentation of symptoms. Animal models that show similarities to the human form of CL after infection with Leishmania should be more representative as to the effect of the parasite within a human. Thus, these models are used to evaluate the efficacy of new anti-leishmanial compounds before human clinical trials. Current animal models aim to investigate (i) host–parasite interactions, (ii) pathogenesis, (iii) biochemical changes/pathways, (iv) in vivo maintenance of parasites, and (v) clinical evaluation of drug candidates. This review focuses on the trends of infection observed between Leishmania parasites, the predictability of different strains, and the determination of parasite load. These factors were used to investigate the overall effectiveness of the current animal models. The main aim was to assess the efficacy and limitations of the various CL models and their potential for drug discovery and evaluation. In conclusion, we found that the following models are the most suitable for the assessment of anti-leishmanial drugs: L. major–C57BL/6 mice (or–vervet monkey, or–rhesus monkeys), L. tropica–CsS-16 mice, L. amazonensis–CBA mice, L. braziliensis–golden hamster (or–rhesus monkey). We also provide in-depth guidance for which models are not suitable for these investigations.

An NLRP3 inflammasome-triggered Th2-biased adaptive immune response promotes leishmaniasis

Leishmaniasis is a major tropical disease that can present with cutaneous, mucocutaneous, or visceral manifestation and affects millions of individuals, causing substantial morbidity and mortality in third-world countries. The development of a Th1-adaptive immune response is associated with resistance to developing Leishmania major (L. major) infection. Inflammasomes are key components of the innate immune system that contribute to host defense against bacterial and viral pathogens; however, their role in regulating adaptive immunity during infection with protozoan parasites is less studied. Here, we demonstrated that the NLRP3 inflammasome balances Th1/Th2 responses during leishmaniasis. Mice lacking the inflammasome components NLRP3, ASC, or caspase 1 on a Leishmania-susceptible BALB/c background exhibited defective IL-1β and IL-18 production at the infection site and were resistant to cutaneous L. major infection. Moreover, we determined that production of IL-18 propagates disease in susceptible BALB/c mice by promoting the Th2 cytokine IL-4, and neutralization of IL-18 in these animals reduced L. major titers and footpad swelling. In conclusion, our results indicate that activation of the NLRP3 inflammasome is detrimental during leishmaniasis and suggest that IL-18 neutralization has potential as a therapeutic strategy to treat leishmaniasis patients.

Leishmania aethiopica field isolates bearing an endosymbiontic dsRNA virus induce pro-inflammatory cytokine response

BACKGROUND

Infection with Leishmania parasites causes mainly cutaneous lesions at the site of the sand fly bite. Inflammatory metastatic forms have been reported with Leishmania species such as L. braziliensis, guyanensis and aethiopica. Little is known about the factors underlying such exacerbated clinical presentations. Leishmania RNA virus (LRV) is mainly found within South American Leishmania braziliensis and guyanensis. In a mouse model of L. guyanensis infection, its presence is responsible for an hyper-inflammatory response driven by the recognition of the viral dsRNA genome by the host Toll-like Receptor 3 leading to an exacerbation of the disease. In one instance, LRV was reported outside of South America, namely in the L. major ASKH strain from Turkmenistan, suggesting that LRV appeared before the divergence of Leishmania subgenera. LRV presence inside Leishmania parasites could be one of the factors implicated in disease severity, providing rationale for LRV screening in L. aethiopica.

METHODOLOGY/PRINCIPAL FINDINGS

A new LRV member was identified in four L. aethiopica strains (LRV-Lae). Three LRV-Lae genomes were sequenced and compared to L. guyanensis LRV1 and L. major LRV2. LRV-Lae more closely resembled LRV2. Despite their similar genomic organization, a notable difference was observed in the region where the capsid protein and viral polymerase open reading frames overlap, with a unique -1 situation in LRV-Lae. In vitro infection of murine macrophages showed that LRV-Lae induced a TLR3-dependent inflammatory response as previously observed for LRV1.

CONCLUSIONS/SIGNIFICANCE

In this study, we report the presence of an immunogenic dsRNA virus in L. aethiopica human isolates. This is the first observation of LRV in Africa, and together with the unique description of LRV2 in Turkmenistan, it confirmed that LRV was present before the divergence of the L. (Leishmania) and (Viannia) subgenera. The potential implication of LRV-Lae on disease severity due to L. aethiopica infections is discussed.

Leishmania braziliensis and Leishmania amazonensis amastigote extracts differ in their enhancement effect on Leishmania infection when injected intradermally

Background

It has been reported that repeated intravenous injections of a relatively large amount of Leishmania amazonensis amastigote extract (LaE) in BALB/c mice exacerbates the infection of these mice by Leishmania braziliensis. The identification of the extract active principle(s) through physicochemical purification often involves dilution and losses of protein in the course of successive purification procedures. The large amount of the extract required to induce the phenomenon, therefore, hinders the carrying out of experiments aimed at identifying the active molecule(s) through extract purification. In the present work, a dose–response experiment was done to find out if smaller amounts of LaE than that necessary to be used by the intravenous route would reproduce the phenomenon when injected by the intradermal route. In addition, it was also investigated whether a Leishmania braziliensis amastigote extract (LbE) would exert the same effect and whether the effect would occur in C57BL/6 mice.

Results

It was found that a single injection of either LaE or LbE containing 5 μg of protein was capable of enhancing the infection in BALB/c but not in C57BL/6 mice. In addition, it was observed that the largest tested doses of LbE (containing 30 and 180 μg of protein) failed to enhance the infection by L. braziliensis, whereas all doses of LaE enhanced equally that infection.

Conclusions

Those results indicate the possible existence in LbE, and not in LaE, of molecules that interfere with the extract infection-enhancing activity when it is injected in large amounts, and that the inoculation of Leishmania extracts through the intravenous and intradermal routes potentiate the infection by L. braziliensis through the same mechanism.

