IL-17 and Regulatory Cytokines (IL-10 and IL-27) in L. braziliensis Infection

IL-17 in skin infections and homeostasis

Interleukin (IL) 17 is a proinflammatory cytokine belonging to a structurally related group of cytokines known as the IL-17 family. It has been profoundly studied for its contribution to the pathology of autoimmune diseases. However, it also plays an important role in homeostasis and the defense against extracellular bacteria and fungi. IL-17 is important for epithelial barriers, including the skin, where some of its cellular targets reside. Most of the research work on IL-17 has focused on its effects in the skin within the context of autoimmune diseases or sterile inflammation, despite also having impact on other skin conditions. In recent years, studies on the role of IL-17 in the defense against skin pathogens and in the maintenance of skin homeostasis mediated by the microbiota have grown in importance. Here we review and discuss the cumulative evidence regarding the main contribution of IL-17 in the maintenance of skin integrity as well as its protective or pathogenic effects during some skin infections.

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.

A Prospective cohort study of zoonotic cutaneous leishmaniasis in tunisia: Clinical and Immunological features and immune correlates of protection

BACKGROUND

This study aimed to define immunological markers of exposure to L. major parasites and identify correlates of protection against infection.

METHODS

We analyzed a cohort of 790 individuals at risk of developing ZCL living in endemic areas with varying L. major infection prevalence. One area had a high infection prevalence indicated by high proportions of leishmanin skin test (LST) positive subjects, while the other areas were recent foci with lower infection prevalence. Blood samples were collected before the transmission season to measure Interferon gamma (IFN-γ), Interleukin 10 (IL-10), and Granzyme B (GrB) levels in response to parasite stimulation in peripheral blood mononuclear cells. A one-year follow-up period involved active detection of new ZCL cases to estimate disease incidence after a transmission season and identify immune correlates of protection.

RESULTS

The study population showed heterogeneity in parasite contact, evident from specific scars and/or positive LST results, significantly higher in the old focus compared to recent foci. IFN-γ and GrB were markers of parasite exposure and reliable indicators of immunity to L. major. Positive correlations were observed between IFN-γ/IL-10 and GrB/IL-10 ratios and LST results. Unexpectedly, only 29 new ZCL cases (4%) appeared after a transmission season, with 27 cases reported in recent foci and 2 in the oldest focus. Our findings indicate that individuals in L. major endemic areas are likely to develop ZCL regardless of their LST status. We showed that high pre-transmission season levels of IFN-γ and GrB produced by PBMC, along with a high IFN-γ/IL-10 ratio, were associated with protection.

CONCLUSION

This study on a large cohort at risk of ZCL confirmed IFN-γ and GrB as protective factors against the disease. A high IFN-γ/IL-10 ratio, but not GrB/IL-10 ratio was associated with resistance. These results are valuable for developing and evaluating of a vaccine against human leishmaniasis.

Single nucleotide polymorphisms in genes involved in immune responses and outcome of tegumentary leishmaniasis

Leishmaniases are neglected tropical diseases with a broad clinical spectrum. Tegumentary leishmaniasis (TL) is a disease caused by different Leishmania species, transmitted by phlebotomine sand flies and distributed worldwide. TL can present a cutaneous (CL) or mucocutaneous (MCL) clinical form depending on factors inherent to the parasite, the host and the vector. Polymorphisms in the immune response genes are host genetic factors that influence the pathogenesis or control of leishmaniasis. Single nucleotide polymorphisms (SNPs) in immune genes have been evaluated in several countries where leishmaniasis is endemic. In this review, we report studies on SNPs in several immune genes that might be associated with susceptibility or resistance to TL. We summarize studies from around the world and in Brazil, highlight the difficulties of these studies and future analyses needed to enhance our knowledge regarding host genetic factors in TL. Understanding the genetic characteristics of the host that facilitate resistance or susceptibility to leishmaniasis can contribute to the development of immunotherapy schedules for this disease. The current treatment methods are toxic, and no human vaccine is available.

Low expression of hypoxia-inducible factor-1α and differential expression of immune mediators during experimental infection with Leishmania (Viannia) spp

Leishmania (Viannia) species are the major agents of cutaneous leishmaniasis (CL) in the Americas. Ulcerative stigmatizing skin lesions generally characterize CL. The microenvironment during Leishmania infection is rich in inflammatory cells and molecules, which contrasts with low oxygen levels. The hypoxia-inducible factor (HIF)-1α activates several genes in response to hypoxia and inflammatory reactions, but its role in the CL course is poorly understood. We investigated the expression pattern of the genes HIF-1α, arginase, inducible NO synthase (iNOS), interferon (IFN)-γ, interleukin (IL)-12, and IL-10 in skin lesions and lymph nodes of golden hamsters infected with L. braziliensis, L. lainsoni, and L. naiffi. The animals were infected and followed for 105 days, with paw volume measurements and photos taken weekly. Euthanasia was performed at 0, 15, 56, and 105 days post-infection. The parasite load of paw and lymph node tissues were measured through absolute quantification at real-time PCR (qPCR), and reverse transcription qPCR (RT-qPCR) was applied to demonstrate the relative mRNA expression of the target genes. Among groups, animals infected with L. braziliensis had the highest parasite load in paws and lymph nodes. HIF-1α mRNA was down-regulated during chronic Leishmania (Viannia) infection but demonstrated less inhibition in hamsters infected with L. lainsoni and L. naiffi. Arginase was the most detectable gene in animals infected by L. braziliensis; IFN-γ and IL-10 genes were the most detectable in L. lainsoni and L. naiffi-infected animals. HIF-1α gene transcription seemed to be down-modulated byL. (Viannia)infection and was less inhibited by L. lainsoni and L. naiffi when compared toL. braziliensis. Animals with L. lainsoni and L. naiffi showed better control of the disease. Further studies are necessary to evaluate the mechanism influencing HIF-1α expression and its role on CL protection; such research could elucidate potential use of HIF-1α as a therapeutic target.

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.

An Insight Into Systemic Immune Response in Leishmania donovani Mediated Atypical Cutaneous Leishmaniasis in the New Endemic State of Himachal Pradesh, India

Leishmaniasis continues to afflict known and newer endemic sites despite global efforts towards its control and elimination. In this regard, the emergence of newer endemic sites with unusual disease formats is recognized wherein Leishmania donovani complex classically known to cause visceral disease is demonstrated to cause cutaneous manifestation. In this context, atypical cutaneous leishmaniasis (CL) cases caused by L. donovani genetic variants from the newer endemic state of Himachal Pradesh (HP) in India are beginning to be understood in terms of parasite determinants. The atypical CL manifestation further needs to be explored to define host immune correlates with a possible role in driving the unusual disease progression. In the given study, we performed comprehensive systemic-immune profiling of the atypical CL patients from the study area in HP, India, in comparison with the classical visceral leishmaniasis (VL) patients from the northeast region of India. The systemic immune response was studied using ELISA-based assessment of Th1, Th2, Th17, Treg, and Th22 specific plasma cytokine expression pattern and parasite-specific total serum IgG/IgG subclasses. The specified immune correlates are known to exhibit heterogeneous association with the different infecting parasite species, infection load, and co-lateral host immunopathology in classical CL and VL. In the atypical CL patient group, altered expression of IL-10 emerged as the key finding that could potentially fine-tune the Th1/Th17/Th22 effector cytokine axis towards a localized cutaneous manifestation. A reduced expression of IL-10 along with a high IFN-γ/IL-10 ratio as a readout of effective parasite killing defined atypical cutaneous outcome. In contrast, high circulatory IL-10 levels and a depressed IFN-γ/IL-10 ratio were seen in classical VL patients in line with an ineffective parasite-killing cytokine response. Overall, the study highlights new knowledge on host immune correlates in terms of cytokine expression pattern and IgG subclasses that underline atypical disease manifestation such that L. donovani, a generally visceralizing parasite species cause skin localized cutaneous lesions.

