Murine visceral leishmaniasis: IgM and polyclonal B-cell activation lead to disease exacerbation

Effect of Leishmania infantum infection on B cell lymphopoiesis and memory in the bone marrow and spleen

Visceral leishmaniasis (VL) is characterized by an uncontrolled infection of internal organs such as the spleen, liver and bone marrow (BM) and can be lethal when left untreated. No effective vaccination is currently available for humans. The importance of B cells in infection and VL protective immunity has been controversial, with both detrimental and protective effects described. VL infection was found in this study to increase not only all analyzed B cell subsets in the spleen but also the B cell progenitors in the BM. The enhanced B lymphopoiesis aligns with the clinical manifestation of polyclonal hypergammaglobulinemia and the occurrence of autoantibodies. In line with earlier reports, flow cytometric and microscopic examination identified parasite attachment to B cells of the BM and spleen without internalization, and transformation of promastigotes into amastigote morphotypes. The interaction appears independent of IgM expression and is associated with an increased detection of activated lysosomes. Furthermore, the extracellularly attached amastigotes could be efficiently transferred to infect macrophages. The observed interaction underscores the potentially crucial role of B cells during VL infection. Additionally, using immunization against a fluorescent heterologous antigen, it was shown that the infection does not impair immune memory, which is reassuring for vaccination campaigns in VL endemic areas.

A link between circulating immune complexes and acute kidney injury in human visceral leishmaniasis

Visceral leishmaniasis (VL) is an infectious disease caused by Leishmania infantum. Clinically, VL evolves with systemic impairment, immunosuppression and hyperactivation with hypergammaglobulinemia. Although renal involvement has been recognized, a dearth of understanding about the underlying mechanisms driving acute kidney injury (AKI) in VL remains. We aimed to evaluate the involvement of immunoglobulins (Igs) and immune complexes (CIC) in the occurrence of AKI in VL patients. Fourteen VL patients were evaluated between early treatment and 12 months post-treatment (mpt). Anti-Leishmania Igs, CIC, cystatin C, C3a and C5a were assessed and correlated with AKI markers. Interestingly, high levels of CIC were observed in VL patients up to 6 mpt. Concomitantly, twelve patients met the criteria for AKI, while high levels of cystatin C were observed up to 6 mpt. Plasmatic cystatin C was positively correlated with CIC and Igs. Moreover, C5a was correlated with cystatin C, CIC and Igs. We did not identify any correlation between amphotericin B use and kidney function markers in VL patients, although this association needs to be further explored in subsequent studies. Our data reinforce the presence of an important renal function impairment during VL, suggesting the involvement of Igs, CIC, and C5a in this clinical condition.

Protective Humoral Immune Response Induced by Recombinant Virus-like Particle Vaccine Expressing Leishmania donovani Surface Antigen

To date, Leishmania spp. vaccine studies have mainly focused on cellular immunity induction, which plays a crucial role in host protection. In contrast, vaccine-induced humoral immunity is largely neglected. Virus-like particle (VLP) vaccines generated using the baculovirus expression system are well-known inducers of humoral immunity and would serve as a suitable platform for evaluating humoral immunity-mediated protection against visceral Leishmaniasis. In this study, we investigated the humoral immunity evoked through VLPs expressing the L. donovani promastigote surface antigen (PSA-VLPs) and assessed their contribution to protection in mice. PSA-VLPs vaccines were generated using the baculovirus expression system and used for mouse immunizations. Mice were intramuscularly immunized twice with PSA-VLPs and challenged with L. donovani to confirm vaccine-induced protective immunity. PSA-VLP immunization elicited parasite-specific antibody responses in the sera of mice, which were induced in a dose-dependent manner. B cell, germinal center B cell, and memory B cell responses in the spleen were found to be higher in vaccinated mice compared to unimmunized controls. PSA-VLP immunization diminished the production of pro-inflammatory cytokines IFN-γ and IL-6 in the liver. Overall, the PSA-VLPs conferred protection against L. donovani challenge infection by reducing the total parasite burden within the internal organs. These results suggest that PSA-VLPs induced protective immunity against the L. donovani challenge infection.

Leishmania donovani Exploits Tunneling Nanotubes for Dissemination and Propagation of B Cell Activation

Polyclonal B cell activation and the resulting hypergammaglobulinemia are a detrimental consequence of visceral leishmaniasis (VL); however, the mechanisms underlying this excessive production of nonprotective antibodies are still poorly understood. Here, we show that a causative agent of VL, Leishmania donovani, induces CD21-dependent formation of tunneling nanotubule (TNT)-like protrusions in B cells. These intercellular connections are used by the parasite to disseminate among cells and propagate B cell activation, and close contact both among the cells and between B cells and parasites is required to achieve this activation. Direct contact between cells and parasites is also observed in vivo, as L. donovani can be detected in the splenic B cell area as early as 14 days postinfection. Interestingly, Leishmania parasites can also glide from macrophages to B cells via TNT-like protrusions. Taken together, our results suggest that, during in vivo infection, B cells may acquire L. donovani from macrophages via TNT-like protrusions, and these connections are subsequently exploited by the parasite to disseminate among B cells, thus propagating B cell activation and ultimately leading to polyclonal B cell activation. IMPORTANCE Leishmania donovani is a causative agent of visceral leishmaniasis, a potentially lethal disease characterized by strong B cell activation and the subsequent excessive production of nonprotective antibodies, which are known to worsen the disease. How Leishmania activates B cells is still unknown, particularly because this parasite mostly resides inside macrophages and would not have access to B cells during infection. In this study, we describe for the first time how the protozoan parasite Leishmania donovani induces and exploits the formation of protrusions that connect B lymphocytes with each other or with macrophages and glides on these structures from one cell to another. In this way, B cells can acquire Leishmania from macrophages and become activated upon contact with the parasites. This activation will then lead to antibody production. These findings provide an explanation for how the parasite may propagate B cell activation during infection.

Efficacy of an Immunotherapy Combining Immunogenic Chimeric Protein Plus Adjuvant and Amphotericin B against Murine Visceral Leishmaniasis

Visceral leishmaniasis (VL) in the Americas is a chronic systemic disease caused by infection with Leishmania infantum parasites. The toxicity of antileishmanial drugs, long treatment course and limited efficacy are significant concerns that hamper adequate treatment against the disease. Studies have shown the promise of an immunotherapeutics approach, combining antileishmanial drugs to reduce the parasitism and vaccine immunogens to activate the host immune system. In the current study, we developed an immunotherapy using a recombinant T cell epitope-based chimeric protein, ChimT, previously shown to be protective against Leishmania infantum, with the adjuvant monophosphoryl lipid A (MPLA) and amphotericin B (AmpB) as the antileishmanial drug. BALB/c mice were infected with L. infantum stationary promastigotes and later they received saline or were treated with AmpB, MPLA, ChimT/Amp, ChimT/MPLA or ChimT/MPLA/AmpB. The combination of ChimT/MPLA/AmpB significantly reduced the parasite load in mouse organs (p < 0.05) and induced a Th1-type immune response, which was characterized by higher ratios of anti-ChimT and anti-parasite IgG2a:IgG1 antibodies, increased IFN-γ mRNA and IFN-γ and IL-12 cytokines and accompanied by lower levels of IL-4 and IL-10 cytokines, when compared to other treatments and controls (all p < 0.05). Organ toxicity was also lower with the ChimT/MPLA/AmpB immunotherapy, suggesting that the inclusion of the vaccine and adjuvant ameliorated the toxicity of AmpB to some degree. In addition, the ChimT vaccine alone stimulated in vitro murine macrophages to significantly kill three different internalized species of Leishmania parasites and to produce Th1-type cytokines into the culture supernatants. To conclude, our data suggest that the combination of ChimT/MPLA/AmpB could be considered for further studies as an immunotherapy for L. infantum infection.