Repeated exposure to Lutzomyia intermedia sand fly saliva induces local expression of interferon-inducible genes both at the site of injection in mice and in human blood

During a blood meal, Lutzomyia intermedia sand flies transmit Leishmania braziliensis, a parasite causing tegumentary leishmaniasis. In experimental leishmaniasis, pre-exposure to saliva of most blood-feeding sand flies results in parasite establishment in absence of any skin damages in mice challenged with dermotropic Leishmania species together with saliva. In contrast, pre-immunization with Lu. intermedia salivary gland sonicate (SGS) results in enhanced skin inflammatory exacerbation upon co-inoculation of Lu. intermedia SGS and L. braziliensis. These data highlight potential unique features of both L. braziliensis and Lu. intermedia. In this study, we investigated the genes modulated by Lu. intermedia SGS immunization to understand their potential impact on the subsequent cutaneous immune response following inoculation of both SGS and L. braziliensis. The cellular recruitment and global gene expression profile was analyzed in mice repeatedly inoculated or not with Lu. intermedia. Microarray gene analysis revealed the upregulation of a distinct set of IFN-inducible genes, an immune signature not seen to the same extent in control animals. Of note this INF-inducible gene set was not induced in SGS pre-immunized mice subsequently co-inoculated with SGS and L. braziliensis. These data suggest the parasite prevented the upregulation of this Lu. intermedia saliva-related immune signature. The presence of these IFN-inducible genes was further analyzed in peripheral blood mononuclear cells (PBMCs) sampled from uninfected human individuals living in a L. braziliensis-endemic region of Brazil thus regularly exposed to Lu. intermedia bites. PBMCs were cultured in presence or absence of Lu. intermedia SGS. Using qRT-PCR we established that the IFN-inducible genes induced in the skin of SGS pre-immunized mice, were also upregulated by SGS in PBMCs from human individuals regularly exposed to Lu. intermedia bites, but not in PBMCs of control subjects. These data demonstrate that repeated exposure to Lu. intermedia SGS induces the expression of potentially host-protective IFN-inducible genes.

Leishmaniasis is a vector-borne parasitic disease of serious public health importance. No efficient vaccine is currently available. Parasites are transmitted to mammalian hosts during sand fly bites. During this process, both parasites and sand fly salivary products are delivered into the skin. Immunization with salivary proteins from most sand fly species can protect mice against cutaneous leishmaniasis; however, immunization with sand fly saliva of Lutzomyia intermedia leads to aggravation of leishmaniasis. We investigated the impact of Lutzomyia intermedia saliva exposure on the development of immune response to Leishmania braziliensis, the major causative agent of tegumentary leishmaniasis in Brazil. To this end, we analyzed in mice the gene expression pattern induced by immunization with salivary gland extracts. Among the genes highly induced were the interferon-inducible genes known to contribute to resistance against parasite infections. These genes were also induced in blood cells of human individuals that were naturally pre-exposed to bites of Lutzomyia intermedia sand flies. Interestingly, subsequent infection with Leishmania braziliensis blocked the induction of these genes in mice. These data show that the induction of potentially protective genes by insect saliva can be altered by the infecting parasite. This should be considered when including salivary components in a vaccine.

Role of Toll-like receptor 9 signaling in experimental Leishmania braziliensis infection

Infection with Leishmania braziliensis causes cutaneous or mucocutaneous leishmaniasis in humans. Toll-like receptor 9 (TLR9) expression has been found in granulomas of lesions in L. braziliensis-infected individuals. L. braziliensis inoculation in mice induces very small lesions that are self-healing, whereas deficiency in the TLR adaptor molecule, MyD88, renders mice susceptible to infection. The TLR involved has not been identified, prompting us to investigate if TLR9 triggering by the parasite contributes to the strong resistance to infection observed in L. braziliensis-inoculated mice. The parasites activated wild-type (WT) dendritic cells (DCs) in vitro but not DCs derived from TLR9(-/-) mice. TLR9(-/-) mice inoculated with L. braziliensis exhibited a transient susceptibility characterized by increased lesion size and parasite burden compared to those of WT mice. Surprisingly, elevated levels of gamma interferon (IFN-γ) were measured at the site of infection and in draining lymph node T cells of TLR9(-/-) mice at the peak of susceptibility, suggesting that unlike observations in vitro, the parasite could induce DC activation leading to the development of Th1 cells in the absence of TLR9 expression. Taken together, these data show that TLR9 signaling is important for the early control of lesion development and parasite burden but is dispensable for the differentiation of Th1 cells secreting IFN-γ, and the high levels of this cytokine are not sufficient to control early parasite replication following L. braziliensis infection.

The immunomodulatory effect of plant lectins: a review with emphasis on ArtinM properties

Advances in the glycobiology and immunology fields have provided many insights into the role of carbohydrate-protein interactions in the immune system. We aim to present a comprehensive review of the effects that some plant lectins exert as immunomodulatory agents, showing that they are able to positively modify the immune response to certain pathological conditions, such as cancer and infections. The present review comprises four main themes: (1) an overview of plant lectins that exert immunomodulatory effects and the mechanisms accounting for these activities; (2) general characteristics of the immunomodulatory lectin ArtinM from the seeds of Artocarpus heterophyllus; (3) activation of innate immunity cells by ArtinM and consequent induction of Th1 immunity; (4) resistance conferred by ArtinM administration in infections with intracellular pathogens, such as Leishmania (Leishmania) major, Leishmania (Leishmania) amazonensis, and Paracoccidioides brasiliensis. We believe that this review will be a valuable resource for more studies in this relatively neglected area of research, which has the potential to reveal carbohydrate targets for novel prophylactic and therapeutic strategies.

Local increase of arginase activity in lesions of patients with cutaneous leishmaniasis in Ethiopia

Background

Cutaneous leishmaniasis is a vector-borne disease that is in Ethiopia mainly caused by the parasite Leishmania aethiopica. This neglected tropical disease is common in rural areas and causes serious morbidity. Persistent nonhealing cutaneous leishmaniasis has been associated with poor T cell mediated responses; however, the underlying mechanisms are not well understood.

Methodology/Principal Findings

We have recently shown in an experimental model of cutaneous leishmaniasis that arginase-induced L-arginine metabolism suppresses antigen-specific T cell responses at the site of pathology, but not in the periphery. To test whether these results translate to human disease, we recruited patients presenting with localized lesions of cutaneous leishmaniasis and assessed the levels of arginase activity in cells isolated from peripheral blood and from skin biopsies. Arginase activity was similar in peripheral blood mononuclear cells (PBMCs) from patients and healthy controls. In sharp contrast, arginase activity was significantly increased in lesion biopsies of patients with localized cutaneous leishmaniasis as compared with controls. Furthermore, we found that the expression levels of CD3ζ, CD4 and CD8 molecules were considerably lower at the site of pathology as compared to those observed in paired PBMCs.

