IL-17 promotes progression of cutaneous leishmaniasis in susceptible mice

An integrated bioinformatic analysis of microarray datasets to identify biomarkers and miRNA-based regulatory networks in leishmaniasis

Micro RNAs (miRNAs, miRs) and relevant networks might exert crucial functions during differential host cell infection by the different Leishmania species. Thus, a bioinformatic analysis of microarray datasets was developed to identify pivotal shared biomarkers and miRNA-based regulatory networks for Leishmaniasis. A transcriptomic analysis by employing a comprehensive set of gene expression profiling microarrays was conducted to identify the key genes and miRNAs relevant for Leishmania spp. infections. Accordingly, the gene expression profiles of healthy human controls were compared with those of individuals infected with Leishmania mexicana, L. major, L. donovani, and L. braziliensis. The enrichment analysis for datasets was conducted by utilizing EnrichR database, and Protein-Protein Interaction (PPI) network to identify the hub genes. The prognostic value of hub genes was assessed by using receiver operating characteristic (ROC) curves. Finally, the miRNAs that interact with the hub genes were identified using miRTarBase, miRWalk, TargetScan, and miRNet. Differentially expressed genes were identified between the groups compared in this study. These genes were significantly enriched in inflammatory responses, cytokine-mediated signaling pathways and granulocyte and neutrophil chemotaxis responses. The identification of hub genes of recruited datasets suggested that TNF, SOCS3, JUN, TNFAIP3, and CXCL9 may serve as potential infection biomarkers and could deserve value as prognostic biomarkers for leishmaniasis. Additionally, inferred data from miRWalk revealed a significant degree of interaction of a number of miRNAs (hsa-miR-8085, hsa-miR-4673, hsa-miR-4743-3p, hsa-miR-892c-3p, hsa-miR-4644, hsa-miR-671-5p, hsa-miR-7106-5p, hsa-miR-4267, hsa-miR-5196-5p, and hsa-miR-4252) with the majority of the hub genes, suggesting such miRNAs play a crucial role afterwards parasite infection. The hub genes and hub miRNAs identified in this study could be potentially suggested as therapeutic targets or biomarkers for the management of leishmaniasis.

Heterologous Expression of Human IFNγ and Anti-IL17 Antibody in Leishmania tarentolae Promastigote

BACKGROUND

Leishmania is an intracellular flagellate protozoan parasite that causes a wide range of clinical diseases in humans. The basis of immunological resistance against leishmaniasis depends on Thl reactions and is within the time period of cytokine function.

METHODS

In this study, human anti-IL17 antibody and IFNγ-producing promastigote were produced to be used in leishmanization. A sequence of light and heavy chains' gene of anti-IL17 antibody and human IFNγ (hIFNγ) was obtained from the NCBI database and synthesized in the ECORV reaction site in the plasmid pGH, which it's called pGH-hIFNγ-antiIL17. The synthesized part using the restriction enzyme ECORV was extracted from the plasmid and after purification by electroporation was transferred to Iranian lizard Leishmania (I.L.L). Evaluation of structural presence in the I.L.L genome at the level of DNA and mRNA was assessed. The expressions of hIFNγ and anti-IL17 were evaluated and confirmed using ELISA and western blot analysis. The hIFNγ secreted from the culture medium was collected at high concentrations of 124.36 ± 6.47 pg/mL.

RESULTS

Targeted gene replacement into the I.L.L genome was successfully performed for the first time using the pGH-hIFNγ-antiIL17 plasmid in an identical replacement process. Stabilized recombinant DNA contains a target gene that has no toxicity to the parasite.

CONCLUSIONS

The effective achievement of producing a recombinant gene was done for the first time by replacing the I.L.L-CPC gene with plasmid pGH-hIFNγ-antiIL17 by targeted gene replacement. This cab can regulate the production of hIFNγ and anti-IL17. This makes it a viable choice for eliminating leishmania.

Th17 Cell and Inflammatory Infiltrate Interactions in Cutaneous Leishmaniasis: Unraveling Immunopathogenic Mechanisms

The inflammatory response during cutaneous leishmaniasis (CL) involves immune and non-immune cell cooperation to contain and eliminate Leishmania parasites. The orchestration of these responses is coordinated primarily by CD4+ T cells; however, the disease outcome depends on the Th cell predominant phenotype. Although Th1 and Th2 phenotypes are the most addressed as steers for the resolution or perpetuation of the disease, Th17 cell activities, especially IL-17 release, are recognized to be vital during CL development. Th17 cells perform vital functions during both acute and chronic phases of CL. Overall, Th17 cells induce the migration of phagocytes (neutrophils, macrophages) to the infection site and CD8+ T cells and NK cell activation. They also provoke granzyme and perforin secretion from CD8+ T cells, macrophage differentiation towards an M2 phenotype, and expansion of B and Treg cells. Likewise, immune cells from the inflammatory infiltrate have modulatory activities over Th17 cells involving their differentiation from naive CD4+ T cells and further expansion by generating a microenvironment rich in optimal cytokines such as IL-1β, TGF-β, IL-6, and IL-21. Th17 cell activities and synergies are crucial for the resistance of the infection during the early and acute stages; however, if unchecked, Th17 cells might lead to a chronic stage. This review discusses the synergies between Th17 cells and the inflammatory infiltrate and how these interactions might destine the course of CL.

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

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

Regulatory T cells control Staphylococcus aureus and disease severity of cutaneous leishmaniasis

Cutaneous leishmaniasis causes alterations in the skin microbiota, leading to pathologic immune responses and delayed healing. However, it is not known how these microbiota-driven immune responses are regulated. Here, we report that depletion of Foxp3+ regulatory T cells (Tregs) in Staphylococcus aureus-colonized mice resulted in less IL-17 and an IFN-γ-dependent skin inflammation with impaired S. aureus immunity. Similarly, reducing Tregs in S. aureus-colonized and Leishmania braziliensis-infected mice increased IFN-γ, S. aureus, and disease severity. Importantly, analysis of lesions from L. braziliensis patients revealed that low FOXP3 gene expression is associated with high IFNG expression, S. aureus burden, and delayed lesion resolution compared to patients with high FOXP3 expression. Thus, we found a critical role for Tregs in regulating the balance between IL-17 and IFN-γ in the skin, which influences both bacterial burden and disease. These results have clinical ramifications for cutaneous leishmaniasis and other skin diseases associated with a dysregulated microbiome when Tregs are limited or dysfunctional.

IL-18 is required for the TH1-adaptation of TREG cells and the selective suppression of TH17 responses in acute and chronic infections

Interleukin (IL)-18, a member of the IL-1 family of alarmins, is abundantly released in the lungs following influenza A (IAV) infections yet its role in orchestrating the local adaptive immune response remains ill defined. Through genetic disruption of the IL-18 receptor, we demonstrate that IL-18 not only promotes pulmonary TH1 responses but also influences regulatory T cells (TREG) function in the infected lungs. As the response unfolds, TREG cells accumulating in the lungs express Helios, T-bet, CXCR3, and IL-18R1 and produce interferon γ in the presence of IL-12. During IAV, IL-18R1 is required for TREG cells to control TH17, but not TH1, responses and promote a return to lung homeostasis, revealing a novel mechanism of selective suppression. Moreover, this observation was not limited to the lungs, as skin-localized TREG cells require an IL-18 signal to specifically suppress IL-17A production by TH17 and γδ T cells in a model of chronic cutaneous Leishmania major infection. Overall, these results uncover how IL-18 orchestrates the tissue adaptation of TREG cells to selectively favor TH1 over TH17 responses during TH1-driven immune responses and provide a novel perspective into how IL-18 dictates the immune response during viral and parasitic infections.

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.