Interleukin 17 Cytokine Profiles in Patients with Cystic Echinococcosis in Babylon Province, Iraq

Cystic Echinococcosis (CE) is the silent chronic Helminthes zoonotic infection caused by the larval stage in intermediate hosts of the dog tapeworm Echicoccous granulosus, which belongs to the Taeniidae family and genus Echinococcu ssp. According to the study of CE, the hospitalization and surgeries of patients indicated the high prevalence of the disease in Iraq.This study aimed to determine some immunological parameters in patients infected with Echinococcus granulose. The study of 53 patients infected with CE showed that in 40 (75.4 %), 5 (9.4%), 4 (7.5%), and 2 (3.7 %) cases the liver, abdominal cavity, kidney, and lungs were involved. In terms of age, most and least number of the patients were within the age ranges of30-40 (n=15, 28.3 %) and60-70 years old (n=7, 13.2 %), respectively. Moreover, 37(56.9%) and 16(43%) of them were female and male, respectively. The enzyme-linked immunosorbent assay (ELISA) was used to measure the level of the Interleukin family among patients. There was a significant increase in the serum level concentration of IL17A and IL17B in patients with hydatid disease, compared to the control group. The changes in different age groups also showed statistically significant differences among them (P≤0.05). The outcome of this study indicated that CE is endemic in Babylon province, Iraq. The ELISA technique is a reliable and efficient test for the early diagnosis and monitoring of human hydatid disease. Moreover, it was found that the liver was the most common site of human hydatid cyst.

Effector functions of Th17 cells are regulated by IL-35 and TGF-β in visceral leishmaniasis

Visceral leishmaniasis (VL) is a debilitating human pathogenesis in which the body's immune functions are severely compromised. Various subsets of T cells, including Th17 cells are important regulators of immune responses observed in various pathologies. The role of Th17 cells and its correlation with immuno-regulatory cytokines are however not well understood in human VL. Herein we studied how IL-17 is associated with the progression of Leishmania donovani infection using murine model of VL. We found induction of a strong IL-17 response at the early phase of infection which progressively reduced to basal level during chronic VL. The mechanistic study of this behavior was found to be linked with the role of regulatory T cells (CD4⁺ CD25⁺ T cells) that suppresses the proliferation of the Th17 cell population. Moreover, TGF-β and IL-35 derived from CD4⁺ CD25⁺ T cells are the key mediators for the downregulation of IL-17 during chronic VL. Thus, this study points to an antagonistic effect of Tregs and Th17 cells that can be used for designing better therapeutic and preventive strategies against leishmaniasis.

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.

Previous History of American Tegumentary Leishmaniasis Alters Susceptibility and Immune Response Against Schistosoma mansoni Infection in Humans

Schistosomiasis and Leishmaniasis are chronic parasitic diseases with high prevalence in some tropical regions and, due to their wide distribution, a risk of co-infections is present in some areas. Nevertheless, the impact of this interaction on human populations is still poorly understood. Thus, the current study evaluated the effect of previous American Tegumentary Leishmaniasis (ATL) on the susceptibility and immune response to Schistosoma mansoni infection in residents from a rural community in Northern of Minas Gerais state, Brazil, an area endemic for both parasitic infections. The participants answered a socioeconomic questionnaire and provided stool and blood samples for parasitological and immunological evaluations. Stool samples were examined by a combination of parasitological techniques to identify helminth infections, especially S. mansoni eggs. Blood samples were used for hemograms and to measure the serum levels of cytokines and chemokines. Reports on previous ATL were obtained through interviews, clinical evaluation forms, and medical records. S. mansoni infection was the most prevalent parasitic infection in the study population (46%), and the majority of the infected individuals had a very low parasite burden. In the same population, 93 individuals (36.2%) reported previous ATL, and the prevalence of S. mansoni infection among these individuals was significantly higher than among individuals with no ATL history. A multiple logistic regression model revealed that S. mansoni infection was positively associated with higher levels of CCL3 and CCL17, and a higher frequency of IL-17 responders. Moreover, this model demonstrated that individuals with an ATL history had a 2-fold higher probability to be infected with S. mansoni (OR = 2.0; 95% CI 1.04–3.68). Among S. mansoni-infected individuals, the logistic regression demonstrated that a previous ATL history was negatively associated with the frequency of IL-17 responders and CXCL10 higher responders, but positively associated with higher IL-27 responders. Altogether, our data suggest that previous ATL may alter the susceptibility and the immune response in S. mansoni-infected individuals, which may likely affect the outcome of schistosomiasis and the severity of the disease in humans.

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.

Astronium fraxinifolium Schott Exerts Leishmanicidal Activity by Providing a Classically Polarized Profile in Infected Macrophages

BACKGROUND

Leishmania braziliensis is prevalent in Latin American countries, including Brazil. It causes cutaneous and mucocutaneous leishmaniasis, leading to high morbidity, and has a low cure rate. Treatment is based on pentavalent antimonials; nonetheless, there are problems related to high toxicity, high cost, and parasitic resistance. Discovery of new leishmanicidal drugs without these limitations and that stimulate the cellular immune response is necessary.

PURPOSE

The present work evaluates whether Astronium fraxinifolium Schott exerts leishmanicidal activity against L. braziliensis by providing a classically polarized profile in infected macrophages.

METHODS

For the evaluation of the A. fraxinifolium Schott leishmanicidal activity, amastigote cell death was demonstrated in infected RAW 267.4 macrophages treated with an ethanolic extract from the plant sapwood (EEAF). For the evaluation of the EEAF capacity in providing a classically polarized profile in infected macrophages, the following analyses were done: detection of LAMP-1 protein by the baculovirus technology, measurement of superoxide anion by the NBT testing, quantification of TNF-α, IL-12p40, IL-10, IL-4, and TGF-β by sandwich-type enzyme immune assays, and iNOS and COX-2 expression by RT-PCR technique.

RESULTS

The EEAF significantly reduced amastigote counts inside the cells. Vacuoles were visualized in infected and treated cells before and after May-Grünwald-Giemsa staining. A strong LAMP-1 protein fluorescence revealed phagosome maturation in infected cells treated with the EEAF. No production of superoxide was visualized in infected cells treated with the plant material. Nonetheless, high levels of TNF-α, IL-12p40, and IL-10 were found in cell supernatants, but reduced levels of TGF-β and no IL-4 production. We identified augmented mRNA expression for COX-2, but no expression of iNOS mRNA.

CONCLUSION

Our results demonstrated that A. fraxinifolium induced a classically polarized profile in infected macrophages but also provided a less harmful environment by stimulating the production of certain anti-inflammatory mediators, such as IL-10.

LEISHMANICIDAL ACTIVITY in vivo OF A MILTEFOSINE DERIVATIVE IN Mesocricetus auratus

Visceral leishmaniasis (VL) is a chronic and systemic disease; if untreated, it can cause death in a large number of cases. The therapy is based on the use of antimonials, which have been used for over 50 years. However, cases of resistance have been reported in some countries. In this context, miltefosine (MIL) was introduced to treat antimonial unresponsive cases. Nonetheless, in recent years MIL unresponsive and relapse cases of VL have increasingly been reported. In the current study, the therapeutic potential of compound 5-(4-(3-methanesulfonatepropyl)-1H-1,2,3-triazol-1-yl)dodecyl methanesulfonate (C11), an MIL derivative, was assessed in an experimental VL hamster model. For this purpose, golden hamsters (Mesocricetus auratus) were infected with Leishmania (L.) infantum chagasi and treated daily for 10 days with C11 and MIL administered orally; in addition, Glucantime (GLU), peritoneal route, were administered at 15, 10, 50 mg/kg body weight/day, respectively. Twenty four hours after the end of treatment the animals were euthanatized; and the specimens were collected to evaluate the relative mRNA expression of cytokines IFN-γ, TNF-α, IL-17, TGF-β, IL-4 and IL-10 in fragments of the spleen and liver; moreover, the parasitism in these organs was evaluated as well as the main histopathological alterations. The C11-treated animals showed greater expression of IL-17 and TNF-α cytokines and reduced expression of IL-10 in the spleen in comparison to the infected untreated group (UTG) (p <0.05). The C11 and GLU groups showed a significant reduction in the IgG levels in comparison to the UTG group (p <0.05). Moreover, the C11-treated animals had fewer parasites in the spleen than the UTG animals (reduction of 95.9%), as well as a greater preservation of white pulp architecture in the spleen than the UTG, GLU and MIL groups (p <0.05). For the liver, the animals from the C11 and MIL groups showed a significant increase in TNF-α relative expression in comparison to the UTG animals, which would explain the increase in the number of granulomas and the reduction in the parasitic load (p <0.05). Combined, these findings indicate that C11 is an interesting compound that should be considered for the development of new drugs against VL, mainly due to its leishmanicidal effect and immunostimulating action.