Conclusion

Our results suggest that increased arginase in lesions of patients with cutaneous leishmaniasis might play a role in the pathogenesis of the disease by impairing T cell effector functions.

The leishmaniases are a complex of diseases caused by Leishmania parasites. Currently, the diseases affect an estimated 12 million people in 88 countries, and approximately 350 million more people are at risk. The leishmaniases belong to the most neglected tropical diseases, affecting the poorest populations, for whom access to diagnosis and effective treatment are often not available. Leishmania parasites infect cells of the immune system called macrophages, which have the capacity to eliminate the intracellular parasites when they receive the appropriate signals from other cells of the immune system. In nonhealing persistent leishmaniasis, lymphocytes are unable to transmit the signals to macrophages required to kill the intracellular parasites. The local upregulation of the enzyme arginase has been shown to impair lymphocyte effector functions at the site of pathology. In this study, we tested the activity of this enzyme in skin lesions of patients presenting with localized cutaneous leishmaniasis. Our results show that arginase is highly upregulated in these lesions. This increase in arginase activity coincides with lower expression of a signalling molecule in lymphocytes, which is essential for efficient activation of these cells. These results suggest that increased arginase expression in the localized cutaneous lesions might contribute to persistent disease in patients presenting with cutaneous leishmaniasis.

The immunobiology of Leishmania braziliensis infection

Leishmaniases are a group of diseases caused by protozoa of the genus Leishmania that affect millions of people worldwide. These diseases are caused by distinct Leishmania species, of which L. braziliensis, a New World representative of the Leishmania genus, has been the least studied. Although leishmaniasis caused by L. braziliensis induces a range of clinical manifestations ranging from mild localized lesions to severe mucosal involvement, few studies have focused on elucidating the immune mechanisms behind this pathology. In this review, we focus on the immunobiology of L. braziliensis infection, emphasizing the innate and adaptive immune responses and taking into consideration both studies performed in endemic areas and experimental models of infection. Additionally, we address recent findings regarding the role of sand fly saliva in disease immunopathogenesis and vaccine development.

BALB/c mice infected with antimony treatment refractory isolate of Leishmania braziliensis present severe lesions due to IL-4 production

Background

Leishmania braziliensis is the main causative agent of cutaneous leishmaniasis in Brazil. Protection against infection is related to development of Th1 responses, but the mechanisms that mediate susceptibility are still poorly understood. Murine models have been the most important tools in understanding the immunopathogenesis of L. major infection and have shown that Th2 responses favor parasite survival. In contrast, L. braziliensis–infected mice develop strong Th1 responses and easily resolve the infection, thus making the study of factors affecting susceptibility to this parasite difficult.

Methodology/Principal Findings

Here, we describe an experimental model for the evaluation of the mechanisms mediating susceptibility to L. braziliensis infection. BALB/c mice were inoculated with stationary phase promastigotes of L. braziliensis, isolates LTCP393(R) and LTCP15171(S), which are resistant and susceptible to antimony and nitric oxide (NO), respectively. Mice inoculated with LTCP393(R) presented larger lesions that healed more slowly and contained higher parasite loads than lesions caused by LTCP15171(S). Inflammatory infiltrates in the lesions and production of IFN-γ, TNF-α, IL-10 and TGF-β were similar in mice inoculated with either isolate, indicating that these factors did not contribute to the different disease manifestations observed. In contrast, IL-4 production was strongly increased in LTCP393(R)-inoculated animals and also arginase I (Arg I) expression. Moreover, anti-IL-4 monoclonal antibody (mAb) treatment resulted in decreased lesion thickness and parasite burden in animals inoculated with LTCP393(R), but not in those inoculated with LTCP15171(S).

Conclusion/Significance

We conclude that the ability of L. braziliensis isolates to induce Th2 responses affects the susceptibility to infection with these isolates and contributes to the increased virulence and severity of disease associated with them. Since these data reflect what happens in human infection, this model could be useful to study the pathogenesis of the L. braziliensis infection, as well as to design new strategies of therapeutic intervention.

Leishmaniasis is a neglected disease that affects more than 12 million people worldwide. In Brazil, the cutaneous disease is more prevalent with about 28,000 new cases reported each year, and L. braziliensis is the main causative agent. The interesting data about the infection with this parasite is the wide variety of clinical manifestations that ranges from single ulcerated lesions to mucocutaneous and disseminated disease. However, experimental models to study the infection with this parasite are difficult to develop due to high resistance of most mouse strains to the infection, and the mechanisms underlying the distinct manifestations remain poorly understood. Here, the authors use a mouse experimental model of infection with different L. braziliensis isolates, known to induce diseases with distinct severity in the human hosts, to elucidate immune mechanisms that may be involved in the different manifestations. They showed that distinct parasite isolates may modulate host response, and increased IL-4 production and Arg I expression was related to more severe disease, resulting in longer length of disease with larger lesions and reduced parasite clearance. These findings may be useful in the identification of immunological targets to control L. braziliensis infection and potential clinical markers of disease progression.

Different isolates from Leishmania braziliensis complex induce distinct histopathological features in a murine model of infection

The aim of this study was to evaluate the histopathological features in tissues of mice infected by human isolates (I, II, and III) or the reference M2903 strain of Leishmania braziliensis complex. BALB/c and C57Bl/6 mice were infected in the hind footpad with 10(6) stationary-phase promastigotes of L. braziliensis complex. The evolution of lesions was observed for 10 weeks and the animals were then euthanized and liver, spleen and popliteal lymph nodes were collected. Tissues were stained with hematoxylin and eosin and analyzed by immunohistochemistry assay. Increased thickness of infected footpads was observed in all animals, lesions were nodular and non-ulcerated. Mice infected with isolate I presented inflammatory infiltrates consisting predominantly of mononuclear cells in all tissues examined, and also a great number of megakaryocytes, compared with other isolates. Infection with isolate II led to an infected footpad enlargement not seen in other isolates. In addition, mononuclear infiltrates in the liver and hemosiderin in spleen were noted. Conversely, mice infected with either isolate III or M2903 strain only showed an increased number of megakaryocytes in spleen. All tissues examined had detectable amastigote forms of Leishmania by immunohistochemistry in all groups. Taking together, our results showed an unforeseen behavior of different isolates of L. braziliensis complex that led to diverse pathological findings.

