Regulatory T cells in the pathogenesis and healing of chronic human dermal leishmaniasis caused by Leishmania (Viannia) species

Consolidation of a Molecular Signature of Healing in Cutaneous Leishmaniasis Is Achieved during the First 10 Days of Treatment

The immune response is central to the pathogenesis of cutaneous leishmaniasis (CL). However, most of our current understanding of the immune response in human CL derives from the analysis of systemic responses, which only partially reflect what occurs in the skin. In this study, we characterized the transcriptional dynamics of skin lesions during the course of treatment of CL patients and identified gene signatures and pathways associated with healing and nonhealing responses. We performed a comparative transcriptome profiling of serial skin lesion biopsies obtained before, in the middle, and at the end of treatment of CL patients (eight who were cured and eight with treatment failure). Lesion transcriptomes from patients who healed revealed recovery of the stratum corneum, suppression of the T cell-mediated inflammatory response, and damping of neutrophil activation, as early as 10 d after initiation of treatment. These transcriptional programs of healing were consolidated before lesion re-epithelization. In stark contrast, downregulation of genes involved in keratinization was observed throughout treatment in patients who did not heal, indicating that in addition to uncontrolled inflammation, treatment failure of CL is mediated by impaired mechanisms of wound healing. This work provides insights into the factors that contribute to the effective resolution of skin lesions caused by Leishmania (Viannia) species, sheds light on the consolidation of transcriptional programs of healing and nonhealing responses before the clinically apparent resolution of skin lesions, and identifies inflammatory and wound healing targets for host-directed therapies for 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.

Is There Any Difference in the In Situ Immune Response in Active Localized Cutaneous Leishmaniasis That Respond Well or Poorly to Meglumine Antimoniate Treatment or Spontaneously Heal?

Localized cutaneous leishmaniasis caused by Leishmania braziliensis can either respond well or poorly to the treatment or heal spontaneously; It seems to be dependent on the parasite and/or host factors, but the mechanisms are not fully understood. We evaluated the in situ immune response in eighty-two active lesions from fifty-eight patients prior to treatment classified as early spontaneous regression (SRL-n = 14); treatment responders (GRL-n = 20); and non-responders (before first treatment/relapse, PRL1/PRL2-n = 24 each). Immunohistochemistry was used to identify cell/functional markers which were correlated with the clinical characteristics. PRL showed significant differences in lesion number/size, clinical evolution, and positive parasitological examinations when compared with the other groups. SRL presented a more efficient immune response than GRL and PRL, with higher IFN-γ/NOS2 and a lower percentage of macrophages, neutrophils, NK, B cells, and Ki-67+ cells. Compared to SRL, PRL had fewer CD4+ Tcells and more CD163+ macrophages. PRL1 had more CD68+ macrophages and Ki-67+ cells but less IFN-γ than GRL. PRL present a less efficient immune profile, which could explain the poor treatment response, while SRL had a more balanced immune response profile for lesion healing. Altogether, these evaluations suggest a differentiated profile of the organization of the inflammatory process for lesions of different tegumentary leishmaniasis evolution.

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.

Early Leukocyte Responses in Ex-Vivo Models of Healing and Non-Healing Human Leishmania (Viannia) panamensis Infections

Early host-pathogen interactions drive the host response and shape the outcome of natural infections caused by intracellular microorganisms. These interactions involve a number of immune and non-immune cells and tissues, along with an assortment of host and pathogen-derived molecules. Our current knowledge has been predominantly derived from research on the relationships between the pathogens and the invaded host cell(s), limiting our understanding of how microbes elicit and modulate immunological responses at the organismal level. In this study, we explored the early host determinants of healing and non-healing responses in human cutaneous leishmaniasis (CL) caused by Leishmania (Viannia) panamensis. We performed a comparative transcriptomic profiling of peripheral blood mononuclear cells from healthy donors (PBMCs, n=3) exposed to promastigotes isolated from patients with chronic (CHR, n=3) or self-healing (SH, n=3) CL, and compared these to human macrophage responses. Transcriptomes of L. V. panamensis-infected PBMCs showed enrichment of functional gene categories derived from innate as well as adaptive immune cells signatures, demonstrating that Leishmania modulates adaptive immune cell functions as early as after 24h post interaction with PBMCs from previously unexposed healthy individuals. Among differentially expressed PBMC genes, four broad categories were commonly modulated by SH and CHR strains: cell cycle/proliferation/differentiation, metabolism of macromolecules, immune signaling and vesicle trafficking/transport; the first two were predominantly downregulated, and the latter upregulated in SH and CHR as compared to uninfected samples. Type I IFN signaling genes were uniquely up-regulated in PBMCs infected with CHR strains, while genes involved in the immunological synapse were uniquely downregulated in SH infections. Similarly, pro-inflammatory response genes were upregulated in isolated macrophages infected with CHR strains. Our data demonstrate that early responses during Leishmania infection extend beyond innate cell and/or phagocytic host cell functions, opening new frontiers in our understanding of the triggers and drivers of human CL.

