Leishmania promastigotes evade interleukin 12 (IL-12) induction by macrophages and stimulate a broad range of cytokines from CD4+ T cells during initiation of infection

Swarna Bhasma Induces Antigen-Presenting Abilities of Macrophages and Helps Antigen Experienced CD4+ T Cells to Acquire Th1 Phenotypes Against Leishmania donovani Antigens

In leishmaniasis, the protective immunity is largely mediated by proinflammatory cytokine producing abilities of T cells and an efficient parasite killing by phagocytic cells. Notwithstanding a substantial progress that has been made during last decades, the mechanisms or factors involved in establishing protective immunity against Leishmania are not identified. In ancient Indian literature, metallic "bhasma," particularly that of "swarna" or gold (fine gold particles), is indicated as one of the most prominent metal-based therapeutic medicine, which is known to impart protective and curative properties in various health issues. In this work, we elucidated the potential of swarna bhasma (SB) on the effector properties of phagocytes and antigen-activated CD4+ T cells in augmenting the immunogenicity of L. donovani antigens. The characterization of SB revealing its shape, size, composition, and measurement of cytotoxicity established the physiochemical potential for its utilization as an immunomodulator. The activation of macrophages with SB enhanced their capacity to produce nitric oxide and proinflammatory cytokines, which eventually resulted in reduced uptake of parasites and their proliferation in infected cells. Further, in Leishmania-infected animals, SB administration reduced the generation of IL-10, an anti-inflammatory cytokine, and enhanced pro-inflammatory cytokine generation by antigen activated CD4+ T cells with increased frequency of double (IFNγ+/TNFα+) and triple (IFNγ+TNFα+IL-2+) positive cells and abrogated disease pathogeneses at the early days of infection. Our results also suggested that cow-ghee (A2) emulsified preparation of SB, either alone or with yashtimadhu, a known natural immune modulator which enhances the SB's potential in enhancing the immunogenicity of parasitic antigens. These findings suggested a definite potential of SB in enhancing the effector functions of phagocytes and CD4+ T cells against L. donovani antigens. Therefore, more studies are needed to elucidate the mechanistic details of SB and its potential in enhancing vaccine-induced immunity.

Determination of Tr1 cell populations correlating with distinct activation states in acute IAV infection

Type I regulatory (Tr1) cells are defined as FOXP3-IL-10-secreting clusters of differentiation (CD4+) T cells that contribute to immune suppression and typically express the markers LAG-3 and CD49b and other co-inhibitory receptors. These cells have not been studied in detail in the context of the resolution of acute infection in the lung. Here, we identify FOXP3- interleukin (IL)-10+ CD4+ T cells transiently accumulating in the lung parenchyma during resolution of the response to sublethal influenza A virus (IAV) infection in mice. These cells were dependent on IL-27Rα, which was required for timely recovery from IAV-induced weight loss. LAG-3 and CD49b were not generally co-expressed by FOXP3- IL-10+ CD4+ T cells in this model and four populations of these cells based on LAG-3 and CD49b co-expression were apparent [LAG-3-CD49b- (double negative), LAG-3+CD49b+ (double positive), LAG-3+CD49b- (LAG-3+), LAG-3-CD49b+ (CD49b+)]. However, each population exhibited suppressive potential consistent with the definition of Tr1 cells. Notably, differences between these populations of Tr1 cells were apparent including differential dependence on IL-10 to mediate suppression and expression of markers indicative of different activation states and terminal differentiation. Sort-transfer experiments indicated that LAG-3+ Tr1 cells exhibited the capacity to convert to double negative and double positive Tr1 cells, indicative of plasticity between these populations. Together, these data determine the features and suppressive potential of Tr1 cells in the resolution of IAV infection and identify four populations delineated by LAG-3 and CD49b, which likely correspond to different Tr1 cell activation states.

Clinical features, immunological interactions and household determinants of visceral leishmaniasis and malaria coinfections in West Pokot, Kenya: protocol for an observational study

INTRODUCTION

Visceral leishmaniasis (VL) and malaria are two deadly parasitic diseases that coexist in West Pokot County, Kenya. The local population is at considerable risk of coinfection with VL and malaria; however, few studies have described the clinical implications of this comorbidity. Questions remain regarding the immune responses responsible for possible predisposing or protective effects. Moreover, characterisation of environmental and household risk factors for co-acquiring VL and malaria is warranted to increase awareness and guide implementation of targeted control strategies. This protocol intends to address these knowledge gaps concerning VL-malaria coinfections.

METHODS AND ANALYSIS

This observational research project will have a multimethod approach, starting with a cross-sectional study at Kacheliba Sub-County Hospital in West Pokot, Kenya. Patients with laboratory confirmation of a VL and/or malaria infection will be clinically assessed and symptomatology of monoinfections and coinfections will be compared. Second, a questionnaire will be addressed to all included patients and to healthy controls in local communities. This case-control study will aim to describe household and environmental determinants associated with VL-malaria coinfection. Lastly, blood samples will be collected from a small cohort of VL and malaria monoinfected and coinfected patients during treatment of their infection(s), and from healthy controls and asymptomatic VL and malaria cases recruited in local communities. These specimens will be used for serum cytokine measurements and molecular quantitation of Plasmodium and Leishmania. In this way, the immune response and parasite dynamics during VL-malaria coinfection will be characterised longitudinally and compared with those observed in clinical and asymptomatic monoinfections.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Ethics and Scientific Research Committee of Amref Health Africa. The study findings will be presented at international conferences and published in open-access, peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ISRCTN Registry (ISRCTN15023306).

Validating Immunomodulatory Responses of r-LdODC Protein and Its Derived HLA-DRB1 Restricted Epitopes against Visceral Leishmaniasis in BALB/c Mice

Vaccination is considered the most appropriate way to control visceral leishmaniasis (VL). With this background, the r-LdODC protein as well as its derived HLA-DRB1-restricted synthetic peptides (P1: RLMPSAHAI, P2: LLDQYQIHL, P3: GLYHSFNCI, P4: AVLEVLSAL, and P5: RLPASPAAL) were validated in BALB/c mice against visceral leishmaniasis. The study was initiated by immunization of the r-LdODC protein as well as its derived peptides cocktail with adjuvants (r-CD2 and MPL-A) in different mice groups, separately. Splenocytes isolated from the challenged and differentially immunized mice group exhibited significantly higher IFN-γ secretion, which was evidenced by the increase in the expression profile of intracellular CD4+IFN-γ T cells. However, the IL-10 secretion did not show a significant increase against the protein and peptide cocktail. Subsequently, the study confirmed the ability of peptides as immunoprophylactic agents, as the IE-I/AD-I molecule overexpressed on monocytes and macrophages of the challenged mice group. The parasitic load in macrophages of the protein and peptides cocktail immunized mice groups, and T cell proliferation rate, further established immunoprophylactic efficacy of the r-LdODC protein and peptide cocktail. This study suggests that the r-LdODC protein, as well as its derived HLA-DRB1-restricted synthetic peptides, have immunoprophylactic potential and can activate other immune cells' functions towards protection against visceral leishmaniasis. However, a detailed study in a humanized mice model can explore its potential as a vaccine candidate.

Docosahexaenoic acid supplementation represses the early immune response against murine cytomegalovirus but enhances NK cell effector function

BACKGROUND

Docosahexaenoic acid (DHA) supplementation is beneficial for several chronic diseases; however, its effect on immune regulation is still debated. Given the prevalence of cytomegalovirus (CMV) infection and because natural killer (NK) cells are a component of innate immunity critical for controlling CMV infection, the current study explored the effect of a DHA-enriched diet on susceptibility to murine (M) CMV infection and the NK cell effector response to MCMV infection.

