Pathogenic CD8 T cell responses are driven by neutrophil-mediated hypoxia in cutaneous leishmaniasis

Cutaneous leishmaniasis caused by Leishmania parasites exhibits a wide range of clinical manifestations. Although parasites influence disease severity, cytolytic CD8 T cell responses mediate disease. While these responses originate in the lymph node, we find that expression of the cytolytic effector molecule granzyme B is restricted to lesional CD8 T cells in Leishmania - infected mice, suggesting that local cues within inflamed skin induce cytolytic function. Expression of Blimp-1 ( Prdm1 ), a transcription factor necessary for cytolytic CD8 T cell differentiation, is driven by hypoxia within the inflamed skin. Hypoxia is further enhanced by the recruitment of neutrophils that consume oxygen to produce reactive oxygen species, ultimately increasing granzyme B expression in CD8 T cells. Importantly, lesions from cutaneous leishmaniasis patients exhibit hypoxia transcription signatures that correlate with the presence of neutrophils. Thus, targeting hypoxia-driven signals that support local differentiation of cytolytic CD8 T cells may improve the prognosis for patients with cutaneous leishmaniasis, as well as other inflammatory skin diseases where cytolytic CD8 T cells contribute to pathogenesis.

Multiomic profiling of cutaneous leishmaniasis infections reveals microbiota-driven mechanisms underlying disease severity

Leishmania braziliensis is a parasitic infection that can result in inflammation and skin injury with highly variable and unpredictable clinical outcomes. Here, we investigated the potential impact of microbiota on infection-induced inflammatory responses and disease resolution by conducting an integrated analysis of the skin microbiome and host transcriptome on a cohort of 62 patients infected with L. braziliensis. We found that overall bacterial burden and microbiome configurations dominated with Staphylococcus spp. were associated with delayed healing and enhanced inflammatory responses, especially by IL-1 family members. Quantification of host and bacterial transcripts on human lesions revealed that high lesional S. aureus transcript abundance was associated with delayed healing and increased expression of IL-1β. This cytokine was critical for modulating disease outcomes in L. braziliensis-infected mice colonized with S. aureus, given that its neutralization reduced pathology and inflammation. These results highlight how the human microbiome can shape disease outcomes in cutaneous leishmaniasis and suggest pathways toward host-directed therapies to mitigate the inflammatory consequences.

NKG2D promotes CD8 T cell-mediated cytotoxicity and is associated with treatment failure in human cutaneous leishmaniasis

Cutaneous leishmaniasis exhibits a spectrum of clinical presentations dependent upon the parasites' persistence and host immunopathologic responses. Although cytolytic CD8 T cells cannot control the parasites, they significantly contribute to pathologic responses. In a murine model of cutaneous leishmaniasis, we previously found that NKG2D plays a role in the ability of cytolytic CD8 T cells to promote disease in leishmanial lesions. Here, we investigated whether NKG2D plays a role in human disease. We found that NKG2D and its ligands were expressed within lesions from L. braziliensis-infected patients and that IL-15 and IL-1β were factors driving NKG2D and NKG2D ligand expression, respectively. Blocking NKG2D reduced degranulation by CD8 T cells in a subset of patients. Additionally, our transcriptional analysis of patients' lesions found that patients who failed the first round of treatment exhibited higher expression of KLRK1, the gene coding for NKG2D, than those who responded to treatment. These findings suggest that NKG2D may be a promising therapeutic target for ameliorating disease severity in cutaneous leishmaniasis caused by L. braziliensis infection.

The skin microbiome enhances disease through IL-1b and delays healing in cutaneous leishmaniasis patients

Leishmania braziliensis infection results in inflammation and skin injury, with highly variable and unpredictable clinical outcomes. Here, we investigated the potential impact of microbiota on infection-induced inflammatory responses and disease resolution by conducting an integrated analysis of the skin microbiome and host transcriptome on a cohort of 62 L. braziliensis -infected patients. We found that overall bacterial burden and microbiome configurations dominated with Staphylococcus spp. were associated with delayed healing and enhanced inflammatory responses, especially by IL-1 family members. Dual RNA-seq of human lesions revealed that high lesional S. aureus transcript abundance was associated with delayed healing and increased expression of IL-1β. This cytokine was critical for modulating disease outcome in L. braziliensis -infected mice colonized with S. aureus , as its neutralization reduced pathology and inflammation. These results implicate the microbiome in cutaneous leishmaniasis disease outcomes in humans and suggest host-directed therapies to mitigate the inflammatory consequences.