Immuno-pharmacokinetics of Meglumine Antimoniate in Patients With Cutaneous Leishmaniasis Caused by Leishmania (Viannia)

BACKGROUND

Control of cutaneous leishmaniasis (CL) relies on chemotherapy, yet gaps in our understanding of the determinants of therapeutic outcome impede optimization of antileishmanial drug regimens. Pharmacodynamic (PD) parameters of antimicrobials are based on the relationship between drug concentrations/exposure and microbial kill. However, viable Leishmania persist in a high proportion of individuals despite clinical resolution, indicating that determinants other than parasite clearance are involved in drug efficacy.

METHODS

In this study, the profiles of expression of neutrophils, monocytes, Th1 and Th17 gene signatures were characterized in peripheral blood mononuclear cells (PBMCs) during treatment with meglumine antimoniate (MA) and clinical cure of human CL caused by Leishmania (Viannia). We explored relationships of immune gene expression with plasma and intracellular antimony (Sb) concentrations.

RESULTS

Our findings show a rapid and orchestrated modulation of gene expression networks upon exposure to MA. We report nonlinear pharmacokinetic/pharmacodynamic (PK/PD) relationships of Sb and gene expression dynamics in PBMCs , concurring with a time lag in the detection of intracellular drug concentrations and with PK evidence of intracellular Sb accumulation.

CONCLUSIONS

Our results quantitatively portray the immune dynamics of therapeutic healing, and provide the knowledge base for optimization of antimonial drug treatments, guiding the selection and/or design of targeted drug delivery systems and strategies for targeted immunomodulation.

Equine Sarcoids-Causes, Molecular Changes, and Clinicopathologic Features: A Review

Equine sarcoid is the most common skin tumor of horses. Clinically, it occurs as a locally invasive, fibroblastic, wart-like lesion of equine skin, which has 6 clinical classes: occult, verrucose, nodular, fibroblastic, mixed, and malignant. Sarcoids may be single but multiple lesions are more frequent. The typical histological feature is increased density of dermal fibroblasts which form interlacing bundles and whorls within the dermis. Lesions are mostly persistent, resist therapy, and tend to recur following treatment. In general, sarcoids are not fatal but their location, size, and progression to the more aggressive form may lead to the withdrawal of a horse from use and serious infringement of their welfare leading to the loss of valuable animals. Bovine papillomavirus (BPV) type 1 and less commonly type 2 contribute to the development of equine sarcoid. The viral genome and proteins are detected in a high percentage of cases. Furthermore, viral oncoprotein activity leads to changes in the fibroblastic tissue similar to changes seen in other types of tumors. Equine sarcoids are characterized by a loss of tumor suppressor activity and changes allowing abnormal formation of the affected tissue, as well as y immune defense abnormalities that weaken the host's immune response. This impaired immune response to BPV infection appears to be crucial for the development of lesions that do not spontaneously regress, as occurs in BPV-infected cows.

In situ study of cellular immune response in human cutaneous lesions caused by Leishmania (Viannia) panamensis in Panama

AIMS

Leishmaniasis is considered a disease with multiple clinical/immunopathological characteristics, depending on the immunity of the host and the species of the parasite. In Panama, the most prevalent species that causes localized cutaneous leishmaniasis (LCL) is Leishmania (Viannia) panamensis, and its immune response is poorly studied. Therefore, we evaluated by immunohistochemistry, the in situ immune response during this infection.

METHODS AND RESULTS

Biopsies from Panamanian patients with LCL were collected and processed by histological techniques. Infection by L. (V.) panamensis was demonstrated by isolation in culture and molecular characterization by Hsp70-RFLP. The in situ immune response was assessed by immunohistochemistry. The immune response was characterized by predominance of T cells, mainly CD8 cells that showed positive correlation with IFN-γ and Granzyme B. CD4 cells presented positive correlation with both IFN-γ and IL-13, pointed by mixed cellular immune response. Regulatory response was characterized by FoxP3 cells, which showed positive correlation to IL-10 but not with TGF-β.

CONCLUSIONS

L. (V.) panamensis infection triggers a mixed cellular immune response, characterized by the presence of pro-inflammatory, anti-inflammatory and regulatory elements in the skin lesion of Panamanian patients. These data contribute to a better understanding of the immunopathogenesis of Leishmania Viannia infection in Panama.