RESULTS

Male C57BL/6 mice fed a control or DHA-enriched diet for 3 weeks were infected with MCMV and sacrificed at the indicated time points postinfection. Compared with control mice, DHA-fed mice had higher liver and spleen viral loads at day 7 postinfection, but final MCMV clearance was not affected. The total numbers of NK cells and their terminal mature cell subset (KLRG1+ and Ly49H+ NK cells) were reduced compared with those in control mice at day 7 postinfection but not day 21. DHA feeding resulted in higher IFN-γ and granzyme B expression in splenic NK cells at day 7 postinfection. A mechanistic analysis showed that the splenic NK cells of DHA-fed mice had enhanced glucose uptake, increased CD71 and CD98 expression, and higher mitochondrial mass than control mice. In addition, DHA-fed mice showed reductions in the total numbers and activation levels of CD4+ and CD8+ T cells.

CONCLUSIONS

These results suggest that DHA supplementation represses the early response to CMV infection but preserves NK cell effector functions by improving mitochondrial activity, which may play critical roles in subsequent MCMV clearance.

Host Immunity Influences the Composition of Murine Gut Microbiota

The influence of gut microbiota on host immunity is widely studied, and its disturbance has been linked to several immune-mediated disorders. Conversely, whether and how inherently disturbed canonical Th1 (pro-inflammatory) and/or Th2 (anti-inflammatory) immune pathways modify the host microbiome is not sufficiently investigated. Here, we characterized the humoral, cellular, and cytokine immunity, and associated alterations in gut microbiota of naïve wild-type mice (C57BL/6 and BALB/c), and mice with deficiencies in Th2 responses (IL-4Rα and IL-33 knockout mice) or in both Th1 and Th2 responses (NOD scid gamma, NSG mice). A global analysis by de novo clustering of 16S rRNA profiles of the gut microbiota independently grouped wild-type immunocompetent (C57BL/6 and BALB/c), Th2-deficient (IL-4Rα-/- and IL-33-/-), and severely immunodeficient (NSG) mice; where wild-type mice, but not Th2 or severely immunodeficient mice, were enriched in gut bacteria that produce short-chain fatty acids. These include members of phyla Firmicutes, Verrucomicrobia, and Bacteroidetes such as Lactobacillus spp., Akkermansia muciniphila, and Odoribacter spp. Further comparison of the two naïve wild-type mouse strains showed higher microbial diversity (Shannon), primarily linked to higher richness (Chao1), as well as a distinct difference in microbial composition (weighted UniFrac) in BALB/c mice compared to C57BL/6. T-cell and blood cytokine analyses demonstrated a Th1-polarization in naïve adaptive immunity in C57BL/6 animals compared to BALB/c mice, and an expected Th2 deficient cellular response in IL-4Rα-/- and IL-33-/- mice compared to its genetic background BALB/c strain. Together, these data suggest that alterations in the Th1/Th2 balance or a complete ablation of Th1/Th2 responses can lead to major alterations in gut microbiota composition and function. Given the similarities between the human and mouse immune systems and gut microbiota, our finding that immune status is a strong driver of gut microbiota composition has important consequences for human immunodeficiency studies.

A Historic Review of the Role of CD4+ T-Cell Subsets in Development of the Immune Responses against Cutaneous and Visceral Leishmaniases

The heterogeneity of CD4+ T cells has been investigated since the late 1970s, when their Th1 and Th2 subsets were coined. Later studies on the cutaneous form of the Leishmaniasis were focused on the experimental models of Leishmania major infection using the susceptible BALB/c and the resistant C57BL/6 mice. At the early 21st century, the regulatory T-cells subpopulation was introduced and its role in concomitant immunity, responsible for lifelong resistance of the host to the reinfection was proposed. Subsequent studies, mainly focused on the visceral form of the infection pointed to the role of IL-17, produced by Th17 subset of CD4+ T cells that along the neutrophils were shown to have important yet equivocal functions in protection against or exacerbation of the infection. Altogether, the current knowledge indicates that the above four subsets could orchestrate the immune, the regulatory and the inflammatory responses of the host against different forms of leishmaniases.

Evaluation of Cellular Immune Responses in Dogs Immunized with Alum-Precipitated Autoclaved Leishmania major along with BCG and Imiquimod

Background:

We aimed to investigate the potential effects of BCG and imiquimod on improvement of current experimental L. major vaccine against dogs in an endemic area of Zoonotic visceral leishmaniasis (ZVL) in Iran.

Methods:

During 2012 till 2014, seven mixed-breed shepherd dogs with no anti-Leishmania antibodies and no response to Leishmanin reagent were immunized with 2 doses of alum-precipitated autoclaved L. major (Alum-AML) while BCG and imiquimod (for skin pre-treatment) were used as adjuvants. The productions of a few characteristic cytokines of T-helper immune responses and the development of delayed-type hypersensitivity (DTH) of the immunized animals were then evaluated, up to 300 days. Blood samples were collected at 0, 30, 80 and 300 d post-vaccination and the concentrations of IFN-γ, IL10, IL-12 and TGF-β cytokines secreted from PBMCs at these time-points were quantified by ELISA. DTH was evaluated by Leishmanin skin test (LST).

Results:

Although a similar LST conversion was observed at all time-points, the cytokine measurement results indicated significantly higher levels of IFN-γ at day 80 and elevated levels of IL-10 at days 80 and 300, post-vaccination. Moreover, a significantly higher IFN-γ/IL-10 ratio was observed at day 30 post-vaccination compared to the other time-points.

Conclusion:

Although a Th1-like response could be observed at day 30 post-vaccination, the development of cytokine profiles was inclined toward mixed Th1 and Th2 responses at days 80 and 300 post-vaccination. This situation may indicate the requirement of an additional boosting by this Alum-AML formula, in order to induce long-lasting protection against ZVL.

Potential biomarkers of immune protection in human leishmaniasis

Leishmaniasis is a vector-borne neglected tropical disease endemic in over 100 countries around the world. Available control measures are not always successful, therapeutic options are limited, and there is no vaccine available against human leishmaniasis, although several candidate antigens have been evaluated over the last decades. Plenty of studies have aimed to evaluate the immune response development and a diverse range of host immune factors have been described to be associated with protection or disease progression in leishmaniasis; however, to date, no comprehensive biomarker(s) have been identified as surrogate marker of protection or exacerbation, and lack of enough information remains a barrier for vaccine development. Most of the current understanding of the role of different markers of immune response in leishmaniasis has been collected from experimental animal models. Although the data generated from the animal models are crucial, it might not always be extrapolated to humans. Here, we briefly review the events during Leishmania invasion of host cells and the immune responses induced against Leishmania in animal models and humans and their potential role as a biomarker of protection against human leishmaniasis.

A primer on cytokines

Cytokines are pleiotropic polypeptides that control the development of and responses mediated by immune cells. Cytokine classification predominantly relies on [1] the target receptor(s), [2] the primary structural features of the extracellular domains of their receptors, and [3] their receptor composition. Functionally, cytokines are either pro-inflammatory or anti-inflammatory, hematopoietic colony-stimulating factors, developmental and would healing maintaining immune homeostasis. When the balance in C can form complex networks amongst themselves that may affect the homeostasis and diseases. Cytokines can affect resistance and susceptibility for many diseases and their availability in the host cytokine production and interaction is disturbed, immunopathogenesis sets in. Therefore, cytokine-targeting bispecific, and chimeric antibodies form a significant mode of immnuo-therapeutics Although the field has grown deep and wide, many areas of cytokine biology remain unknown. Here, we have reviewed these cytokines along with the organization, signaling, and functions through respective cytokine-receptor-families. Being part of the special issue on the Role of Cytokines in Leishmaniasis, this review is intended to be used as an organized primer on cytokines and not a resource for detailed discussion- for which a two-volume Handbook of cytokines is available- on each of the cytokines. Priming the readers on cytokines, we next brief the role of cytokines in Leishmaniasis. In the brief, we do not provide an account of each of the involved cytokines known to date, instead, we offer a temporal relationship between the cytokines and the progress of the infection towards the alternate outcomes- healing or non-healing- of the infection.