Hypoxia promotes cytolytic activity of CD8 T cells and pathogenesis in cutaneous leishmaniasis

Leishmaniasis is a disease caused by protozoan parasites of the genus Leishmania and the most common form of the disease is cutaneous leishmaniasis (CL). A fundamental question in CL is what regulates the development of severe disease, information that is critical to develop therapies to ameliorate disease. In a series of studies, we demonstrated CD8 T cell-dependent cytotoxicity as the main inducer of immunopathology in CL. This result was unexpected since IFN-γ production by CD8 T cells plays a protective role by promoting pathogen elimination. To resolve this paradox, we studied the CD8 T cells in different anatomic sites and found that the effector function of CD8 T cells in CL depends on their location: while CD8 T cells are cytotoxic (GzmB+) and produce little IFN-γ in leishmania lesions, CD8 T cells in the draining lymph nodes (dLN) have the opposite profile. Importantly, GzmB− CD8 T cells from dLN quickly upregulate GzmB after injection into CL lesions. By transcriptional profiling, we found that CD8 T cells in lesions and not dLN have a hypoxic signature. In vivo, we observed that leishmania lesions are hypoxic using the Oxyphor G4 oxygen probe and pimonidazole staining. In vitro, we found that induction of hypoxia was sufficient to convert GzmB− into GzmB+ CD8 T cells. In vivo, blocking the dimerization of HIF-α, a master regulator of hypoxia, with acriflavine decreased lesion development in mice. Transcriptional profiling in patients showed that hypoxia is a signature of human CL and correlates with GZMB expression. Together, our results suggest that the hypoxic microenvironment of leishmania lesions alter the function of CD8 T cells and convert protective CD8 T cells into pathogenic cytotoxic T cells.

Supported by Host Defense and Microbial Biology (OSU)

The microbiome enhances transcriptional inflammatory signatures and delays clinical resolution in cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is a protozoal infection in which the immune response plays a major role in lesion development. The activation of local responses such as cytolysis by CD8+ T cells and release of IL-1β by myeloid cells is associated with poor clinical outcome in patients. We found that lesions from cutaneous leishmaniasis patients also exhibit a bacterial dysbiosis, but whether this dysbiosis affects immune responses and consequently impacts chemotherapy to heal the patients is unknown. We carried out an integrative multi-omics analysis of 64 patients, including RNA-seq and 16S-seq from lesion biopsies and clinical metadata. Staphylococcus was the dominant overrepresented genus in lesions from most patients, so we generated an in-house S. aureus pangenome to quantify transcript abundances through dual RNA-seq mapping analysis. Increased overall bacterial burden assessed by qPCR and the presence of S. aureus assessed by dual RNA-seq indicated enrichment for cytokines (e.g., IL1B), inflammatory responses (e.g., PTGS2), and chemotaxis (e.g., CXCL8) by Gene Ontology analysis. Of particular importance, we found that lesions with increased S. aureus transcript abundances exhibited high expression of inflammatory-related genes that have been associated with treatment failure, such as PRF1, GNLY, and GZMB. Correspondingly, we found that patients with a Staphylococcus spp. dysbiosis exhibited a delay in resolving their lesions following treatment. These results indicate that the microbiome influences the local immune responses in CL, affecting how patients respond to therapy by delaying the healing time. These results suggest that the use of antibiotics combined with chemotherapy may improve treatment outcome for CL.

Supported by grant from NIH (R01 AI149456)

A systemic inflammatory response primes blood monocytes in cutaneous leishmaniasis

Cutaneous leishmaniasis is a localized infection controlled by CD4+ T cells that produce IFN-y within lesions. Phagocytic cells recruited to lesions are exposed to IFN-y which triggers their ability to kill the intracellular parasites. To determine what systemic responses are occurring that might influence the disease, we performed RNA sequencing (RNA-seq) on the blood of 50 L. braziliensis-infected patients, as well as 14 healthy controls. Genes reflecting Interferon downstream activation such as GBP1-6, STAT1, IDO1, AIM2, BATF2, SOCS1 and FCGR-related genes, were upregulated in patients and functional enrichment analysis identified a transcriptional type II Interferon-stimulated gene (ISG) signature as the dominant response. An increase in monocytes and macrophages in the blood, estimated from our RNA-seq dataset, was positively correlated with this type II ISG signature. Consistent with this result, patients had circulating IFN-y in their serum. Monocytes in the bone marrow and circulating in the blood of mice infected with leishmania exhibited increased expression of Class II, further supporting the premise that there is a systemic response to infection. Together, these results suggest that there is a mechanism to limit systemic spread of the parasites, as well as enhance parasite control by pre-activating cells prior to lesion entry.