Decoding systems immunological model of sphingolipids with IL-6/IL-17/IL-23 axes in L. major infection

IL-6, IL-17, IL-23 and IL-1β are the crucial cytokines controlling inflammatory and immune response during L. major infection. During cutaneous leishmaniasis, an important T helper cell type CD4⁺ Th17 subset plays a deterministic role in lesion formation through channelling infected macrophages and production of IL-1β, IL-6, IL-23 and IFN-γ. Ceramide derived sphingosine precursors may assist in pro-inflammatory cytokine response. However, the role of these metabolites in inflammation with pleiotropic pro-inflammatory cytokines in L. major infection is unknown. The present study indicates IL-6/IL-17/IL-23 and SPHK1-S1P-S1PRs signaling axes with the overexpression of SATB1 aiding in disease progression. Targeting SATB1 might modulate the secretion of pro-inflammatory cytokines and abnormal immune functioning, thereby killing the intracellular parasite. Systems immunological methods assisted in a step towards identifying the key to the mystery of crucial components and serving as an approach for therapeutic intervention in L. major infection.

Central and Effector Memory Human CD4+ and CD8+ T Cells during Cutaneous Leishmaniasis and after In Vitro Stimulation with Leishmania (Viannia) braziliensis Epitopes

Cutaneous Leishmaniasis (CL) is a Neglected Tropical Disease characterized by skin ulcers caused by Leishmania spp. protozoans and there is no safe and effective vaccine to reduce its negative consequences. In a previous work by our group, we identified T cell epitopes of Leishmania (Viannia) braziliensis which stimulated patients' T cells in vitro. In the present work, the peptides were tested as two pools for their ability to rescue memory T cells during natural infection by Leishmania. We analyzed the frequency of central memory (TCM, CD45RA-CD62L+) and effector memory (TEM, CD45RA + CD62L-) cells during active CL and post-treatment. In parallel, we investigated cell proliferation levels and the cytokines produced after stimulation. Interestingly, we observed higher frequencies (%) in CD4+ TEM during CL, and CD8+ TEM and CD8+ TCM during CL and post-treatment. Cell proliferation was increased, and a significant difference in expression was observed on T-bet and RORγT. Besides that, IFN-γ, IL-2, and IL-10 were detected in patient samples. Collectively, this dataset suggests that during CL there is an increase in the frequency of TCM and TEM, especially in the CD8 compartment. These results indicate a potentially immunogenic profile of the peptide pools, which can support the development of anti-Leishmania formulations.

IL-17 and IL-17-producing cells in protection versus pathology

IL-17 cytokine family members have diverse biological functions, promoting protective immunity against many pathogens but also driving inflammatory pathology during infection and autoimmunity. IL-17A and IL-17F are produced by CD4⁺ and CD8⁺ T cells, γδ T cells, and various innate immune cell populations in response to IL-1β and IL-23, and they mediate protective immunity against fungi and bacteria by promoting neutrophil recruitment, antimicrobial peptide production and enhanced barrier function. IL-17-driven inflammation is normally controlled by regulatory T cells and the anti-inflammatory cytokines IL-10, TGFβ and IL-35. However, if dysregulated, IL-17 responses can promote immunopathology in the context of infection or autoimmunity. Moreover, IL-17 has been implicated in the pathogenesis of many other disorders with an inflammatory basis, including cardiovascular and neurological diseases. Consequently, the IL-17 pathway is now a key drug target in many autoimmune and chronic inflammatory disorders; therapeutic monoclonal antibodies targeting IL-17A, both IL-17A and IL-17F, the IL-17 receptor, or IL-23 are highly effective in some of these diseases. However, new approaches are needed to specifically regulate IL-17-mediated immunopathology in chronic inflammation and autoimmunity without compromising protective immunity to infection.

Leishmania major Strain-Dependent Macrophage Activation Contributes to Pathogenicity in the Absence of Lymphocytes

Infection of C57BL/6 wild-type mice with Leishmania major 5-ASKH or Friedlin strains results in relatively similar pathogenicity with self-healing lesions within weeks. Parasite clearance depends on nitric oxide production by activated macrophages in response to cytokines produced mainly by CD4⁺ Th1 cells. In contrast, C57BL/6 Rag2 knockout mice, which lack T and B lymphocytes, show distinct pathologies during infection with these strains. Despite of the similar parasite number, the 5-ASKH infection induced severe inflammation rather than the Friedlin. To determine the immunological factors behind this phenomenon, we infected C57BL/6 Rag2 knockout mice with these two strains and compared immune cell kinetics and macrophage activation status. Compared with the Friedlin strain, the 5-ASKH strain elicited increased pathology associated with the accumulation of CD11b^high, Ly6G^high neutrophils by week four and increased the expression of macrophage activation markers. We then analyzed the differentially expressed transcripts in infected bone marrow-derived macrophages by RNA sequencing. It showed upregulation of multiple inflammatory transcripts, including Toll-like receptor 1/2 (TLR1/2), CD69, and CARD14, upon 5-ASKH infection. Our findings suggest that different L. major strains can trigger distinct macrophage activation, contributing to the disease outcome observed in the absence of lymphocytes but not in the presence of lymphocytes. IMPORTANCE Disease manifestations of cutaneous leishmaniasis (CL) range from self-healing cutaneous lesions to chronic forms of the disease, depending on the infecting Leishmania sp. and host immune protection. Previous works on mouse models of CL show the distinct pathogenicity of Leishmania major strains in the absence of lymphocytes. However, the mechanisms of this pathology remain uncovered. In the trial to understand the immunological process involved in lymphocyte-independent pathology, we have found a specific induction of macrophages by different L. major strains that affect their ability to mount innate responses leading to neutrophilic pathology when lymphocytes are ablated.

Cytokines and Signaling Networks Regulating Disease Outcomes in Leishmaniasis

Cytokines play crucial roles in commencing and coordinating the organized recruitment and activation of immune cells during infection. These molecular regulators play an important part in deciding the fate of disease outcomes in leishmaniasis, a parasitic disease of tropical and subtropical countries. T helper 1 (Th1) cell-mediated inflammatory cytokines usually play a host-protective role, while T helper 2 (Th2) cell activation produces an anti-inflammatory milieu necessary for parasite survival. It is noteworthy that in such a multifaceted disease, the role played by any particular cytokine cannot be generalized as either beneficial or detrimental. For example, a "host-favorable" cytokine in one form of the disease has been found to be "pathogen friendly" in another form of leishmaniasis. On the other hand, the complex signaling network regulating the production of cytokines is further complicated by the nature of the host as well as the presence of other cytokines in the milieu. The present review focuses on the differential roles played by cytokines and the intricate signaling network responsible for the regulation of such cytokines during infection by different species of Leishmania. While many more studies are required in the future to better understand the role of these molecules in both animal models and patient samples, current studies indicate that these molecules are potential candidates to be targeted for therapy against this deadly disease.

The metamorphosis of neutrophil transcriptional program during Leishmania infection

The role of neutrophils in the course of Leishmania infection remains controversial, displaying tremendous variability depending on the species of parasite, stage of infection, host genetic background, and methodological discrepancies among studies. Although neutrophils have long been categorized as short-lived cells with limited capacity to express proteins de novo, recent advances have revealed significant plasticity in neutrophil transcriptional programs and intrapopulation heterogeneity, which can be regulated by both intrinsic and extrinsic factors that together determine the profile of neutrophil effector response. In this review, we focus on the current understanding of neutrophil transcriptional plasticity, neutrotime, evidence of Leishmania-mediated alterations in neutrophil transcriptome leading to the rise of subpopulations, and finally, functional implications of those findings to the course of Leishmania infection.

Immune Responses in Leishmaniases: An Overview

Leishmaniasis is a parasitic, widespread, and neglected disease that affects more than 90 countries in the world. More than 20 Leishmania species cause different forms of leishmaniasis that range in severity from cutaneous lesions to systemic infection. The diversity of leishmaniasis forms is due to the species of parasite, vector, environmental and social factors, genetic background, nutritional status, as well as immunocompetence of the host. Here, we discuss the role of the immune system, its molecules, and responses in the establishment, development, and outcome of Leishmaniasis, focusing on innate immune cells and Leishmania major interactions.