Immune response to Leishmania mexicana: the host-parasite relationship

Leishmaniosis is currently considered a serious public health problem and it is listed as a neglected tropical disease by World Health Organization (WHO). Despite the efforts of the scientific community, it has not been possible to develop an effective vaccine. Current treatment consists of antimonials that is expensive and can cause adverse effects. It is essential to fully understand the immunopathogenesis of the disease to develop new strategies to prevent, treat and eradicate the disease. Studies on animal models have shown a new paradigm in the resolution or establishment of infection by Leishmania mexicana where a wide range of cytokines, antibodies and cells are involved. In recent years, the possibility of a new therapy with monoclonal antibodies has been considered, where isotype, specificity and concentration are critical for effective therapy. Would be better to create/generate a vaccine to induce host protection or produce passive immunization with engineering monoclonal antibodies to a defined antigen? This review provides an overview that includes the current known information on the immune response that are involved in the complex host-parasite relationship infection caused by L. mexicana.

Cytokine saga in visceral leishmaniasis

In humans, infection with Leishmania manifests into a spectrum of diseases. The manifestation of the diseases depend on the resultant evasion of the parasite to immune responses namely by macrophages, which is an exclusive host of Leishmania. The B cells valiantly mount antibody responses, however, to no avail as the Leishmania parasites occupy the intracellular niches of the macrophages and subvert the immune response. Extensive studies have been documented on the role of cell-mediated immunity (CMI) in protection and counter survival strategies of the parasites leading to downregulation of CMI. The present review attempts to discuss the cytokines in progression or resolution of visceral form of leishmaniasis or kala-azar, predominantly affecting the Indian subcontinent. The components/cytokine(s) responsible for the regulation of the critical balance of T helper cells and their subsets have been discussed in the perspective. Therefore, any strategy involving the treatment of visceral leishmania (VL) needs to consider the balance and regulation of T cell function.

Conundrums in leishmaniasis

Parasites of the genus Leishmania cause the disease leishmaniasis. As the sandfly vector transfers the promastigotes into the skin of the human host, the infection is either cured or exacerbated. In the process, there emerge several unsolved paradoxes of leishmaniasis. Chronologically, as the infections starts in skin, the role of the salivary proteins in supporting the infection or the host response to these proteins influencing the induction of immunological memory becomes a conundrum. As the parasite invokes inflammation, the infiltrating neutrophils may act as "Trojan Horse" to transfer parasites to macrophages that, along with dendritic cells, carry the parasite to lymphoid organs to start visceralization. As the visceralized infection becomes chronic, the acutely enhanced monocytopoiesis takes a downturn while neutropenia and thrombocytopenia ensue with concomitant rise in splenic colony-forming-units. These responses are accompanied by splenic and hepatic granulomas, polyclonal activation of B cells and deviation of T cell responses. The granuloma formation is both a containment process and a form of immunopathogenesis. The heterogeneity in neutrophils and macrophages contribute to both cure and progression of the disease. The differentiation of T-helper subsets presents another paradox of visceral leishmaniasis, as the counteractive T cell subsets influence the curing or non-curing outcome. Once the parasites are killed by chemotherapy, in some patients the cured visceral disease recurs as a cutaneous manifestation post-kala azar dermal leishmaniasis (PKDL). As no experimental model exists, the natural history of PKDL remains almost a black box at the end of the visceral disease.

Single nucleotide polymorphisms of the genes IL-2, IL-2RB, and JAK3 in patients with cutaneous leishmaniasis caused by Leishmania (V.) guyanensis in Manaus, Amazonas, Brazil

Leishmaniasis is a disease caused by intracellular protozoan parasites of the genus Leishmania. In endemic areas, only a portion of exposed subjects develops cutaneous leishmaniasis (CL), suggesting that the genetic inheritance of the host plays a vital role in both resistance and susceptibility to the disease. Interleukin-2 (IL-2) is a cytokine that plays a central role in the regulation of the immune response in infection through the axis IL-2/IL-2R (receptor) complex, triggering a series of intracellular events, among which the signaling of Janus kinase/signal transducers and activators of transcription (JAK-STAT). The present study aimed at verifying the possible relationship between single nucleotide polymorphism (s) (SNP s) in the genes IL-2, IL-2RB, and JAK3 in subjects with CL caused by Leishmania guyanensis in the city of Manaus, state of Amazonas, Brazil. 820 patients with CL and 850 healthy subjects (control group) coming from the same endemic areas as the patients were examined. The SNPs -2425G/A (rs4833248) and -330 T/G (rs2069762), located in the IL-2 gene promoter region, seem to influence the expression of the gene and the SNP +10558G/A (rs1003694) and +13295T/C (rs3212760) located in the 3rd intron of the IL-2RB gene and the 13th intron of the JAK3 gene, respectively, were studied by PCR-RFLP. Genotypes and alleles frequencies were obtained by direct counting. For the comparison between the two groups, the χ2 test with OR (odds ratio) and the 95% confidence interval (CI) were used. Similar genotypes and alleles frequencies for the different SNPs were observed in both patients with CL and healthy controls. Comparison of genotypic and allelic frequency between patients with CL and healthy subjects did not show any difference. These polymorphisms do not predict susceptibility to, or protection against the development of CL caused by L. guyanensis in the Amazonas.

Model-based Evaluation of Gene Expression Changes in Response to Leishmania Infection

Since the development of high-density microarray technology in the late 1990s, global host gene expression changes in response to various stimuli have been extensively studied. More than a dozen peer-reviewed publications have investigated the effect of Leishmania infection in various models since 2001. This review covers the transcriptional changes in macrophage models induced by various Leishmania species and summarizes the resulting impact these studies have on our understanding of the host response to leishmaniasis in vitro. Characterization of the similarities and differences between various model systems will not only further our understanding of Leishmania-induced changes to macrophage gene expression but also identify potential therapeutic targets in the future.

Emerging IL-12 family cytokines in the fight against fungal infections

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IL-12 and IL-23 have established roles during anti-fungal immunity.

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IL-27 promotes regulatory effector responses during fungal infections.

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IL-35 drives T cell differentiation to produce anti-inflammatory responses.

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Increasing evidence for IL-12 family cytokines in maintaining anti-fungal immune homeostasis.

Invasive fungal infections cause approximately 1.5 million deaths per year worldwide and are a growing threat to human health. Current anti-fungal therapies are often insufficient, therefore studies into host-pathogen interactions are critical for the development of novel therapies to improve mortality rates. Myeloid cells, such as macrophages and dendritic cells, express pattern recognition receptor (PRRs), which are important for fungal recognition. Engagement of these PRRs by fungal pathogens induces multiple cytokines, which in turn activate T effector responses. Interleukin (IL)-12 family members (IL-12p70, IL-23, IL-27 and IL-35) link innate immunity with the development of adaptive immunity and are also important for regulating T cell responses. IL-12 and IL-23 have established roles during anti-fungal immunity, whereas emerging roles for IL-27 and IL-35 have recently been reported. Here, we discuss the IL-12 family, focusing on IL-27 and IL-35 during anti-fungal immune responses to pathogens such as Candida and Aspergillus.