Localized skin inflammation during cutaneous leishmaniasis drives a chronic, systemic IFN-γ signature

Cutaneous leishmaniasis is a localized infection controlled by CD4+ T cells that produce IFN-γ within lesions. Phagocytic cells recruited to lesions, such as monocytes, are then exposed to IFN-γ which triggers their ability to kill the intracellular parasites. Consistent with this, transcriptional analysis of patient lesions identified an interferon stimulated gene (ISG) signature. To determine whether localized L. braziliensis infection triggers a systemic immune response that may influence the disease, we performed RNA sequencing (RNA-seq) on the blood of L. braziliensis-infected patients and healthy controls. Functional enrichment analysis identified an ISG signature as the dominant transcriptional response in the blood of patients. This ISG signature was associated with an increase in monocyte- and macrophage-specific marker genes in the blood and elevated serum levels IFN-γ. A cytotoxicity signature, which is a dominant feature in the lesions, was also observed in the blood and correlated with an increased abundance of cytolytic cells. Thus, two transcriptional signatures present in lesions were found systemically, although with a substantially reduced number of differentially expressed genes (DEGs). Finally, we found that the number of DEGs and ISGs in leishmaniasis was similar to tuberculosis-another localized infection-but significantly less than observed in malaria. In contrast, the cytolytic signature and increased cytolytic cell abundance was not found in tuberculosis or malaria. Our results indicate that systemic signatures can reflect what is occurring in leishmanial lesions. Furthermore, the presence of an ISG signature in blood monocytes and macrophages suggests a mechanism to limit systemic spread of the parasite, as well as enhance parasite control by pre-activating cells prior to lesion entry.

Host-Directed Therapies for Cutaneous Leishmaniasis

Cutaneous leishmaniasis exhibits a wide spectrum of clinical presentations from self-resolving infections to severe chronic disease. Anti-parasitic drugs are often ineffective in the most severe forms of the disease, and in some cases the magnitude of the disease can result from an uncontrolled inflammatory response rather than unrestrained parasite replication. In these patients, host-directed therapies offer a novel approach to improve clinical outcome. Importantly, there are many anti-inflammatory drugs with known safety and efficacy profiles that are currently used for other inflammatory diseases and are readily available to be used for leishmaniasis. However, since leishmaniasis consists of a wide range of clinical entities, mediated by a diverse group of leishmanial species, host-directed therapies will need to be tailored for specific types of leishmaniasis. There is now substantial evidence that host-directed therapies are likely to be beneficial beyond autoimmune diseases and cancer and thus should be an important component in the armamentarium to modulate the severity of cutaneous leishmaniasis.

Granzyme B Produced by Natural Killer Cells Enhances Inflammatory Response and Contributes to the Immunopathology of Cutaneous Leishmaniasis

BACKGROUND

Skin lesions from patients infected with Leishmania braziliensis has been associated with inflammation induced by cytotoxic CD8+ T cells. In addition, CD8+ T cell-mediated cytotoxicity has not been linked to parasite killing. Meanwhile, the cytotoxic role played by natural killer (NK) cells in cutaneous leishmaniasis (CL) remains poorly understood.

METHODS

In this study, we observed higher frequencies of NK cells in the peripheral blood of CL patients compared with healthy subjects, and that NK cells expressed more interferon-γ, tumor necrosis factor (TNF), granzyme B, and perforin than CD8+ T cells.

RESULTS

We also found that most of the cytotoxic activity in CL lesions was triggered by NK cells, and that the high levels of granzyme B produced in CL lesions was associated with larger lesion size. Furthermore, an in vitro blockade of granzyme B was observed to decrease TNF production.

CONCCLUSIONS

Our data, taken together, suggest an important role by NK cells in inducing inflammation in CL, thereby contributing to disease immunopathology.