Host–Pathogen Interaction in Leishmaniasis: Immune Response and Vaccination Strategies

Leishmaniasis is a zoonotic and vector-borne infectious disease that is caused by the genus Leishmania belonging to the trypanosomatid family. The protozoan parasite has a digenetic life cycle involving a mammalian host and an insect vector. Leishmaniasisis is a worldwide public health problem falling under the neglected tropical disease category, with over 90 endemic countries, and approximately 1 million new cases and 20,000 deaths annually. Leishmania infection can progress toward the development of species–specific pathologic disorders, ranging in severity from self-healing cutaneous lesions to disseminating muco-cutaneous and fatal visceral manifestations. The severity and the outcome of leishmaniasis is determined by the parasite’s antigenic epitope characteristics, the vector physiology, and most importantly, the immune response and immune status of the host. This review examines the nature of host–pathogen interaction in leishmaniasis, innate and adaptive immune responses, and various strategies that have been employed for vaccine development.

The expression of PD-1 and its ligands increases in Leishmania infection and its blockade reduces the parasite burden

The expression of programmed cell death protein-1 (PD-1) and its ligands- PD-L1 and PD-L2- on T cells and macrophages', respectively, increases in Leishmania infection. The PD-1/PD-L1 interaction induces T cell anergy, T cell apoptosis and exhaustion, diversion of T cells toward T_H2 and T-reg cells but inhibits M1 macrophage activities by suppression of nitric oxide (NO) and reactive oxygen species (ROS) production. These changes exacerbate Leishmania infection. As PD-L1-deficient, but not PD-L2-deficient, mice were protected againstL. mexicanainfection, differential roles have been proposed for PD-L1 and PD-L2 in mouse models of leishmaniasis. Blockade of PD-1/PD-L1 interaction in various in vitro and Leishmania-infected mouse, hamster and dog models enhanced IFN-γ and NO production, reduced IL-10 and TGF-β generation, promoted T cell proliferation and reduced parasite burden. Therefore, PD-1/PD-L1 blockade is being considered as a potential therapeutic strategy to restore protective immunity during leishmaniasis, particularly, in drug-resistant cases.

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.

Effect of immunosuppression by UV-B radiation on components of the innate immune response in skin lesions with Leishmania mexicana: Effect of UVB on the innate immune response in cutaneous infection by L. mexicana

Cutaneous leishmaniasis is the most common form of leishmaniasis in humans, factors such as poverty, poor housing, inadequate domestic hygiene, malnutrition, mobility, and occupational exposure are risk factors associated with the condition, however, there are few studies focused on determining the immune mechanism involved in the resolution of cutaneous leishmaniasis caused by the species Leishmania mexicana, as well as possible environmental factors such as solar radiation, which could contribute to its establishment. through mechanisms immunosuppressants, of which to date is unknown. In this study, the effect of UV-B light was evaluated as a risk factor affecting components of the innate immune response 3 days after infection with L. mexicana. A delayed-type hypersensitivity reaction (DTH) was used to evaluate immunosuppression induced by UV-B light. Through a histological analysis, the skin lesions of the mice (Hematoxylin & Eosin) were evaluated, the presence of mast cells and their level of degranulation (toluidine blue staining), the presence of IL-10⁺ and MOMA2⁺ cells were analyzed by immunohistochemistry and finally, the cytokine profile was evaluated by qPCR in the skin lesions tissue. An alteration in the architecture of the tissue was observed, as well as a greater number of mast cells, both complete and degranulated, as well as an increase in IL-10⁺ and MOMA2⁺ cells in the skin lesions of the mice that were irradiated and subsequently infected, when compared with the lesions of infected mice (P> 0.0001), immunomodulation was also observed in the profile of cytokines expressed between both groups analyzed. This is the first study to demonstrate the effects of UV-B radiation on components of the innate immune response at short times of infection by L. mexicana.

Immunomodulatory role of Th17 pathway in experimental visceral leishmaniasis

Visceral leishmaniasis (VL) or Kala-azar is a vector borne protozoan infection caused by Leishmania donovani in the Indian subcontinent mainly India, Nepal and Bangladesh. It is a major public health problem in these countries mostly affecting the socio-economically poor population. Leishmaniasis ranks the third most important disease after malaria and filariasis but is still considered as one of the neglected tropical diseases of the world. For development of better therapeutic agents and effective vaccine against VL, there is a need to understand host immunological changes that play a vital role during course of infection. Therefore, we investigated the role of Th17 pathway in Balb/c mice during Leishmania donovani infection and treatment with amphotericin B. Mice were divided in four groups i.e. Control, Infected, Uninfected treated and Infected treated. The cytokine levels were estimated in the spleen of Balb/c mice on days 1, 3, 7, 14, 17, 21, 28, 35, 45 and 60 post infection and during course of treatment. The mRNA levels of the Th17 pathway during active Leishmania donovani infection and after treatment were determined by real time polymerase chain reaction (RT-PCR) and protein levels by flow cytometry and ELISA. Results of our study revealed that active infection was associated with low levels of Th17 cytokines IL-17, IL-22 and IL-23 and elevated levels of IL-6, IL-1β and TGF-β. Amphotericin B treatment restored production of pro-inflammatory cytokines IL-17 and IL-22. The levels of transcription factor RORγt were found to correlate with the levels of IL-17 during infection and also after chemotherapy whereas STAT3 levels were elevated during infection and vice versa after treatment. The findings of this study suggest that Th17 cytokines IL-17 and IL-22 are associated with protection against VL infection and development of any interventions or chemotherapeutic agents targeting Th17 pathway could be an important approach for VL treatment.

Epidemiologic, Clinical and Immunological Consequences of Co-Infections during Canine Leishmaniosis

Simple Summary

Canine leishmaniosis (CanL), the most severe, visceralizing form of disease caused by Leishmania infantum transmitted by phlebotomine sand flies. CanL is frequently diagnosed in the Mediterranean basin and South America, although it is also found in other regions, including the United States (U.S.). Dogs in these regions are at risk for co-infections, prominently tick-borne diseases. Our review examines epidemiologic, clinical, and immunologic mechanisms found during the most common eight CanL co-infections reported in published literature. Co-infections alter immunologic processes and disease progression impacting CanL diagnosis, therapeutic responses, and prognosis.

Abstract

Canine leishmaniosis (CanL) is a vector-borne, parasitic disease. CanL is endemic in the Mediterranean basin and South America but also found in Northern Africa, Asia, and the U.S. Regions with both competent sand fly vectors and L. infantum parasites are also endemic for additional infectious diseases that could cause co-infections in dogs. Growing evidence indicates that co-infections can impact immunologic responses and thus the clinical course of both CanL and the comorbid disease(s). The aim for this review is to summarize epidemiologic, clinical, and immunologic factors contributing to eight primary co-infections reported with CanL: Ehrlichia spp., Anaplasma spp., Borrelia spp., Babesia spp., Trypanosoma cruzi, Toxoplasma gondii, Dirofilaria immitis, Paracoccidioides braziliensis. Co-infection causes mechanistic differences in immunity which can alter diagnostics, therapeutic management, and prognosis of dogs with CanL. More research is needed to further explore immunomodulation during CanL co-infection(s) and their clinical impact.

Protective immune response mediated by neutrophils in experimental visceral leishmaniasis is enhanced by IL-32γ

Neutrophils are important cells in protection against microbial infections including visceral leishmaniasis (VL). It is well known that IL-32γ increases the protective T helper 17 cell mediated immune response against Leishmania infantum. Thus, in this study we evaluated whether IL-32 γ can increase the protective role of neutrophils against VL. In comparison with wild type (WT) mice, transgenic mice for human IL-32 γ (IL-32 γ Tg) presented a higher frequency and absolute number of neutrophils in both spleen and liver after the establishment of L. infantum infection. The IL-32 concentrations correlated with neutrophil numbers in the infected tissues. The IL-32 γ -induced recruitment of neutrophils was dependent on IL-17, since inhibition of Th17 T cells generation and IL-17 production with digoxin treatment reversed the effects of IL-32 γ. In murine neutrophils, the presence of IL-32 γ enhanced the phagocytosis of L. infantum via CR3. In addition, murine IL-32 γ Tg neutrophils were able to kill L. infantum due to the increased production of ROS when compared with WT neutrophils. In fact, IL-32 γ Tg mice lost their ability to control infection by L. infantum when neutrophils were depleted. In parallel, treatment of human neutrophils with recombinant IL-32 γ increased phagocytosis and ROS-dependent killing of L. infantum, similarly to murine IL-32 γ Tg neutrophils. The data show that IL-32 γ induces neutrophil recruitment to organs affected by VL and increases phagocytosis and killing of L. infantum by neutrophils. Together, data indicate the pivotal axis IL-32 γ -Th17-neutrophils to control VL.