A natural cell-penetrating nanopeptide combined with pentavalent antimonial as experimental therapy against cutaneous leishmaniasis

The inadequacy of available treatments for leishmaniasis has presented up to 40% therapeutic failure. This fact suggests an urgency in the discovery of new drugs or alternative approaches for treating this disease. The objective of this study was to evaluate the antileishmanial activity of combined therapy between crotamine (CTA) from Crotalus durissus terrificus and the pentavalent antimonial Glucantime® (GLU). The assays were in vitro performed measuring the inhibition of Leishmania amazonensis amastigotes, followed by the evaluation of cellular production of cytokines and nitrites. After that, analytical methods were performed in order to characterize the molecules involved in the study by Mass Spectrometry, molecular affinity through an in silico assay and Surface Plasmon Resonance. In vivo experiments with BALB/c mice were performed by analyzing parasitemia, lesion size and immunological mediators. In the in vitro experiments, the pharmacological association improved the inhibition of the amastigotes, modulated the production of cytokines and nitric oxide. The therapy improved the effectiveness of the GLU, demonstrating a decreased parasitemia in the infected tissues. Altogether, the results suggest that the combined approach with CTA and GLU may be a promising alternative for the treatment of cutaneous leishmaniasis.

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.

Profiles of Local and Systemic Inflammation in the Outcome of Treatment of Human Cutaneous Leishmaniasis Caused by Leishmania (Viannia)

The immune mechanisms that contribute to the efficacy of treatment of cutaneous leishmaniasis (CL) are not fully understood. The aim of this study was to define immune correlates of the outcome of treatment of CL caused by Leishmania (Viannia) species during standard of care treatment with pentavalent antimonials. We conducted a comparative expression profiling of immune response genes in peripheral blood mononuclear cells (PBMCs) and lesion biopsy specimens obtained from CL patients before and at the end of treatment (EoT) with meglumine antimoniate. The ex vivo response of PBMCs to L (V) panamensis partially reflected that of lesion microenvironments. Significant downregulation of gene expression profiles consistent with local innate immune responses (monocyte and neutrophil activation and chemoattractant molecules) was observed at EoT in biopsy specimens of patients who cured (n = 8), compared to those from patients with treatment failure (n = 8). Among differentially expressed genes, pretreatment expression of CCL2 was significantly predictive of the therapeutic response (receiver operating characteristic [ROC] curve, area under the curve [AUC] = 0.82, P = 0.02). Polymorphisms in regulatory regions of the CCL2 promoter were analyzed in a pilot cohort of DNA samples from CL patients (cures, n = 20, and treatment failure, n = 20), showing putative association of polymorphisms rs13900(C/T) and rs2857656(G/C) with treatment outcome. Our data indicate that dampening gene expression profiles of monocyte and neutrophil activation characterize clinical cure after treatment of CL, supporting participation of parasite-sustained inflammation or deregulated innate immune responses in treatment failure.

A Comparative Evaluation of Regulatory T Cells Profile among Acute and Chronic Cutaneous Leishmaniasis Using Flow Cytometry

BACKGROUND

Cutaneous leishmaniasis (CL) is described as a major health problem in many countries of the world. Regulatory T cells (Tregs) are characterized as one of immunologic indexes. One of the best methods to determine of Tregs percentage is flow cytometry. The aim of this study was determination of the role of Tregs profile among acute and chronic forms of human CL using flow cytometry analysis.

METHODS

This study was conducted on 24 patients referred to Laboratory of Leishmaniasis, Tehran University of Medical Sciences, Tehran, Iran with acute and 14 patients with chronic phases of CL as well as 15 healthy individuals as control group in 2015-2016. After microscopic examination, 2 ml of peripheral blood samples were collected for determining percentage of CD₄ ⁺ CD₂₅ ⁺ CD₁₂₇ low Tregs by using flow cytometry method.

RESULTS

Using flow cytometry analysis, the average percentage of Tregs were calculated 5.73, 6.71 and 6.61 for acute, chronic and healthy individuals, respectively. With SPSS software and Scheffe multiple comparison tests, the differences within in these groups are statistically significant (P=0.04) and between the acute and chronic group, there was marginally significant with approximately 91% of confidence level (P=0.088).

CONCLUSION

Marginally differences were found significantly among averages of Regulatory T cells, acute and chronic phases of CL. Further comprehensive studies can be needed to verify the role of Tregs in both phases of CL cases.