Leishmania Hijacks Myeloid Cells for Immune Escape

Protozoan parasites of the Leishmania genus are the causative agents of leishmaniasis, a group of neglected tropical diseases whose clinical manifestations vary depending on the infectious Leishmania species but also on host factors. Recognition of the parasite by host myeloid immune cells is a key to trigger an effective Leishmania-specific immunity. However, the parasite is able to persist in host myeloid cells by evading, delaying and manipulating host immunity in order to escape host resistance and ensure its transmission. Neutrophils are first in infiltrating infection sites and could act either favoring or protecting against infection, depending on factors such as the genetic background of the host or the parasite species. Macrophages are the main host cells where the parasites grow and divide. However, macrophages are also the main effector population involved in parasite clearance. Parasite elimination by macrophages requires the priming and development of an effector Th1 adaptive immunity driven by specific subtypes of dendritic cells. Herein, we will provide a comprehensive outline of how myeloid cells regulate innate and adaptive immunity against Leishmania, and the mechanisms used by the parasites to promote their evasion and sabotage. Understanding the interactions between Leishmania and the host myeloid cells may lead to the development of new therapeutic approaches and improved vaccination to leishmaniases, an important worldwide health problem in which current therapeutic or preventive approaches are limited.

Inhibitor of serine peptidase 2 enhances Leishmania major survival in the skin through control of monocytes and monocyte-derived cells

Leishmania major is the causative agent of the neglected tropical disease, cutaneous leishmaniasis. In the mouse, protective immunity to Leishmania is associated with inflammatory responses. Here, we assess the dynamics of the inflammatory responses at the lesion site during experimental long-term, low-dose intradermal infection of the ear, employing noninvasive imaging and genetically modified L. major. Significant infiltrates of neutrophils and monocytes occurred at 1-4 d and 2-4 wk, whereas dermal macrophage and dendritic cell (DC) numbers were only slightly elevated in the first days. Quantitative whole-body bioluminescence imaging of myeloperoxidase activity and the quantification of parasite loads indicated that the Leishmania virulence factor, inhibitor of serine peptidase 2 (ISP2), is required to modulate phagocyte activation and is important for parasite survival at the infection site. ISP2 played a role in the control of monocyte, monocyte-derived macrophage, and monocyte-derived DC (moDC) influx, and was required to reduce iNOS expression in monocytes, monocyte-derived cells, and dermal DCs; the expression of CD80 in moDCs; and levels of IFN-γ in situ. Our findings indicate that the increased survival of L. major in the dermis during acute infection is associated with the down-regulation of inflammatory monocytes and monocyte-derived cells via ISP2.-Goundry, A., Romano, A., Lima, A. P. C. A., Mottram, J. C., Myburgh, E. Inhibitor of serine peptidase 2 enhances Leishmania major survival in the skin through control of monocytes and monocyte-derived cells.

Redundant and regulatory roles for Toll-like receptors in Leishmania infection

Toll-like receptors (TLRs) are germline-encoded, non-clonal innate immune receptors, which are often the first receptors to recognize the molecular patterns on pathogens. Therefore, the immune response initiated by TLRs has far-reaching consequences on the outcome of an infection. As soon as the cell surface TLRs and other receptors recognize a pathogen, the pathogen is phagocytosed. Inclusion of TLRs in the phagosome results in quicker phagosomal maturation and stronger adaptive immune response, as TLRs influence co-stimulatory molecule expression and determinant selection by major histocompatibility complex (MHC) class II and MHC class I for cross-presentation. The signals delivered by the TCR-peptide-MHC complex and co-stimulatory molecules are indispensable for optimal T cell activation. In addition, the cytokines induced by TLRs can skew the differentiation of activated T cells to different effector T cell subsets. However, the potential of TLRs to influence adaptive immune response into different patterns is severely restricted by multiple factors: gross specificity for the molecular patterns, lack of receptor rearrangements, sharing of limited number of adaptors that assemble signalling complexes and redundancy in ligand recognition. These features of apparent redundancy and regulation in the functioning of TLRs characterize them as important and probable contributory factors in the resistance or susceptibility to an infection.

Immunoprotective responses of T helper type 1 stimulatory protein-S-adenosyl-L-homocysteine hydrolase against experimental visceral leishmaniasis

It is well known that a patient in clinical remission of visceral leishmaniasis (VL) remains immune to reinfection, which provides a rationale for the feasibility of a vaccine against this deadly disease. In earlier studies, observation of significant cellular responses in treated Leishmania patients as well as in hamsters against leishmanial antigens from different fractions led to its further proteomic characterization, wherein S-adenosyl-L-homocysteine hydrolase (AdoHcy) was identified as a helper type 1 (Th1) stimulatory protein. The present study includes immunological characterization of this protein, its cellular responses [lymphoproliferation, nitric oxide (NO) production and cytokine responses] in treated Leishmania-infected hamsters and patients as well as prophylactic efficacy against Leishmania challenge in hamsters and the immune responses generated thereof. Significantly higher cellular responses were noticed against recombinant L. donovani S-adenosyl-L-homocysteine hydrolase (rLdAdoHcy) compared to soluble L. donovani antigen in treated samples. Moreover, stimulation of peripheral blood mononuclear cells with rLdAdoHcy up-regulated the levels of interferon (IFN)-γ, interleukin (IL)-12 and down-regulated IL-10. Furthermore, vaccination with rLdAdoHcy generated perceptible delayed-type hypersensitivity response and exerted considerably good prophylactic efficacy (∼70% inhibition) against L. donovani challenge. The efficacy was confirmed by the increased expression levels of inducible NO synthase and Th1-type cytokines, IFN-γ and IL-12 and down-regulation of IL-4, IL-10 and transforming growth factor (TGF)-β. The results indicate the potentiality of rLdAdoHcy protein as a suitable vaccine candidate against VL.

Mechanisms of immune evasion in leishmaniasis

Diseases caused by Leishmania present a worldwide problem, and current therapeutic approaches are unable to achieve a sterile cure. Leishmania is able to persist in host cells by evading or exploiting host immune mechanisms. A thorough understanding of these mechanisms could lead to better strategies for effective management of Leishmania infections. Current research has focused on parasite modification of host cell signaling pathways, entry into phagocytic cells, and modulation of cytokine and chemokine profiles that alter immune cell activation and trafficking to sites of infection. Immuno-therapeutic approaches that target these mechanisms of immune evasion by Leishmania offer promising areas for preclinical and clinical research.

Differential Impact of LPG-and PG-Deficient Leishmania major Mutants on the Immune Response of Human Dendritic Cells

Background

Leishmania major infection induces robust interleukin-12 (IL12) production in human dendritic cells (hDC), ultimately resulting in Th1-mediated immunity and clinical resolution. The surface of Leishmania parasites is covered in a dense glycocalyx consisting of primarily lipophosphoglycan (LPG) and other phosphoglycan-containing molecules (PGs), making these glycoconjugates the likely pathogen-associated molecular patterns (PAMPS) responsible for IL12 induction.

Methodology/Principal Findings

Here we explored the role of parasite glycoconjugates on the hDC IL12 response by generating L. major Friedlin V1 mutants defective in LPG alone, (FV1 lpg1-), or generally deficient for all PGs, (FV1 lpg2-). Infection with metacyclic, infective stage, L. major or purified LPG induced high levels of IL12B subunit gene transcripts in hDCs, which was abrogated with FV1 lpg1- infections. In contrast, hDC infections with FV1 lpg2- displayed increased IL12B expression, suggesting other PG-related/LPG2 dependent molecules may act to dampen the immune response. Global transcriptional profiling comparing WT, FV1 lpg1-, FV1 lpg2- infections revealed that FV1 lpg1- mutants entered hDCs in a silent fashion as indicated by repression of gene expression. Transcription factor binding site analysis suggests that LPG recognition by hDCs induces IL-12 in a signaling cascade resulting in Nuclear Factor κ B (NFκB) and Interferon Regulatory Factor (IRF) mediated transcription.

Conclusions/Significance

These data suggest that L. major LPG is a major PAMP recognized by hDC to induce IL12-mediated protective immunity and that there is a complex interplay between PG-baring Leishmania surface glycoconjugates that result in modulation of host cellular IL12.