Granzyme B Inhibition by Tofacitinib Blocks the Pathology Induced by CD8 T Cells in Cutaneous Leishmaniasis

In cutaneous leishmaniasis, the immune response is not only protective but also mediates immunopathology. We previously found that cytolytic CD8 T cells promote inflammatory responses that are difficult to treat with conventional therapies that target the parasite. Therefore, we hypothesized that inhibiting CD8 T-cell cytotoxicity would reduce disease severity in patients. IL-15 is a potential target for such a treatment because it is highly expressed in human patients with cutaneous leishmaniasis lesions and promotes granzyme B‒dependent CD8 T-cell cytotoxicity. Here we tested whether tofacitinib, which inhibits IL-15 signaling by blocking Jak3, might decrease CD8-dependent pathology. We found that tofacitinib reduced the expression of granzyme B by CD8 T cells in vitro and in vivo systemic and topical treatment, with tofacitinib protecting mice from developing severe cutaneous leishmaniasis lesions. Importantly, tofacitinib treatment did not alter T helper type 1 responses or parasite control. Collectively, our results suggest that host-directed therapies do not need to be limited to autoimmune disorders and that topical tofacitinib application should be considered a strategy for the treatment of cutaneous leishmaniasis disease in combination with antiparasitic drugs.

Variable gene expression and parasite load predict treatment outcome in cutaneous leishmaniasis

Patients infected with Leishmania braziliensis develop chronic lesions that often fail to respond to treatment with antiparasite drugs. To determine whether genes whose expression is highly variable in lesions between patients might influence disease outcome, we obtained biopsies of lesions from patients before treatment with pentavalent antimony and performed transcriptomic profiling on these clinical samples. We identified genes that were highly variably expressed between patients, and the variable expression of these genes correlated with treatment outcome. Among the most variable genes in all the patients were components of the cytolytic pathway, and the expression of these genes correlated with parasite load in the skin. We demonstrated that treatment failure was linked to the cytolytic pathway activated during infection. Using a host-pathogen marker profile of as few as three genes, we showed that eventual treatment outcome could be predicted before the start of treatment in two separate cohorts of patients with cutaneous leishmaniasis (n = 21 and n = 25). These findings raise the possibility of point-of-care diagnostic screening to identify patients at high risk of treatment failure and provide a rationale for a precision medicine approach to drug selection in cutaneous leishmaniasis. This work more broadly demonstrates the value of identifying genes of high variability in other diseases to better understand and predict diverse clinical outcomes.

CD8+ T Cells Lack Local Signals To Produce IFN-γ in the Skin during Leishmania Infection

Resolution of leishmaniasis depends upon parasite control and limiting inflammation. CD4⁺ Th1 cells are required to control parasites, whereas CD8⁺ T cells play a dual role: they promote Th1 cell differentiation but can also increase inflammation at the site of infection as a consequence of cytolysis. Although CD8⁺ T cells taken from leishmanial lesions are cytolytic, in this study, we showed that only a few CD8⁺ T cells produced IFN-γ. Correspondingly, only low levels of IL-12 and/or IL-12 mRNA were present in lesions from infected mice, as well as patients. Addition of IL-12 increased IFN-γ production by CD8⁺ T cells isolated from leishmanial lesions, suggesting that a lack of IL-12 at the site of infection limits IFN-γ production by CD8⁺ T cells. To determine whether CD8⁺ T cells could promote resistance in vivo if IL-12 was present, we administered IL-12 to Leishmania-infected RAG mice reconstituted with CD8⁺ T cells. IL-12 treatment increased the ability of CD8⁺ T cells to make IFN-γ, but CD8⁺ T cells still failed to control the parasites. Furthermore, despite the ability of CD8⁺ T cells to promote immunity to secondary infections, we also found that CD8⁺ T cells from immune mice were unable to control Leishmania in RAG mice. Taken together, these results indicate that lesional CD8⁺ T cells fail to make IFN-γ because of a deficit in IL-12 but that, even with IL-12, CD8⁺ T cells are unable to control Leishmania in the absence of CD4⁺ T cells.

Cutaneous Leishmaniasis Induces a Transmissible Dysbiotic Skin Microbiota that Promotes Skin Inflammation

Skin microbiota can impact allergic and autoimmune responses, wound healing, and anti-microbial defense. We investigated the role of skin microbiota in cutaneous leishmaniasis and found that human patients infected with Leishmania braziliensis develop dysbiotic skin microbiota, characterized by increases in the abundance of Staphylococcus and/or Streptococcus. Mice infected with L. major exhibit similar changes depending upon disease severity. Importantly, this dysbiosis is not limited to the lesion site, but is transmissible to normal skin distant from the infection site and to skin from co-housed naive mice. This observation allowed us to test whether a pre-existing dysbiotic skin microbiota influences disease, and we found that challenging dysbiotic naive mice with L. major or testing for contact hypersensitivity results in exacerbated skin inflammatory responses. These findings demonstrate that a dysbiotic skin microbiota is not only a consequence of tissue stress, but also enhances inflammation, which has implications for many inflammatory cutaneous diseases.