A detrimental role for IgG and FcgammaR in Leishmania mexicana infection

The intracellular protozoan parasite Leishmania causes leishmaniasis, which is the second biggest killer worldwide among parasitic diseases, after malaria. As drug therapy for leishmaniasis is toxic and resistance is growing, a vaccine is an important weapon against this disease. Unfortunately, no effective vaccine exists for any human parasitic infection. Worse yet, nearly all effective vaccines whose mechanisms are known work through the induction of protective antibodies. Leishmania mexicana causes primarily chronic cutaneous disease. Not only are antibodies not effective at killing Leishmania, as it hides inside the parasitophorous vacuole of the host cell, but new research indicates that IgG antibodies may be crucial in suppressing the host immune response by generating an immunosuppressive interleukin-10 response. IL-10 is able to decrease the needed Th1-generated IFN-gamma and downregulates production of nitric oxide, a required effector mechanism of parasite killing. We have been studying the pathways that the host uses to partially control L. mexicana infection, which include STAT4, IFN-gamma, and inducible nitric oxide synthase, but found that the IL-12 pathway is suppressed by IL-10. We are now studying the mechanisms by which IgG, bound to parasites, can induce IL-10 through FcgammaR ligation and how this suppresses a healing immune response. We are examining which IgG isotypes bind to which FcgammaRs and whether macrophages are the necessary source of IL-10 for chronic disease. Elucidation of these mechanisms may help us to design vaccines that will not induce antibody-mediated immunosuppressive IL-10 responses.

Cytokines, signaling pathways, and effector molecules required for the control of Leishmania (Viannia) braziliensis in mice

Cutaneous leishmaniasis is caused by protozoan parasites of the genus Leishmania. The mechanisms of pathogen control have been established primarily in the mouse model of Leishmania major infection, but they might not hold true for other Leishmania species associated with cutaneous disease. Here, we analyzed the role of cytokines, signaling components, and effector molecules in the control of New World cutaneous leishmaniasis due to L. braziliensis. Unlike L. major, L. braziliensis caused small, nonulcerative, and self-healing skin swelling in C57BL/6 mice, as well as BALB/c mice. In contrast to the results obtained for L. mexicana, mice deficient for interleukin-12 or its key signaling molecule, signal transducer and activator of transcription 4, rapidly succumbed to severe visceral leishmaniasis. Infection of tumor necrosis factor knockout mice with L. braziliensis led to progressive, nonhealing skin lesions with erosions and hemorrhagic ulcerations, but in contrast to the results with L. major, only 20 to 30% of the mice developed fatal visceral disease. As seen with L. major, mice with a deleted inducible nitric oxide synthase gene (iNOS(-/-)) were unable to contain L. braziliensis in the skin, whereas the control of the parasite in the spleen remained unimpaired. Unlike what happens in L. major infections, NADPH oxidase had no impact on the course of disease in L. braziliensis-infected mice. These results not only define essential components of a protective immune response to L. braziliensis but also illustrate that the requirements for the control of cutaneous leishmaniasis vary between different parasite species.

Inflammatory lesion and parasite load are inversely associated in Leishmania amazonensis infected mice genetically selected according to oral tolerance susceptibility

Two strains of mice selected according to extreme phenotypes of susceptibility and resistance to oral tolerance (TS and TR mice, respectively) were infected with 1 x 10(7) Leishmania amazonensis promastigotes and studied comparatively. TS mice developed a minor pathology while permitting parasite growth with the presence of increased IL-4, IL-10 and IFN-gamma, and lower NO and IL-2 levels and delayed-type hypersensitivity (DTH). In contrast, in TR mice, footpad swelling was increased but parasite growth was reduced. They produced lower IL-4, IL-10 and IFN-gamma but increased NO, IL-2 levels, DTH, activated spleen macrophages and periarteriolar lymphoid sheaths. The results suggest that the tolerogenic TS mouse profile, with higher IL-10 production, impaired lesion development but also avoided macrophage leishmanicidal activity, maintaining in this manner a silent parasite load. On the other hand, the TR mouse profile contributed to lesion progression with controlled parasite load. To directly address the influence of oral tolerance on infection, mice were gavaged with OVA, and 7 days afterwards were infected and challenged to bystander suppression with OVA in the same footpad. In TR mice gavaged with 25 mg OVA the inflammatory lesion was largely enhanced, while with 5 mg OVA the lesion was diminished. In TS mice the footpad swelling was always lower. However, the bystander effect did not modify the establishment of infection; and similarly to the control non-bystander mice, parasite clearance was maintained in TR and prevented in TS mice. Therefore, a better comprehension of immunoregulation of innate and adaptive immunity in the early stages of infection is necessary for the development of protocols preventing inflammation and contributing to the elimination of parasites.

Saliva fromLutzomyia longipalpisInduces CC Chemokine Ligand 2/Monocyte Chemoattractant Protein-1 Expression and Macrophage Recruitment

Saliva of bloodfeeding arthropods has been incriminated in facilitating the establishment of parasite in their host. We report on the leukocyte chemoattractive effect of salivary gland homogenate (SGH) from Lutzomyia longipalpis on saliva-induced inflammation in an air pouch model. SGH (0.5 pair/animal) was inoculated in the air pouch formed in the back of BALB/c or C57BL/6 mice. L. longipalpis SGH induced a significant influx of macrophages in BALB/c but not in C57BL/6 mice. SGH-induced cell recruitment reached a peak at 12 h after inoculation and was higher than that induced by the LPS control. This differential cell recruitment in BALB/c mice was directly correlated to an increase in CCL2/MCP-1 expression in the air pouch lining tissue. In fact, treatment with bindarit, an inhibitor of CCL2/MCP-1 synthesis, and also with a specific anti-MCP-1 mAb resulted in drastic reduction of macrophage recruitment and inhibition of CCL2/MCP-1 expression in the lining tissue. CCL2/MCP-1 production was also seen in vitro when J774 murine macrophages were exposed to L. longipalpis SGH. The SGH effect was abrogated by preincubation with serum containing anti-SGH IgG Abs as well as in mice previously sensitized with L. longipalpis bites. Interestingly, the combination of SGH with Leishmania chagasi induced an increased recruitment of neutrophils and macrophages when compared with L. chagasi alone. Taken together these results suggest that SGH not only induces the recruitment of a greater number of macrophages by enhancing CCL2/MCP-1 production but also synergizes with L. chagasi to recruit more inflammatory cells to the site of inoculation.