Leishmaniasis: Immune Cells Crosstalk in Macrophage Polarization

Leishmaniasis is a complex infectious parasitic disease caused by protozoa of the genus Leishmania, belonging to a group of neglected tropical diseases. It establishes significant global health challenges, particularly in socio-economically disadvantaged regions. Macrophages, as innate immune cells, play a crucial role in initiating the inflammatory response against the pathogens responsible for this disease. Macrophage polarization, the process of differentiating macrophages into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, is essential for the immune response in leishmaniasis. The M1 phenotype is associated with resistance to Leishmania infection, while the M2 phenotype is predominant in susceptible environments. Notably, various immune cells, including T cells, play a significant role in modulating macrophage polarization by releasing cytokines that influence macrophage maturation and function. Furthermore, other immune cells can also impact macrophage polarization in a T-cell-independent manner. Therefore, this review comprehensively examines macrophage polarization's role in leishmaniasis and other immune cells' potential involvement in this intricate process.

Deletion of MIF gene from live attenuated LdCen-/- parasites enhances protective CD4+ T cell immunity

Vaccination with live attenuated Leishmania parasites such as centrin deleted Leishmania donovani (LdCen^-/-) against visceral leishmaniasis has been reported extensively. The protection induced by LdCen^-/- parasites was mediated by both CD4⁺ and CD8⁺ T cells. While the host immune mediators of protection are known, parasite determinants that affect the CD4⁺ and CD8⁺ T cell populations remain unknown. Parasite encoded inflammatory cytokine MIF has been shown to modulate the T cell differentiation characteristics by altering the inflammation induced apoptosis during contraction phase in experimental infections with Leishmania or Plasmodium. Neutralization of parasite encoded MIF either by antibodies or gene deletion conferred protection in Plasmodium and Leishmania studies. We investigated if the immunogenicity and protection induced by LdCen^-/- parasites is affected by deleting MIF genes from this vaccine strain. Our results showed that LdCen^-/-MIF^-/- immunized group presented higher percentage of CD4⁺ and CD8⁺ central memory T cells, increased CD8⁺ T cell proliferation after challenge compared to LdCen^-/- immunization. LdCen^-/-MIF^-/- immunized group presented elevated production of IFN-γ⁺ and TNF-α⁺ CD4⁺ T cells concomitant with a reduced parasite load in spleen and liver compared to LdCen^-/-group following challenge with L. infantum. Our results demonstrate the role of parasite induced factors involved in protection and long-term immunity of vaccines against VL.

Gene Signatures of Symptomatic and Asymptomatic Clinical-Immunological Profiles of Human Infection by Leishmania (L.) chagasi in Amazonian Brazil

Individuals infected with Leishmania (L.) chagasi may present different asymptomatic and symptomatic stages of infection, which vary in the clinical–immunological profiles that can be classified as asymptomatic infection (AI), subclinical resistant infection (SRI), indeterminate initial infection (III), subclinical oligosymptomatic infection (SOI), and symptomatic infection (SI) (=American visceral leishmaniasis, AVL). However, little is known about the molecular differences between individuals having each profile. Here, we performed whole-blood transcriptomic analyses of 56 infected individuals from Pará State (Brazilian Amazon), covering all five profiles. We then identified the gene signatures of each profile by comparing their transcriptome with those of 11 healthy individuals from the same area. Symptomatic individuals with SI (=AVL) and SOI profiles showed higher transcriptome perturbation when compared to those asymptomatic III, AI and SRI profiles, suggesting that disease severity may be associated with greater transcriptomic changes. Although the expression of many genes was altered on each profile, very few genes were shared among the profiles. This indicated that each profile has a unique gene signature. The innate immune system pathway was strongly activated only in asymptomatic AI and SRI profiles, suggesting the control of infection. In turn, pathways such as MHC Class II antigen presentation and NF-kB activation in B cells seemed to be specifically induced in symptomatic SI (=AVL) and SOI profiles. Moreover, cellular response to starvation was down-regulated in those symptomatic profiles. Overall, this study revealed five distinct transcriptional patterns associated to the clinical–immunological (symptomatic and asymptomatic) profiles of human L. (L.) chagasi-infection in the Brazilian Amazon.

Humoral response in Leishmaniasis

Leishmaniasis presents different types of clinical manifestations that can be divided into cutaneous leishmaniasis and visceral leishmaniasis. The host's immune system, associated with genetic and nutritional factors, is strongly involved in the evolution of the disease or parasite escape. Humoral immunity is characterized by the production of antibodies capable of promoting neutralization, opsonization, and activation of the complement system. In this scenario, B lymphocytes produce antibodies that play an important role in Leishmania infection although neglected for a long time. Thus, relevant aspects in the establishment of Leishmania infection will be addressed, highlighting the importance of humoral immunity during the entire process of Leishmania infection.

Anti-Leishmania infantum Antibody-Producing Plasma Cells in the Spleen in Canine Visceral Leishmaniasis

The spleen is involved in visceral leishmaniasis immunopathogenesis, and presents alterations in white-pulp microenvironments that are associated with an increased susceptibility to coinfections and patient death. Plasmacytosis in splenic red pulp (RP) is one observed alteration, but the specificity of antibody-secreting cells and the distribution of them has not yet been evaluated. We biotinylated soluble L. infantum membrane antigens (bSLMA) used as probes in modified immunohistochemistry, and detected the presence of anti-L. infantum antibody-secreting cells. Were used spleens from eight dogs from the endemic area for canine visceral leishmaniasis (CanL), and three healthier controls. The spleen sections were cryopreserved, and we performed modified immunohistochemistry. The ratio of plasma cells which were reactive to bSLMA (Anti-Leish-PC) in the spleen RP and periarteriolar lymphatic sheath (PALS) were calculated. Dogs with CanL present hyperglobulinemia and more plasma cells in their RP than the controls. Furthermore, dogs with CanL presented a lower proportion of Anti-Leish-PC in their RP than in PALS. Likewise, dysproteinemia was related to RP and PALS plasmacytosis, and a more severe clinical profile.

Protective Efficacy in a Hamster Model of a Multivalent Vaccine for Human Visceral Leishmaniasis (MuLeVaClin) Consisting of the KMP11, LEISH-F3+, and LJL143 Antigens in Virosomes, Plus GLA-SE Adjuvant

Visceral leishmaniasis (VL) is the most severe clinical form of leishmaniasis, fatal if untreated. Vaccination is the most cost-effective approach to disease control; however, to date, no vaccines against human VL have been made available. This work examines the efficacy of a novel vaccine consisting of the Leishmania membrane protein KMP11, LEISH-F3+ (a recombinant fusion protein, composed of epitopes of the parasite proteins nucleoside hydrolase, sterol-24-c-methyltransferase, and cysteine protease B), and the sand fly salivary protein LJL143, in two dose ratios. The inclusion of the TLR4 agonist GLA-SE as an adjuvant, and the use of virosomes (VS) as a delivery system, are also examined. In a hamster model of VL, the vaccine elicited antigen-specific immune responses prior to infection with Leishmania infantum. Of note, the responses were greater when higher doses of KMP11 and LEISH-F3+ proteins were administered along with the GLA-SE adjuvant and/or when delivered within VS. Remarkably, hamsters immunized with the complete combination (i.e., all antigens in VS + GLA-SE) showed significantly lower parasite burdens in the spleen compared to those in control animals. This protection was underpinned by a more intense, specific humoral response against the KMP11, LEISH-F3+, and LJL143 antigens in vaccinated animals, but a significantly less intense antibody response to the pool of soluble Leishmania antigens (SLA). Overall, these results indicate that this innovative vaccine formulation confers protection against L. infantum infection, supporting the advancement of the vaccine formulation into process development and manufacturing and the conduction of toxicity studies towards future phase I human clinical trials.