CD8+ T cell cytotoxicity mediates pathology in the skin by inflammasome activation and IL-1β production

Deregulated CD8+ T cell cytotoxicity plays a central role in enhancing disease severity in several conditions. However, we have little understanding of the mechanisms by which immunopathology develops as a consequence of cytotoxicity. Using murine models of inflammation induced by the protozoan parasite leishmania, and data obtained from patients with cutaneous leishmaniasis, we uncovered a previously unrecognized role for NLRP3 inflammasome activation and IL-1β release as a detrimental consequence of CD8+ T cell-mediated cytotoxicity, ultimately resulting in chronic inflammation. Critically, pharmacological blockade of NLRP3 or IL-1β significantly ameliorated the CD8+ T cell-driven immunopathology in leishmania-infected mice. Confirming the relevance of these findings to human leishmaniasis, blockade of the NLRP3 inflammasome in skin biopsies from leishmania-infected patients prevented IL-1β release. Thus, these studies link CD8+ T cell cytotoxicity with inflammasome activation and reveal novel avenues of treatment for cutaneous leishmaniasis, as well as other of diseases where CD8+ T cell-mediated cytotoxicity induces pathology.

Leishmaniasis is a neglected tropical disease endemic in 98 countries and approximately 1 million new cases occur each year. Disease caused by Leishmania braziliensis, the main causative agent of leishmaniasis in South America, leads to skin ulcers that are difficult to heal with drugs that target the parasites. This is because disease severity seen in patients infected with L. braziliensis is largely due to the immune response that develops, rather than the number of parasites in the skin. CD8+ T cells induce cell death in the lesions of L. braziliensis-infected mice, as well as in the lesions from L. braziliensis-infected patients, which promotes disease. However, the mechanism mediating CD8+ T cell dependent pathology is unknown. Here, using studies in mice and experiments with L. braziliensis patients’ samples we show that increased disease severity is due to inflammasome activation, and furthermore that therapies that block either inflammasome activation or IL-1β ameliorate disease in mouse models of severe leishmaniasis. Based on these studies we propose a novel strategy of therapy for L. braziliensis infection and other diseases in which cytotoxicity plays a central role in promoting disease severity.

Meta-transcriptome Profiling of the Human-Leishmania braziliensis Cutaneous Lesion

Host and parasite gene expression in skin biopsies from Leishmania braziliensis-infected patients were simultaneously analyzed using high throughput RNA-sequencing. Biopsies were taken from 8 patients with early cutaneous leishmaniasis and 17 patients with late cutaneous leishmaniasis. Although parasite DNA was found in all patient lesions at the time of biopsy, the patients could be stratified into two groups: one lacking detectable parasite transcripts (PT^Neg) in lesions, and another in which parasite transcripts were readily detected (PT^Pos). These groups exhibited substantial differences in host responses to infection. PT^Pos biopsies contained an unexpected increase in B lymphocyte-specific and immunoglobulin transcripts in the lesions, and an upregulation of immune inhibitory molecules. Biopsies without detectable parasite transcripts showed decreased evidence for B cell activation, but increased expression of antimicrobial genes and genes encoding skin barrier functions. The composition and abundance of L. braziliensis transcripts in PT^Pos lesions were surprisingly conserved among all six patients, with minimal meaningful differences between lesions from patients with early and late cutaneous leishmaniasis. The most abundant parasite transcripts expressed in lesions were distinct from transcripts expressed in vitro in human macrophage cultures infected with L. amazonensis or L. major. Therefore in vitro gene expression in macrophage monolayers may not be a strong predictor of gene expression in lesions. Some of the most highly expressed in vivo transcripts encoded amastin-like proteins, hypothetical genes, putative parasite virulence factors, as well as histones and tubulin. In summary, RNA sequencing allowed us to simultaneously analyze human and L. braziliensis transcriptomes in lesions of infected patients, and identify unexpected differences in host immune responses which correlated with active transcription of parasite genes.