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.

Leishmania infantum induces high phagocytic capacity and intracellular nitric oxide production by human proinflammatory monocyte

BACKGROUND

The mechanism of resistance to Sb^III in Leishmania is complex, multifactorial and involves not only biochemical mechanisms, but also other elements, such as the immune system of the host.

OBJECTIVES

In this study, putative changes in the immunological profile of human monocytes infected with wild-type (WT) and antimony (Sb^III)-resistant Leishmania (Viannia) braziliensis and Leishmania (Leishmania) infantum lines were evaluated.

METHODS

Susceptibility assays WT and SbIII-resistant L. braziliensis and L. infantum were performed using lines THP-1 human monocytic lineage. Phagocytic capacity, cytokine profile, intracellular nitric oxide (NO) production and surface carbohydrate residues profile were performed in peripheral blood monocytes by flow cytometry.

FINDINGS

The phagocytic capacity and intracellular NO production by classical (CD14⁺⁺CD16^-) and proinflammatory (CD14⁺⁺CD16⁺) monocytes were higher in the presence of L. infantum lines compared to L. braziliensis lines. The results also highlight proinflammatory monocytes as the cellular subpopulation of major relevance in a phagocytosis event and NO expression. It is important to note that L. infantum induced a proinflammatory cytokine profile characterised by higher levels of TNF-α in culture supernatant than L. braziliensis. Conversely, both Leishmania lines induce high levels of IL-6 in culture supernatant. Analysis of the expression profile of surface carbohydrates showed that L. braziliensis presents 4.3-fold higher expression of galactose(β1,4)N-acetylglucosamine than L. infantum line. Interestingly, the expression level of α-N-acetylgalactosamine residues was 2-fold lower in the Sb^III-resistant L. braziliensis line than its counterpart WT line, indicating differences in surface glycoconjugates between these lines.

MAIN CONCLUSIONS

Our results showed that L. braziliensis and L. infantum induce different innate immune responses and a highly inflammatory profile, which is characteristic of infection by L. infantum, the species associated with visceral disease.

Genetic variation in Interleukin-32 influence the immune response against New World Leishmania species and susceptibility to American Tegumentary Leishmaniasis

Interleukin-32 is a novel inflammatory mediator that has been described to be important in the immunopathogenesis and control of infections caused by Leishmania parasites. By performing experiments with primary human cells in vitro, we demonstrate that the expression of IL-32 isoforms is dependent on the time exposed to L. amazonensis and L. braziliensis antigens. Moreover, for the first time we show the functional consequences of three different genetic variations in the IL32 (rs4786370, rs4349147, rs1555001) modulating IL-32γ expression, influencing innate and adaptive cytokine production after Leishmania exposure. Using a Brazilian cohort of 107 American Tegumentary Leishmaniasis patients and a control cohort of 245 healthy individuals, the IL32 rs4786370 genetic variant was associated with protection against ATL, whereas the IL32 rs4349147 was associated with susceptibility to the development of localized cutaneous and mucosal leishmaniasis. These novel insights may help improve therapeutic strategies and lead to benefits for patients suffering from Leishmania infections.

In this study, we described how IL-32 isoforms are crucial to host defense against new world Leishmania species infections. Furthermore, by accessing the genotype frequency of genetic variations in IL32 in a cohort of Brazilian patients with American Tegumentary Leishmaniasis (ATL) and controls, we have obtained indications that IL-32 is associated with disease susceptibility and the development of different clinical manifestations. Thus, this study provides us an extra evidence that the isoforms of IL-32 shape the immune response favoring the development of different cytokines produced by peripheral blood mononuclear cells that might contribute to skin/mucosal inflammation and host defense.

Study of association of the rs2275913 IL-17A single nucleotide polymorphism and susceptibility to cutaneous leishmaniasis caused by Leishmania braziliensis

Cutaneous leishmaniasis (CL) caused by Leishmania braziliensis is the most spread clinical form of leishmaniasis in Brazil. However, only a few part of the people infected develop clinically perceptive disease, suggesting the influence of human genetic components in the CL pathogeny. The rs2275913 SNP is the nucleotide variant of the IL17A gene. The A allele is associated with a vast number of infectious and non-infectious diseases. Here, we investigated the association of the rs2275913 SNP (G/A) from IL-17A and two forms of susceptibility to CL in Brazil by case-control study. Furthermore, we evaluated the functional relevance of this SNP during the immune response of the host and analyzed its impact in the parasite elimination. Weak associations of A allele with susceptibility to L. braziliensis infection or to symptomatic CL were observed, and a tendency of A allele carriers to be more susceptible to infection and cutaneous disease. Functional analysis of the Th17 cell phenotypes revealed lower frequencies of CD4+ IL-17+ cells in samples of infected people with AA/AG genotypes. Furthermore, people carrying the A allele maintain higher parasite loads, reinforcing the genetic susceptibility findings. This study adds knowledge about the influence of a significant genetic variation on IL-17 promoter on CL pathogenesis, and may contribute to enhance the knowledge about the role of IL-17 in the L. braziliensis infections.

Combination of flow cytometry and qPCR to study the immune response of american cutaneous leishmaniasis patients

American Cutaneous leishmaniasis (ACL) is a public health problem. The immunological response is mainly dependent on T cell cytokine responses and might influence disease presentation, susceptibility and development. The understanding of the host immune response role in the control and in the pathology of leishmaniasis is relevant and has implications on diagnosis, follow-up and vaccine development. In this study, the differences in the immune response and T cell profile of patients before treatment was investigated through flow cytometry and real time PCR in peripheral blood mononuclear cells after different antigenic stimulations. Among the main findings are the significant presence of TNF and IFN-γ gene expression after 24 h of in vitro stimulation, and 48 h later the presence of CD4⁺ T and CD8⁺ T cells producing IL-10 and IL-4. This may be due to the differences in cytokine release over time and the presence of cells other than lymphocytes influencing the mRNA transcript detection. Evaluation of the immune response of individuals with leishmaniasis or other diseases should associate different technologies and times points for a clear and more reliable assessment of the immune response. This would help in the design of vaccine strategies/immunotherapies.

Dual immune effect of iNKT cells considering human cutaneous and visceral leishmaniasis: An example of cell plasticity according to different disease scenarios

Although the semi-invariant natural killer T cells (iNKT) are a small subpopulation of cells in the peripheral blood, they are presumed to play a role in early stages of infection against various pathogens, including protozoa. This work investigates the activation status and cytokine profile of iNKT cells during human Leishmania infantum and Leishmania braziliensis infection. We studied iNKT cells in patients with symptomatic active visceral leishmaniasis (AVL) (n = 8), patients with symptomatic active cutaneous leishmaniasis (ACL) (n = 13), negative endemic controls (NEC) (n = 6) and non-endemic controls (NonEC) (n = 6), with and without total Leishmania antigen stimulus (TLA). The number of iNKT cells in the peripheral blood of patients with ACL and AVL unaltered in relation to control groups. Moreover, the iNKT cells from ACL showed a hyperactivation profile compared to patients with AVL. Additionally, TLA induced IFN-gamma production in iNKT cells from patients with ACL, while in iNKT of patients with AVL, TLA induced a decrease in this cytokine. Higher IL-17 and IL-10 production by iNKT cells from patients with ACL were also observed compared to all other groups. There were no changes in iNKT IL-10-producing cells in AVL after TLA stimulation. However, TLA induced increase in IL-10 in iNKT cells in patients with ACL. These findings suggest that, although iNKT cells showed distinct profiles in patients with ACL and AVL, they play a dual role in immune modulation in both Leishmania infections.