Modulation of Splenic B Cell Subsets during Experimental Leishmania donovani Infection in BALB/c Mice

Sodium antimonials are one of the major and common drugs used against visceral form leishmaniasis (VL). However, the development of drug resistance makes it difficult to manage this disease. Current work investigates the modulation of splenic B cells during experimental infection with antimony-sensitive and -resistant Leishmania donovani infection. Here we phenotypically characterized splenic B cell subsets in BALB/c mice infected with antimony drug-sensitive and -resistant VL strains using flow-cytometry method. In the splenocytes we noticed increased number of Transitional T3 B cells and B1a B cells in drug-resistant VL strain infection. Besides, we also observed alteration in Follicular B cell population of antimony-resistant strain infected mice. Drug-resistant strain induced secretion of elevated level of IL-10 from B1a B cells and IL-6 from Transitional T3 B cell subsets in the splenocytes. Purified splenic B cells from antimony drug-resistant strain infected mice showed decrease in the Lyn kinase gene expression compared to sensitive strain infected and uninfected mice. The current study provides insight into changes in host splenic B-cell subsets during experimental infection with antimony-sensitive and -resistant L. donovani in murine model.

Visualizing the In Vivo Dynamics of Anti-Leishmania Immunity: Discoveries and Challenges

Intravital microscopy, such as 2-photon microscopy, is now a mainstay in immunological research to visually characterize immune cell dynamics during homeostasis and pathogen infections. This approach has been especially beneficial in describing the complex process of host immune responses to parasitic infections in vivo, such as Leishmania. Human-parasite co-evolution has endowed parasites with multiple strategies to subvert host immunity in order to establish chronic infections and ensure human-to-human transmission. While much focus has been placed on viral and bacterial infections, intravital microscopy studies during parasitic infections have been comparatively sparse. In this review, we will discuss how in vivo microscopy has provided important insights into the generation of innate and adaptive immunity in various organs during parasitic infections, with a primary focus on Leishmania. We highlight how microscopy-based approaches may be key to providing mechanistic insights into Leishmania persistence in vivo and to devise strategies for better parasite control.

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.

Investigations on the effects of anti-Leishmania major serum on the progression of Leishmania infantum infection in vivo and in vitro - implications of heterologous exposure to Leishmania spp

Leishmaniasis is a vector-borne parasitic disease caused by protozoa of the genus Leishmania. Twenty different species are known to cause disease in humans with varying degrees of pathology. These diseases are transmitted throughout the geographic range of phlebotomine sandflies, found between the latitudes 50°N and 40°S. This study explores antibody dependent enhancement (ADE) as the cause of disease exacerbation in heterologous exposure of L. major primed mice to L. infantum challenge. BALB/c mice received serum from L. major infected or naive mice. All mice were challenged with L. infantum and tissue parasite burdens were recorded. Animals that received anti-L. major serum exhibited significantly higher parasite burdens. Surprisingly, these parasite burdens were higher than those of mice infected with L. major and challenged with L. infantum. In vitro phagocytosis assays were carried out to measure parasite uptake in the presence of naive vs. anti-L. major serum. J774A.1 murine monocytes were cultured with either L. major or L. infantum in the presence of anti-L. major serum, naive serum, or no serum. Significantly higher rates of L. major uptake by J774A.1 cells occurred in the presence of anti-L. major serum, but no measurable increase of L. infantum phagocytosis was seen. Our results suggest that increased disease severity observed in vivo in mice previously exposed to L. major and challenged with L infantum is not a result of extrinsic ADE. We speculate that intrinsic ADE, due to biased memory T cell responses caused by Fcγ signaling, could account for disease exacerbation seen in the animal model.

Immune response dynamics and Lutzomyia longipalpis exposure characterize a biosignature of visceral leishmaniasis susceptibility in a canine cohort

Background

Reports have shown correlations between the immune response to vector saliva and Leishmaniasis outcome. We followed dogs in an endemic area for two years characterizing resistance or susceptibility to canine visceral leishmaniasis (CVL) according to Leishmania infantum diagnosis and clinical development criteria. Then, we aimed to identify a biosignature based on parasite load, serum biological mediators’ interactions, and vector exposure intensity associated with CVL resistance and susceptibility.

Methodology/Principal findings

A prospective two-year study was conducted in an area endemic for CVL. Dogs were evaluated at 6-month intervals to determine infection, clinical manifestations, immune profile, and sandfly exposure. CVL resistance or susceptibility was determined upon the conclusion of the study. After two years, 78% of the dogs were infected with L. infantum (53% susceptible and 47% resistant to CVL). Susceptible dogs presented higher splenic parasite load as well as persistence of the parasite during the follow-up, compared to resistant ones. Susceptible dogs also displayed a higher number of correlations among the investigated biological mediators, before and after infection diagnosis. At baseline, anti-saliva antibodies, indicative of exposure to the vector, were detected in 62% of the dogs, reaching 100% in one year. Higher sandfly exposure increased the risk of susceptibility to CVL by 1.6 times (CI: 1.11–2.41). We identified a discriminatory biosignature between the resistant and susceptible dogs assessing splenic parasite load, interaction of biological mediators, PGE₂ serum levels and intensity of exposure to sandfly. All these parameters were elevated in susceptible dogs compared to resistant animals.

Conclusions/Significance

The biosignature identified in our study reinforces the idea that CVL is a complex multifactorial disease that is affected by a set of factors which are correlated and, for a better understanding of CVL, should not be evaluated in an isolated way.

Visceral Leishmaniasis (VL) is a disease that can affect humans and dogs, caused by a parasite called Leishmania transmitted through the bite of sandfly insects. During the bite, together with the parasite, the insects also inoculate their saliva into the host. The host immune response produces molecules to the sandfly saliva, such as antibodies and cytokines that can impact VL resistance or susceptibility. The presence of these molecules also indicates if the insects bit the hosts. We followed dogs of a VL endemic area for two years to study Canine Visceral Leishmaniasis (CVL) and immune response to sandfly saliva. Dogs were evaluated at 6-month intervals to determine Leishmania infection, clinical manifestations, parasite load, immune response, and sandfly exposure. CVL resistance or susceptibility was determined upon the conclusion of the study. Dogs living in the endemic area were intensely bitten, as at the beginning of the study, 62% of the dogs present anti-saliva antibodies, reaching 100% after one year. Our findings revealed a biosignature of CVL susceptibility characterized by elevated parasite load, interaction of cytokines, and higher exposure to the sandfly. This data reinforced that CVL is a complex disease affected by several factors related to each other.

Role of Cytokines in Experimental and Human Visceral Leishmaniasis

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

Leishmania Immunity: Advancing Immunotherapy and Vaccine Development

Parasitic diseases still constitute a major global health problem affecting billions of people around the world. These diseases are capable of becoming chronic and result in high morbidity and mortality. Worldwide, millions of people die each year from parasitic diseases, with the bulk of those deaths resulting from parasitic protozoan infections. Leishmaniasis, which is a disease caused by over 20 species of the protozoan parasite belonging to the genus Leishmania, is an important neglected disease. According to the World Health Organization (WHO), an estimated 12 million people are currently infected in about 98 countries and about 2 million new cases occur yearly, resulting in about 50,000 deaths each year. Current treatment methods for leishmaniasis are not very effective and often have significant side effects. In this review, we discussed host immunity to leishmaniasis, various treatment options currently being utilized, and the progress of both immunotherapy and vaccine development strategies used so far in leishmaniasis. We concluded with insights into what the future holds toward the fight against this debilitating parasitic disease.