Leishmania spp are intracellular protozoan parasites that replicate primarily within host tissue macrophages. In this paper we simultaneously query host and parasite gene expression in human cutaneous L. braziliensis lesions. We observe an unexpectedly prominent role for B cells and immunoglobulins in lesions in which actively transcribing parasites reside. We also observe that parasite gene expression is surprisingly conserved among L. braziliensis lesions, and the genes that are expressed in lesions are not those that have been previously associated with parasite growth in vitro. This analysis of parasite and host gene expression in lesions may lead to the identification of new parasite virulence factors and may identify host responses that promote parasite persistence in lesions.

Lymphocytic Choriomeningitis Virus Expands a Population of NKG2D+CD8+ T Cells That Exacerbates Disease in Mice Coinfected with Leishmania major

Leishmaniasis is a significant neglected tropical disease that is associated with a wide range of clinical presentations and a lifelong persistent infection. Because of the chronic nature of the disease, there is a high risk for coinfection occurring in patients, and how coinfections influence the outcome of leishmaniasis is poorly understood. To address this issue, we infected mice with Leishmania major and 2 wk later with lymphocytic choriomeningitis virus (LCMV) and then monitored the course of infection. Leishmania parasites are controlled by production of IFN-γ, which leads to macrophage-mediated parasite killing. Thus, one might predict that coinfection with LCMV, which induces a strong systemic type 1 response, would accelerate disease resolution. However, we found that infection with LCMV led to significantly enhanced disease in L. major-infected animals. This increased disease correlated with an infiltration into the leishmanial lesions of NKG2D(+) CD8(+) T cells producing granzyme B, but surprisingly little IFN-γ. We found that depletion of CD8 T cells after viral clearance, as well as blockade of NKG2D, reversed the increased pathology seen in coinfected mice. Thus, this work highlights the impact a secondary infection can have on leishmaniasis and demonstrates that even pathogens known to promote a type 1 response may exacerbate leishmanial infections.

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.

Matrix metalloproteinase 9 production by monocytes is enhanced by TNF and participates in the pathology of human cutaneous Leishmaniasis

Introduction

Cutaneous leishmaniasis (CL) due to L.braziliensis infection is characterized by a strong inflammatory response with high levels of TNF and ulcer development. Less attention has been given to the role of mononuclear phagocytes to this process. Monocytes constitute a heterogeneous population subdivided into classical, intermediate and non-classical, and are known to migrate to inflammatory sites and secrete inflammatory mediators. TNF participates in the induction of matrix metalloproteinases (MMPs). MMP-9 is an enzyme that degrades basal membrane and its activity is controlled by the tissue inhibitor of metalloproteinase.

Methods

Mononuclear cells were obtained from ex-vivo labeling sub-populations of monocytes and MMP-9, and the frequency was determined by flow cytometry. Culture was performed during 72 hours, stimulating the cells with SLA, levels of MMP-9 and TIMP-1 in the supernatants were determined by ELISA.

Results

We observed that cells from CL lesions secrete high amounts of MMP-9 when compared to healthy subjects. Although MMP-9 was produced by monocytes, non-classical ones were the main source of this enzyme. We also observed that TNF produced in high level during CL contributes to MMP-9 production.

Conclusions

These observations emphasize the role of monocytes, TNF and MMP-9 in the pathogenesis of L. braziliensis infection.

To examine the participation of MMP-9 in the pathogenesis of L. braziliensis infection, we realized a cross-sectional study with CL patients in an early phase of the disease or with a classical ulcer, and healthy controls. We evaluated the frequency of MMP-9 in monocyte subsets and its mechanism of production. Our results showed that monocytes were the major cells producing MMP-9. The MMP-9 production by CL patients was presented in higher levels when compared with healthy subjects and early cutaneous leishmaniasis (ECL) patients, and the levels of MMP-9 inhibitor, TIMP-1, were lower in CL patients when compared to healthy subjects. The production of MMP-9 was enhanced by TNF, a cytokine associated with tissue damage in CL patients. Thus, therapeutic modulation of MMP-9 may be a useful approach for improving disease outcome in L. braziliensis patients.