Human Interleukin-32γ Plays a Protective Role in an Experimental Model of Visceral Leishmaniasis in Mice

Visceral leishmaniasis (VL) is a chronic parasitic disease caused by Leishmania infantum in the Americas. During VL, several proinflammatory cytokines are produced in spleen, liver, and bone marrow. However, the role of interleukin-32 (IL-32) has not been explored in this disease. IL-32 can induce production of proinflammatory cytokines in innate immune cells and polarize the adaptive immune response. Herein, we discovered that L. infantum antigens induced expression of mRNA mainly for the IL-32γ isoform but also induced low levels of the IL-32β transcript in human peripheral blood mononuclear cells. Furthermore, infection of human IL-32γ transgenic mice (IL-32γTg mice) with L. infantum promastigote forms increased IL-32γ expression in the spleen and liver. Interestingly, IL-32γTg mice harbored less parasitism in the spleen and liver than wild-type (WT) mice. In addition, IL-32γTg mice showed increased granuloma formation in the liver compared to WT mice. The protection against VL was associated with increased production of nitric oxide (NO), interferon gamma (IFN-γ), IL-17A, and tumor necrosis factor alpha by splenic cells restimulated ex vivo with L. infantum antigens. In parallel, there was an increase in the number of Th1 and Th17 T cells in the spleens of IL-32γTg mice infected with L. infantum IL-32γ induction of IFN-γ and IL-17A expression was found to be essential for NO production by splenic cells of infected animals. These data indicate that IL-32γ potentiates the Th1/Th17 immune response during experimental VL, thus contributing to the control of L. infantum infection.

Oliveira CN, de Lorena VMB, de Paiva-Cavalcanti M. The Equivocal Role of Th17 Cells and Neutrophils on Immunopathogenesis of Leishmaniasis

Advances in the understanding of leishmaniasis progression indicate that cellular interactions more complex than the Th1/Th2 paradigm define the course of infection. Th17 cells are a crucial modulator of adaptive immunity against Leishmania parasites acting mainly on neutrophil recruitment and playing a dual role at the site of infection. This review describes the roles of both these cell types in linking innate defense responses to the establishment of specific immunity. We focus on the Th17-neutrophil interaction as a crucial component of anti-Leishmania immunity, and the clinical evolution of cutaneous or visceral leishmaniasis. To date, information obtained through experimental models and patient evaluations suggests that the influence of the presence of interleukin (IL)-17 (the main cytokine produced by Th17 cells) and neutrophils during Leishmania infections is strictly dependent on the tissue (skin or liver/spleen) and parasite species. Also, the time at which neutrophils are recruited, and the persistence of IL-17 in the infection microenvironment, may also be significant. A clearer understanding of these interactions will enable better measurement of the influence of IL-17 and its regulators, and contribute to the identification of disease/resistance biomarkers.

F1 Domain of the Leishmania (Leishmania) donovani Nucleoside Hydrolase Promotes a Th1 Response in Leishmania (Leishmania) infantum Cured Patients and in Asymptomatic Individuals Living in an Endemic Area of Leishmaniasis

The Leishmania (Leishmania) donovani nucleoside hydrolase NH36 is the main antigen of the Leishmune® vaccine and one of the promising candidates for vaccination against visceral leishmaniasis. The antigenicity of the N-terminal (F1), the central (F2), or the C-terminal recombinant domain (F3) of NH36 was evaluated using peripheral blood mononuclear cells (PBMC) from individuals infected with L. (L.) infantum from an endemic area of visceral leishmaniasis of Spain. Both NH36 and F1 domains significantly increased the PBMC proliferation stimulation index of cured patients and infected asymptomatic individuals compared to healthy controls. Moreover, F1 induced a 19% higher proliferative response than NH36 in asymptomatic exposed subjects. In addition, in patients cured from visceral leishmaniasis, proliferation in response to NH36 and F1 was accompanied by a significant increase of IFN-γ and TNF-α secretion, which was 42-43% higher, in response to F1 than to NH36. The interleukin 17 (IL-17) secretion was stronger in asymptomatic subjects, in response to F1, as well as in cured cutaneous leishmaniasis after NH36 stimulation. While no IL-10 secretion was determined by F1, a granzyme B increase was detected in supernatants from cured patients after stimulation with either NH36 or F1. These data demonstrate that F1 is the domain of NH36 that induces a recall cellular response in individuals with acquired resistance to the infection by L. (L.) infantum. In addition, F1 and NH36 discriminated the IgG3 humoral response in patients with active visceral leishmaniasis due to L. (L.) donovani (Ethiopia) and L. (L.) infantum (Spain) from that of endemic and non-endemic area controls. NH36 showed higher reactivity with sera from L. (L.) donovani-infected individuals, indicating species specificity. We conclude that the F1 domain, previously characterized as an inducer of the Th1 and Th17 responses in cured/exposed patients infected with L. (L.) infantum chagasi, may also be involved in the generation of a protective response against L. (L.) infantum and represents a potential vaccine candidate for the control of human leishmaniasis alone, or in combination with other HLA epitopes/antigens.

Cutaneous Manifestations of Human and Murine Leishmaniasis

The leishmaniases are diseases caused by pathogenic protozoan parasites of the genus Leishmania. Infections are initiated when a sand fly vector inoculates Leishmania parasites into the skin of a mammalian host. Leishmania causes a spectrum of inflammatory cutaneous disease manifestations. The type of cutaneous pathology is determined in part by the infecting Leishmania species, but also by a combination of inflammatory and anti-inflammatory host immune response factors resulting in different clinical outcomes. This review discusses the distinct cutaneous syndromes described in humans, and current knowledge of the inflammatory responses associated with divergent cutaneous pathologic responses to different Leishmania species. The contribution of key hematopoietic cells in experimental cutaneous leishmaniasis in mouse models are also reviewed and compared with those observed during human infection. We hypothesize that local skin events influence the ensuing adaptive immune response to Leishmania spp. infections, and that the balance between inflammatory and regulatory factors induced by infection are critical for determining cutaneous pathology and outcome of infection.

Yin and yang of interleukin-17 in host immunity to infection

The interleukin-17 (IL-17) family cytokines, such as IL-17A and IL-17F, play important protective roles in host immune response to a variety of infections such as bacterial, fungal, parasitic, and viral. The IL-17R signaling and downstream pathways mediate induction of proinflammatory molecules which participate in control of these pathogens. However, the production of IL-17 can also mediate pathology and inflammation associated with infections. In this review, we will discuss the yin-and-yang roles of IL-17 in host immunity to pathogens.

Comparison of pro-inflammatory cytokines of non-healing and healing cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) heals spontaneously within several weeks or months, but, in rare cases, CL-active lesions last for many years. In this study, we assessed cell-mediated immunity in non-healing CL through the measurement of three pro-inflammatory cytokines: Interferon-γ (IFN-γ), IL-17a and CXCL-11. For this, 32 patients afflicted with healing or non-healing CL were recruited in this study. Peripheral blood mononuclear cells (PBMCs) of every patient were treated with three antigens: purified protein derivative (PPD), soluble Leishmania antigen (SLA) and phytohaemagglutinin (PHA). Cytokine quantification was performed using enzyme-linked immunosorbent assay (ELISA) method. Results of our study showed that neither cytokine produced in the presence of a PPD stimulator (as an irrelevant antigen) significantly differed between the healing and non-healing groups (P-value ≥0.05 for all of them). However, IFN-γ, CXCL-11 and IL-17a levels produced in the presence of PHA or SLA were significantly higher within the healing than in the non-healing group (P-value <0.01 for all of them). It seems that appropriate levels of IFN-γ, as well as IL-17a and CXCL-11, contribute to the control of Leishmania infection.