Microbiota instruct IL-17A-producing innate lymphoid cells to promote skin inflammation in cutaneous leishmaniasis

Innate lymphoid cells (ILCs) comprise a heterogeneous population of immune cells that maintain barrier function and can initiate a protective or pathological immune response upon infection. Here we show the involvement of IL-17A-producing ILCs in microbiota-driven immunopathology in cutaneous leishmaniasis. IL-17A-producing ILCs were RORγt+ and were enriched in Leishmania major infected skin, and topical colonization with Staphylococcus epidermidis before L. major infection exacerbated the skin inflammatory responses and IL-17A-producing RORγt+ ILC accumulation without impacting type 1 immune responses. IL-17A responses in ILCs were directed by Batf3 dependent CD103+ dendritic cells and IL-23. Moreover, experiments using Rag1-/- mice established that IL-17A+ ILCs were sufficient in driving the inflammatory responses as depletion of ILCs or neutralization of IL-17A diminished the microbiota mediated immunopathology. Taken together, this study indicates that the skin microbiota promotes RORγt+ IL-17A-producing ILCs, which augment the skin inflammation in cutaneous leishmaniasis.

Variants of MIRNA146A rs2910164 and MIRNA499 rs3746444 are associated with the development of cutaneous leishmaniasis caused by Leishmania guyanensis and with plasma chemokine IL-8

Leishmania are intracellular protozoan parasites that cause a wide spectrum of clinical manifestations in genetically susceptible individuals with an insufficient or balanced Th1 immune response to eliminate the parasite. MiRNAs play important regulatory role in numerous biological processes including essential cellular functions. miR146-a acts as an inhibitor of interleukin 1 receptor associated kinase 1 (IRAK1) and tumour necrosis factor (TNF) receptor associated factor 6 (TRAF6) present in the toll-like receptors pathway while miR499a modulates TGF-β and TNF signalling pathways. Here, we investigated whether MIRNA146A rs2910164 and MIRNA499 rs3746444 variants are associated with the development of L. guyanensis (Lg)-cutaneous leishmaniasis (CL). The variants MIR146A rs2910164 and MIR499A rs3746444 were assessed in 850 patients with Lg-CL and 891 healthy controls by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP). Plasma cytokines were measured using the BioPlex assay. Carriers of rs2910164 CC genotype have 30% higher odds of developing CL (ORadj_age/sex = 1.3 [95%CI 0.9–1.8]; Padj_age/sex 0.14) compared to individuals with the genotype GG (ORadj_age/sex = 0.77 [95%CI 0.56–1.0]; Padj_age/sex 0.14) if exposed to Lg-infection. Heterozygous GC individuals also showed lower odds of developing CL (ORadj_age/sex = 0.77 [95%CI 0.5–1.1]; Padj_age/sex 0.09). Homozygosity for the allele C is suggestive of an association with the development of Lg-CL among exposed individuals to Lg-infection. However, the odds of developing CL associated with the CC genotype was evident only in male individuals (OR_adjage = 1.3 [95% CI = 0.9–2.0]; P_adjage = 0.06). Individuals homozygous for the G allele tend to have higher plasma IL-8 and CCL5. Similarly, for the MIR499A rs3746444, an association with the G allele was only observed among male individuals (OR = 1.4 [1.0–1.9]; P = 0.009). In a dominant model, individuals with the G allele (GG-GA) when compared to the AA genotype reveals that carriers of the G allele have 40% elevated odds of developing Lg-CL (ORadj_age = 1.4 [1.1–1.9]). Individuals with the GG genotype have higher odds of developing Lg-CL (ORadj_age/sex = 2.0 [95%CI 0.83–5.0]; P_adjage = 0.01. Individuals homozygous for the G allele have higher plasma IL-8. Genetic combinations of both variants revealed that male individuals exposed to Lg bearing three or four susceptible alleles have higher odds of developing Lg-CL (OR = 2.3 [95% CI 1.0–4.7]; p = 0.017). Both MIR146A rs2910164 and MIR499A rs3746444 are associated with the development of Lg-CL and this association is prevalent in male individuals.

Leishmaniasis is caused by infection with Leishmania parasites. In regions with the presence of Leishmania parasites, all people do not develop the disease despite similar exposure. Only a proportion of inhabitants progress to the development of disease. Clinical manifestations depend on the vector and Leishmania species, as well the host genetic background and genetically determined immune responses. miRNAs play important roles in regulating gene expression and many biological processes including immune pathways. miR-146a targets TRAF6 and IRAK1 genes, that encode key adaptor molecules downstream of toll-like receptors (TLRs). TLRs are critical in immune response to Leishmania-infection. miR499-a modulates inflammation-related signalling pathways such as TGFβ, TNFα and TLR pathways. In this study, we showed that MIR146A and MIR499A variants are risk factors to developing cutaneous leishmaniasis caused by L. guyanensis in Amazonas state of Brazil. Individuals with these variants are susceptible to the development of CL.

IL-23R variant rs11805303 is associated with susceptibility to the development of cutaneous leishmaniasis in Leishmania guyanensis-infected individuals

BACKGROUND

Emerging evidence suggests that the IL-17/IL-23 axis may play a role in the pathogenesis of leishmaniasis. Our aim was to investigate whether the IL-23R variant rs11805303 is a risk factor for the development of cutaneous leishmaniasis (CL) in Leishmania guyanensis-infected individuals.

METHODS

We genotyped by polymerase chain reaction-restriction fragment length polymorphism the rs11805303 C/T in 828 patients with CL and 806 healthy individuals. Plasma TNF-α, IL-6, IFG-γ, IL-1β and IL-17 were measured with the Bioplex assay.

RESULTS

The distribution of the genotypes differed between patients with CL and HC with a common odds ratio (OR) of 1.78 (p = 2.2 x10 -11) for the disease-associated T allele. L. guyanensis-infected individuals homozygous for the T allele show a 200% increased risk of progressing to disease development, with a 95% confidence interval (CI) ranging from 81% to 400% (P = 9.9 x 10 -6) in comparison to individuals homozygous for the C allele. Males homozygous for the T allele have higher plasma levels of IL-17 compared with heterozygous or homozygous CC individuals.

CONCLUSION

The present association of the IL-23R variant rs11805303 with the development of cutaneous leishmaniasis suggests that the IL-17/IL-23 axis may play an important role in the pathogenesis of CL.

Leishmania Parasites Drive PD-L1 Expression in Mice and Human Neutrophils With Suppressor Capacity

Neutrophils play an important role in the outcome of leishmaniasis, contributing either to exacerbating or controlling the progression of infection, a dual effect whose underlying mechanisms are not clear. We recently reported that CD4⁺ and CD8⁺ T cells, and dendritic cells of Leishmania amazonensis-infected mice present high expression of PD-1 and PD-L1, respectively. Given that the PD-1/PD-L1 interaction may promote cellular dysfunction, and that neutrophils could interact with T cells during infection, we investigated here the levels of PD-L1 in neutrophils exposed to Leishmania parasites. We found that both, promastigotes and amastigotes of L. amazonensis induced the expression of PD-L1 in the human and murine neutrophils that internalized these parasites in vitro. PD-L1-expressing neutrophils were also observed in the ear lesions and the draining lymph nodes of L. amazonensis-infected mice, assessed through cell cytometry and intravital microscopy. Moreover, expression of PD-L1 progressively increased in neutrophils from ear lesions as the disease evolved to the chronic phase. Co-culture of infected neutrophils with in vitro activated CD8⁺ T cells inhibits IFN-γ production by a mechanism dependent on PD-1 and PD-L1. Importantly, we demonstrated that in vitro infection of human neutrophils by L braziliensis induced PD-L1⁺ expression and also PD-L1⁺ neutrophils were detected in the lesions of patients with cutaneous leishmaniasis. Taken together, these findings suggest that the Leishmania parasite increases the expression of PD-L1 in neutrophils with suppressor capacity, which could favor the parasite survival through impairing the immune response.