Abnormal B-Cell Subset and Blimp-1-Mediated Humoral Responses Associated With Visceral Leishmaniasis Pathogenesis

B-cells have a spectrum of functions ranging from antibody production to antigen presentation and have additional vital roles in immune mechanisms. There is rudimentary knowledge about the role of B-cells in intracellular infections with contradictory findings. We explored the role of B-cell dysfunctions in visceral leishmaniasis (VL) pathogenesis in terms of the phenotypic and functional properties of B-cells during the course of disease. This study was performed on blood and splenic aspirates (SA) of VL cases pre- and post-treatment. Whole blood was used for flow cytometric studies for determining the profiles of B-cells at different time-points of treatment. Peripheral blood mononuclear cells were used for magnetic purification of B-cells, for transcriptional studies by real-time polymerase chain reaction (RT-PCR). Serum/plasma was used for direct agglutination test for determining parasite-specific antibodies and SA were used for scoring the presence of parasite by microscopic examination. Flow cytometric studies depicted decreased B-cell percentages during the entire course of disease and attainment of exhaustive phenotype with tissue-like memory cell markers, indicative of B-cell dysfunctions in VL. In addition, B-cells had compromised abilities of antigen processing and presentation and altered levels of B-lymphocyte-induced maturation protein-1 (Blimp-1). Blimp-1 expression goes hand in hand with B-cell maturation antigen and transmembrane activator and calcium modulator (TACI) and cyclophilin ligand interactor, suggestive of its role in promoting plasma cell survival and antibody production. Elevated level of VL-specific antibody titre was directly correlated with exhausted phenotype and also with disease severity during VL. This study indicated for impaired B-cell functions during chronic infection which may lead to pathological consequences in human VL.

How to B(e)-1 Important Cell During Leishmania Infection

B-1 cells are an innate-like population of B lymphocytes that are subdivided into B-1a and B-1b distinguished by the presence or absence of CD5, respectively. B-1 cells can act as regulatory B cells, are able to present antigen and produce IL-10. Leishmaniasis in humans is a complex of diseases caused by parasites of the genus Leishmania. More than 20 species can infect humans, with each species causing the development of different immunological responses in the host. Susceptibility is usually related to the production of anti-inflammatory cytokines while the production of Th1 cytokines is indicative of resistance. However, few studies have attempted to evaluate the role of B-1 cells during either the in vivo infection or in vitro interaction with Leishmania parasites. In vivo studies were performed using XID mice model, BALB/Xid mice have a mutation in the Bruton's tyrosine kinase, which is an important enzyme for developing B-1 and maturing B-2 lymphocytes leading to the presence of immature B-2 cells. Here, we compile these studies and assess the influence of B-1 cells on disease progression with different Leishmania species.

The Potent ITK/BTK Inhibitor Ibrutinib Is Effective for the Treatment of Experimental Visceral Leishmaniasis Caused by Leishmania donovani

Background

New drugs are needed for leishmaniasis because current treatments such as pentavalent antimonials are toxic and require prolonged administration, leading to poor patient compliance. Ibrutinib is an anticancer drug known to modulate T-helper type 1 (Th1)/Th2 responses and has the potential to regulate immunity against infectious disease.

Methods

In this study, we evaluated the efficacy of oral ibrutinib as a host-targeted treatment for visceral leishmaniasis (VL) caused by Leishmania donovani using an experimental mouse model.

Results

We found that oral ibrutinib was significantly more effective than the pentavalent antimonial sodium stibogluconate (70 mg/kg) for the treatment of VL caused by L. donovani. Ibrutinib treatment increased the number of interleukin 4- and interferon γ-producing natural killer T cells in the liver and spleen and enhanced granuloma formation in the liver. Further, ibrutinib treatment reduced the influx of Ly6Chi inflammatory monocytes, which mediate susceptibility to L. donovani. Finally, ibrutinib treatment was associated with the increased production of the cytokines interferon γ, tumor necrosis factor α, interleukin 4, and interleukin 13 in the liver and spleen, which are associated with protection against L. donovani.

Conclusions

Our findings show that oral ibrutinib is highly effective for the treatment of VL caused by L. donovani and mediates its antileishmanial activity by promoting host immunity. Therefore, ibrutinib could be a novel host-targeted drug for the treatment of VL.

B-1 lymphocytes are able to produce IL-10, but is not pathogenic during Leishmania (Leishmania) amazonensis infection

Over the years research has found an association between B lymphocytes and pathogenesis during Leishmania sp. infections. Recently we demonstrated that B-2 lymphocytes are the main producers of IL-10 during L. amazonensis infection, and that the disease severity in BALB/c mice was attributed to these IL-10-producing B-2 lymphocytes. Here, we aim to understand the role of peritoneal B-1 lymphocytes in the pathogenesis of L. amazonensis infection. We found that infection resulted in a decrease in the number of B-1a lymphocytes and increase in B-1b lymphocytes in the peritoneal cavity of WT BALB/c mice but not in B lymphocyte deficient mice (BALB/Xid) mice. In vitro interaction between B-1 lymphocytes and L. amazonensis showed that the amastigote form of the parasite was able to induce higher levels of IL-10 in B-1 lymphocytes derived from infected BALB/c mice than the promastigote. Moreover, B-1 lymphocytes derived from infected mice produced more IL-10 than B-1 lymphocytes derived from naïve mice under amastigote interaction. However, the repopulation of BALB/Xid mice with B-1 lymphocytes from WT BALB/c mice did not affect the lesion development. Together, these results suggest that although B-1 lymphocytes are able to produce IL-10 during in vitro interaction with L. amazonensis, they are not directly related to pathogenesis in vivo.

IL-4 Mediated Resistance of BALB/c Mice to Visceral Leishmaniasis Is Independent of IL-4Rα Signaling via T Cells

Previous studies infecting global IL-4Rα^−/−, IL-4^−/−, and IL-13^−/−mice on a BALB/c background with the visceralizing parasite Leishmania donovani have shown that the T helper 2 cytokines, IL-4, and IL-13, play influential but not completely overlapping roles in controlling primary infection. Subsequently, using macrophage/neutrophil-specific IL-4Rα deficient BALB/c mice, we demonstrated that macrophage/neutrophil unresponsiveness to IL-4 and IL-13 did not have a detrimental effect during L. donovani infection. Here we expand on these findings and show that CD4⁺ T cell-(Lck^cre), as well as pan T cell-(iLck^cre) specific IL-4Rα deficient mice, on a BALB/c background, unlike global IL-4Rα deficient mice, are also not adversely affected in terms of resistance to primary infection with L. donovani. Our analysis suggested only a transient and tissue specific impact on disease course due to lack of IL-4Rα on T cells, limited to a reduced hepatic parasite burden at day 30 post-infection. Consequently, the protective role(s) demonstrated for IL-4 and IL-13 during L. donovani infection are mediated by IL-4Rα-responsive cell(s) other than macrophages, neutrophils and T cells.

Hypergammaglobulinemia sustains the development of regulatory responses during chronic Leishmania donovani infection in mice

Visceral leishmaniasis, a chronic, potentially fatal disease, is characterized by high production of low-affinity antibodies. In humans, hypergammaglobulinemia is prediction of disease progression. Nevertheless, the contribution of hypermutated and/or class-switched immunoglobulins to disease pathogenesis has never been studied. Using Aicda^-/- mice and the experimental model of Leishmania donovani infection, we demonstrate that the absence of hypermutated and/or class-switched antibodies was associated with increased resistance to disease, stronger protective Th1 responses, and a lower frequency of regulatory IFNγ⁺ IL-10⁺ CD4 T cells. Interestingly, stronger Th1 responses and the absence of IFNγ⁺ IL-10⁺ CD4 T cells during chronic infection in infected Aicda^-/- mice were not caused by a T-cell intrinsic effect of AID, but by changes in the cytokine environment during chronic disease. Indeed TNF, IL-10 and IFN-ß expressions were only upregulated in the presence of hypermutated, class-switched antibodies and hypergammaglobulinemia at later stages of infection. Taken together, our results suggest that hypergammaglobulinemia sustains inhibitory responses during chronic visceral leishmaniasis.