Evaluation of Regulatory Immune Response in Skin Lesions of Patients Affected by Nonulcerated or Atypical Cutaneous Leishmaniasis in Honduras, Central America

In Honduras, Leishmania (L.) infantum chagasi causes both visceral leishmaniasis (LV) and nonulcerated or atypical cutaneous leishmaniasis (NUCL). NUCL is characterized by mononuclear inflammatory infiltration of the dermis, composed mainly of lymphocytes followed by macrophages with discrete parasitism. Considering that little is known about the pathogenesis of NUCL, the aim of this study was to evaluate the regulatory response in situ in skin lesions of patients affected by NUCL. Biopsies (n = 20) from human cutaneous nonulcerative lesions were collected and processed by usual histological techniques. The in situ regulatory immune response was evaluated by immunohistochemistry using antihuman CD4, FoxP3, IL-10, and TGF-β antibodies. CD4⁺, FoxP3⁺, TGF-β⁺, and IL-10⁺ cells were observed in the dermis with inflammatory infiltration in all studied cases and at higher densities compared to the normal skin controls. A positive and strong correlation was observed between CD4⁺ and FoxP3⁺ cells, and a positive and moderate correlation was observed between FoxP3⁺ and TGF-β⁺ but not with IL-10⁺ cells. The data suggest that T regulatory FoxP3⁺ cells and the regulatory cytokines, especially TGF-β, play an important role in the immunopathogenesis of NUCL, modulating a cellular immune response in the skin, avoiding tissue damage, and leading to low tissue parasitic persistence.

Local Delivery of the Toll-Like Receptor 9 Ligand CpG Downregulates Host Immune and Inflammatory Responses, Ameliorating Established Leishmania (Viannia) panamensis Chronic Infection

Infection by Leishmania (Viannia) panamensis, the predominant etiologic agent for cutaneous leishmaniasis in Colombia, is characterized by a chronic mixed inflammatory response. Current treatment options are plagued by toxicity, lengthy treatment regimens, and growing evidence of drug resistance. Immunotherapy, modulating the immune system to mount a protective response, may provide an alternate therapeutic approach. We investigated the ability of the Toll-like receptor 9 (TLR9) ligand CpG to modulate established disease in the L (V) panamensis mouse model. Treatment of established infection with a high dose (50 μg) of CpG ameliorated disease and lowered parasite burden. Interestingly, immediately after treatment there was a significant increase in transforming growth factor β (TGF-β) and concomitantly an increase in T regulatory cell (Treg) function. Although a general reduction in cell-mediated immune cytokine and chemokine (gamma interferon [IFN-γ], interleukin 10 [IL-10], IL-13, IL-6, granulocyte-macrophage colony-stimulating factor [GM-CSF], IL-4, and MIP-1α) responses of the treated mice was observed, certain chemokines (RANTES, monocyte chemoattractant protein 1[MCP-1], and IP-10) were increased. Further, in peripheral blood mononuclear cells (PBMCs) from patients with cutaneous leishmaniasis, CpG treatment similarly exhibited a dose-response effect on the production of IFN-γ, IL-17, IL-10, and IL-13, with reductions observed at higher doses. To further understand the underlying mechanisms and cell populations driving the CpG mediated response, we examined the ex vivo dose effects mediated by the TLR9⁺ cell populations (dendritic cells, macrophages, and B cells) found to accumulate labeled CpG in vivo Notably, B cells altered the production of IL-17, IL-13, and IFN-γ, supporting a role for B cells functioning as antigen-presenting cells (APCs) and/or regulatory cells during infection. Interestingly, B cells have been previously demonstrated as a primary type of APC in patients infected with L (V) panamensis and thus may be useful targets of immunotherapy. Collectively, our results show that CpG-induced immune regulation leads to a dampening of the host immune response and healing in the mouse model, and it may provide an alternate approach to treatment of cutaneous leishmaniasis caused by L (V) panamensis.

Asymptomatic infection with American cutaneous leishmaniasis: epidemiological and immunological studies

American cutaneous leishmaniasis (ACL) is a major public health problem caused by vector-borne protozoan intracellular parasites from the genus Leishmania, subgenera Viannia and Leishmania. Asymptomatic infection is the most common outcome after Leishmania inoculation. There is incomplete knowledge of the biological processes explaining the absence of signs or symptoms in most cases while other cases present a variety of clinical findings. Most studies of asymptomatic infection have been conducted in areas of endemic visceral leishmaniasis. In contrast, asymptomatic ACL infection has been neglected. This review is focused on the following: (1) epidemiological studies supporting the existence of asymptomatic ACL infection and (2) immunological studies conducted to understand the mechanisms responsible for controlling the parasite and avoiding tissue damage.