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.

MicroRNA155 Plays a Critical Role in the Pathogenesis of Cutaneous Leishmania major Infection by Promoting a Th2 Response and Attenuating Dendritic Cell Activity

Interferon (IFN)-γ is indispensable in the resolution of cutaneous leishmaniasis (CL), while the Th2 cytokines IL-4, IL-10, and IL-13 mediate susceptibility. A recent study found that miR155, which promotes CD4⁺ Th1 response and IFN-γ production, is dispensable in the control of Leishmania donovani infection. Here, the role of miR155 in CL caused by L. major was investigated using miR155-deficient (miR155^-/-) mice. Infection was controlled significantly quicker in the miR155^-/- mice than in their wild-type (WT) counterparts, indicating that miR155 contributes to the pathogenesis of CL. Faster resolution of infection in miR155^-/- mice was associated with increased levels of Th1-associated IL-12 and IFN-γ and reduced production of Th2- associated IL-4, IL-10, and IL-13. Concentrations of IFN-γ⁺CD8⁺ T cells and natural killer cells in draining lymph nodes were significantly higher in the L. major-infected miR155^-/- mice than in the infected WT mice, as indicated by flow-cytometry. After in vitro IFN-γ stimulation, nitric oxide and IL-12 production were increased, IL-10 production was decreased, and parasite clearance was enhanced in L. major-infected miR155^-/- DCs compared to those in WT DCs. Furthermore, IFN-γ production from activated miR155^-/- T cells was significantly enhanced in L. major-infected miR155^-/- DCs. Together, these findings demonstrate that miR155 promotes susceptibility to CL caused by L. major by promoting Th2 response and inhibiting DC function.

Unraveling the Role of Immune Checkpoints in Leishmaniasis

Leishmaniasis are Neglected Tropical Diseases affecting millions of people every year in at least 98 countries and is one of the major unsolved world health issues. Leishmania is a parasitic protozoa which are transmitted by infected sandflies and in the host they mainly infect macrophages. Immunity elicited against those parasites is complex and immune checkpoints play a key role regulating its function. T cell receptors and their respective ligands, such as PD-1, CTLA-4, CD200, CD40, OX40, HVEM, LIGHT, 2B4 and TIM-3 have been characterized for their role in regulating adaptive immunity against different pathogens. However, the exact role those receptors perform during Leishmania infections remains to be better determined. This article addresses the key role immune checkpoints play during Leishmania infections, the limiting factors and translational implications.

Protein methyltransferase 7 deficiency in Leishmania major increases neutrophil associated pathology in murine model

Leishmania major is the main causative agent of cutaneous leishmaniasis in the Old World. In Leishmania parasites, the lack of transcriptional control is mostly compensated by post-transcriptional mechanisms. Methylation of arginine is a conserved post-translational modification executed by Protein Arginine Methyltransferase (PRMTs). The genome from L. major encodes five PRMT homologs, including the cytosolic protein associated with several RNA-binding proteins, LmjPRMT7. It has been previously reported that LmjPRMT7 could impact parasite infectivity. In addition, a more recent work has clearly shown the importance of LmjPRMT7 in RNA-binding capacity and protein stability of methylation targets, demonstrating the role of this enzyme as an important epigenetic regulator of mRNA metabolism. In this study, we unveil the impact of PRMT7-mediated methylation on parasite development and virulence. Our data reveals that higher levels of LmjPRMT7 can impair parasite pathogenicity, and that deletion of this enzyme rescues the pathogenic phenotype of an attenuated strain of L. major. Interestingly, lesion formation caused by LmjPRMT7 knockout parasites is associated with an exacerbated inflammatory reaction in the tissue correlated with an excessive neutrophil recruitment. Moreover, the absence of LmjPRMT7 also impairs parasite development within the sand fly vector Phlebotomus duboscqi. Finally, a transcriptome analysis shed light onto possible genes affected by depletion of this enzyme. Taken together, this study highlights how post-transcriptional regulation can affect different aspects of the parasite biology.

Understanding the genetics of Leishmania, a protozoan parasite causing leishmaniasis, is relevant for understanding fundamental questions on the pathogen’s biology and its interaction with hosts. We explore mechanisms used by Leishmania to promptly adapt to different hosts investigating the control of gene expression occurring at the post-transcriptional level in the parasite. Methylation of arginine performed by Protein Arginine Methyltransferase (PRMTs), among other post-translational modifications, may alter the function and interactions of target proteins, some of them are RNA binding proteins, known regulators of gene expression. In this study, we unveil the impact of PRMT7 on parasite development and pathogenicity. In addition to a negative correlation between the levels of LmjPRMT7 and parasite pathogenicity, we observed an impairment of the parasite development in the sand fly vector. Remarkably, despite a severe lesion development in mice, we observed no differences in parasite burden between infections with the pathogenic LmjPRMT7 knockout parasite or the attenuated parental line. Instead, the severe pathology observed is associated with an exacerbated inflammatory response correlated with excessive neutrophil recruitment.

The Impact of Neutrophil Recruitment to the Skin on the Pathology Induced by Leishmania Infection

Leishmania (L.) are obligate intracellular protozoan parasites that cause the leishmaniases, a spectrum of neglected infectious vector-borne diseases with a broad range of clinical manifestations ranging from local cutaneous, to visceral forms of the diseases. The parasites are deposited in the mammalian skin during the blood meal of an infected female phlebotomine sand fly. The skin is a complex organ acting as the first line of physical and immune defense against pathogens. Insults to skin integrity, such as that occurring during insect feeding, induces the local secretion of pro-inflammatory molecules generating the rapid recruitment of neutrophils. At the site of infection, skin keratinocytes play a first role in host defense contributing to the recruitment of inflammatory cells to the infected dermis, of which neutrophils are the first recruited cells. Although neutrophils efficiently kill various pathogens including Leishmania, several Leishmania species have developed mechanisms to survive in these cells. In addition, through their rapid release of cytokines, neutrophils modulate the skin microenvironment at the site of infection, a process shaping the subsequent development of the adaptive immune response. Neutrophils may also be recruited later on in unhealing forms of cutaneous leishmaniasis and to the spleen and liver in visceral forms of the disease. Here, we will review the mechanisms involved in neutrophil recruitment to the skin following Leishmania infection focusing on the role of keratinocytes in this process. We will also discuss the distinct involvement of neutrophils in the outcome of 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.

Evaluation of the cutaneous inflammatory cells in dogs with leishmaniosis and in dogs without the disease that were naturally infected by Leishmania infantum (syn. L. chagasi)

BACKGROUND

Canine leishmaniosis (CanL) is associated with an aberrant cutaneous immune response. Few studies have compared cutaneous immune cells among dogs with leishmaniosis or infected without leishmaniosis, and noninfected dogs.

HYPOTHESIS/OBJECTIVE

Evaluate the number of neutrophils, histiocytes, T lymphocytes, T-bet-positive, GATA3-positive, FoxP3-positive and interleukin (IL)-17-positive cells, in lesional (Group A) and normal-looking (Group B) skin of nine dogs with stage II/III leishmaniosis; in normal-looking PCR-positive (Group C; n = 6) or PCR-negative (Group D; n = 6) skin of infected dogs; and in the normal-looking skin of 12 noninfected dogs (Group E).