Leishmaniasis is a group of parasitic diseases caused by intracellular protozoa belonging to the genus Leishmania, pathological manifestations ranging from self-healing cutaneous forms to severe visceral infections that result in death. These clinical outcomes are dictated by the Leishmania species initiating the infection and are influenced by early responses of host immune cells, which ultimately initiate an IL12 mediated immune response in resolving infections. Like the diseases themselves, the magnitude of IL12 induction in hDCs is Leishmania-species and strain specific, where species that elicit visceral disease do not induce IL12, while most cutaneous disease-causing L. major strains induce robust IL12 responses and confer life-long immunity. The molecular mechanisms that mediate the ability of these innate immune cells to discriminate between pathogens remain elusive and have been primarily investigated in murine model systems. Here we identified L. major LPG as a major PAMP that induces IL12 in hDCs. Elucidation of this critical component of human immunity to L. major has ramifications for leishmaniasis vaccine development.

Identification of Th1/Th2 regulatory switch to promote healing response during leishmaniasis: a computational approach

Leishmania devices its survival strategy by suppressing the host's immune functions. The antigen molecules produced by Leishmania interferes with the host's cell signaling cascades and consequently changes the protein expression pattern of the antigen-presenting cell (APC). This creates an environment suitable for the switching of the T-cell responses from a healing Th1 response to a non-healing Th2 response that is favorable for the continued survival of the parasite inside the host APC. Using a reconstructed signaling network of the intracellular and intercellular reactions between a Leishmania infected APC and T-cell, we propose a computational model to predict the inhibitory effect of the Leishmania infected APC on the T-cell and to identify the regulators of this Th1-/Th2-switching behavior as observed during Leishmania infection. In this work, we hypothesize that a complete removal of the parasite could only be achieved with a simultaneous up-regulation of the healing Th1 response and stimulation of nitric oxide (NO) production from the APCs, and downregulation of the non-healing Th2 response and thereby propose several unique combinations of protein molecules that could elicit this anti-Leishmania immune response. Our results indicate that TLR3 may play a positive role in eliciting NO synthesis, while TLR2 may be responsible for inhibiting an anti-Leishmania immune response. Also, TLR3 overexpression (in the APC), when combined with SHP2 inhibition (in the T cell), produces an anti-Leishmania response that is better than the conventional IFN-gamma or IL12 treatment. A similar anti-Leishmania response is also obtained in another combination where TLR3 (in APC) is overexpressed, and SHC and MKP (of T cell) are inhibited and activated, respectively. Through our study, we also observe that Leishmania infection may induce an upregulation of IFN-beta production from the APC that may lead to an upregulation of the RAP1 and SOCS3 proteins inside the T cell, the potential inhibitors of MAPK and JAK-STAT signaling pathways, respectively, via the TYK2-mediated pathway. This study not only enhances our knowledge in understanding the Th1/Th2 regulatory switch to promote healing response during leishmaniasis but also helps to identify novel combinations of proteins as potential immunomodulators.

The involvement of TLR2 and TLR4 in cytokine and nitric oxide production in visceral leishmaniasis patients before and after treatment with anti-leishmanial drugs

Toll-like receptors (TLRs) have significant involvement in Leishmania infection, although little is known about the relationship between these receptors, cytokines and nitric oxide (NO) in patients with visceral leishmaniasis (VL) before or after treatment with anti-leishmanial drugs. The goal of this study was to evaluate the expression of TLR2 and TLR4 in CD3+ and CD14+ cells and the production of TNF-α, IFN-γ, IL-17, IL-10, TGF-β and NO in peripheral blood mononuclear cells (PBMCs) from VL patients pre- and post-treatment with anti-leishmanial drugs. In addition, we investigated whether these receptors were involved in the production of these cytokines and NO. In the active VL patients, increased TLR2 and TLR4 expression in lymphocytes and monocytes, increased production of TNF-α, IL-10 and TGF-β and decreased production of IFN-γ, IL-17 and NO were observed. After treatment, TLR2 and TLR4 were still expressed in lymphocytes and monocytes, the TNF-α and IL-10 levels were lower, the production of IFN-γ, IL-17 and NO was higher, and the TGF-β level remained high. Before treatment, the production of TNF-α and NO was associated with TLR2 and TLR4 expression, while IL-10 production was only associated with TLR2 expression. After treatment, both receptors were associated with the production of TNF-α, IFN-γ, IL-10 and NO, while the production of IL-17 was associated only with TLR4 expression. The results presented in this study suggest that both TLR2 and TLR4 participate in the modulation of cytokine and NO production in VL patients, contributing to the pathogenesis of VL prior to treatment and the protective immune response after treatment.

Proteomic-based approach to gain insight into reprogramming of THP-1 cells exposed to Leishmania donovani over an early temporal window

Leishmania donovani, a protozoan parasite, is the causative agent of visceral leishmaniasis. It lives and multiplies within the harsh environment of macrophages. In order to investigate how intracellular parasite manipulate the host cell environment, we undertook a quantitative proteomic study of human monocyte-derived macrophages (THP-1) following infection with L. donovani. We used the isobaric tags for relative and absolute quantification (iTRAQ) method and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to compare expression profiles of noninfected and L. donovani-infected THP-1 cells. We detected modifications of protein expression in key metabolic pathways, including glycolysis and fatty acid oxidation, suggesting a global reprogramming of cell metabolism by the parasite. An increased abundance of proteins involved in gene transcription, RNA splicing (heterogeneous nuclear ribonucleoproteins [hnRNPs]), histones, and DNA repair and replication was observed at 24 h postinfection. Proteins involved in cell survival and signal transduction were more abundant at 24 h postinfection. Several of the differentially expressed proteins had not been previously implicated in response to the parasite, while the others support the previously identified proteins. Selected proteomics results were validated by real-time PCR and immunoblot analyses. Similar changes were observed in L. donovani-infected human monocyte-derived primary macrophages. The effect of RNA interference (RNAi)-mediated gene knockdown of proteins validated the relevance of the host quantitative proteomic screen. Our findings indicate that the host cell proteome is modulated after L. donovani infection, provide evidence for global reprogramming of cell metabolism, and demonstrate the complex relations between the host and parasite at the molecular level.

l-Asparaginase as a new molecular target against leishmaniasis: insights into the mechanism of action and structure-based inhibitor design

l-Asparaginases belong to a family of amidohydrolases that catalyze the conversion of l-asparagine into l-aspartic acid and ammonia.

In vitro cytokines profile and ultrastructural changes of microglia and macrophages following interaction with Leishmania

In the present study, we assessed morphological changes and cytokine production after in vitro interaction with causative agents of American cutaneous leishmaniasis and compared the microglia and macrophage immune responses. Cultures of microglia and macrophages infected with stationary-phase promastigotes of Leishmania (Viannia) shawi, Leishmania (Viannia) braziliensis or Leishmania (Leishmania) amazonensis were evaluated 24, 48 and 72 h after interaction. Macrophages only presented the classical phagocytic process while microglia also displayed large cytoplasmic projections similar to the ruffles described in macropinocytosis. In the macrophage cultures, the percentage of infected cells increased over time, in a fashion that was dependent on the parasite species. In contrast, in microglial cells as the culture time progressed, there was a significant reduction in the percentage of infected cells independent of parasite species. Measurements of cytokines in macrophage cultures 48 h after interactions revealed distinct expression patterns for different parasites, whereas in microglial cultures they were similar for all Leishmania tested species. Taken together, our results suggest that microglia may have a higher phagocytic ability and cytotoxic potential than macrophages for all investigated species. The robust response of microglia against all parasite species may suggest microglia have an important role in the defence against cerebral leishmaniasis.