Interleukin-27 Early Impacts Leishmania infantum Infection in Mice and Correlates with Active Visceral Disease in Humans

The complexity of Leishmania–host interactions, one of the main leishmaniasis issues, is yet to be fully understood. We detected elevated IL-27 plasma levels in European patients with active visceral disease caused by Leishmania infantum, which returned to basal levels after successful treatment, suggesting this cytokine as a probable infection mediator. We further addressed this hypothesis recurring to two classical susceptible visceral leishmaniasis mouse models. BALB/c, but not C57BL/6 mice, showed increased IL-27 systemic levels after infection, which was associated with an upregulation of IL-27p28 expression by dendritic cells and higher parasite burdens. Neutralization of IL-27 in acutely infected BALB/c led to decreased parasite burdens and a transient increase in IFN-γ⁺ splenic T cells, while administration of IL-27 to C57BL/6 promoted a local anti-inflammatory cytokine response at the site of infection and increased parasite loads. Overall, we show that, as in humans, BALB/c IL-27 systemic levels are infection dependently upregulated and may favor parasite installation by controlling inflammation.

Role of pro-inflammatory cytokine IL-17 in Leishmania pathogenesis and in protective immunity by Leishmania vaccines

The clinical outcome of Leishmania pathogenesis ranges from active skin lesions to fatal visceral dissemination and severely impaired T cell immunity. It is well established that a strong Th1 immune response is protective against cutaneous forms of the disease, however a mixed Th1/Th2 response is most commonly observed against visceral infections as evident from previous studies. Aside from Th1/Th2 cytokines, the pro-inflammatory IL-17 cytokine family plays an important role in the clearance of intracellular pathogens. In Leishmania induced skin lesions, IL-17 produced by Th17 cells is shown to exacerbate the disease, suggesting a role in pathogenesis. However, a protective role for IL-17 is indicated by the expansion of IL-17 producing cells in vaccine-induced immunity. In human visceral leishmaniasis (VL) it has been demonstrated that IL-17 and IL-22 are associated with protection against re-exposure to Leishmania, which further suggests the involvement of IL-17 in vaccine induced protective immunity. Although there is no vaccine against any form of leishmaniasis, the development of genetically modified live attenuated parasites as vaccine candidates prove to be promising, as they successfully induce a robust protective immune response in various animal models. However, the role of IL-17 producing cells and Th17 cells in response to these vaccine candidates remains unexplored. In this article, we review the role of IL-17 in Leishmania pathogenesis and the potential impact on vaccine induced immunity, with a special focus on live attenuated Leishmania parasites.

Immunologic Markers of Protection in Leishmania (Viannia) braziliensis Infection: A 5-Year Cohort Study

BACKGROUND

The control of Leishmania braziliensis by individuals with subclinical infection (SC) are unknown.

METHODS

A cohort of 308 household contacts (HCs) of patients with cutaneous leishmaniasis (CL) was established in 2010 in an endemic area and followed up for 5 years. Whole-blood cultures stimulated with soluble Leishmania antigen and a Leishmania skin test (LST) were performed in years 0, 2, and 4. The identification of the lymphocyte subsets secreting interferon (IFN) γ and the ability of monocytes to control Leishmania were determined.

RESULTS

During follow-up, 118 subjects (38.3%) had evidence of L. braziliensis infection. Of the HCs, CL was documented in 45 (14.6%), 101 (32.8%) had SC infection, and 162 (52.6%) did not have evidence of exposure to L. braziliensis The ratio of infection to disease was 3.2:1. IFN-γ production, mainly by natural killer cells, was associated with protection, and a positive LST result did not prevent development of disease. Moreover, monocytes from subjects with SC infection were less permissive to parasite penetration and had a greater ability to control L. braziliensis than cells from patients with CL.

CONCLUSIONS

Protection against CL was associated with IFN-γ production, negative LST results, impaired ability of Leishmania to penetrate monocytes, and increased ability to control Leishmania growth.

Leishmania tarentolae secreting the sand fly salivary antigen PpSP15 confers protection against Leishmania major infection in a susceptible BALB/c mice model

Cutaneous leishmaniasis is a zoonotic, vector-borne disease causing a major health problem in several countries. No vaccine is available and there are limitations associated with the current therapeutic regimens. Immune responses to sand fly saliva have been shown to protect against Leishmania infection. A cellular immune response to PpSP15, a protein from the sand fly Phlebotomus papatasi, was sufficient to control Leishmania major infection in mice. This work presents data supporting the vaccine potency of recombinant live non-pathogenic Leishmania (L.) tarentolae secreting PpSP15 in mice and its potential as a new vaccine strategy against L. major. We generated a recombinant L. tarentolae-PpSP15 strain delivered in the presence of CpG ODN and evaluated its immunogenicity and protective immunity against L. major infection in BALB/c mice. In parallel, different vaccination modalities using PpSP15 as the target antigen were compared. Humoral and cellular immune responses were evaluated before and at three and eight weeks after challenge. Footpad swelling and parasite load were assessed at eight and eleven weeks post-challenge. Our results show that vaccination with L. tarentolae-PpSP15 in combination with CpG as a prime-boost modality confers strong protection against L. major infection that was superior to other vaccination modalities used in this study. This approach represents a novel and promising vaccination strategy against Old World cutaneous leishmaniasis.

CD8+ T cells in cutaneous leishmaniasis: the good, the bad, and the ugly

CD8(+) T lymphocytes are components of the adaptive immune response and play an important role in protection against many viral and bacterial infections. However, their role in parasitic infections is less well understood. In leishmaniasis, a disease caused by intracellular protozoan parasites of the genus Leishmania, CD8(+) T cells have been shown to be protective. However, increasing evidence indicates that CD8(+) T cells may also exacerbate disease. In this review, we will describe the situations where CD8(+) T cells are either good or bad for the outcome of the infection and attempt to reconcile the dual role played by CD8(+) T cells in cutaneous leishmaniasis.

Protective and pathological functions of CD8+ T cells in Leishmania braziliensis infection

Cutaneous leishmaniasis (CL) caused by Leishmania braziliensis is characterized by a strong Th1 response that leads to skin lesion development. In areas where L. braziliensis transmission is endemic, up to 15% of healthy subjects have tested positive for delayed-type hypersensitivity to soluble leishmania antigen (SLA) and are considered to have subclinical (SC) infection. SC subjects produce less gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) than do CL patients, but they are able to control the infection. The aim of this study was to characterized the role of CD8(+) T cells in SC infection and in CL. Peripheral blood mononuclear cells (PBMC) were stimulated with SLA to determine the frequencies of CD4(+) IFN-γ(+) and CD8(+) IFN-γ(+) T cells. Monocytes from PBMC were infected with L. braziliensis and cocultured with CD8(+) T cells, and the frequencies of infected monocytes and levels of cytotoxicity markers, target cell apoptosis, and granzyme B were determined. The frequency of CD8(+) IFN-γ(+) cells after SLA stimulation was higher for SC individuals than for CL patients. The frequency of infected monocytes in SC cells was lower than that in CL cells. CL CD8(+) T cells induced more apoptosis of infected monocytes than did SC CD8(+) T cells. Granzyme B production in CD8(+) T cells was higher in CL than in SC cells. While the use of a granzyme B inhibitor decreased the number of apoptotic cells in the CL group, the use of z-VAD-FMK had no effect on the frequency of these cells. These results suggest that CL CD8(+) T cells are more cytotoxic and may be involved in pathology.