Toward a novel experimental model of infection to study American cutaneous leishmaniasis caused by Leishmania braziliensis

Leishmania spp. cause a broad spectrum of diseases collectively known as leishmaniasis. Leishmania braziliensis is the main etiological agent of American cutaneous leishmaniasis (ACL) and mucocutaneous leishmaniasis. In the present study, we have developed an experimental model of infection that closely resembles ACL caused by L. braziliensis. In order to do so, BALB/c mice were infected in the ear dermis with 10(5) parasites and distinct aspects of the infection were evaluated. Following inoculation, parasite expansion in the ear dermis was accompanied by the development of an ulcerated dermal lesion which healed spontaneously, as seen by the presence of a scar. Histological analysis of infected ears showed the presence of a mixed inflammatory infiltrate consisting of both mononuclear and polymorphonuclear cells. In draining lymph nodes, parasite replication was detected throughout the infection. In vitro restimulation of draining lymph node cells followed by intracellular staining showed an up-regulation in the production of gamma interferon (IFN-gamma) and in the frequency of IFN-gamma-secreting CD4(+) and CD8(+) T cells. Reverse transcription-PCR of ears and draining lymph node cells showed the expression of CC chemokines. The dermal model of infection with L. braziliensis herein is able to reproduce aspects of the natural infection, such as the presence of an ulcerated lesion, parasite dissemination to lymphoid areas, and the development of a Th1-type immune response. These results indicate that this model shall be useful to address questions related to the concomitant immunity to reinfection and parasite persistence leading to mucocutaneous leishmaniasis.

Leishmania braziliensis isolates differing at the genome level display distinctive features in BALB/c mice

Leishmania braziliensis is the species responsible for the majority of cases of human cutaneous leishmaniasis in Brazil. In the present study, L. braziliensis isolates from two different geographic areas in Brazil were studied by RAPD, using arbitrary primers. We also evaluated other biological features of these two isolates. We compared (a) the clinical features they initiate or not once delivered subcutaneously as stationary-phase promastigotes in the footpad of BALB/c mice; (b) the parasite load in both the footpad and the draining lymph node; (c) the cytokines present in the supernatant of cultures of the cell suspensions from the draining lymph nodes; and (d) the cell types present at the site of parasite delivery. The results show that the L. braziliensis strain from Ceará (H3227) is genotypically different from the L. braziliensis strain from Bahia (BA788). H3227-parasitized mice developed detectable lesions, whereas BA788-parasitized mice did not. Fifteen days post parasite inoculation there was an increase in the numbers of macrophages and lymphocytes in the footpads, whatever the parasite inoculum. Parasite load at the inoculation site--namely the footpad--did not differ significantly; in draining lymph nodes, however, it increased over the period under study. Early after parasite inoculation, the cells recovered from the draining lymph nodes of BA788-parasitized mice produced higher levels of IFN-gamma, a feature coupled to a higher number of NK cells. Later, after the parasite inoculation, there was an increased content of IL-12p70 and IL-10 in the supernatant of cells recovered from the lymph nodes of H3227-parasitized mice. This comparative analysis points out that L. braziliensis isolates differing in their genomic profiles do establish different parasitic processes in BALB/c mice.

Influence of H2 complex and non-H2 genes on progression of cutaneous lesions in mice infected with Leishmania amazonensis

Susceptibility to infection with Leishmania amazonensis promastigotes was examined in six B10 congenic mouse strains, including C57BL/10J (H2b), B10.BR (H2k), B10.M (H2f), B10.S (H2s), B10.RIII (H2r), and B10.D2 (H2d). All strains of mice developed skin nodules with punch-out ulcers by 8 weeks post-infection, but B10.M and B10.S mice showed resolution of cutaneous leishmaniasis lesions by 16 weeks post-infection. In addition, the skin lesions were much larger in BALB congenic mice than in B10 and C3H mice, even though these mice share the same H2 haplotypes. These results suggest that H2 complex controls the growth of L. amazonensis in cutaneous lesions, and that non-H2 genes inherited by BALB congenic mice have a more potent role than the H2 complex in lesion progression.

Immune response induced by New World Leishmania species in C57BL/6 mice

In the present study, C57BL/6 mice were inoculated with metacyclic Leishmania amazonensis or L. braziliensis promastigotes. While these animals were capable of controlling the infection by L. braziliensis, they developed chronic lesions with elevated numbers of parasites when infected by L. amazonensis. The differences in parasite control were associated with a decreased production of IFN-gamma and TNF by lymph node cells from L. amazonensis-infected mice. Furthermore, these animals presented decreased spleen cell proliferation and activation of germinal centers. In addition, we compared the ability of these parasites to hydrolyze extracellular ATP and AMP. While the ATPase activity of both parasite species was similar, L. amazonensis promastigotes presented higher AMP hydrolytic activity. This increased activity may lead to an increased production of adenosine, which has been shown to present anti-inflammatory activity and may thus be involved in the establishment of the immunosuppression observed in mice infected by L. amazonensis.

CD4+ Th1 cells induced by dendritic cell-based immunotherapy in mice chronically infected with Leishmania amazonensis do not promote healing

The susceptibility of mice to Leishmania amazonensis infection is thought to result from an inability to develop a Th1 response. Our data show that the low levels of gamma interferon (IFN-gamma) produced by the draining lymph node (DLN) cells of chronically infected mice could be enhanced in vitro and in vivo with L. amazonensis antigen-pulsed bone marrow-derived dendritic cells (BM-DC) and the Th1-promoting cytokine interleukin-12 (IL-12). Given intralesionally to chronically infected mice, this treatment induced the upregulation of mRNA levels for IFN-gamma, the transcription factor T-box expressed in T cells, and IL-12 receptor beta 2 in CD4(+) T cells from the DLN and an increase in parasite-specific immunoglobulin G2a in the serum. However, this Th1 response was not associated with healing, and the antigen-specific enhancement of IFN-gamma production remained impaired in the DLN. However, addition of IL-12 to the in vitro recall response was able to recover this defect, suggesting that antigen-presenting cell-derived IL-12 production may be limited in infected mice. This was supported by the fact that L. amazonensis amastigotes limited the production of IL-12p40 from BM-DC in vitro. Altogether, our data indicate that the immune response of mice chronically infected with L. amazonensis can be enhanced towards a Th1 phenotype but that the presence of Th1 CD4(+) T cells does not promote healing. This suggests that the phenotype of the CD4(+) T cells may not always be indicative of protection to L. amazonensis infection. Furthermore, our data support growing evidence that antigen-presenting cell function, such as IL-12 production, may limit the immune response in L. amazonensis-infected mice.