Leishmania major inhibits IL-12 in macrophages by signalling through CR3 (CD11b/CD18) and down-regulation of ETS-mediated transcription

Leishmania major is an aetiological agent of cutaneous leishmaniasis. The parasite primarily infects immune sentinel cells, specifically macrophages and dendritic cells, in the mammalian host. Infection is receptor mediated and is known to involve parasite binding to cell surface protein complement receptor 3 (CR3, Mac-1, CD11b/CD18). Engagement of CR3 by various ligands inhibits production of interleukin-12 (IL-12), the cytokine that drives antileishmanial T helper 1-type immune responses. Likewise, L. major infection inhibits IL-12 production and activation of host macrophages. Our data indicate that in the absence of CR3, L. major-infected bone marrow-derived macrophages produce more IL-12 and nitric oxide compared with WT cells upon lipopolysaccharide (LPS) stimulation. We therefore investigated multiple signalling pathways by which L. major may inhibit IL-12 transcription through CR3 ligation. We demonstrate that L. major infection does not elicit significant NFκB p65, MAPK, IRF-1 or IRF-8 activation in WT or CD11b-deficient macrophages. Furthermore, infection neither inhibits LPS-induced MAPK or NFκB activation nor blocks IFN-γ-activated IRF-1 and IRF-8. ETS-mediated transcription, however, is inhibited by L. major infection independently of CR3. Our data indicate that L. major-mediated inhibition of IL-12 occurs through CR3 engagement; however, the mechanism of inhibition is independent of NFκB, MAPK, IRF and ETS.

Distinct strains of Leishmania major induce different cytokine mRNA expression in draining lymph node of BALB/c mice

Four genotypically distinct strains of L. major collected from persons residing in different endemic areas of cutaneous leishmaniasis in Iran were evaluated in BALB/c mice. Parasite virulence was evaluated by measuring the parasite burden in the lymph nodes. Immunogenicity of the strains was assessed by analysis of cytokines mRNA expression levels in popliteal lymph nodes of the mice in early (3, 16, 40 h) and late (week 1, W3, W5 and W8) time periods after infection. The expression of cytokines mRNA, namely Ifng, Il2,Il4,Il10 and Il12, was quantitated by real-time PCR. The lowest and the highest parasite loads were induced by Damghan (2·15 × 10⁷) and Shiraz (9·59 × 10⁹) strains, respectively. Moreover, Damghan strain elicited higher expression levels of Ifng and Il2 mRNA and the highest ratio of Ifng/Il4 mRNA expression compared with the other strains at 40 h and 8 weeks post-infection. The results indicate that the inoculation of BALB/c mice with different strains induced high diversity in parasite burden and cytokines gene expression. Amongst the four strains, Damghan strain showed the lowest parasite load and the highest tendency to induce expression of Th1 cytokines gene and might be considered as a safe and immunogenic strain.

Electrospray encapsulation of toll-like receptor agonist resiquimod in polymer microparticles for the treatment of visceral leishmaniasis

Leishmaniasis is a disease caused by the intracellular protozoan, Leishmania. A current treatment for cutaneous leishmaniasis involves the delivery of imidazoquinolines via a topical cream. However, there are no parenteral formulations of imidazoquinolines for the most deadly version of the disease, visceral leishmaniasis. This work investigates the use of electrospray to encapsulate the imidazoquinoline adjuvant resiquimod in acid sensitive microparticles composed of acetalated dextran (Ac-DEX) or Ac-DEX/Tween blends. The particles were characterized and tested both in vitro and in vivo. Solutions of Ac-DEX and resiquimod in ethanol were electrosprayed to generate approximately 2 μm Ac-DEX particles containing resiquimod with an encapsulation efficiency of 85%. To prevent particle aggregation, blends of Ac-DEX with Tween 20 and Tween 80 were investigated. Tween 80 was then blended with the Ac-DEX at ∼10% (w/w) of total polymer and particles containing resiquimod were formed via electrospray with encapsulation efficiencies between 40% and 60%. In vitro release profiles of resiquimod from Ac-DEX/Tween 80 particles exhibited the acid-sensitive nature of Ac-DEX, with 100% drug release after 8 h at pH 5 (phagosomal pH) and after 48 h at pH 7.4 (physiological pH). Treatment with Ac-DEX/Tween 80 particles elicited significantly greater immune response in RAW macrophages over free drug. When injected intravenously into mice inoculated with Leishmania, parasite load reduced significantly in the bone marrow compared to blank particles and phosphate-buffered saline controls. Overall, electrospray appears to offer an elegant, scalable way to encapsulate adjuvant into an acid sensitive delivery vehicle for use in treating visceral leishmaniasis.

Human hepatic stellate cells in primary culture are safe targets forLeishmania donovani

Leishmaniaparasites can escape the immune response by invading cell types lacking leishmanicidal mechanisms. Silent persistence ofLeishmaniaparasites in the host organism is responsible for asymptomatic carriage and relapses after cured leishmaniasis. Here, we studied the interaction between Hepatic Stellate Cells (HSC) andLeishmania.An original model of human HSC in primary culture infected withL. donovaniwas developed. The presence of intracellular parasites was studied and quantified using optical and confocal microscopy. HSC characteristics were studied using microscopy, methylene blue assay, long-term cultures and qPCR. We showed for the first time that human HSC are permissive toL. donovaniinfection, with no modification of HSC survival, growth rate and proinflammatory and fibrogenic characteristics. Intracellular parasites did not replicate but HSC had no effect on their survival. Indeed, after a 40-day culture, infected HSC cultures transferred on NNN medium yielded new promastigotes that were able to proliferate and efficiently infect new cells. HSC are permissive toL. donovani, with neither parasite killing nor apparent cell damage. Thus, HSC could act as potent sanctuary cells forLeishmaniain the liver, which could partially explain parasite reactivation after an asymptomatic carriage or a cured visceral leishmaniasis.

Dendritic cells in Leishmania major infections: mechanisms of parasite uptake, cell activation and evidence for physiological relevance

Leishmaniasis is one of the most important infectious diseases worldwide; a vaccine is still not available. Infected dendritic cells (DC) are critical for the initiation of protective Th1 immunity against Leishmania major. Phagocytosis of L. major by DC leads to cell activation, IL-12 release and (cross-) presentation of Leishmania antigens by DC. Here, we review the role of Fcγ receptor- and B cell-mediated processes for parasite internalization by DC. In addition, the early events after parasite inoculation that consist of mast cell activation, parasite uptake by skin-resident macrophages (MΦ), followed by neutrophil and monocyte immigration and DC activation are described. All these events contribute significantly to antigen processing in infected DC and influence resulting T cell priming in vivo. A detailed understanding of the role of DC for the development of efficient anti-Leishmania immunity will aid the development of potent anti-parasite drugs and/or vaccines.

Leishmania donovani triose phosphate isomerase: a potential vaccine target against visceral leishmaniasis

Visceral leishmaniasis (VL) is one of the most important parasitic diseases with approximately 350 million people at risk. Due to the non availability of an ideal drug, development of a safe, effective, and affordable vaccine could be a solution for control and prevention of this disease. In this study, a potential Th1 stimulatory protein- Triose phosphate isomerase (TPI), a glycolytic enzyme, identified through proteomics from a fraction of Leishmania donovani soluble antigen ranging from 89.9–97.1 kDa, was assessed for its potential as a suitable vaccine candidate. The protein- L. donovani TPI (LdTPI) was cloned, expressed and purified which exhibited the homology of 99% with L. infantum TPI. The rLdTPI was further evaluated for its immunogenicity by lymphoproliferative response (LTT), nitric oxide (NO) production and estimation of cytokines in cured Leishmania patients/hamster. It elicited strong LTT response in cured patients as well as NO production in cured hamsters and stimulated remarkable Th1-type cellular responses including IFN-ã and IL-12 with extremely lower level of IL-10 in Leishmania-infected cured/exposed patients PBMCs in vitro. Vaccination with LdTPI-DNA construct protected naive golden hamsters from virulent L. donovani challenge unambiguously (∼90%). The vaccinated hamsters demonstrated a surge in IFN-ã, TNF-á and IL-12 levels but extreme down-regulation of IL-10 and IL-4 along with profound delayed type hypersensitivity and increased levels of Leishmania-specific IgG2 antibody. Thus, the results are suggestive of the protein having the potential of a strong candidate vaccine.