Immunomodulatory nanoparticles ameliorate disease in the Leishmania (Viannia) panamensis mouse model

Leishmania (Viannia) panamensis (L. (V.) panamensis) is a species of protozoan parasites that causes New World leishmaniasis, which is characterized by a hyper-inflammatory response. Current treatment strategies, mainly chemotherapeutic, are suboptimal due to adverse effects, long treatment regimens, and increasing drug resistance. Recently, immunotherapeutic approaches have shown promise in preclinical studies of leishmaniasis. As NPs may enable broad cellular immunomodulation through internalization in phagocytic and antigen-presenting cells, we tested the therapeutic efficacy of biodegradable NPs encapsulating a pathogen-associated molecular pattern (PAMP), CpG-rich oligonucleotide (CpG; NP-CpG), in mice infected with L. (V.) panamensis. NP-CpG treatment reduced lesion size and parasite burden, while neither free CpG nor empty NP showed therapeutic effects. NP-encapsulation led to CpG persistence at the site of infection along with an unexpected preferential cellular uptake by myeloid derived suppressor cells (MDSCs; CD11b(+)Ly6G(+)Ly6C(-)) as well as CD19(+) dendritic cells. This corresponded with the suppression of the ongoing immune response measured by the reduction of pathogenic cytokines IL-10 and IL-13, as well as IL-17 and IFNγ, in comparison to other treatment groups. As chronic inflammation is generally associated with the accumulation of MDSCs, this study may enable the rational design of cost-effective, safe, and scalable delivery systems for the treatment of inflammation-mediated diseases.

Cutaneous leishmaniasis: immune responses in protection and pathogenesis

Cutaneous leishmaniasis is a major public health problem and causes a range of diseases from self-healing infections to chronic disfiguring disease. Currently, there is no vaccine for leishmaniasis, and drug therapy is often ineffective. Since the discovery of CD4(+) T helper 1 (TH1) cells and TH2 cells 30 years ago, studies of cutaneous leishmaniasis in mice have answered basic immunological questions concerning the development and maintenance of CD4(+) T cell subsets. However, new strategies for controlling the human disease have not been forthcoming. Nevertheless, advances in our knowledge of the cells that participate in protection against Leishmania infection and the cells that mediate increased pathology have highlighted new approaches for vaccine development and immunotherapy. In this Review, we discuss the early events associated with infection, the CD4(+) T cells that mediate protective immunity and the pathological role that CD8(+) T cells can have in cutaneous leishmaniasis.

American tegumentary leishmaniasis: T-cell differentiation profile of cutaneous and mucosal forms-co-infection with Trypanosoma cruzi

American tegumentary leishmaniasis displays two main clinical forms: cutaneous (CL) and mucosal (ML). ML is more resistant to treatment and displays a more severe and longer evolution. Since both forms are caused by the same Leishmania species, the immunological response of the host may be an important factor determining the evolution of the disease. Herein, we analyzed the differentiation and memory profile of peripheral CD4(+) and CD8(+) T lymphocytes of patients with CL and ML and their Leishmania-T. cruzi co-infected counterparts. We measured the expression of CD27, CD28, CD45RO, CD127, PD-1 and CD57, together with interferon-γ and perforin. A highly differentiated phenotype was reflected on both T subsets in ML and preferentially on CD8(+) T cells in CL. A positive trend toward a higher T differentiation profile was found in T. cruzi-infected CL and ML patients as compared with Leishmania single infections. Association between CD8(+) T-cell differentiation and illness duration was found within the first year of infection, with progressive increase of highly differentiated markers over time. Follow-up of patients with good response to therapy showed predominance of early differentiated CD8(+) T cells and decrease of highly differentiated cells, while patients with frequent relapses presented the opposite pattern. CD8(+) T cells showed the most striking changes in their phenotype during leishmaniasis. Patients with long-term infections showed the highest differentiated degree implying a relation between T differentiation and parasite persistence. Distinct patterns of CD8(+) T differentiation during follow-up of different clinical outcomes suggest the usefulness of this analysis in the characterization of Leishmania-infected patients.

The Immunology of a Healing Response in Cutaneous Leishmaniasis Treated with Localized Heat or Systemic Antimonial Therapy

Background

The effectiveness of systemic antimonial (sodium stibogluconate, Pentostam, SSG) treatment versus local heat therapy (Thermomed) for cutaneous leishmaniasis was studied previously and showed similar healing rates. We hypothesized that different curative immune responses might develop with systemic and local treatment modalities.

Methods

We studied the peripheral blood immune cells in a cohort of 54 cutaneous Leishmania major subjects treated with SSG or TM. Multiparameter flow cytometry, lymphoproliferative assays and cytokine production were analyzed in order to investigate the differences in the immune responses of subjects before, on and after treatment.