Immunoregulation in human American leishmaniasis: balancing pathology and protection

Leishmaniasis covers a broad spectrum of diseases with distinct, and sometimes overlapping, characteristics. The common thread in all forms of leishmaniasis is the infection by the parasite Leishmania belonging to the genus Leishmania. Upon infection of humans, there can be at least three outcomes, (i) control of Leishmania by the host immune response resulting in asymptomatic disease, (ii) patent infection and development of a relatively mild form of leishmaniasis and (iii) patent infection and development of severe clinical forms. The factors that determine the outcome of an initial inoculation with Leishmania are many, with the species of Leishmania representing one of the strongest predictive factors for the development of a given clinical form of disease. This is seen with L. braziliensis and L. amazonensis, infection leading mostly to tegumentary forms of disease, and L. infantum with the potential to induce visceral disease. However, it is also clear that the host immune response is a key factor in disease progression, not only responsible for control of Leishmania, but also playing an important role in disease progression and pathology. This duality between protective and pathogenic immune responses in individuals infected with Leishmania in the Americas is the focus of this review.

IL-27 enhances Leishmania amazonensis infection via ds-RNA dependent kinase (PKR) and IL-10 signaling

The protozoan parasite Leishmania infects and replicates in macrophages, causing a spectrum of diseases in the human host, varying from cutaneous to visceral clinical forms. It is known that cytokines modulate the immunological response against Leishmania and are relevant for infection resolution. Here, we report that Interleukin (IL)-27 increases Leishmania amazonensis replication in human and murine macrophages and that the blockage of the IL-10 receptor on the surface of infected cells abolished the IL-27-mediated enhancement of Leishmania growth. IL-27 induced the activation/phosphorylation of protein kinase R (PKR) in macrophages, and PKR blockage or PKR gene deletion abrogated the enhancement of the parasite growth driven by IL-27, as well as the L. amazonensis-induced macrophage production of IL-27. We also observed that L. amazonensis-induced expression of IL-27 depends on type I interferon signaling and the engagement of Toll-like receptor 2. Treatment of Leishmania-infected mice with IL-27 increased lesion size and parasite loads in the footpad and lymph nodes of infected animals, indicating that this cytokine exerts a local and a systemic effect on parasite growth and propagation. In conclusion, we show that IL-27 is a L. amazonensis-enhancing factor and that the PKR/IFN1 axis and IL-10 are critical mediators of this IL-27 induced effect.

Comparative evaluation of lesion development, tissue damage, and cytokine expression in golden hamsters (Mesocricetus auratus) infected by inocula with different Leishmania (Viannia) braziliensis concentrations

The golden hamster (Mesocricetus auratus) is a susceptible model to Leishmania (Viannia) spp.; however, available studies employ different infection protocols, which account for clinical and pathological presentation differences. Herein, L. (V.) braziliensis preparations were standardized to contain 10(4), 10(5), or 10(6) parasites to determine an optimal inoculum that ensured cutaneous lesions without causing a disseminated infection in hamsters. Lesion development was followed for 105 days by size measurements, and skin, draining lymph node, spleen, and sera were investigated to check parasite load, spleen visceralization, cytokine expression, histopathological changes, and anti-Leishmania IgG levels. The lesion emergence time was inversely proportional to the parasite concentration in the inocula. Animals infected by 10(4) parasites presented nodular lesions, while those infected with 10(6) parasites often exhibited ulcerated lesions. The differences in the final lesion sizes were observed between 10(4) and 10(5) inocula or 10(4) and 10(6) inocula. High IFNG expression, anti-Leishmania IgG levels, and parasite load occurred independently of the inoculum used. A mild inflammatory skin involvement was observed in animals infected with 10(4) parasites, while extensive tissue damage and parasite spleen visceralization occurred with 10(5) and 10(6) parasites. These results indicate that inocula with different concentrations of parasites generate differences in the time of lesion emergence, clinical presentation, and systemic commitment, despite high and similar IFNG expression and parasite load. This suggests that a modulation in the immune response to different parasite numbers occurs in an early phase of the infection, which could dictate the establishment and magnitude of the chronic phase of the disease.

The Role of CD4 and CD8 T Cells in Human Cutaneous Leishmaniasis

Leishmaniasis, caused by infection with parasites of the Leishmania genus, affects millions of individuals worldwide. This disease displays distinct clinical manifestations ranging from self-healing skin lesions to severe tissue damage. The control of Leishmania infection is dependent on cellular immune mechanisms, and evidence has shown that CD4 and CD8 T lymphocytes play different roles in the outcome of leishmaniasis. Although the presence of CD4 T cells is important for controlling parasite growth, the results in the literature suggest that the inflammatory response elicited by these cells could contribute to the pathogenesis of lesions. However, recent studies on CD8 T lymphocytes show that these cells are mainly involved in tissue damage through cytotoxic mechanisms. In this review, we focus on the recent advances in the study of the human adaptive immunological response in the pathogenesis of tegumentary leishmaniasis.

Tr-1-like CD4+CD25-CD127-/lowFOXP3- cells are the main source of interleukin 10 in patients with cutaneous leishmaniasis due to Leishmania braziliensis

CD4(+)CD25(+)FOXP3(+) regulatory T cells have long been shown to mediate susceptibility to Leishmania infection, mainly via interleukin 10 production. In this work, we showed that the main sources of interleukin 10 in peripheral blood mononuclear cells (PBMCs) from patients with cutaneous leishmaniasis due to Leishmania braziliensis are CD4(+)CD25(-)CD127(-/low)FOXP3(-) cells. Compared with uninfected controls, patients with CL had increased frequencies of circulating interleukin 10-producing CD4(+)CD25(-)CD127(-/low) cells, which efficiently suppressed tumor necrosis factor α production by the total PBMC population. Also, in CL lesions, interleukin 10 was mainly produced by CD4(+)CD25(-) cells, and interleukin 10 messenger RNA expression was associated with interleukin 27, interleukin 21, and interferon γ expression, rather than with FOXP3 or transforming growth factor β expressions. Active production of both interleukin 27 and interleukin 21, together with production of interferon γ and interleukin 10, was also detected in the lesions. Since these cytokines are associated with the differentiation and activity of Tr-1 cells, our results suggest that this cell population may play an important role in the immunomodulation of CL. Therefore, development of treatments that interfere with this pathway may lead to faster parasite elimination.

The immunotherapeutic role of regulatory T cells in Leishmania (Viannia) panamensis infection

Leishmania (Viannia) parasites are etiological agents of cutaneous leishmaniasis in the New World. Infection is characterized by a mixed Th1/Th2 inflammatory response, which contributes to disease pathology. However, the role of regulatory T cells (Tregs) in Leishmania (Viannia) disease pathogenesis is unclear. Using the mouse model of chronic L. (V.) panamensis infection, we examined the hypothesis that Treg functionality contributes to control of pathogenesis. Upon infection, Tregs (CD4(+)Foxp3(+)) presented with a dysregulated phenotype, in that they produced IFN-γ, expressed Tbet, and had a reduced ability to suppress T cell proliferation in vitro. Targeted ablation of Tregs resulted in enlarged lesions, increased parasite load, and enhanced production of IL-17 and IFN-γ, with no change in IL-10 and IL-13 levels. This indicated that an increased inflammatory response was commensurate with disease exacerbation and that the remaining impaired Tregs were important in regulation of disease pathology. Conversely, adoptive transfer of Tregs from naive mice halted disease progression, lowered parasite burden, and reduced cytokine production (IL-10, IL-13, IL-17, IFN-γ). Because Tregs appeared to be important for controlling infection, we hypothesized that their expansion could be used as an immunotherapeutic treatment approach. As a proof of principle, chronically infected mice were treated with rIL-2/anti-IL-2 Ab complex to expand Tregs. Treatment transitorily increased the numbers and percentage of Tregs (draining lymph node, spleen), which resulted in reduced cytokine responses, ameliorated lesions, and reduced parasite load (10(5)-fold). Thus, immunotherapy targeting Tregs could provide an alternate treatment strategy for leishmaniasis caused by Leishmania (Viannia) parasites.