Evaluation of antileishmanial efficacy of Salidroside against the SSG-sensitive and resistant strain of Leishmania donovani

The successful control and eradication of leishmaniasis are still challenging in view of the lack of adequate chemotherapy and potential prophylaxis. Research is going on for finding an appropriate anti-leishmanial drug which should be acceptable in terms of cost and safety. In view of this, the current study investigated the anti-leishmanial efficacy of salidroside (SAL) which is a phenylpropanoid glycoside. The leishmanicidal capacity of SAL was verified in vitro as well as in vivo. The SAL exhibited leishmanicidal activity against the promastigotes of L. donovani which was further validated by propidium iodide staining and its ability to arrest the promastigotes at the sub G₀/G₁ stage. SAL decreased and controlled the VL infection in mice as estimated by real-time PCR. Active immunomodulation was exhibited upon SAL treatment in BALB/c mice. The characteristic features like pronounced DTH reaction, polarization of immune status to Th1 type of immune response, increased the production of CD4⁺ and CD8⁺ T cells indicated the immune-stimulatory property of SAL. In addition to this the expression of NF-ĸB, iNOS genes along with the levels of leishmanicidal species, NO and ROS were found to be augmented in SAL treated infected animals. Moreover, SAL exhibited minimal toxicity to the THP-1 cells and it revealed no toxicity against liver and kidney. The capability of SAL in promoting the immune status in favor of host during VL infection without causing any side-effects may be used as an effective strategy to fight the disease.

Pam3CSK4 adjuvant given intranasally boosts anti-Leishmania immunogenicity but not protective immune responses conferred by LaAg vaccine against visceral leishmaniasis

The use of adjuvants in vaccine formulations is a well-established practice to improve immunogenicity and protective immunity against diseases. Previously, we have demonstrated the feasibility of intranasal vaccination with the antigen of killed Leishmania amazonensis promastigotes (LaAg) against experimental leishmaniasis. In this work, we sought to optimize the immunogenic effect and protective immunity against murine visceral leishmaniasis conferred by intranasal delivery of LaAg in combination with a synthetic TLR1/TLR2 agonist (Pam3CSK4). Intranasal vaccination with LaAg/PAM did not show toxicity or adverse effects, induced the increase of delayed-type hypersensitivity response and the production of inflammatory cytokines after parasite antigen recall. However, mice vaccinated with LaAg/PAM and challenged with Leishmania infantum presented significant reduction of parasite burden in both liver and spleen, similar to those vaccinated with LaAg. Although LaAg/PAM intranasal vaccination had induced higher frequencies of specific CD4⁺ and CD8⁺ T cells and increased levels of IgG2a antibody isotype in serum, both LaAg and LaAg/PAM groups presented similar levels of IL-4 and IFN-y and decreased production of IL-10 when compared to controls. Our results provide the first evidence of the feasibility of intranasal immunization with antigens of killed Leishmania in association with a TLR agonist, which may be explored for developing an effective and alternative strategy for vaccination against visceral leishmaniasis.

The circulating immunoglobulins negatively impact on the parasite clearance in the liver of Leishmania donovani-infected mice via dampening ROS activity

Visceral leishmaniasis, the most severe form of leishmaniasis, is caused by Leishmania donovani and L. infantum. Immunity to Leishmania infection has been shown to depend on the development of Th1 cells; however, the roles of B cells and antibodies during infection remain unclear. In the present study, we showed that AID and μs double-deficient mice (DKO), which have B cells but not circulating immunoglobulins (cIgs), became resistant to L. donovani infection, whereas μs or AID single-deficient mice did not. This resistance in DKO mice occurred in the liver from an early stage of the infection. The depletion of IFN-γ did not affect the rapid reduction of parasite burden, whereas NADPH oxidases was up-regulated in the livers of infected DKO mice. The inhibition of the reactive oxygen species pathway in vivo by apocynin, a NADPH oxidase inhibitor, resulted in a significant increase in the parasite burden in DKO mice. These results indicate that a circulating Ig deficiency induces a protective response against L. donovani infection by elevating IFN-γ-independent NADPH oxidase activity, and also that cIgs play a regulatory role in controlling L. donovani infection in mice.

High-through identification of T cell-specific phage-exposed mimotopes using PBMCs from tegumentary leishmaniasis patients and their use as vaccine candidates against Leishmania amazonensis infection

In the current study, phage-exposed mimotopes as targets against tegumentary leishmaniasis (TL) were selected by means of bio-panning cycles employing sera of TL patients and healthy subjects, besides the immune stimulation of peripheral blood mononuclear cells (PBMCs) collected from untreated and treated TL patients and healthy subjects. The clones were evaluated regarding their specific interferon-γ (IFN-γ) and interleukin-4 (IL-4) production in the in vitro cultures, and selectivity and specificity values were calculated, and those presenting the best results were selected for the in vivo experiments. Two clones, namely A4 and A8, were identified and used in immunization protocols from BALB/c mice to protect against Leishmania amazonensis infection. Results showed a polarized Th1 response generated after vaccination, being based on significantly higher levels of IFN-γ, IL-2, IL-12, tumour necrosis factor-α (TNF-α) and granulocyte-macrophage colony-stimulating factor (GM-CSF); which were associated with lower production of specific IL-4, IL-10 and immunoglobulin G1 (IgG1) antibodies. Vaccinated mice presented significant reductions in the parasite load in the infected tissue and distinct organs, when compared with controls. In conclusion, we presented a strategy to identify new mimotopes able to induce Th1 response in PBMCs from TL patients and healthy subjects, and that were successfully used to protect against L. amazonensis infection.

Analysis of the Antigenic and Prophylactic Properties of the Leishmania Translation Initiation Factors eIF2 and eIF2B in Natural and Experimental Leishmaniasis

Different members of intracellular protein families are recognized by the immune system of the vertebrate host infected by parasites of the genus Leishmania. Here, we have analyzed the antigenic and immunogenic properties of the Leishmania eIF2 and eIF2B translation initiation factors. An in silico search in Leishmania infantum sequence databases allowed the identification of the genes encoding the α, β, and γ subunits and the α, β, and δ subunits of the putative Leishmania orthologs of the eukaryotic initiation factors F2 (LieIF2) or F2B (LieIF2B), respectively. The antigenicity of these factors was analyzed by ELISA using recombinant versions of the different subunits. Antibodies against the different LieIF2 and LieIF2B subunits were found in the sera from human and canine visceral leishmaniasis patients, and also in the sera from hamsters experimentally infected with L. infantum. In L. infantum (BALB/c) and Leishmania major (BALB/c or C57BL/6) challenged mice, a moderate humoral response against these protein factors was detected. Remarkably, these proteins elicited an IL-10 production by splenocytes derived from infected mice independently of the Leishmania species employed for experimental challenge. When DNA vaccines based on the expression of the LieIF2 or LieIF2B subunit encoding genes were administered in mice, an antigen-specific secretion of IFN-γ and IL-10 cytokines was observed. Furthermore, a partial protection against murine CL development due to L. major infection was generated in the vaccinated mice. Also, in this work we show that the LieIF2α subunit and the LieIF2Bβ and δ subunits have the capacity to stimulate IL-10 secretion by spleen cells from naïve mice. B-lymphocytes were identified as the major producers of this anti-inflammatory cytokine. Taking into account the data found in this study, it may be hypothesized that these proteins act as virulence factors implicated in the induction of humoral responses as well as in the production of the down-regulatory IL-10 cytokine, favoring a pathological outcome. Therefore, these proteins might be considered markers of disease.