Results

Healing cutaneous leishmaniasis lead to a significant decline in circulating T cells and NKT-like cells, accompanied by an expansion in NK cells, regardless of treatment modality. Functional changes involved decreased antigen specific CD4⁺ T cell proliferation (hyporesponsiveness) seen with CD8⁺ T cell depletion. Moreover, the healing (or healed) state was characterized by fewer circulating regulatory T cells, reduced IFN-γ production and an overall contraction in polyfunctional CD4⁺ T cells.

Conclusion

Healing from cutaneous Leishmaniasis is a dynamic process that alters circulating lymphocyte populations and subsets of T, NK and NKT-like cells. Immunology of healing, through local or systemic treatments, culminated in similar changes in frequency, quality, and antigen specific responsiveness with immunomodulation possibly via a CD8⁺ T cell dependent mechanism. Understanding the evolving immunologic changes during healing of human leishmaniasis informs protective immune mechanisms.

Globally, leishmaniasis treatment relies on the use of antimonial drugs (i.e. SSG). In an earlier study we showed that skin lesions due to L. major treated by the ThermoMed (TM) device healed at a similar rate and with less associated systemic toxicity than lesions treated with intravenous SSG. The current study compared the immune responses of these two therapeutic groups before, during and after therapy which may be relevant to resistance to reinfection and also in consideration for the development of local (versus systemic) therapy. Antimonials have immune effects on both the host and parasite while heat treatment locally kills the parasite and induces inflammation from a secondary burn. We demonstrated that healing from cutaneous leishmaniasis is a dynamic process associated with a modulation of immune responses independent of treatment modalities.

Glucocorticoid-induced tumour necrosis factor receptor-related protein: a key marker of functional regulatory T cells

Glucocorticoid-induced tumour necrosis factor receptor-related protein (GITR, TNFRSF18, and CD357) is expressed at high levels in activated T cells and regulatory T cells (Tregs). In this review, we present data from mouse and human studies suggesting that GITR is a crucial player in the differentiation of thymic Tregs (tTregs), and expansion of both tTregs and peripheral Tregs (pTregs). The role of GITR in Treg expansion is confirmed by the association of GITR expression with markers of memory T cells. In this context, it is not surprising that GITR appears to be a marker of active Tregs, as suggested by the association of GITR expression with other markers of Treg activation or cytokines with suppressive activity (e.g., IL-10 and TGF-β), the presence of GITR(+) cells in tissues where Tregs are active (e.g., solid tumours), or functional studies on Tregs. Furthermore, some Treg subsets including Tr1 cells express either low or no classical Treg markers (e.g., FoxP3 and CD25) and do express GITR. Therefore, when evaluating changes in the number of Tregs in human diseases, GITR expression must be evaluated. Moreover, GITR should be considered as a marker for isolating Tregs.

FOXP3 expression and frequency of regulatory T cells in healed individuals from Leishmania major infection and the asymptomatic cases

Two groups of residents in an endemic area of Leishmania major infection in Iran with positive leishmanin skin tests who were either asymptomatic or had healed cutaneous leishmaniasis lesions were compared with respect to their T helper responses. The percentages of regulatory T cells (Treg; CD4(+)CD25(high) FoxP3(+)) from the peripheral blood and CD4(+) T cells producing intracellular cytokines (IL-4, IL-10, IL-17 and IFN-γ) from the stimulated PBMCs were evaluated by flow cytometry and the expressions of RORC and FOXP3 genes were quantified by real-time RT-PCR. T responder (CD4(+)CD25(-)) and Treg-enriched (CD4(+)CD25(+)) cells were isolated magnetically and the suppressive capacity of the latter and the cytokines (IFN-γ, TGF-β and IL-10) secreted from them were evaluated by in vitro assays. The results showed that the frequency of Treg in the studied groups were similar and Treg from both groups exhibited high yet similar suppressive capacities while significantly higher levels of FOXP3 expression was observed in the asymptomatic group. Taken together, similar frequency and suppressiveness of Treg combined with high ratios of IFN-γ/IL-10 producing CD4(+) T cells were common in both groups; however the members of the asymptomatic group appeared to require higher expression of FOXP3 to maintain their immunity to re-infection.

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.