Leishmania braziliensis: partial control of experimental infection by interleukin-12 p40 deficient mice

Resistance to infection by Leishmania major has been associated with the development of a Th1 type response that is dependent on the presence of interleukin 12 (IL-12). In this work the involvement of this cytokine in the response to infection by L. braziliensis, a less virulent species in the mouse model, was evaluated. Our results show that while interferon (IFN-gamma) deficient (-/-) mice inoculated L. braziliensis develop severe uncontrolled lesions, chronic lesions that remained under control up to 12 weeks of infection were observed in IL-12p40 -/- mice. IL 12p40 -/- mice had fewer parasites in their lesions than IFN-gamma (-/-) mice. Lymph node cells from IL-12p40 -/- were capable of producing low but consistent levels of IFN-gamma suggestive of its involvement in parasite control. Furthermore, as opposed to previous reports on L. major-infected animals, no switch to a Th2 response was observed in IL-12p40 -/- infected with L. braziliensis.

Pretreatment of leishmania homologue of receptors for activated C kinase (LACK) promotes disease progression caused by Leishmania amazonensis

A cDNA coding Leishmania homologue of receptors for activated C kinase (LACK), which was known to play an important role in the early phase of Leishmania infection, was molecularly cloned from Leishmania amazonensis promastigote by using reverse transcription and nested polymerase chain reaction, and was sequenced. The L. amazonenis LACK cDNA showed 97.3 to 99.3% homology and its deduced amino acid sequence showed 98.7 to 99.7% identity in comparison with LACK sequences from five other species. The amino acid sequences in the immunodominant peptide region were completely conserved among Leishmania spp. tested. Intravenous pretreatment of the recombinant L. amazonensis LACK into BALB/c mice showed progressive lesion development compared to PBS (-) injected control mice, suggesting the important role of LACK in the early phase of L. amazonensis infection.

Early enhanced Th1 response after Leishmania amazonensis infection of C57BL/6 interleukin-10-deficient mice does not lead to resolution of infection

C3H and C57BL/6 mice are resistant to Leishmania major but develop chronic lesions with persistent parasite loads when they are infected with Leishmania amazonensis. These lesions develop in the absence of interleukin-4 (IL-4), indicating that susceptibility to this parasite is not a result of development of a Th2 response. Expression of the cytokine IL-10 during infection could account for the lack of IL-12 expression and poor cell-mediated immunity towards the parasite. Therefore, we tested the hypothesis that IL-10 plays a central role in downmodulating the Th1 response after L. amazonensis infection. Infection of C57BL/6 IL-10-deficient mice indicated that in the absence of IL-10 there was early enhancement of a Th1 response, which was downregulated during the more chronic stage of infection. In addition, although there were 1- to 2-log reductions in the parasite loads within the lesions, the parasites continued to persist, and they were associated with chronic lesions whose size was similar to that of the control lesions. These experiments indicated that L. amazonensis resistance to killing in vivo is only partially dependent on expression of host IL-10. However, IL-10-deficient mice had an enhanced delayed-type hypersensitivity response during the chronic phase of infection, indicating that there were Th1 type effector cells in vivo at this late stage of infection. These results indicate that although IL-10 plays a role in limiting the Th1 response during the acute infection phase, other immunomodulatory factors are responsible for limiting the Th1 response during the chronic phase.

Different Leishmania species determine distinct profiles of immune and histopathological responses in CBA mice

Most experimental studies on leishmaniasis compare two different inbred strains of mice that are resistant or susceptible to one species of Leishmania. In the present study we characterized some cytokines and nitric oxide production as well as histological changes related to resistance and susceptibility in isogenic CBA mice infected with Leishmania major or Leishmania amazonensis. CBA mice are capable of controlling infection with L. major, but they succumb to infection with L. amazonensis. Cells from susceptible L. amazonensis-infected CBA mice produced interleukin (IL)-4 and IL-10 but no interferon (IFN)-gamma. On the other hand, resistant L. major-infected CBA mice produced IFN-gamma and IL-10, but IL-4 was detected only in the first week of infection. Histopathological studies showed patterns of tissue responses at the site of the infection and in the draining lymph nodes that correlated with resistance or susceptibility. Resistant mice showed a mixed inflammatory cell infiltration and granulomas in the lesions, whereas in susceptible mice only heavily parasitized macrophages were seen. Our results indicate an important role of the parasite species in determining the pattern of immune response. L. amazonensis induces a Th2-type immune response, whereas L. major induces a Th1-type response. These factors must be identified and taken into account in the strategies for the development of vaccines against leishmaniasis. The model presented here will be useful for the study of such factors.

Resolution of an infection with Leishmania braziliensis confers complete protection to a subsequent challenge with Leishmania major in BALB/c mice

Both Leishmania major and L. braziliensis induce cutaneous leishmaniasis in BALB/c mice. Whereas BALB/c mice die of infection with L. major, they cure an infection with L. braziliensis. We report here that after curing an infection with L. braziliensis, BALB/c mice are resistant to challenge with L. major. When challenged with L. major, L. braziliensis pre-treated BALB/c mice mounted a delayed-type hypersensitivity response to L. major and produced high amounts of interferon-gamma (IFN-gamma) but low amounts of interleukin-4. The IFN-gamma produced by the L. braziliensis pre-infected mice was involved in the protection seen against L. major challenge since treating the mice with a neutralizing anti-IFN-gamma abrogated the protection. This suggests that cross-reactive antigen epitopes exist between L. braziliensis and L. major and that pre-infection with L. braziliensis primes BALB/c mice to epitopes on L. major that can elicit a protective Th1 response to the parasite.