The Deadly Dance of B Cells with Trypanosomatids

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

Evaluation of Experimental Infection with L. ( L.) Amazonensis in X-Linked Immunodeficient Mice

B-1 cells are a subtype of B cells with peculiar characteristics. These cells are distinct from B-2 lymphocytes in their morphology, ontogeny, tissue distribution, and phenotypic functional features. B-1 cells can participate in the immune response in several ways, for example, by being recruited to inflammatory foci, producing large amounts of IL-10 cytokine, and differentiating into IgM-secreting cells or phagocytes. Nevertheless, the role of B-1 cells in the pathogenesis of experimental leishmaniasis has not been fully elucidated. Here we evaluated the role of B-1 cells in Leishmania ( L.) amazonensis infection using X-linked immunodeficient (XID) mice that possess a mutation in Bruton's tyrosine kinase (Btk) that leads to a reduced number of B-1 cells. The course of infection and the corresponding immune response were analyzed in infected mice. XID mice showed an increase in parasite number in paws, lymph nodes, and spleen compared to BALB/c infected controls. Infected XID mice had higher IL-10 levels and lower anti- Leishmania IgM. The adoptive transfer of peritoneal B-1 cells into XID mice restored peritoneal B-1 cells and parasite burden in the footpad in a pattern similar to that observed in the BALB/c controls at 10 wk. Our results demonstrate the higher susceptibility of XID mice to infection with L. ( L.) amazonensis compared to controls. In addition, we show that the presence of B-1 cells contributes to improved animal resistance to parasites, suggesting that these cells are involved in the control of cutaneous infection caused by L. ( L.) amazonensis.

Dependency of B-1 Cells in the Maintenance of Splenic Interleukin-10 Producing Cells and Impairment of Macrophage Resistance in Visceral Leishmaniasis

Visceral leishmaniasis is a neglected disease caused by Leishmania protozoa parasites transmitted by infected sand fly vectors. This disease represents the second in mortality among tropical infections and is associated to a profound immunosuppression state of the host. The hallmark of this infection-induced host immunodeviation is the characteristic high levels of the regulatory interleukin-10 (IL-10) cytokine. In the present study, we investigated the role of B-1 cells in the maintenance of splenic IL-10 levels that could interfere with resistance to parasite infection. Using an experimental murine infection model with Leishmania (L.) infantum chagasi we demonstrated an improved resistance of B-1 deficient BALB/XID mice to infection. BALB/XID mice developed a reduced splenomegaly with diminished splenic parasite burden and lower levels of IL-10 secretion of purified splenocytes at 30 days post-infection, as compared to BALB/c wild-type control mice. Interestingly, we found that resident peritoneal macrophages isolated from BALB/XID mice were more effective to control the parasite load in comparison to cells isolated from BALB/c wild-type mice. Our findings point to a role of B-1 cells in the host susceptibility to visceral leishmaniasis.

What do we know about the role of regulatory B cells (Breg) during the course of infection of two major parasitic diseases, malaria and leishmaniasis?

Parasitic diseases, such as malaria and leishmaniasis, are relevant public health problems worldwide. For both diseases, the alarming number of clinical cases and deaths reported annually has justified the incentives directed to better understanding of host's factors associated with susceptibility to infection or protection. In this context, over recent years, some studies have given special attention to B lymphocytes with a regulator phenotype, known as Breg cells. Essentially important in the maintenance of immunological tolerance, especially in autoimmune disease models such as rheumatoid arthritis and experimentally induced autoimmune encephalomyelitis, the function of these lymphocytes has so far been poorly explored during the course of diseases caused by parasites. As the activation of Breg cells has been proposed as a possible therapeutic or vaccine strategy against several diseases, here we reviewed studies focused on understanding the relation of parasite and Breg cells in malaria and leishmaniasis, and the possible implications of these strategies in the course of both infections.

Transcriptional Profiling in Experimental Visceral Leishmaniasis Reveals a Broad Splenic Inflammatory Environment that Conditions Macrophages toward a Disease-Promoting Phenotype

Visceral Leishmaniasis (VL), caused by the intracellular protozoan Leishmania donovani, is characterized by relentlessly increasing visceral parasite replication, cachexia, massive splenomegaly, pancytopenia and ultimately death. Progressive disease is considered to be due to impaired effector T cell function and/or failure of macrophages to be activated to kill the intracellular parasite. In previous studies, we used the Syrian hamster (Mesocricetus auratus) as a model because it mimics the progressive nature of active human VL. We demonstrated previously that mixed expression of macrophage-activating (IFN-γ) and regulatory (IL-4, IL-10, IL-21) cytokines, parasite-induced expression of macrophage arginase 1 (Arg1), and decreased production of nitric oxide are key immunopathologic factors. Here we examined global changes in gene expression to define the splenic environment and phenotype of splenic macrophages during progressive VL. We used RNA sequencing coupled with de novo transcriptome assembly, because the Syrian hamster does not have a fully sequenced and annotated reference genome. Differentially expressed transcripts identified a highly inflammatory spleen environment with abundant expression of type I and type II interferon response genes. However, high IFN-γ expression was ineffective in directing exclusive M1 macrophage polarization, suppressing M2-associated gene expression, and restraining parasite replication and disease. While many IFN-inducible transcripts were upregulated in the infected spleen, fewer were induced in splenic macrophages in VL. Paradoxically, IFN-γ enhanced parasite growth and induced the counter-regulatory molecules Arg1, Ido1 and Irg1 in splenic macrophages. This was mediated, at least in part, through IFN-γ-induced activation of STAT3 and expression of IL-10, which suggests that splenic macrophages in VL are conditioned to respond to macrophage activation signals with a counter-regulatory response that is ineffective and even disease-promoting. Accordingly, inhibition of STAT3 activation led to a reduced parasite load in infected macrophages. Thus, the STAT3 pathway offers a rational target for adjunctive host-directed therapy to interrupt the pathogenesis of VL.

Visceral leishmaniasis (VL) is a neglected parasitic disease that is caused by the intracellular protozoan Leishmania donovani. Patients with this disease suffer from muscle wasting, enlargement of the spleen, reduced blood counts and ultimately will die without treatment. Progressive disease is considered to be due to impaired cellular immunity, with T cell or macrophage dysfunction, or both. We studied the Syrian hamster as an infection model because it mimics the progressive nature of human disease. We examined global changes in gene expression in the spleen and splenic macrophages during experimental VL and identified a highly inflammatory spleen environment with abundant expression of interferon and interferon-response genes that would be expected to control the infection. However, the high level of IFN-γ expression was ineffective in mediating a protective macrophage response, restraining parasite replication and halting progression of disease. We found that IFN-γ itself stimulated parasite growth in splenic macrophages and induced expression of counter-regulatory molecules, which may paradoxically make the host more susceptible. These data give insights into the nature of the immune response that promotes the infection, and identifies potential targets for therapeutic intervention.

Protozoan Parasites and Type I IFNs

For many years, the role of interferon (IFN)-I has been characterized primarily in the context of viral infections. However, regulatory functions mediated by IFN-I have also been described against bacterial infections and in tumor immunology. Only recently, the interest in understanding the immune functions mediated by IFN-I has dramatically increased in the field of protozoan infections. In this review, we discuss the discrete role of IFN-I in the immune response against major protozoan infections: Plasmodium, Leishmania, Trypanosoma, and Toxoplasma.

Comment on "Regulation of immunity during visceral Leishmania infection" and further discussions about the role of antibodies in infections with Leishmania

Comments on the article "Regulation of immunity during visceral Leishmania infection" published in Parasites & Vectors 2016, 9:118, and further discussions about the role of antibodies in infections with Leishmania.