Characterization of regulatory T cell (Treg) function in patients infected with Leishmania braziliensis

Th1 immune responses are crucial for eliminating Leishmania parasites. However, despite strong Th1 responses, cutaneous leishmaniasis (CL) patients infected with Leishmania braziliensis develop the disease, while milder Th1 responses are found in sub-clinical (SC) infections. Therefore, CL patients may experience impaired regulatory T cell (Treg) function, causing excessive Th1 responses and tissue damage. To address this hypothesis, we characterized the function of circulating Tregs in L. braziliensis infected CL patients and compared them to Tregs from uninfected controls (UC) and SC subjects. The frequency of circulating Tregs was similar in CL patients, UC and SC subjects. Moreover, CL patients Tregs suppressed lymphocyte proliferation and PBMC pro-inflammatory cytokine production more efficiently than UC Tregs, and also produced higher levels of IL-10 than UC and SC Tregs. Furthermore, PBMC and mononuclear cells from lesions of CL patients responded normally to Treg-induced suppression. Therefore, the lesion development in CL patients infected with L. braziliensis is not associated with impairment in Treg function or failure of cells to respond to immunomodulation. Rather, the increased Treg activation in CL patients may impair parasite elimination, resulting in establishment of chronic infection. Thus, immunological strategies that interfere with this response may improve leishmaniasis treatment.

Cytotoxic T cells mediate pathology and metastasis in cutaneous leishmaniasis

Disease progression in response to infection can be strongly influenced by both pathogen burden and infection-induced immunopathology. While current therapeutics focus on augmenting protective immune responses, identifying therapeutics that reduce infection-induced immunopathology are clearly warranted. Despite the apparent protective role for murine CD8⁺ T cells following infection with the intracellular parasite Leishmania, CD8⁺ T cells have been paradoxically linked to immunopathological responses in human cutaneous leishmaniasis. Transcriptome analysis of lesions from Leishmania braziliensis patients revealed that genes associated with the cytolytic pathway are highly expressed and CD8⁺ T cells from lesions exhibited a cytolytic phenotype. To determine if CD8⁺ T cells play a causal role in disease, we turned to a murine model. These studies revealed that disease progression and metastasis in L. braziliensis infected mice was independent of parasite burden and was instead directly associated with the presence of CD8⁺ T cells. In mice with severe pathology, we visualized CD8⁺ T cell degranulation and lysis of L. braziliensis infected cells. Finally, in contrast to wild-type CD8⁺ T cells, perforin-deficient cells failed to induce disease. Thus, we show for the first time that cytolytic CD8⁺ T cells mediate immunopathology and drive the development of metastatic lesions in cutaneous leishmaniasis.

IL-17 mediates immunopathology in the absence of IL-10 following Leishmania major infection

Leishmaniasis, resulting from infection with the protozoan parasite Leishmania, consists of a wide spectrum of clinical manifestations, from healing cutaneous lesions to fatal visceral infections. A particularly severe form of cutaneous leishmaniasis, termed mucosal leishmaniasis, exhibits decreased IL-10 levels and an exaggerated inflammatory response that perpetuates the disease. Using a mouse model of leishmaniasis, we investigated what cytokines contribute to increased pathology when IL-10-mediated regulation is absent. Leishmania major infected C57BL/6 mice lacking IL-10 regulation developed larger lesions than controls, but fewer parasites. Both IFN-γ and IL-17 levels were substantially elevated in mice lacking the capacity to respond to IL-10. IFN-γ promoted an increased infiltration of monocytes, while IL-17 contributed to an increase in neutrophils. Surprisingly, however, we found that IFN-γ did not contribute to increased pathology, but instead regulated the IL-17 response. Thus, blocking IFN-γ led to a significant increase in IL-17, neutrophils and disease. Similarly, the production of IL-17 by cells from leishmaniasis patients was also regulated by IL-10 and IFN-γ. Additional studies found that the IL-1 receptor was required for both the IL-17 response and increased pathology. Therefore, we propose that regulating IL-17, possibly by downregulating IL-1β, may be a useful approach for controlling immunopathology in leishmaniasis.

Leishmaniasis is a tropical disease transmitted by sand flies that causes visceral and cutaneous lesions. In humans, the most severe form of cutaneous leishmaniasis is the mucosal form, causing disfiguring lesions in the nasal and oral mucosa. Why these patients develop severe disease is not clear. It is known, however, that the severe disease is not due to an overwhelming number of parasites, but rather appears to be due to an uncontrolled inflammatory response that includes elevated production of IFN-γ and IL-17. Here, we used a murine model of leishmaniasis to identify the factors involved in this pathology, and found that mice infected with Leishmania major developed severe lesions in the absence of IL-10 or IL-10 signaling, and similar to patients, contained high levels of IFN-γ and IL-17. While both of these cytokines have the potential to induce pathology, we found that IL-17 was responsible for the severe pathology seen in the absence of IL-10 regulation, and furthermore that IL-17 levels were higher and pathology greater in the absence of IFN-γ. Thus, our study suggests that IL-17, but not the IFN-γ, is a strong candidate to be targeted in strategies to control the severe immunopathology observed in mucosal leishmaniasis patients.

IFN-γ production to leishmania antigen supplements the leishmania skin test in identifying exposure to L. braziliensis infection

Background

Cutaneous leishmaniasis due to L. braziliensis (CL) is characterized by a positive delayed type hypersensitivity test (DTH) leishmania skin test (LST) and high IFN-γ production to soluble leishmania antigen (SLA). The LST is used for diagnosis of CL and for identification of individuals exposed to leishmania infection but without disease. The main aim of the present study was to identify markers of exposure to L. braziliensis infection.

Methodolgy/Principal Findings

This cohort study enrolled 308 household contacts (HC) of 76 CL index cases. HC had no active or past history of leishmaniasis. For the present cross-sectional study cytokines and chemokines were determined in supernatants of whole blood culture stimulated with SLA. Of the 308 HC, 36 (11.7%) had a positive LST but in these IFN-γ was only detected in 22 (61.1%). Moreover of the 40 HC with evidence of IFN-γ production only 22 (55%) had a positive LST. A total of 54 (17.5%) of 308 HC had specific immune response to SLA. Only a moderate agreement (Kappa = 0.52; 95% CI: 0.36–0.66) was found between LST and IFN-γ production. Moreover while enhancement of CXCL10 in cultures stimulated with SLA was observed in HC with DTH+ and IFN-γ+ and in patients with IFN-γ⁺ and DTH⁻, no enhancement of this chemokine was observed in supernatants of cells of HC with DTH⁺ and IFN-γ⁻.

Conclusions/Significance

This study shows that in addition of LST, the evaluation of antigen specific IFN-γ production should be performed to determine evidence of exposure to leishmania infection. Moreover it suggests that in some HC production of IFN-γ and CXCL10 are performed by cells not involved with DTH reaction.

Both control of L. braziliensis infection and development of cutaneous leishmaniasis (CL) are dependent on the host immunological response. Due to the difficulty of finding parasites in leishmanial lesions, a delayed type hypersensitivity reaction - leishmania skin test (LST), is widely used to diagnose CL. In areas of L. braziliensis transmission a positive LST is also documented in up to 18% of individuals without disease, who are considered to be putatively resistant to leishmania infection. However the mechanisms involved in the control of parasite grow is not known. The aim of this study is to identify tests that could determine in house contact of CL (HC) without past or current evidence of leishmaniasis exposure to leishmania infection. We found that of the 308 HC, 36 (11.7%) had a positive LST but in these IFN-γ was only detected in 22 (61.1%). Moreover of the 40 HC with evidence of IFN-γ production only 22 (55%) had a positive LST. Therefore at least the two tests, the LST and IFN-γ production, should be used to determine exposure to L. braziliensis. Identification of subjects exposed to leishmania infection that may or may not develop CL is highly relevant to understand pathogenesis of L. braziliensis infection.