METHODS AND MATERIALS

Diagnosis of CanL considered clinical signs, clinicopathological abnormalities, detection of Leishmania amastigotes in lymph nodes, and/or bone marrow and positive serological results. Paraffin-embedded skin biopsies were processed for routine immunofluorescence and positive cells were identified using commercially available anti-canine antibodies.

RESULTS

In Group A, there was a significantly higher number of neutrophils (P < 0.001), histiocytes (P = 0.012), T lymphocytes (P = 0.011), GATA3-positive (P = 0.02) and IL-17A-positive (P = 0.002) cells compared to Group E. In Group B, there was a significantly higher number of histiocytes (P = 0.02), T lymphocytes (P = 0.004), GATA3-positive (P = 0.006) and FoxP3-positive (P = 0.028) cells compared to Group E. There was no difference in between groups A and B and between groups C or D and E.

CONCLUSIONS AND CLINICAL IMPORTANCE

In the lesional and/or normal-looking skin of dogs with moderate/severe CanL there is an infiltration of neutrophils, histiocytes, T lymphocytes, GATA3-, FoxP3- and IL17A-positive cells. By contrast, the number of these cells is not increased in the normal-looking skin of infected dogs without CanL compared to the skin of noninfected dogs.

Semaphorin 3E Promotes Susceptibility to Leishmania major Infection in Mice by Suppressing CD4+ Th1 Cell Response

Protective immunity to cutaneous leishmaniasis is mediated by IFN-γ-secreting CD4⁺ Th1 cells. IFN-γ binds to its receptor on Leishmania-infected macrophages, resulting in their activation, production of NO, and subsequent destruction of parasites. This study investigated the role of Semaphorin 3E (Sema3E) in host immunity to Leishmania major infection in mice. We observed a significant increase in Sema3E expression at the infection site at different timepoints following L. major infection. Sema3E-deficient (Sema3E knockout [KO]) mice were highly resistant to L. major infection, as evidenced by significantly (p < 0.05-0.01) reduced lesion sizes and lower parasite burdens at different times postinfection when compared with their infected wild-type counterpart mice. The enhanced resistance of Sema3E KO mice was associated with significantly (p < 0.05) increased IFN-γ production by CD4⁺ T cells. CD11c⁺ cells from Sema3E KO mice displayed increased expression of costimulatory molecules and IL-12p40 production following L. major infection and were more efficient at inducing the differentiation of Leishmania-specific CD4⁺ T cells to Th1 cells than their wild-type counterpart cells. Furthermore, purified CD4⁺ T cells from Sema3E KO mice showed increased propensity to differentiate into Th1 cells in vitro, and this was significantly inhibited by the addition of recombinant Sema3E in vitro. These findings collectively show that Sema3E is a negative regulator of protective CD4⁺ Th1 immunity in mice infected with L. major and suggest that its neutralization may be a potential therapeutic option for treating individuals suffering from cutaneous leishmaniasis.

Neutrophils and Visceral Leishmaniasis: Impact on innate immune response and cross-talks with macrophages and dendritic cells

Neutrophils with their array of microbicidal activities are the first innate immune cells to guard against infection. They are also most crucial for the host's initial defense against Leishmania parasites which cause clinically diverse diseases ranging from self-healing cutaneous leishmaniasis (CL) to a more severe visceral form, visceral leishmaniasis (VL). Neutrophils are recruited in large numbers at the infection site after bite of sandfly, which is the vector for the disease. The initial interaction of neutrophils with the parasites may modulate the subsequent innate and adaptive immune responses and hence affect the disease outcome. The purpose of this review is to comprehensively appraise the role of neutrophils during the early stages of Leishmania infection with a focus on the visceral form of the disease. In the past decade, new insights regarding the role of neutrophils in VL have surfaced which have been extensively elaborated in the present review. In addition, since much of the information regarding neutrophil-Leishmania early interaction has accumulated through studies on mouse models of CL, these studies are also revisited. We begin by reviewing the factors which drive the recruitment of neutrophils at the site of injection by the sandfly. We then discuss the studies delineating the molecular mechanisms involved in the uptake of the Leishmania parasite by neutrophils and how the parasite subverts their microbicidal functions. In the end, the interaction of infected neutrophils with macrophages and dendritic cells is summarized.

Unravelling the unsolved paradoxes of cytokine families in host resistance and susceptibility to Leishmania infection

Leishmaniasis is a neglected disease caused by protozoan parasites of the genus Leishmania. Successful clearance of Leishmania relies on a robust human immune response and various cytokines have been implicated in resistance and susceptibility to Leishmania infection. Accordingly, various immunotherapeutic approaches involving cytokines and cytokine receptors are being considered as novel avenues of treatment given the limited efficacy of current anti-leishmanial drugs. These approaches target canonical T helper (Th)1/Type 1 cytokines as intended mediators of host-protection to infection whilst concomitantly suppressing Th2/Type 2 cytokines and their anticipated disease-promoting roles. However, the use of cytokine and cytokine receptor gene-deficient mice over the years has challenged this simplistic view of Th1/Type 1-mediated resistance and Th2/Type 2-mediated susceptibility. Indeed, contribution to susceptibility vs resistance is only a partial consequence to cytokine action as the overall response is multi-faceted due to the pleiotropic, redundant, antagonistic and synergistic action of cytokines and interactions with immune cells in the diseased state. Notably, while the responses of certain cytokines are selectively host-protective or characteristic disease-enhancers, some ligands exert a response depending on the parasite-species initiating infection. Paradoxically, others play dual or contradictory roles in different Leishmania immunopathologies. Hence, cytokines in disease is an unsolved paradox and a comprehensive knowledge of cytokine interplay is important to guide the development of novel immunotherapeutics against leishmaniasis. In this review, we characterize various cytokine families in persistence and clearance of the Leishmania parasite and particularly elucidate unsolved cytokine puzzles in leishmaniasis based on information acquired from "gain of knowledge by loss of function" studies in cytokine and cytokine receptor gene-deficient mice.

The Long Pentraxin 3 (PTX3) Suppresses Immunity to Cutaneous Leishmaniasis by Regulating CD4+ T Helper Cell Response

The long pentraxin 3 (PTX3) plays a critical role in inflammation, tissue repair, and wound healing. Here, we show that PTX3 regulates disease pathogenesis in cutaneous leishmaniasis (CL). PTX3 expression increases in skin lesions in patients and mice during CL, with higher expression correlating with severe disease. PTX3-deficient (PTX3^-/-) mice are highly resistant to L. major and L. braziliensis infections. This enhanced resistance is associated with increases in Th17 and IL-17A responses. The neutralization of IL-17A abolishes this enhanced resistance, while rPTX3 treatment results in decrease in Th17 and IL-17A responses and increases susceptibility. PTX3^-/- CD4⁺ T cells display increased differentiation to Th17 and expression of Th17-specific transcription factors. The addition of rPTX3 suppresses the expression of Th17 transcription factors, Th17 differentiation, and IL-17A production by CD4⁺ T cells from PTX3^-/- mice. Collectively, our results show that PTX3 contributes to the pathogenesis of CL by negatively regulating Th17 and IL-17A responses.