Susceptibility and resistance to Leishmania amazonensis in H-2q syngeneic high and low antibody responder mice (Biozzi mice)

H-2 syngeneic H and L (Biozzi) mice provide a model to study Leishmania infections in which polar resistant and susceptible phenotypes are independent from H-2 differences. High-Ab-responder (H) and low-Ab-responder (L) mice syngeneic at the H-2 locus (H-2q) were, respectively, susceptible and highly resistant to Leishmania amazonensis infection. L-mice resistance was associated with high IFN-gamma and transient IL-4 production by lymph node (LN) cells, in contrast with sustained IL-4 and decreasing IFN-gamma production by susceptible H mice. IL-12 production could be detected only in LN from resistant mice. The cytokine production pattern was consistent with preferential progression to a Th1-type response in resistant L-mice, and to a Th2-type response in susceptible H-mice. We also investigated whether this shift towards Th1- or Th2-type cytokine responses was dependent upon H or L antigen presenting cells' (APC) intrinsic ability to preferentially stimulate either T-cell subset. To this end, LN-derived T-cell lines were grown from 12-day infected mice, when both strains produced IFN-gamma and IL-4. L-derived T-cell lines developed a Th2 cytokine pattern whereas H-derived T-cell lines produced IFN-gamma, IL-4 and IL-10 whatever the APC origin (H or L) used for their derivation. This work constitutes the first characterization of cellular immune responses to the intracellular parasite, L. amazonensis in H-2 syngeneic mice, an infection model in which polar resistant and susceptible phenotypes are determined by non-MHC genes.

Leishmania tropica: the identification and purification of metacyclic promastigotes and use in establishing mouse and hamster models of cutaneous and visceral disease

Few experimental studies on Leishmania tropica have been undertaken despite the importance of this parasite as the cause of cutaneous leishmaniasis, and now visceral disease, in the Old World. In part, this is due to the absence of convenient animals models, especially mice, for L. tropica infections. An anti-lipophosphoglycan (LPG) monoclonal antibody XCIV 1H2-A8 (T11), specific for L. tropica, was found to distinguish between culture-derived procyclic and metacyclic promastigotes. The antibody was used to negatively select for nonagglutinated metacyclic forms in stationary cultures, and the exceptional virulence of the purified metacyclics was verified by their infectivity for mouse macrophages in vitro and by their ability to produce cutaneous lesions in footpads of BALB/c mice. The lesions produced by three cutaneous isolates of L. tropica were nonulcerative and nonprogressive. Nonetheless, the lesions failed to heal, and high numbers of parasites could be recovered from footpads and draining lymph nodes up to 9 months after infection. Infections using L. tropica metacyclics purified from cutaneous, visceral and viscerotropic (Desert Storm) isolates of L. tropica were compared in both mouse and hamster models. Differences in disease progression were found that may reflect the parasite tissue tropism and virulence displayed by these strains in their human hosts. These findings suggest a role for parasite-related determinants in the clinical spectrum of disease.

Analysis of the immune responses of mice to infection with Leishmania braziliensis

Leishmania major and Leishmania braziliensis both cause cutaneous leishmaniasis, but the former kills BALB/c mice while the latter is killed by the mice. This killing of L. braziliensis occurred by a gamma interferon-dependent mechanism, potentially made possible by the observed lack of high interleukin-4 production.

Characterization of an antigen from Leishmania amazonensis amastigotes able to elicit protective responses in a murine model

Lymphoproliferative responses to an antigen from Leishmania amazonensis amastigotes with an apparent molecular mass of 30 kDa, termed p30, were evaluated with BALB/c mice. The p30 antigen was purified after separation of parasite extracts by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by electroelution. Lymphoproliferative responses to p30 were obtained by subcutaneous immunization of animals with L. amazonensis amastigote extracts, and maximal stimulation indices were observed at an antigen concentration of 5 microg/ml. Induction of lymphoproliferation by p30 is stage specific, and no differences in the responses to this antigen between mice susceptible and resistant to L. amazonensis were detected. The predominant T cells characterized in the lymphocyte cultures were CD4+. Lymphokine analysis of the supernatants from these cultures indicated that Th1 is the subset involved in the lymphoproliferative responses to the antigen. BALB/c mice immunized with p30 and challenged with L. amazonensis amastigotes showed a very low level of infection, indicating a protective role for p30 and a correlation between Th1 and protection. Further biochemical characterization studies showed that this antigen presents cysteine proteinase activity.

Leishmania aethiopica: experimental infections in non-human primates

Six Cercopithecus aethiops monkeys, 4 Theropithecus gelada baboons and 2 Papio anubis baboons were infected using Leishmania aethiopica isolates originating either from localized (LCL) or diffuse (DCL) cutaneous leishmaniasis patients. The history of lesions in 4 C. aethiops monkeys infected by LCL strains mimicked the process in human LCL patients. Infection of 2 C. aethiops monkeys using a DCL strain resulted in localized, non-ulcerative, self-healing nodular lesions. Such lesions were also observed in 2 T. gelada baboons infected by LCL strains. Active lesions and healing in C. aethiops and T. gelada, after infection by LCL stains, were accompanied by positive DTH and immunity to challenge by LCL or DCL strains.

Site-specific immunity to Leishmania major in SWR mice: the site of infection influences susceptibility and expression of the antileishmanial immune response

Inbred strains of mice usually develop either of two divergent patterns of infection in response to Leishmania major. Resistant mice, which develop self-limiting infections, respond immunologically with the activation of gamma interferon-secreting Th1 helper T cells, while nonhealing infections in susceptible mice are characterized by the proliferation of interleukin-4-secreting Th2 cells. Development of these divergent responses is dependent primarily on the strain of mouse infected, although factors such as the infective dose, species, and strain of parasite can also influence the degree of resistance. In this study, we show that a single mouse strain, SWR, can develop totally divergent patterns of infection depending on the site of parasite inoculation. Both SWR mice and highly susceptible BALB/c mice developed progressive, ultimately fatal disease when inoculated in the dorsal skin over the base of the tail. However, SWR mice infected in the hind footpad developed far less severe infections, which were for the most part controlled, whereas BALB/c mice infected in this site developed severe, nonhealing lesions. Production of gamma interferon and interleukin-4 and measurement of immunoglobulin E levels in serum were used to assess the degree of Th1 and Th2 cell activation in infected mice. Cytokine profiles early in infection had characteristics of a mixed Th1-Th2 response and were similar in SWR mice infected at either site. These early cytokine responses were not predictive of the ultimate disease outcome, since lymph node cells from healing mice eventually produced higher levels of gamma interferon than did those from nonhealing mice, and healing mice had lower levels of immunoglobulin E in serum, suggesting a functional bias toward Th1 cell activity in these animals. The differential ability of SWR mice to heal infections at different cutaneous sites provides a new model for the study of resistance to cutaneous leishmaniasis. Unlike traditional models of infection in which resistant and susceptible strains of mice are compared, this model allows for the study of factors that contribute to healing and nonhealing infections in a genetically identical strain of mouse.