Immunopathogenesis of non-healing American cutaneous leishmaniasis and progressive visceral leishmaniasis

The outcomes of Leishmania infection are determined by host immune and nutrition status, parasite species, and co-infection with other pathogens. While subclinical infection and self-healing cutaneous leishmaniasis (CL) are common, uncontrolled parasite replication can lead to non-healing local lesions or visceral leishmaniasis (VL). It is known that infection control requires Th1-differentiation cytokines (IL-12, IL-18, and IL-27) and Th1 cell and macrophage activation. However, there is no generalized consensus for the mechanisms of host susceptibility. The recent studies on regulatory T cells and IL-17-producing cells help explain the effector T cell responses that occur independently of the known Th1/Th2 cell signaling pathways. This review focuses on the immunopathogenesis of non-healing American CL and progressive VL. We summarize recent evidence from human and animal studies that reveals the mechanisms of dysregulated, hyper-responses to Leishmania braziliensis, as well as the presence of disease-promoting or the absence of protective responses to Leishmania amazonensis and Leishmania donovani. We highlight immune-mediated parasite growth and immunopathogenesis, with an emphasis on the putative roles of IL-17 and its related cytokines as well as arginase. A better understanding of the quality and regulation of innate immunity and T cell responses triggered by Leishmania will aid in the rational control of pathology and the infection.

Protective and pathologic immune responses in human tegumentary leishmaniasis

Studies in the recent years have advanced the knowledge of how host and parasite factors contribute to the pathogenesis of human tegumentary leishmaniasis. Polymorphism within populations of Leishmania from the same species has been documented; indicating that infection with different strains may lead to distinct clinical pictures and can also interfere in the response to treatment. Moreover, detection of parasite genetic tags for the precise identification of strains will improve diagnostics and therapy against leishmaniasis. On the host side, while a predominant Th1 type immune response is important to control parasite growth, it does not eradicate Leishmania and, in some cases, does not prevent parasite dissemination. Evidence has accumulated showing the participation of CD4⁺ and CD8⁺ T cells, as well as macrophages, in the pathology associated with L. braziliensis, L. guayanensis, and L. major infection. The discovery that a large percentage of individuals that are infected with Leishmania do not develop disease will help to understand how the host controls Leishmania infection. As these individuals have a weaker type 1 immune response than patients with cutaneous leishmaniasis, it is possible that control of parasite replication in these individuals is dependent, predominantly, on innate immunity, and studies addressing the ability of neutrophils, macrophages, and NK cells to kill Leishmania should be emphasized.

Transcriptome patterns from primary cutaneous Leishmania braziliensis infections associate with eventual development of mucosal disease in humans

Introduction

Localized Cutaneous Leishmaniasis (LCL) and Mucosal Leishmaniasis (ML) are two extreme clinical forms of American Tegumentary Leishmaniasis that usually begin as solitary primary cutaneous lesions. Host and parasite factors that influence the progression of LCL to ML are not completely understood. In this manuscript, we compare the gene expression profiles of primary cutaneous lesions from patients who eventually developed ML to those that did not.

Methods

Using RNA-seq, we analyzed both the human and Leishmania transcriptomes in primary cutaneous lesions.

Results

Limited number of reads mapping to Leishmania transcripts were obtained. For human transcripts, compared to ML patients, lesions from LCL patients displayed a general multi-polarization of the adaptive immune response and showed up-regulation of genes involved in chemoattraction of innate immune cells and in antigen presentation. We also identified a potential transcriptional signature in the primary lesions that may predict long-term disease outcome.

Conclusions

We were able to simultaneously sequence both human and Leishmania mRNA transcripts in primary cutaneous leishmaniasis lesions. Our results suggest an intrinsic difference in the immune capacity of LCL and ML patients. The findings correlate the complete cure of L. braziliensis infection with a controlled inflammatory response and a balanced activation of innate and adaptive immunity.

In Brazil, American tegumentary leishmaniasis is mainly caused by Leishmania braziliensis infection. Usually, it begins as a solitary skin lesion, which is called Localized Cutaneous Leishmaniasis (LCL). However, after this lesion heals, 5% of the patients may develop destructive lesions of the mucosa of nose and throat, which is called Mucosal Leishmaniasis (ML). Currently, there is no technology to identify individuals at risk for ML, and the factors that control the evolution to ML remain unknown. This work aims to study the human gene expression patterns that may contribute to the clinical manifestation of the disease. We used the RNA-Seq technique to study skin lesions from individuals that had LCL (LCL group) and those who developed ML (ML group). Our results suggest that individuals that progressed to ML expressed low levels of genes involved in the immune and inflammatory responses, which might lead to insufficient control of the infection. We were also able to identify a potential gene expression signature to predict long-term disease outcome.

Influence of HTLV-1 on the clinical, microbiologic and immunologic presentation of tuberculosis

Background

HTLV-1 is associated with increased susceptibility to Mycobacterium tuberculosis infection and severity of tuberculosis. Although previous studies have shown that HTLV-1 infected individuals have a low frequency of positive tuberculin skin test (TST) and decreasing in lymphoproliferative responses compared to HTLV-1 uninfected persons, these studies were not performed in individuals with history of tuberculosis or evidence of M. tuberculosis infection. Therefore the reasons why HTLV-1 infection increases susceptibility to infection and severity of tuberculosis are not understood.The aim of this study was to evaluate how HTLV-1 may influence the clinical, bacteriologic and immunologic presentation of tuberculosis.

Methods

The study prospectively enrolled and followed 13 new cases of tuberculosis associated with HTLV-1 (cases) and 25 patients with tuberculosis without HTLV-1 infection (controls). Clinical findings, bacterial load in the sputum, x-rays, immunological response and death were compared in the two groups.

Results

There were no differences in the demographic, clinical and TST response between the two study groups. IFN-γ and TNF-α production was higher in unstimulated cultures of mononuclear cells of case than in control patients (p < 0.01). While there was no difference in IFN-γ production in PPD stimulated cultures, TNF-α levels were lower in cases than in controls (p = 0.01). There was no difference in the bacterial load among the groups but sputum smear microscopy results became negative faster in cases than in controls. Death only occurred in two co-infected patients.

Conclusion

While the increased susceptibility for tuberculosis infection in HTLV-1 infected subjects may be related to impairment in TNF-α production, the severity of tuberculosis in co-infected patients may be due to the enhancement of the Th1 inflammatory response, rather than in their decreased ability to control bacterial growth.

Cytokine responses to novel antigens in a peri-urban population in Brazil exposed to Leishmania infantum chagasi

Visceral leishmaniasis (VL) is fatal if untreated, and there are no vaccines for this disease. High levels of CD4-derived interferon-γ (IFN-γ) in the presence of low levels of interleukin-10 (IL-10) predicts vaccine success. Tumor necrosis factor-α (TNF-α) is also important in this process. We characterized human immune responses in three groups exposed to Leishmania infantum chagasi in Brazil: 1) drug-cured VL patients (recovered VL); 2) asymptomatic persons with positive Leishmania-specific delayed-type hypersensitivity skin reactions (DTH+); and 3) DTH-negative household contacts. Magnitude of DTH correlated with crude Leishmania antigen-driven IFN-γ, TNF-α, and IL-5, but not IL-10. DTH+ persons showed equivalent levels of IFN-γ, but higher levels of IL-10, to tryparedoxin peroxidase and Leishmania homolog of receptor for activated C kinase compared with recovered VL patients. The IFN-γ:IL-10 and TNF-α:IL-10 ratios were higher in recovered VL patients than in DTH+ persons. Seven of 11 novel candidates (R71, L37, N52, L302.06, M18, J41, and M22) elicited cytokine responses (36-71% of responders) in recovered VL patients and DTH+ persons. This result confirmed their putative status as cross-species vaccine/immunotherapeutic candidates.