Involvement of the Inflammasome and Th17 Cells in Skin Lesions of Human Cutaneous Leishmaniasis Caused by Leishmania (Viannia) panamensis

Localized cutaneous leishmaniasis (LCL) caused by Leishmania (Viannia) panamensis is an endemic disease in Panama. This condition causes ulcerated skin lesions characterized by a mixed Th1/Th2 immune response that is responsible for disease pathology. However, the maintenance of the in situ inflammatory process involves other elements, such as Th17 and inflammasome responses. Although these processes are associated with parasite elimination, their role in the increase in disease pathology cannot be discarded. Thus, the role in Leishmania infection is still unclear. In this sense, the present study aimed at characterizing the Th17 and inflammasome responses in the skin lesions of patients with LCL caused by L. (V.) panamensis to help elucidate the pathogenesis of this disease in Panama. Th17 and inflammasome responses were evaluated by immunohistochemistry (IHQ) in 46 skin biopsies from patients with LCL caused by L. (V.) panamensis. The Th17 immune response was assessed using CD3, CD4, RoRγt, IL-17, IL-6, IL-23, and TGF-β1 antibodies, and the inflammasome response was assessed by IL-1β, IL-18, and caspase-1 antibodies. The presence of the Th17 and inflammasome responses was evidenced by a positive reaction for all immunological markers in the skin lesions. An inverse correlation between the density of amastigotes and the density of RoRγt⁺, IL-17⁺, IL-1β⁺, and caspase-1⁺ cells was observed, but no correlation between Th17 and the inflammasome response with evolutionary disease pathology was reported. These data showed the participation of Th17 cells and the inflammasome in the inflammatory response of the skin lesions of LCL caused by L. (V.) panamensis infection. These results suggest a role in the control of tissue parasitism of IL-17 and the activation of the NLRP3 inflammasome dependent on IL-1β but cannot exclude their role in the development of disease pathology.

Role of host genetics and cytokines in Leishmania infection

Cytokines and chemokines are important regulators of innate and specific responses in leishmaniasis, a disease that currently affects 12 million people. We overviewed the current information about influences of genetically engineered mouse models of cytokine and chemokine on leishmaniasis. We found that genetic background of the host, parasite species and sub-strain, as well as experimental design often modify effects of genetically engineered cytokine genes. Next we analyzed genes and QTLs (quantitative trait loci) that control response to Leishmania species in mouse in order to establish relationship between genetic control of cytokine expression and organ pathology. These studies revealed a network-like complexity of the combined effects of the multiple functionally diverse QTLs and their individual specificity. Genetic control of organ pathology and systemic immune response overlap only partially. Some QTLs control both organ pathology and systemic immune response, but the effects of genes and loci with the strongest impact on disease are cytokine-independent, whereas several loci modify cytokines levels in serum without influencing organ pathology. Understanding this genetic control might be important in development of vaccines designed to stimulate certain cytokine spectrum.

A historical review of the role of cytokines involved in leishmaniasis

Leishmaniasis is an infectious disease caused by the Leishmania genus, affecting millions of persons in the world. Despite increased studies, no vaccine has been developed against leishmaniasis, and drug resistance is evolving in some Leishmania species (spp). Innate and acquired immune cells and their associated cytokines interplay together to determine the immune responses related outcomes in leishmaniasis. Interferon (IFN)-γ or macrophage activating factor (MAF) is the first effective lymphokine (LK), with a related function to leishmaniasis, discovered in 1979. This review article discussed the history of cytokines involved in Leishmania infection, and it is the first report demonstrating the involvement in the disease by focusing on cutaneous leishmaniasis. Up to now, the role of many cytokines has been determined and the literature review showed that IL-35 is the latest known cytokine involved in leishmaniasis. This review revealed that the cytokines have pleiotropic effects, depending upon the cytokine environment, generated during the infection and the host genetic background or infecting Leishmania spp. Overall, advances in our knowledge of immune cells and their secreted cytokines, contributing to the protection or pathological process of leishmaniasis may help to reach new approaches for immunotherapy.

Interleukin-27 Functional Duality Balances Leishmania Infectivity and Pathogenesis

IL-27 is a cytokine that exerts diverse effects on the cells of innate and adaptive immune systems. Chiefly expressed in macrophages and dendritic cells during the early phase of Leishmania infection, IL-27 contributes to the protection against L. major infection but suppresses the protective Th1 response against L. donovani, L. infantum, L. amazonensis and L. braziliensis infections, suggesting its functional duality. During the late stage of Leishmania infection, IL-27 limits the immunopathogenic reactions and tissue damages. Herein, we analyze the mechanism of the functional duality of IL-27 in the resistance or susceptibility to Leishmania infection, prompting IL-27 for anti-Leishmanial therapy.

IL-17A/F in Leishmania major-resistant C57BL/6 mice

Proinflammatory IL-17 plays an important role in various diseases and defence against extracellular microorganisms. Healing of leishmaniasis is promoted by Th1/Tc1 cells, whereas Th2/Treg are associated with worsened disease outcome. In addition, high expression of IL-17A in Leishmania-susceptible BALB/c and artificial overexpression of IL-17A in T cells in resistant C57BL/6 mice worsened disease outcome. Since C57BL/6 mice lacking only IL-17A exhibited no phenotype, and IL-17A and IL-17F share similar receptors, but differentially regulate chemokine secretion, we studied mice lacking both IL-17A and IL-17F (IL-17A/F^-/- ) in infections with Leishmania major. Interestingly, lesion volumes and parasite burdens were comparable to controls, IL-17A/F^-/- mice developed a Th1/Tc1 phenotype, and exhibited normal lesion resolution. Thus, in C57BL/6 mice, secretion of IL-17A and IL-17F does not influence disease progression. It appears that-depending on the genetic background-cytokines of the IL-17 family might be responsible for disease progression primarily in susceptible mice.

Th17 lymphocytes in atypical cutaneous leishmaniasis caused by Leishmania (L.) infantum chagasi in Central America

Skin lesions in nonulcerated cutaneous leishmaniasis (NUCL) caused by Leishmania (L.) infantum chagasi are characterized by a mononuclear inflammatory infiltrate in the dermis, which is composed mainly of lymphocytes, followed by macrophages, few plasma cells and epithelioid granulomas with mild tissue parasitism. Previous studies have shown that the main population of lymphocytes present in the dermal infiltrate is CD8⁺ T cells, followed by CD4⁺ T cells, which are correlated with IFN-γ⁺ cells. To improve the knowledge of cellular immune responses in NUCL, skin biopsies were submitted to immunohistochemistry using anti-ROR-γt, anti-IL-17, anti-IL-6, anti-TGF-β, and anti-IL-23 antibodies to characterize the involvement of Th17 cells in the skin lesions of patients affected by NUCL. ROR-γt⁺ , IL-17⁺ , IL-6⁺ , TGF-β⁺ and IL-23⁺ cells were observed in the dermal inflammatory infiltrate of NUCL skin lesions. A positive correlation between CD4⁺ T-lymphocytes and ROR-γt⁺ and IL-17⁺ cells suggests that some of the CD4⁺ T-lymphocytes in NUCL could be Th17 lymphocytes. Moreover, a positive correlation between ROR-γt⁺ cells and TGF-β⁺ , IL-6⁺ , IL-17⁺ and IL-23⁺ cells could indicate the role of these cytokines in the differentiation and maintenance of Th17 lymphocytes. Our findings improve knowledge of the pathogenesis of this rare and atypical clinical form of leishmaniasis.

Review on the Role of Host Immune Response in Protection and Immunopathogenesis during Cutaneous Leishmaniasis Infection

Cutaneous leishmaniasis (CL) is a major public health problem worldwide and spreads to human via the bite of sand flies during blood meal. Following its inoculation, the promastigotes are immediately taken up by phagocytic cells and these leishmania-infected host cells produce proinflammatory cytokines that activate other immune cells and these infected host cells produce more cytokines and reactive nitrogen and oxygen species for efficient control of leishmania infection. Many experimental studies showed that resistance to infection with leishmania paraites is associated with the production of proinflammatory cytokines and activation of CD4⁺ Th1 response. On the other hand, vulnerability to this parasitic infection is correlated to production of T helper 2 cytokines that facilitate persistence of parasites and disease progression. In addition, some studies have also indicated that CD8⁺ T cells play a vital role in immune defense through cytokine production and their cytotoxic activity and excessive production of proinflammatory mediators promote amplified recruitment of cells. This could be correlated with excessive inflammatory reaction and ultimately resulted in tissue destruction and development of immunopathogenesis. Thus, there are contradictions regarding the role of immune responses in protection and immunopathogenesis of CL disease. Therefore, the aim of this paper was to review the role of host immune response in protection and its contribution to disease severity for CL infection. In order to obtain more meaningful data regarding the nature of immune response to leishmania, further in-depth studies focused on immune modulation should be conducted to develop better therapeutic strategies.