Immune responses associated with susceptibility of C57BL/10 mice to Leishmania amazonensis

Leishmaniae are protozoans which, depending upon both the host and parasite species, can cause either a healing or nonhealing infection. While C57BL/10 mice are able to heal following infection with Leishmania major, they fail to heal following infection with Leishmania amazonensis. In order to address the role of Th1 and Th2 cell responses in the outcome of these infections in C57BL/10 mice, gamma interferon (IFN-gamma) and interleukin-4 (IL-4) production was assessed. While cells from L. major-infected C57BL/10 mice produced high levels of IFN-gamma, cells from L. amazonensis-infected animals produced little or no IFN-gamma. On the other hand, IL-4 was produced only by cells from L. amazonensis-infected C57BL/10 mice, but this production was restricted to the first few weeks of infection. Later in infection, when lesions were evident, no IL-4 was detected. Treatment of BALB/c mice with a monoclonal antibody (11B11) directed against IL-4 induced a dramatic reduction in L. amazonensis lesions. This reduction was associated with a decrease in IL-4 levels and an increase in IFN-gamma production. However, only a slight reduction in lesion sizes and parasite numbers was observed when anti-IL-4-treated C57BL/10 mice were infected with L. amazonensis. These results suggest that IL-4 may have an important role in mediating susceptibility to L. amazonensis in BALB/c mice, as previously demonstrated for L. major. More importantly, however, the data suggest that susceptibility to L. amazonensis in C57BL/10 mice is due to the absence of a Th1 cell response, rather than to the presence of a Th2 cell response.

The pathogenesis of Leishmania aethiopica infection in BALB/c mice

A mouse model for L. aethiopica infection is described. BALB/c mice were unable to clear an infection with 1 x 10(7) promastigotes injected into the hind footpad. However, there was no ulceration of the lesion and no development of overt clinical symptoms after 203 days of infection. Spread of viable organisms was evident in the draining lymph node but not in the spleen or liver. The control of the infection was associated with the development of classical delayed hypersensitivity responses to phenolized promastigotes and appeared as a localized granulomtaous infiltration. The infiltration had features of classical tuberculoid granulomas, but superimposed on it was a strong eosinophilic infiltration. The relevance of such cells though unclear is discussed.

Leishmania aethiopica: infections in laboratory animals

Leishmania aethiopica parasites were inoculated into 11 different strains and species of small laboratory animals. Clinical lesions were only produced following inoculation of hamster noses and thus this parasite is highly selective in both species and site for the laboratory animals tested. Parasites could, however, be recovered from draining lymph nodes 3 weeks after infection of BALB/c mice. Lesions in hamsters were progressive and nonulcerating (up to 1 year) and histologically resembled diffuse cutaneous leishmaniasis (DTH) in man. Pronounced delayed hypersensitivity responses to L. aethiopica antigens only developed in mice despite the absence of clinical lesions. Weak DTH responses were produced in hamsters with clinical lesions only after 25 weeks of infection.

Cutaneous leishmaniasis in germfree, gnotobiotic, and conventional mice

Cutaneous leishmaniasis was much more severe in conventional than in gnotobiotic mice as revealed by macro and microscopic examination. An inoculum of Leishmania mexicana amazonensis was used.

Leishmania braziliensis: development of primary and satellite lesions in the experimentally infected owl monkey, Aotus trivirgatus

Twelve male and 8 female feral owl monkeys, Aotus trivirgatus, were inoculated intradermally at the dorsal base of the tail with 2 X 10(7) promastigotes (strains WR 128 or WR 539) or 5 X 10(5) amastigotes (strain WR 128) of Leishmania braziliensis panamensis, and the progression and regression of subsequent lesions were examined for up to 13 or 54 weeks after inoculation. Three of these monkeys had been infected previously with L. donovani, had been treated with meglumine antimoniate, and had recovered clinically from visceral leishmaniasis. All monkeys developed a cutaneous nodule at the inoculation site, but the size of the nodule varied (maximum 78 to 326 mm2 between 4 and 16 weeks after inoculation.) The initial nodule became ulcerated after 4 to 8 weeks in 17 of the 20 monkeys, and the ulcers persisted for 4 to 16 weeks until covered by a crust. Primary lesions disappeared by 17 to 52 weeks after inoculation, but satellite lesions, of similar morphology to the primary lesions but smaller, developed after 4 to 21 weeks in 14 of the monkeys. The primary nodule was excised in 4 monkeys at 6 weeks and did not recur nor did satellite lesions subsequently develop. The satellite lesions (median total number of 4, range 1 to 25) were adjacent to or at a maximum distance of 6 cm from the primary lesion, varied in size from 3 to 117 mm2, and persisted for 10 to 37 weeks. At 6 and 8 weeks after inoculation, tissue from the cutaneous leishmanial lesions from five monkeys was excised and examined. The granulomatous leishmanial lesions, located primarily in the dermis and subcutis, consisted of macrophages containing parasites, lymphocytes, plasma cells, and occasionally eosinophils. Satellite lesions at 14 weeks after inoculation were similar grossly and microscopically to the initial nodule. No significant differences were observed between promastigote or amastigote derived infections, between the two strains of L. b. panamensis, or between the course of infection based on the sex, age, karyotype, or country of origin of the owl monkeys. Cutaneous lesions developed when 5 X 10(5) amastigotes of L. b. panamensis (strain WR 128) were inoculated intradermally into the dorsal base of the tail, the upper eyelid, and the thorax of three monkeys. Leishmanial nodules which developed on the thorax regressed rapidly (after 2 to 5 weeks) whereas those on the upper eyelid and at the dorsal base of the tail persisted for 5 to 45 weeks after inoculation.(ABSTRACT TRUNCATED AT 400 WORDS)