In vitro activity and in vivo efficacy of a combination therapy of diminazene and chloroquine against murine visceral leishmaniasis

The present study evaluated the in vitro activity and in vivo efficacy of diminazene combined with chloroquine as a potential drug against Leishmania donovani. Amphotericin B was used as a positive control drug. In vitro activity involved incubation of various drug concentrations with promastigotes or vero cells in culture before determination of parasite growth inhibition or cell death while in vivo evaluations involved infection of various mice groups with virulent L. donovani parasites and treatment with test drug compounds following disease establishment. Weight changes in experimental mice were also evaluated before infection and throughout the experiment. The results indicated that the diminazene–chloroquine combination was at least nine times more efficacious than individual drugs in killing promastigotes in culture. The diminazene–chloroquine combination was safer (Ld₅₀ = 0.03±0.04) than Amphotericin B (Ld₅₀ = 0.02±0.01). Body weight in infected mice increased significantly (P = 0.0007) from day 7 to day 37 following infection (P = 0.026). However, body weight remained comparable in all mice groups during treatment (P = 0.16). The diminazene–chloroquine combination significantly reduced splenic parasite numbers as compared to individual drug therapies (P = 0.0001) although Amphotericin B was still more efficacious than any other treatment (P = 0.0001). Amongst the test compounds, the diminazene–chloroquine combination showed the lowest level of IgG antibody responses with results indicating significant negative correlation between antileishmanial antibody responses and protection against disease. These findings demonstrate the positive advantage and the potential use of a combined therapy of diminazene–chloroquine over the constituent drugs. Further evaluation is recommended to determine the most efficacious combination ratio of the two compounds.

Leishmania infantum amastigotes trigger a subpopulation of human B cells with an immunoregulatory phenotype

Visceral leishmaniasis is caused by the protozoan parasites Leishmania infantum and Leishmania donovani. This infection is characterized by an uncontrolled parasitization of internal organs which, when left untreated, leads to death. Disease progression is linked with the type of immune response generated and a strong correlation was found between disease progression and serum levels of the immunosuppressive cytokine IL-10. Other studies have suggested a role for B cells in the pathology of this parasitic infection and the recent identification of a B-cell population in humans with regulatory functions, which secretes large amounts of IL-10 following activation, have sparked our interest in the context of visceral leishmaniasis. We report here that incubation of human B cells with Leishmania infantum amastigotes resulted in upregulation of multiple cell surface activation markers and a dose-dependent secretion of IL-10. Conditioned media from B cells incubated with Leishmania infantum amastigotes were shown to strongly inhibit CD4⁺ T-cell activation, proliferation and function (i.e. as monitored by TNF and IFNγ secretion). Blockade of IL-10 activity using a soluble IL-10 receptor restored only partially TNF and IFNγ production to control levels. The parasite-mediated IL-10 secretion was shown to rely on the activity of Syk, phosphatidylinositol-3 kinase and p38, as well as to require intracellular calcium mobilization. Cell sorting experiments allowed us to identify the IL-10-secreting B-cell subset (i.e. CD19⁺CD24⁺CD27^-). In summary, exposure of human B cells to Leishmania infantum amastigotes triggers B cells with regulatory activities mediated in part by IL-10, which could favor parasite dissemination in the organism.

Leishmaniasis is an infection caused by protozoan parasites of the genus Leishmania and is a significant neglected tropical disease, with 350 million people in 98 countries at risk of developing one of the forms of the disease. Visceral leishmaniasis is characterized by an uncontrolled parasitization of internal organs, which leads to death when left untreated. Disease progression is linked with the type of immune response generated and a strong correlation was found between disease progression and serum levels of the immunosuppressive cytokine IL-10. We demonstrate that a contact between human B cells with Leishmania infantum amastigotes resulted in upregulation of multiple cell surface activation markers and a dose-dependent secretion of IL-10. Conditioned media from B cells incubated with Leishmania infantum amastigotes were shown to strongly inhibit CD4⁺ T-cell activation, proliferation and function (i.e. TNF and IFNγ production). Blockade of IL-10 activity using a soluble IL-10 receptor restored to some degree TNF and IFNγ secretion. Cell sorting experiments allowed us to identify a major IL-10-secreting B cell subset characterized as CD24⁺ and CD27^-. Exposure of human B cells to Leishmania infantum amastigotes thus triggers B cells with regulatory activities mediated in part by IL-10, which could promote parasite dissemination in the organism.

Severity of old world cutaneous leishmaniasis is influenced by previous exposure to sandfly bites in Saudi Arabia

BACKGROUND

The sandfly Phlebotomus papatasi is the vector of Leishmania major, the main causative agent of Old World cutaneous leishmaniasis (CL) in Saudi Arabia. Sandflies inject saliva while feeding and the salivary protein PpSP32 was previously shown to be a biomarker for bite exposure. Here we used recombinant PpSP32 to evaluate human exposure to Ph. papatasi bites, and study the association between antibody response to saliva and CL in endemic areas in Saudi Arabia.

METHODOLOGY/PRINCIPAL FINDINGS

In this observational study, anti-PpSP32 antibodies, as indicators of exposure to sandfly bites, were measured in sera from healthy individuals and patients from endemic regions in Saudi Arabia with active and cured CL. Ph. papatasi was identified as the primary CL vector in the study area. Anti-PpSP32 antibody levels were significantly higher in CL patients presenting active infections from all geographical regions compared to CL cured and healthy individuals. Furthermore, higher anti-PpSP32 antibody levels correlated with the prevalence and type of CL lesions (nodular vs. papular) observed in patients, especially non-local construction workers.

CONCLUSIONS

Our findings suggest a possible correlation between the type of immunity generated by the exposure to sandfly bites and disease outcome.

Clinical severity of visceral leishmaniasis is associated with changes in immunoglobulin g fc N-glycosylation

Visceral leishmaniasis (VL) has a high fatality rate if not treated; nevertheless, the majority of human infections with the causative agent, Leishmania infantum chagasi, are asymptomatic. Although VL patients often present with increased levels of serum immunoglobulins, the contribution of antibodies to resistance or progression to disease remains unknown. Effector and regulatory functions of antibodies rely on their interactions with type I and II Fc receptors, and these interactions are tuned by the patterns of antibody Fc N-glycosylation. In view of these facts, we applied a robust method of IgG Fc N-glycopeptide profiling of serum samples from 187 patients with VL, 177 asymptomatic individuals, 116 endemic controls (individuals residing in areas where VL is endemic) and 43 nonendemic controls (individuals living in an area where VL is not endemic). We show that, in comparison to the overall IgG Fc N-glycan profiles of asymptomatic or uninfected healthy individuals, those of patients with VL are profoundly altered. These changes correlate with levels of serum cytokines and the inflammation marker C-reactive protein. We also fitted univariate and multivariate ordinal logistic regression models to demonstrate the ability of IgG Fc N-glycosylation features and immunity regulators present in serum to predict disease severity in VL patients. Importantly, we show that Fc N-glycosylation profiles change after treatment of VL. This study introduces important concepts contributing to the understanding of antibody responses in infections with Leishmania parasites and provides new insights into the pathology of human VL.

Immunoglobulins (Ig) have been shown to present pro- and anti-inflammatory functions according to the profile of carbohydrates attached to their Fc region. Glycosylation features of serum IgG have been examined in relation to several autoimmune and infectious diseases and provide a mechanistic basis for the protective or pathogenic role of antibodies. Leishmania infantum chagasi is the causative agent of visceral leishmaniasis (VL) in South America, and we show that VL patients produce IgG with patterns of Fc glycans similar to those found in other inflammatory conditions. Specific Fc N-glycosylation features and levels of serum cytokines and C-reactive protein are significantly associated with the development of severe clinical symptoms and, notably, Fc glycosylation changes after treatment. The modifications detected in the N-glycosylation features of IgG Fc from VL patients raise new perspectives on the effector or regulatory role of antibodies in immune responses elicited by infection with Leishmania parasites.