Intermediate monocytes contribute to pathologic immune response in Leishmania braziliensis infections

Ulcer development in patients with cutaneous leishmaniasis (CL) caused by Leishmania braziliensis is associated with high levels of tumor necrosis factor (TNF). We found that early after infection, before ulcer development, the frequency of CD16(+) (both intermediate [CD14(+)CD16(+)] and nonclassical [CD14(dim)CD16(+)]) monocytes was increased in the peripheral blood of patients with L. braziliensis, compared with uninfected controls. These results suggest that CD16(+) monocytes might promote disease. Also, we found that intermediate monocytes expressed CCR2 and that increased levels of CCL2 protein were present in lesions from patients, suggesting that intermediate monocytes are more likely than nonclassical monocytes to migrate to the lesion site. Finally, we found that the intermediate monocytes produced TNF. Our results show that intermediate monocytes are increased in frequency soon after infection; express CCR2, which would promote their migration into the lesions; and, owing to their production of TNF, can enhance the inflammatory response.

Genomic profiling of human Leishmania braziliensis lesions identifies transcriptional modules associated with cutaneous immunopathology

The host immune response plays a critical role not only in protection from human leishmaniasis, but also in promoting disease severity. Although candidate gene approaches in mouse models of leishmaniasis have been extremely informative, a global understanding of the immune pathways active in lesions from human patients is lacking. To address this issue, genome-wide transcriptional profiling of Leishmania braziliensis-infected cutaneous lesions and normal skin controls was carried out. A signature of the L. braziliensis skin lesion was defined that includes over 2,000 differentially regulated genes. Pathway-level analysis of this transcriptional response revealed key biological pathways present in cutaneous lesions, generating a testable ‘metapathway’ model of immunopathology, and providing new insights for treatment of human leishmaniasis.

Human classical monocytes control the intracellular stage of Leishmania braziliensis by reactive oxygen species

Leishmania braziliensis are intracellular parasites that cause unique clinical forms of cutaneous leishmaniasis. Previous studies with other leishmania species demonstrated that reactive oxygen species (ROS) control promastigotes, the infective stage of the parasite, but not the amastigote form that exists in the mammalian host. Here we show that ROS inhibits growth of L. braziliensis amastigotes in resting monocytes, and that classical monocytes are primarily responsible for this control. ROS, but not nitric oxide, also contributed to killing of L. braziliensis by IFN-γ activated monocytes. Furthermore, by gene expression profiling of human lesions we found greater expression of genes associated with ROS, but not nitric oxide, compared to normal skin. This study shows that ROS are important for control of L. braziliensis both at the initial stages of infection, as well as at later time points, and highlights that monocyte subsets may play different roles during leishmaniasis.

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.

Immunity to Lutzomyia intermedia saliva modulates the inflammatory environment induced by Leishmania braziliensis

Background

During blood feeding, sand flies inject Leishmania parasites in the presence of saliva. The types and functions of cells present at the first host-parasite contact are critical to the outcome on infection and sand fly saliva has been shown to play an important role in this setting. Herein, we investigated the in vivo chemotactic effects of Lutzomyia intermedia saliva, the vector of Leishmania braziliensis, combined or not with the parasite.

Methods and Findings

We tested the initial response induced by Lutzomyia intermedia salivary gland sonicate (SGS) in BALB/c mice employing the air pouch model of inflammation. L. intermedia SGS induced a rapid influx of macrophages and neutrophils. In mice that were pre-sensitized with L. intermedia saliva, injection of SGS was associated with increased neutrophil recruitment and a significant up-regulation of CXCL1, CCL2, CCL4 and TNF-α expression. Surprisingly, in mice that were pre-exposed to SGS, a combination of SGS and L. braziliensis induced a significant migration of neutrophils and an important modulation in cytokine and chemokine expression as shown by decreased CXCL10 expression and increased IL-10 expression.

Conclusion

These results confirm that sand fly saliva modulates the initial host response. More importantly, pre-exposure to L. intermedia saliva significantly modifies the host's response to L. braziliensis, in terms of cellular recruitment and expression of cytokines and chemokines. This particular immune modulation may, in turn, favor parasite multiplication.

Transmission of Leishmania parasites occurs during blood feeding, when infected female sand flies inject humans with parasites and saliva. Chemokines and cytokines are secreted proteins that regulate the initial immune responses and have the potential of attracting and activating cells. Herein, we studied the expression of such molecules and the cellular recruitment induced by salivary proteins of the Lutzomyia intermedia sand fly. Of note, Lutzomyia intermedia is the main vector of Leishmania braziliensis, a parasite species that causes cutaneous leishmaniasis, a disease associated with the development of destructive skin lesions that can be fatal if left untreated. We observed that L. intermedia salivary proteins induce a potent cellular recruitment and modify the expression profile of chemokines and cytokines in mice. More importantly, in mice previously immunized with L. intermedia saliva, the alteration in the initial inflammatory response was even more pronounced, in terms of the number of cells recruited and in terms of gene expression pattern. These findings indicate that an existing immunity to L. intermedia sand fly induces an important modulation in the initial immune response that may, in turn, promote parasite multiplication, leading to the development of cutaneous leishmaniasis.