Evaluation of Leishmania donovani protein disulfide isomerase as a potential immunogenic protein/vaccine candidate against visceral Leishmaniasis

In Leishmania species, Protein disulfide isomerase (PDI) - a redox chaperone, is reported to be involved in its virulence and survival. This protein has also been identified, through proteomics, as a Th1 stimulatory protein in the soluble lysate of a clinical isolate of Leishmania donovani (LdPDI). In the present study, the molecular characterization of LdPDI was carried out and the immunogenicity of recombinant LdPDI (rLdPDI) was assessed by lymphocyte proliferation assay (LTT), nitric oxide (NO) production, estimation of Th1 cytokines (IFN-γ and IL-12) as well as IL-10 in PBMCs of cured/endemic/infected Leishmania patients and cured L. donovani infected hamsters. A significantly higher proliferative response against rLdPDI as well as elevated levels of IFN-γ and IL-12 were observed. The level of IL-10 was found to be highly down regulated in response to rLdPDI. A significant increase in the level of NO production in stimulated hamster macrophages as well as IgG2 antibody and a low level of IgG1 in cured patient's serum was observed. Higher level of IgG2 antibody indicated its Th1 stimulatory potential. The efficacy of pcDNA-LdPDI construct was further evaluated for its prophylactic potential. Vaccination with this construct conferred remarkably good prophylactic efficacy (∼90%) and generated a robust cellular immune response with significant increases in the levels of iNOS transcript as well as TNF-α, IFN-γ and IL-12 cytokines. This was further supported by the high level of IgG2 antibody in vaccinated animals. The in vitro as well as in vivo results thus indicate that LdPDI may be exploited as a potential vaccine candidate against visceral Leishmaniasis (VL).

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

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

Innate immune activation and subversion of Mammalian functions by leishmania lipophosphoglycan

Leishmania promastigotes express several prominent glycoconjugates, either secreted or anchored to the parasite surface. Of these lipophosphoglycan (LPG) is the most abundant, and along with other phosphoglycan-bearing molecules, plays important roles in parasite infectivity and pathogenesis in both the sand fly and the mammalian host. Besides its contribution for parasite survival in the sand fly vector, LPG is important for modulation the host immune responses to favor the establishment of mammalian infection. This review will summarize the current knowledge regarding the role of LPG in Leishmania infectivity, focusing on the interaction of LPG and innate immune cells and in the subversion of mammalian functions by this molecule.

Immune and inflammatory responses to Leishmania amazonensis isolated from different clinical forms of human leishmaniasis in CBA mice

Leishmania amazonensis causes different diseases depending on the host and parasitic virulence factors. In this study, CBA mice were infected with L. amazonensis isolates from patients with localized (Ba125), diffuse cutaneous (Ba276) or visceral leishmaniasis (Ba109). Mice infected with Ba125 and Ba276 progressed rapidly and lesions displayed an infiltrate rich in parasitized macrophages and were necrotic and ulcerated. Ba109 induced smaller lesions and a mixed inflammatory infiltrate without necrosis or ulceration. Ba109 induced an insidious disease with lower parasite load in CBA mice, similar to human disease. Levels of IFN-γ, IL-4 and IL-10 did not differ among the groups. Because all groups were unable to control the infection, expression of IL-4 associated with low production of IFN-γ in the early phase of infection may account for susceptibility, but others factors may contribute to the differences observed in inflammatory responses and infection progression. Evaluation of some parasitic virulence factors revealed that Ba276 exhibits higher ecto-ADPase and 5'-nucleotidase activities compared to the Ba109 and Ba125 strains. Both Ba276 and Ba125 had higher arginase activity in comparison to Ba109. Finally, these data suggest that the differences in enzyme activities among parasites can account for differences in host inflammatory responses and infection progression.

Pathogen-derived oligosaccharides improve innate immune response to intracellular parasite infection

Pathogen glycolipids, including Leishmania spp. lipophosphoglycan (LPG) and Mycobacterium tuberculosis mannosylated lipoarabinomannan (ManLAM), modulate essential interactions with host phagocytic cells. Polysaccharide and lipid components promote immunomodulation. Owing to the stereochemistry required to synthesize oligosaccharides, the roles for oligosaccharides in the pathogenesis of infectious diseases have remained largely unknown. Recent advances in carbohydrate chemistry allowed us to synthesize pathogen surface oligosaccharides to discern their immune response-altering activities. Trimannose cap carbohydrates from ManLAM and LPG altered the production of proinflammatory cytokines via a toll-like receptor (TLR2)-mediated mechanism in vitro and in vivo. In vivo treatment with trimannose led to increased Th1-polarizing, IL-12p40-producing cells from the draining lymph nodes of treated Leishmania major-infected mice compared with cells from untreated infected mice. Trimannose treatment increased the production of other Th1 proinflammatory cytokines (ie, interferon-γ, IL-6, and tumor necrosis factor-α) critical for a productive immune response to either pathogen. This significant difference in cytokine production between trimannose cap sugar-treated and control groups was not observed in draining lymph node cells from TLR2(-/-) mice. Type of inflammation and rate of bead entry into macrophages and dendritic cells were different for trimannose-coated beads compared with control oligosaccharide-coated beads, indicating selective lectin receptor/oligosaccharide interactions mediating cell entry and cytokine production. These novel findings may prompt the development of targeted oligosaccharide adjuvants against chronic infections.

Cell biology and immunology of Leishmania

More than 20 years ago, immunologists discovered that resistance and susceptibility to experimental infection with the intracellular protozoan Leishmania major was associated with the development of T-helper 1 (Th1)- and Th2-dominated immune responses, respectively. This infectious disease model was later used to identify and assess the role of key factors, such as interleukin-12 (IL-12) and IL-4, in Th1 and Th2 maturation. While infection by Leishmania remains a popular model for immunologists who wish to assess the role of their favorite molecule in T-cell differentiation, other investigators have tried to better understand how Leishmania interact with its insect and mammalian hosts. In this review, we discuss some of these new data with an emphasis on the early events that shape the immune response to Leishmania and on the immune evasion mechanisms that allow this parasite to avoid the development of sterilizing immunity and to secure its transmission to a new host.

How pathogen-derived cysteine proteases modulate host immune responses

In mammals, cysteine proteases are essential for the induction and development of both innate and adaptive immune responses. These proteases play a role in antigen-and pathogen-recognition and elimination, signal processing and cell homeostasis. Many pathogens also secrete cysteine proteases that often act on the same target proteins as the mammalian proteases and thereby can modulate host immunity from initial recognition to effector mechanisms. Pathogen-derived proteases range from nonspecific proteases that degrade multiple proteins involved in the immune response to enzymes that are very specific in their mode of action. Here, we overview current knowledge of pathogen-derived cysteine proteases that modulate immune responses by altering the normal function of key receptors or pathways in the mammalian immune system.

mTOR signaling pathway regulates the IL-12/IL-10 axis in Leishmania donovani infection

Leishmania-induced interleukin-12 (IL-12) expression is negatively regulated by the phosphatidylinositol 3-kinase (PI3K) and extracellular signal regulated kinase (ERK) 1/2 pathways in human monocyte derived macrophages (MDMs). To extend these studies, we examined the pathways downstream from PI3K in L. donovani-induced reciprocal regulation of IL-12/IL-10 axis in THP-1-derived macrophages. We show for the first time that in THP-1-derived macrophages and human monocytes, mTOR inhibition by rapamycin reversed L. donovani-induced IL-12 and IL-10 modulation. L. donovani-induced phosphorylation of P70S6K, a correlate of mTOR activity, in TLR-stimulated THP-1 derived macrophages. This increase in P70S6K phosphorylation was completely blocked by rapamycin (mTOR inhibitor) and partially by wortmannin (PI3K inhibitor). These observations suggest that a PI3K independent pathway is operative in the modulation of IL-12 and IL-10. Blocking of TLR2 significantly attenuated IL-10 induced by the parasite, but did not affect IL-12 production. Thus, our data suggests that intracellular network of PI3K and mTOR pathway control IL-12/IL-10 modulation by L. donovani. mTOR inhibitors may be attractive molecules to reverse this modulation and may result in control of disease.