IL-1 family and Cutaneous Leishmaniasis: A poorly understood relationship

The cytokines of the interleukin (IL) -1 family act in the initiation of an effective immune response in Leishmania infection, represented mainly by the T helper 1 (Th1) profile, in addition to being associated with disease exacerbation and controversial contributions in the Th2 responses. The family also includes members who self-regulate inflammation, such as antagonists and anti-inflammatory cytokines, most of which have not yet been studied in Cutaneous Leishmaniasis (CL) in humans. Here we summarize findings about what is known so far about the role of these cytokines in mice, the main study model, and in humans. We reinforce the importance of studies of these cytokines as new targets in the context of CL.

Targeting of antitumor ımmune responses with live-attenuated Leishmania strains in breast cancer model

BACKGROUND

Cancer is a major cause of death worldwide and most of the therapeutic approaches are relatively ineffective in eliminating cancer especially due to drug resistance. As an alternative, therapy with live microorganisms can induce a robust proinflammatory and anti-cancer immune response in the microenvironment of the tumor. In the present study, we aimed to establish a model for taking the advantages of immune responses against intracellular protozoan parasites for cancer treatment.

METHODS

Leishmania infantum and L. tropica were used in our study as agents of visceral and cutaneous forms of the infection, respectively. After establishing 4T1 breast cancer in mice groups, live-attenuated L. infantum (At-Li) and live-attenuated L. tropica (At-Lt) treatments were performed and results were evaluated according to tumor volume, immune markers and histological examination.

RESULTS

Live-attenuated Leishmania strains regressed 4T1-breast cancer in mice and are nonpathogenic, and these strains induce an immune response against 4T1 breast cancer. It is shown that At-Lt is found to be more effective than At-Li in breast cancer treatment using different methods included in the study as analyses of immune parameters, and histopathological examination in tumor tissue besides spleen cells. The tumor grew more slowly by the immune-stimulant effect of live-attenuated Leishmania parasites.

CONCLUSION

This promising therapy should be investigated for optimization in further studies with different cancer types and L. tropica may be designed to express antigens to enhance tumor antigen-specific responses, which may further improve efficacy and immune memory development.

Interleukin-17 mediated immunity during infections with Trypanosoma cruzi and other protozoans

Host resistance during infection with Trypanosoma cruzi, and other protozoans, is dependent on a balanced immune response. Robust immunity against these pathogens requires of the concerted action of many innate and adaptive cell populations including macrophages, neutrophils, dendritic cells, CD4+, and CD8+ T cells and B cells among others. Indeed, during most protozoan infections only a balanced production of inflammatory (TH1) and anti-inflammatory (TH2/regulatory) cytokines will allow the control of parasite spreading without compromising host tissue integrity. The description of TH17 cells, a novel effector helper T cell lineage that produced IL-17 as signature cytokine, prompted the revision of our knowledge about the mechanisms that mediate protection and immunopathology during protozoan infections. In this manuscript we discuss the general features of IL-17 mediated immune responses as well as the cellular sources, effector mechanisms and overall role of IL-17 in the immune response to T. cruzi and other protozoan infections.

Leishmania major adenylate kinase immunization offers partial protection to a susceptible host

Leishmania major causes mild-to-severe cutaneous lesions resulting in significant disfigurations, if untreated. The drugs are toxic, and drug-resistance parasites are emerging. Therefore, a prophylactic vaccination is an urgent need. As no vaccine is available, we compared the genes expressed by virulent and avirulent parasites. We identify L major adenylate kinase (AdeK) as a probable vaccine candidate after a series of experimentations. We cloned the gene in mammalian pcDNA6/HisA and pet28a⁺ vector for in vivo expression following immunization and in vitro protein expression for booster, respectively. We observed that immunization of susceptible BALB/c mice with AdeK resulted in significant protection against L major challenge infection. The protection was accompanied by increased IFN-γ producing lymphocytes and reduced IL-4, IL-17 and IL-10 secreting central and effector Th2, Th17 and Treg memory cells, respectively. These observations indicate L major AdeK as a potential vaccine candidate.

Immunogenicity of Potential CD4+ and CD8+ T Cell Epitopes Derived From the Proteome of Leishmania braziliensis

Background: A safe and effective vaccine against human leishmaniasis still requires the identification of better antigens for immunization and adequate models to evaluate the immune response. To support vaccine development, this work tested the immunogenicity of 10 different peptides derived from the proteome of Leishmania braziliensis, which were selected by their in silico affinity to MHC complexes.

Research design and Methods: Comparative cell proliferation assays were performed by culturing, in the presence of each peptide, PBMC cells from subclinical subjects (SC), cutaneous leishmaniasis patients with active disease (AD), post-treatment (PT) individuals, and healthy controls. Culture supernatants were then used for Th1, Th2, and Th17 cytokine measurements. Cells from selected PT samples were also used to assess the expression, by T cells, of the T-bet Th1 transcription factor.

Results: A robust cell proliferation was observed for the SC group, for all the tested peptides. The levels of Th1 cytokines were peptide-dependent and had substantial variations between groups, where, for instance, IFN-γ and TNF levels were some of the highest, particularly on PT cultures, when compared to IL-2. On the other hand, Th2 cytokines displayed much less variation. IL-6 was the most abundant among all the evaluated cytokines while IL-4 and IL-10 could be found at much lower concentrations. IL-17 was also detected with variations in SC and AD groups. T-bet was up-regulated in CD4⁺ and CD8⁺ T cells from the PT group after stimulation with all peptides.

Conclusions: The peptide epitopes can differentially stimulate cells from SC, AD, and PT individuals, leading to distinct immune responses.

Obesity impairs resistance to Leishmania major infection in C57BL/6 mice

An association between increased susceptibility to infectious diseases and obesity has been described as a result of impaired immunity in obese individuals. It is not clear whether a similar linkage can be drawn between obesity and parasitic diseases. To evaluate the effect of obesity in the immune response to cutaneous Leishmania major infection, we studied the ability of C57BL/6 mice fed a hypercaloric diet (HSB) to control leishmaniasis. Mice with diet-induced obesity presented thicker lesions with higher parasite burden and a more intense inflammatory infiltrate in the infected ear after infection with L. major. There was no difference between control and obese mice in IFN-gamma or IL-4 production by auricular draining lymph node cells, but obese mice produced higher levels of IgG1 and IL-17. Peritoneal macrophages from obese mice were less efficient to kill L. major when infected in vitro than macrophages from control mice. In vitro stimulation of macrophages with IL-17 decreased their capacity to kill the parasite. Moreover, macrophages from obese mice presented higher arginase activity. To confirm the role of IL-17 in the context of obesity and infection, we studied lesion development in obese IL-17R-/- mice infected with L. major and found no difference in skin lesions and the leukocyte accumulation in the draining lymph node is redcuced in knockout mice compared between obese and lean animals. Our results indicate that diet-induced obesity impairs resistance to L. major in C57BL/6 mice and that IL-17 is involved in lesion development.

Obesity is a serious and increasing public health problem, and also induces a spectrum of metabolic disorders. Some diseases are known to be more severe in the presence of obesity. However, the interactions of obesity with the immune response to infectious agents have not been fully explored. In this study, we investigated the response of obese mice to infection with Leishmania major. C57BL/6 mice were fed a hypercaloric diet (HSB) and infected afterward with L. major. In obese mice, lesions were ticker and more ulcerative, and cells from draining lymph nodes produced more IL-17 when compared with cells from lean mice fed a control diet. Macrophages from obese and lean mice were infected in vitro and stimulated with IL-17 to test the role of this cytokine in effect produced by obesity. Macrophages from obese mice were more infected by L. major than the macrophages from control mice and the number of parasites was increased by treatment with IL-17. IL-17R deficient mice treated with hypercaloric diet showed no difference in lesion size when compared to mice fed control diet. Our findings suggest that diet-induced obesity decrease the resistance to L. major infection of C57BL/6 mice and the IL-17 cytokine may be involved in the lesion formation.