Leishmania donovani Nucleoside Hydrolase Terminal Domains in Cross-Protective Immunotherapy Against Leishmania amazonensis Murine Infection

Nucleoside hydrolases of the Leishmania genus are vital enzymes for the replication of the DNA and conserved phylogenetic markers of the parasites. Leishmania donovani nucleoside hydrolase (NH36) induced a main CD4(+) T cell driven protective response against L. chagasi infection in mice which is directed against its C-terminal domain. In this study, we used the three recombinant domains of NH36: N-terminal domain (F1, amino acids 1-103), central domain (F2 aminoacids 104-198), and C-terminal domain (F3 amino acids 199-314) in combination with saponin and assayed their immunotherapeutic effect on Balb/c mice previously infected with L. amazonensis. We identified that the F1 and F3 peptides determined strong cross-immunotherapeutic effects, reducing the size of footpad lesions to 48 and 64%, and the parasite load in footpads to 82.6 and 81%, respectively. The F3 peptide induced the strongest anti-NH36 antibody response and intradermal response (IDR) against L. amazonenis and a high secretion of IFN-γ and TNF-α with reduced levels of IL-10. The F1 vaccine, induced similar increases of IgG2b antibodies and IFN-γ and TNF-α levels, but no IDR and no reduction of IL-10. The multiparameter flow cytometry analysis was used to assess the immune response after immunotherapy and disclosed that the degree of the immunotherapeutic effect is predicted by the frequencies of the CD4(+) and CD8(+) T cells producing IL-2 or TNF-α or both. Total frequencies and frequencies of double-cytokine CD4 T cell producers were enhanced by F1 and F3 vaccines. Collectively, our multifunctional analysis disclosed that immunotherapeutic protection improved as the CD4 responses progressed from 1+ to 2+, in the case of the F1 and F3 vaccines, and as the CD8 responses changed qualitatively from 1+ to 3+, mainly in the case of the F1 vaccine, providing new correlates of immunotherapeutic protection against cutaneous leishmaniasis in mice based on T-helper TH1 and CD8(+) mediated immune responses.

Critical stoichiometric ratio of CD4(+) CD25(+) FoxP3(+) regulatory T cells and CD4(+) CD25(-) responder T cells influence immunosuppression in patients with B-cell acute lymphoblastic leukaemia

Regulatory T (Treg) cells act to suppress activation of the immune system and thereby maintain immunological homeostasis and tolerance to self-antigens. The frequency and suppressing activity of Treg cells in general are high in different malignancies. We wanted to identify the role and regulation of CD4(+)  CD25(+)  FoxP3(+) Treg cells in B-cell acute lymphoblastic leukaemia (B-ALL). We have included patients at diagnosis (n = 54), patients in clinical remission (n = 32) and normal healthy individuals (n = 35). These diagnosed patients demonstrated a lower number of CD4(+)  CD25(+) cells co-expressing a higher level of FoxP3, interleukin-10, transforming growth factor-β and CD152/CTLA-4 than the normal population. Treg cells from patients showed a higher suppressive capability on CD4(+)  CD25(-) responder T (Tresp) cells than normal. The frequency and immunosuppressive potential of CD4(+)  CD25(+)  FoxP3(+) Treg cells became high with the progression of malignancy in B-ALL. Relative distribution of Tresp and Treg cells was only ~5 : 1 in B-ALL but ~35 : 1 in normal healthy individuals, further confirming the elevated immunosuppression in patients. A co-culture study at these definite ex vivo ratios, indicated that Treg cells from B-ALL patients exhibited higher immunosuppression than Treg cells from normal healthy individuals. After chemotherapy using the MCP841 protocol, the frequency of CD4(+)  CD25(+) cells was gradually enhanced with the reduction of FoxP3, interleukin-10 positivity corresponded with disease presentation, indicating reduced immunosuppression. Taken together, our study indicated that the CD4(+)  CD25(+)  FoxP3(+) Treg cells played an important role in immunosuppression, resulting in a positive disease-correlation in these patients. To the best of our knowledge, this is the first detailed report on the frequency, regulation and functionality of Treg cells in B-ALL.

Comparison of immune regulatory factors in acute and chronic lesions of cutaneous leishmaniasis due to Leishmania major

BACKGROUND

Adaptive immune response is an important factor in the healing process and development of protection in cutaneous leishmaniasis (CL). Little information is available in human CL about the importance of the balance between effector and regulatory immune responses. Therefore, the aim of this study was to asses messenger ribonucleic acid (mRNA) expression of interleukin-10 (IL-10), IL-4, transforming growth factor-β1 (TGF-β1), interferon-g (IFN-γ), and forkhead box P3 (Foxp3) (as a marker of regulatory T cells) in acute and chronic CL lesions caused by Leishmania major compared with normal skin samples.

MATERIALS AND METHODS

Thirty biopsies were obtained from CL patients with acute lesions (AL, n = 13), chronic lesions (CH, n = 11) and healthy volunteers (n = 6). Relative expressions of target genes were determined by means of reverse transcription real time polymerase chain reaction and were compared with the controls.