Neutrophils and macrophages cooperate in host resistance against Leishmania braziliensis infection

Neutrophils play an active role in the control of infections caused by intracellular pathogens such as Leishmania. In the present study, we investigated the effect of neutrophil depletion at the time of Leishmania braziliensis infection of BALB/c mice and how neutrophils interact with the infected macrophage to promote parasite elimination. The in vivo depletion of neutrophils led to a significant increase in parasite load and enhanced the Th1-Th2 immune response in this experimental model of infection. BALB/c mice coinoculated with both parasites and live neutrophils displayed lower parasite burdens at the site of infection and in the draining lymph nodes. In vitro, we observed that live neutrophils significantly reduced the parasite load in L. braziliensis-infected murine macrophages, an effect not observed with Leishmania major. L. braziliensis elimination was dependent on the interaction between neutrophils and macrophages and was associated with TNF-alpha as well as superoxide production. Furthermore, cooperation between neutrophils and macrophages toward parasite elimination was also observed in experiments performed with L. braziliensis-infected human cells and, importantly, with two other New World Leishmania species. These results indicate that neutrophils play an important and previously unappreciated role in L. braziliensis infection, favoring the induction of a protective immune response.

The value of the otorhinolaryngologic exam in correct mucocutaneous leishmaniasis diagnosis

An increase in mucocutaneous leishmaniasis (ML) cases in northern (Brazil) motivated this study. In 44 ML patients with clinical diagnosis, only 13 parasitologically confirmed cases exhibited mucosal lesion suggestive of ML. Other conditions involving nasal manifestations are frequently confounded with ML. Therefore, otorhinolaryngologic examination is important in the clinical management of ML.

Toward a novel experimental model of infection to study American cutaneous leishmaniasis caused by Leishmania braziliensis

Leishmania spp. cause a broad spectrum of diseases collectively known as leishmaniasis. Leishmania braziliensis is the main etiological agent of American cutaneous leishmaniasis (ACL) and mucocutaneous leishmaniasis. In the present study, we have developed an experimental model of infection that closely resembles ACL caused by L. braziliensis. In order to do so, BALB/c mice were infected in the ear dermis with 10(5) parasites and distinct aspects of the infection were evaluated. Following inoculation, parasite expansion in the ear dermis was accompanied by the development of an ulcerated dermal lesion which healed spontaneously, as seen by the presence of a scar. Histological analysis of infected ears showed the presence of a mixed inflammatory infiltrate consisting of both mononuclear and polymorphonuclear cells. In draining lymph nodes, parasite replication was detected throughout the infection. In vitro restimulation of draining lymph node cells followed by intracellular staining showed an up-regulation in the production of gamma interferon (IFN-gamma) and in the frequency of IFN-gamma-secreting CD4(+) and CD8(+) T cells. Reverse transcription-PCR of ears and draining lymph node cells showed the expression of CC chemokines. The dermal model of infection with L. braziliensis herein is able to reproduce aspects of the natural infection, such as the presence of an ulcerated lesion, parasite dissemination to lymphoid areas, and the development of a Th1-type immune response. These results indicate that this model shall be useful to address questions related to the concomitant immunity to reinfection and parasite persistence leading to mucocutaneous leishmaniasis.

Polymerase chain reaction (PCR) is highly sensitive for diagnosis of mucosal leishmaniasis

We evaluated the use of polymerase chain reaction (PCR) for diagnosis of mucosal leishmaniasis (ML) in an endemic area in Acre, Brazil, where Leishmania braziliensis is present. Leishmania DNA was detected 34 of 35 cases, yielding a positivity rate of 97.1%, which was higher than the positivity rates for all of the other diagnostic methods studied, namely Montenegro skin test (MST), anti-Leishmania serological testing and microscopic examination of lesion biopsy specimens. These findings have led us to propose guidelines for the diagnosis of ML that use PCR as the principal method of parasitological confirmation of cases.