Immune responses during cutaneous and visceral leishmaniasis

SUMMARY Leishmania are protozoan parasites spread by a sandfly insect vector and causing a spectrum of diseases collectively known as leishmaniasis. The disease is a significant health problem in many parts of the world, resulting in an estimated 1·3 million new cases and 30 000 deaths annually. Current treatment is based on chemotherapy, which is difficult to administer, expensive and becoming ineffective in several endemic regions. To date there is no vaccine against leishmaniasis, although extensive evidence from studies in animal models indicates that solid protection can be achieved upon immunization. This review focuses on immune responses to Leishmania in both cutaneous and visceral forms of the disease, pointing to the complexity of the immune response and to a range of evasive mechanisms utilized by the parasite to bypass those responses. The amalgam of innate and acquired immunity combined with the paucity of data on the human immune response is one of the major problems currently hampering vaccine development and implementation.

Abortive T follicular helper development is associated with a defective humoral response in Leishmania infantum-infected macaques

Leishmania infantum causes a chronic infectious disease named visceral leishmaniasis (VL). We employed a non-human primate model to monitor immune parameters over time and gain new insights into the disease. Rhesus macaques were infected with L. infantum and the T helper and B cell immunological profiles characterized during acute and chronic phases of infection. Parasite detection in visceral compartments during the acute phase was associated with differentiation of effector memory CD4 T cells and increased levels of Th1 transcripts. At the chronic phase, parasites colonized novel lymphoid niches concomitant with increased expression of IL10. Despite the occurrence of hypergammaglobulinemia, the production of parasite-specific IgG was poor, being confined to the acute phase and positively correlated with the frequency of an activated memory splenic B cell population. We noticed the expansion of a splenic CD4 T cell population expressing CXCR5 and Bcl-6 during acute infection that was associated with the differentiation of the activated memory B cell population. Moreover, the number of splenic germinal centers peaked at one month after infection, hence paralleling the production of specific IgG. However, at chronic infection these populations contracted impacting the production of parasite-specific IgG. Our study provides new insights into the immune events taking place in a physiologically relevant host and a mechanistic basis for the inefficient humoral response during VL.

Immune responses of Iranian patients with visceral leishmaniasis and recovered individuals to LCR1 of Leishmania infantum

Visceral leishmaniasis is a serious public health problem. Leishmania infantum is one of its causative agents. LCR1 is an immunogen from L. infantum. Antibodies against this protein have been detected in visceral leishmaniasis patients. The aim of this study was to define the antibody and cellular immune responses against LCR1 in Iranian visceral leishmaniasis patients and recovered individuals. The LCR1 protein was produced in recombinant form. Antibody responses against this protein were studied in Iranian individuals with a recent history of visceral leishmaniasis. Responses of peripheral blood mononuclear cells to this protein were studied in Iranian individuals who had recovered from visceral leishmaniasis. Our data show that (i) there was an antibody response to LCR1 in each individual with a recent history of visceral leishmaniasis studied, (ii) there was neither a proliferative response nor production of gamma interferon (IFN-γ) or interleukin 10 in response to LCR1 by mononuclear cells from individuals who had recovered from visceral leishmaniasis, and (iii) individuals who have recovered from visceral leishmaniasis show ongoing immune responses long after recovery from the disease. These data show that there are no detectable cellular memory responses to LCR1 in Iranian individuals who have recovered from visceral leishmaniasis, while there are detectable antibody responses in patients with this disease. Our data suggest that LCR1 has potential applications for the diagnosis of leishmaniasis through antibody detection, while the application of LCR1 alone for induction of IFN-γ in individuals who recovered from this disease is not supported. The presence of long-lasting immune reactivities in individuals who recovered from the disease may show the necessity of extended medical surveillance for these individuals.

CD4 T cell activation by B cells in human Leishmania (Viannia) infection

Background

An effective adaptive immune response requires activation of specific CD4 T cells. The capacity of B cells to activate CD4 T cells in human cutaneous leishmaniasis caused by Leishmania (Viannia) has not been evaluated.

Methods

CD4 T cell activation by B cells of cutaneous leishmaniasis patients was evaluated by culture of PBMCs or purified B cells and CD4 T cells with Leishmania panamensis antigens. CD4 T cell and B cell activation markers were evaluated by flow cytometry and 13 cytokines were measured in supernatants with a bead-based capture assay. The effect of Leishmania antigens on BCR-mediated endocytosis of ovalbumin was evaluated in the Ramos human B cell line by targeting the antigen with anti-IgM-biotin and anti-biotin-ovalbumin-FITC.

Results

Culture of PBMCs from cutaneous leishmaniasis patients with Leishmania antigens resulted in upregulation of the activation markers CD25 and CD69 as well as increased frequency of CD25^hiCD127^- cells among CD4 T cells. Concomitantly, B cells upregulated the costimulatory molecule CD86. These changes were not observed in PBMCs from healthy subjects, indicating participation of Leishmania-specific lymphocytes expanded in vivo. Purified B cells from these patients, when interacting with purified CD4 T cells and Leishmania antigens, were capable of inducing significant increases in CD25 and CD69 expression and CD25^hiCD127^- frequency in CD4 T cells. These changes were associated with upregulation of CD86 in B cells. Comparison of changes in CD4 T cell activation parameters between PBMC and B cell/CD4 T cell cultures showed no statistically significant differences; further, significant secretion of IFN-γ, TNF-α, IL-6 and IL-13 was induced in both types of cultures. Additionally, culture with Leishmania antigens enhanced BCR-mediated endocytosis of ovalbumin in Ramos human B cells.

Conclusions

The capacity of B cells specific for Leishmania antigens in peripheral blood of cutaneous leishmaniasis patients to activate CD4 T cells and induce cytokine secretion is similar to that of all cell populations present in PBMCs. This capacity implicates B cells as a plausible target for modulation of the immune response to Leishmania infection as a therapeutic strategy.

IL-4 contributes to failure, and colludes with IL-10 to exacerbate Leishmania donovani infection following administration of a subcutaneous leishmanial antigen vaccine

Background

Visceral leishmaniasis caused by the protozoan parasite Leishmania donovani complex is a potentially fatal disease if left untreated. Few treatment options exist and are toxic, costly and ineffective against resistant strains. Thus a safe and efficacious vaccine to combat this disease is needed. Previously, we reported that intraperitoneal administration of leishmanial antigens (LAg) entrapped in liposomes conferred protection to BALB/c mice against L. donovani challenge infection. However, this vaccine failed to protect mice when administered subcutaneously. We therefore evaluated whether formulation of LAg in combination with two commonly used human-compatible adjuvants, alum and saponin, could improve the protective efficacy of subcutaneously administered LAg, to a level comparable to that of the intraperitoneal liposomal vaccination.

Results

Vaccine formulations of LAg with alum or saponin failed to reduce parasite burden in the liver, and alum + LAg immunized mice also failed to reduce parasite burden in the spleen. Interestingly, saponin + LAg vaccination actually resulted in an increased L. donovani parasitic load in the spleen following L. donovani challenge, suggesting this regimen exacerbates the infection. In contrast, mice immunized intraperitoneally with Lip + LAg demonstrated significant protection in both liver and spleen, as expected. Mechanistically, we found that failure of alum + LAg to protect mice was associated with elevated levels of IL-4, whereas both IL-4 and IL-10 levels were increased in saponin + LAg immunized mice. This outcome served to exacerbate L. donovani infection in the saponin + LAg group, despite a concurrent increase in proinflammatory IFN-γ production. On the contrary, protection against L. donovani challenge in Lip + LAg immunized mice was associated with elevated levels of IFN-γ in conjunction with low levels of IL-4 and IL-10 production.

Conclusions

These findings indicate that elevated levels of IL-4 may contribute to LAg vaccine failure, whereas combined elevation of IL-4 together with IL-10 exacerbated the disease as observed in saponin + LAg immunized mice. In contrast, a robust IFN-γ response, in the absence of IL-4 and IL-10 production, was associated with protective immunity following administration of the Lip + LAg vaccine. Together these findings suggest that optimization of antigen/adjuvant formulations to minimize IL-4 and IL-10 induction may be helpful in the development of high efficacy vaccines targeting Leishmania.