RESULTS

Expression of Foxp3, IL-4, and IFN-γ were significantly more in CH than AL group of patients (Foxp3: Median 0.48, inter-quartile range 0.32-0.76 [arbitrary units] for AL, and 0.97 (0.75-1.30) for CH, P = 0.006; IFN-γ: 45.98 (33.39-173.48) for AL, and 200.53 (97.49-361.76) for CH, P = 0.023; IL-4: 0.49 (0.34-2.16) for AL, and 2.14 (1.30-7.11) for CH, P = 0.021). Expression of TGF-β was not significantly different between groups.

CONCLUSION

The results indicate that IL-4 secretion at the site of L. major infection rather than low IFN-γ production might have a role in prolongation of disease. Despite a moderate increase of Foxp3 expression in chronic lesions, function of Tregs in persistent infection is not clear.

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

Background

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

Methods

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

Results

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

Conclusions

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

Increase in TGF-β secreting CD4⁺CD25⁺ FOXP3⁺ T regulatory cells in anergic lepromatous leprosy patients

BACKGROUND

Lepromatous leprosy caused by Mycobacterium leprae is associated with antigen specific T cell unresponsiveness/anergy whose underlying mechanisms are not fully defined. We investigated the role of CD25(+)FOXP3(+) regulatory T cells in both skin lesions and M.leprae stimulated PBMC cultures of 28 each of freshly diagnosed patients with borderline tuberculoid (BT) and lepromatous leprosy (LL) as well as 7 healthy household contacts of leprosy patients and 4 normal skin samples.

METHODOLOGY/PRINCIPLE FINDINGS

Quantitative reverse transcribed PCR (qPCR), immuno-histochemistry/flowcytometry and ELISA were used respectively for gene expression, phenotype characterization and cytokine levels in PBMC culture supernatants. Both skin lesions as well as in vitro antigen stimulated PBMC showed increased percentage/mean fluorescence intensity of cells and higher gene expression for FOXP3(+), TGF-β in lepromatous (p<0.01) as compared to tuberculoid leprosy patients. CD4(+)CD25(+)FOXP3(+) T cells (Tregs) were increased in unstimulated basal cultures (p<0.0003) and showed further increase in in vitro antigen but not mitogen (phytohemaglutinin) stimulated PBMC (iTreg) in lepromatous as compared to tuberculoid leprosy patients (p<0.002). iTregs of lepromatous patients showed intracellular TGF-β which was further confirmed by increase in TGF-β in culture supernatants (p<0.003). Furthermore, TGF-β in iTreg cells was associated with phosphorylation of STAT5A. TGF-β was seen in CD25(+) cells of the CD4(+) but not that of CD8(+) T cell lineage in leprosy patients. iTregs did not show intracellular IFN-γ or IL-17 in lepromatous leprosy patients.

CONCLUSIONS/SIGNIFICANCE

Our results indicate that FOXP3(+) iTregs with TGF-β may down regulate T cell responses leading to the antigen specific anergy associated with lepromatous leprosy.

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.

Chemokines and chemokine receptors expression in the lesions of patients with American cutaneous leishmaniasis

American cutaneous leishmaniasis (ACL) presents distinct active clinical forms with different grades of severity, known as localised (LCL), intermediate (ICL) and diffuse (DCL) cutaneous leishmaniasis. LCL and DCL are associated with a polarised T-helper (Th)1 and Th2 immune response, respectively, whereas ICL, or chronic cutaneous leishmaniasis, is associated with an exacerbated immune response and a mixed cytokine expression profile. Chemokines and chemokine receptors are involved in cellular migration and are critical in the inflammatory response. Therefore, we evaluated the expression of the chemokines CXCL10, CCL4, CCL8, CCL11 and CXCL8 and the chemokine receptors CCR3, CXCR3, CCR5 and CCR7 in the lesions of patients with different clinical forms of ACL using immunohistochemistry. LCL patients exhibited a high density of CXCL10+, CCL4+ and CCL8+ cells, indicating an important role for these chemokines in the local Th1 immune response and the migration of CXCR3+ cells. LCL patients showed a higher density of CCR7+ cells than ICL or DCL patients, suggesting major dendritic cell (DC) migration to lymph nodes. Furthermore, DCL was associated with low expression levels of Th1-associated chemokines and CCL11+ epidermal DCs, which contribute to the recruitment of CCR3+ cells. Our findings also suggest an important role for epidermal cells in the induction of skin immune responses through the production of chemokines, such as CXCL10, by keratinocytes.