The protective Th1 response in mice is induced in the T-cell zone only three weeks after infection with Leishmania major and not during early T-cell activation

The protozoan parasite Leishmania spp. causes clinical pictures ranging in severity from spontaneously healing skin ulcers to systemic disease. The immune response associated with healing involves the differentiation of IFNγ-producing Th1 cells, whereas the non-healing phenotype is associated with IL4-producing Th2 cells. The widespread assumption has been that the T-cell differentiation that leads to a healing or non-healing phenotype is established at the time of T-cell activation early after infection. By selectively analyzing the expression of cytokine genes in the T-cell zones of lymph nodes of resistant (Th1) C57BL/6 mice and susceptible (Th2) BALB/c mice during an infection with Leishmania major in vivo, we show that the early T-cell response does not differ between C57BL/6 mice and BALB/c mice. Instead, Th1/Th2 polarization appears suddenly 3 weeks after infection. At the same time point, the number of parasites increases in lymph nodes of both mouse strains, but about 100-fold more in susceptible BALB/c mice. We conclude that the protective Th1 response in C57BL/6 mice is facilitated by the capacity of their innate effector cells to keep parasite numbers at low levels.

Leishmania infantum and Toxoplasma gondii: Mixed infection of macrophages in vitro and in vivo

Although macrophages have a microbicidal role in the immune system they themselves can be infected by pathogens. Often a simultaneous infection by more than one microbe may occur in a single cell. This is the first report of coinfection of macrophages with Toxoplasma gondii and Leishmania infantum, in vitro and in vivo. L. infantum does not cause severe disease in mice but T. gondii, RH strain, is lethal. Cell culture studies using THP-1 macrophages dually infected in vitro revealed that 4.3% harbored both parasites 24h after infection. When mice were infected with both parasites on the same day 7.3% of the infected cells carried both parasites 7 days later. Yet, if mice were first infected with L. infantum and then with Toxoplasma (5 days post-infection) 18.7% of the macrophages hosted either parasite but concomitant infection could not be found and mice, already harboring L. infantum, survived Toxoplasma's lethal effect.

Potency, efficacy and durability of DNA/DNA, DNA/protein and protein/protein based vaccination using gp63 against Leishmania donovani in BALB/c mice

Background

Visceral leishmaniasis (VL) caused by an intracellular protozoan parasite Leishmania, is fatal in the absence of treatment. At present there are no effective vaccines against any form of leishmaniasis. Here, we evaluate the potency, efficacy and durability of DNA/DNA, DNA-prime/Protein-boost, and Protein/Protein based vaccination against VL in a susceptible murine model.

Methods and Findings

To compare the potency, efficacy, and durability of DNA, protein and heterologous prime-boost (HPB) vaccination against Leishmania donovani, major surface glycoprotein gp63 was cloned into mammalian expression vector pcDNA3.1 for DNA based vaccines. We demonstrated that gp63 DNA based vaccination induced immune responses and conferred protection against challenge infection. However, vaccination with HPB approach showed comparatively enhanced cellular and humoral responses than other regimens and elicited early mixed Th1/Th2 responses before infection. Moreover, challenge with parasites induced polarized Th1 responses with enhanced IFN-γ, IL-12, nitric oxide, IgG2a/IgG1 ratio and reduced IL-4 and IL-10 responses compared to other vaccination strategies. Although, vaccination with gp63 DNA either alone or mixed with CpG- ODN or heterologously prime-boosting with CpG- ODN showed comparable levels of protection at short-term protection study, DNA-prime/Protein-boost in presence of CpG significantly reduced hepatic and splenic parasite load by 10⁷ fold and 10¹⁰ fold respectively, in long-term study. The extent of protection, obtained in this study has till now not been achieved in long-term protection through HPB approach in susceptible BALB/c model against VL. Interestingly, the HPB regimen also showed marked reduction in the footpad swelling of BALB/c mice against Leishmania major infection.

Conclusion/Significance

HPB approach based on gp63 in association with CpG, resulted in robust cellular and humoral responses correlating with durable protection against L. donovani challenge till twelve weeks post-vaccination. These results emphasize the potential of DNA-prime/Protein-boost vaccination over DNA/DNA and Protein/Protein based vaccination in maintaining long-term immunity against intracellular pathogen like Leishmania.

PKCδ regulates IL-12p40/p70 production by macrophages and dendritic cells, driving a type 1 healer phenotype in cutaneous leishmaniasis

The protein kinase C (PKC) family is involved in the regulation of many intracellular signalling pathways. Here, we report that the PKCδ isoform regulates IL-12p40/p70 production in macrophages and DC and that PKCδ deficiency in mice transforms the 129/Sv healer to a non-healer strain during cutaneous leishmaniasis. Leishmania major-infected PKCδ(-/-) 129/Sv mice developed a rapid increase in footpad swelling and parasite burden with disease progression, leading to necrosis and ulceration similar to non-healer BALB/c mice. Moreover, PKCδ(-/-) mice failed to develop delayed-type hypersensitivity responses against Leishmania antigen. PKCδ(-/-) macrophages were fully functional with normal MHC class II surface expression and GM-CSF production, recruitment to the draining lymph node and killing effector functions by NO production. In contrast, macrophages and DC produced significantly reduced IL-12p40 and IL-12p70 compared to the WT cells. Decreased IL-12 production resulted in diminished Th1 differentiation, as determined by a striking reduction in IFN-γ by antigen-specific stimulated CD4(+) T cells isolated from popliteal lymph nodes of L. major-infected PKCδ(-/-) mice, explaining the "non-healer" phenotype. We conclude from these data that PKCδ is a regulator of IL-12p40/p70 production by DC and macrophages, driving the healer phenotype during cutaneous leishmaniasis.

Evaluation of T cell responses in healing and nonhealing leishmaniasis reveals differences in T helper cell polarization ex vivo and in vitro

Experimental leishmaniasis is widely used to study the effector functions of T helper cell subsets in vivo. Healing and nonhealing Leishmania major infections have been correlated with T helper 1 and T helper 2 responses, respectively. In the present study, we determined T cell effector functions ex vivo, without any further restimulation and compared them to those obtained following antigen-specific restimulation in vitro. Our results show that T helper cell responses are significantly less polarized when determined ex vivo as compared to those measured after restimulation in vitro. Moreover, the differences in CD4⁺ T cell proliferation observed between healer and nonhealer strains of mice differed ex vivo and in vitro. Our results suggest that determination of both ex vivo as well as in vitro T cell responses is crucial to characterize immune responses during experimental leishmaniasis.

Cytokine-secreting follicular T cells shape the antibody repertoire

High-affinity antibodies are critical for host protection and underlie successful vaccines. The generation of such antibodies requires T cell-dependent help, which mediates germinal center reactions in which mutation and selection of B cells occurs. Using an interleukin 4-reporter system, we show here that CD4(+) follicular helper T cells constituted essentially all of the cytokine-secreting T cells in lymph nodes and were functionally distinct from T cells secreting the same cytokine in peripheral tissues. Follicular helper T cells with different cytokine profiles could be isolated as conjugates with B cells undergoing cytokine-specific immunoglobulin class switching with evidence of somatic hypermutation. Our findings support a model in which B cells compete for cytokines produced by follicular helper T cells that shape the affinity and isotype of the antibody response.