Cellular and molecular determinants of bacterial burden in leprosy granulomas revealed by single-cell multimodal omics.

BACKGROUND: Which cell populations that determine the fate of bacteria in infectious granulomas remain unclear. Leprosy, a granulomatous disease with a strong genetic predisposition, caused by Mycobacterium leprae infection, exhibits distinct sub-types with varying bacterial load and is considered an outstanding disease model for studying host-pathogen interactions. METHODS: We performed single-cell RNA and immune repertoire sequencing on 11 healthy controls and 20 patients with leprosy, and integrated single-cell data with genome-wide genetic data on leprosy. Multiplex immunohistochemistry, and in vitro and in vivo infection experiments were conducted to confirm the multimodal omics findings. FINDINGS: Lepromatous leprosy (L-LEP) granulomas with high bacterial burden were characterised by exhausted CD8+ T cells, and high RGS1 expression in CD8+ T cells was associated with L-LEP. By contrast, tuberculoid leprosy (T-LEP) granulomas with low bacterial burden displayed enrichment in resident memory IFNG+ CD8+ T cells (CD8+ Trm) with high GNLY expression. This enrichment was potentially attributable to the communication between IL1B macrophages and CD8+ Trm via CXCL10-CXCR3 signalling. Additionally, IL1B macrophages in L-LEP exhibited anti-inflammatory phenotype, with high APOE expression contributing to high bacterial burden. Conversely, IL1B macrophages in T-LEP were distinguished by interferon-γ induced GBP family genes. INTERPRETATION: The state of IL1B macrophages and functional CD8+ T cells, as well as the relationship between them, is crucial for controlling bacterial persistence within granulomas. These insights may indicate potential targets for host-directed immunotherapy in granulomatous diseases caused by mycobacteria and other intracellular bacteria. FUNDING: The Key research and development program of Shandong Province (2021LCZX07), Natural Science Foundation of Shandong Province (ZR2023MH046), Youth Science Foundation Cultivation Funding Plan of Shandong First Medical University (Shandong Academy of Medical Sciences) (202201-123), National Natural Science Foundation of China (82471800, 82230107, 82273545, 82304039), the China Postdoctoral Science Foundation (2023M742162), Shandong Province Taishan Scholar Project (tspd20230608), Joint Innovation Team for Clinical & Basic Research (202410), Central guidance for local scientific and technological development projects of Shandong Province (YDZX2023058).

The red flags of ulnar neuropathy in leprosy.

The diagnosis of pure neural leprosy is more challenging because patients share characteristics with other common pathologies, such as ulnar compression, which should be taken into consideration for differential diagnosis. In this study, we identify ulnar nerve conduction characteristics to aid in the differential diagnosis of ulnar neuropathy (UN) in leprosy and that of non-leprosy etiology. In addition, we include putative markers to better understand the inflammatory process that may occur in the nerve. Data were extracted from a database of people affected by leprosy (leprosy group) diagnosed with UN at leprosy diagnosis. A non-leprosy group of patients diagnosed with mechanical neuropathy (compressive, traumatic) was also included. Both groups were submitted to clinical, neurological, neurophysiological and immunological studies. Nerve enlargement and sensory impairment were significantly higher in leprosy patients than in patients with compressive UN. Bilateral impairment was significantly higher in the leprosy group than in the non-leprosy group. Leprosy reactions were associated to focal demyelinating lesions at the elbow and to temporal dispersion (TD). Clinical signs such as sensory impairment, nerve enlargement and bilateral ulnar nerve injury associated with eletrodiagnostic criteria such as demyelinating finds, specifically temporal dispersion, could be tools to help us decided on the best conduct in patients with elbow ulnar neuropathy and specifically decide if we should perform a nerve biopsy for diagnosis of pure neural leprosy.

Mycobacterium leprae induces a tolerogenic profile in monocyte-derived dendritic cells via TLR2 induction of IDO.

The enzyme IDO-1 is involved in the first stage of tryptophan catabolism and has been described in both microbicidal and tolerogenic microenvironments. Previous data from our group have shown that IDO-1 is differentially regulated in the distinctive clinical forms of leprosy. The present study aims to investigate the mechanisms associated with IDO-1 expression and activity in human monocyte-derived dendritic cells (mDCs) after stimulation with irradiated Mycobacterium leprae and its fractions. M. leprae and its fractions induced the expression and activity of IDO-1 in human mDCs. Among the stimuli studied, irradiated M. leprae and its membrane fraction (MLMA) induced the production of proinflammatory cytokines TNF and IL-6 whereas irradiated M. leprae and its cytosol fraction (MLSA) induced an increase in IL-10. We investigated if TLR2 activation was necessary for IDO-1 induction in mDCs. We observed that in cultures treated with a neutralizing anti-TLR2 antibody, there was a decrease in IDO-1 activity and expression induced by M. leprae and MLMA. The same effect was observed when we used a MyD88 inhibitor. Our data demonstrate that coculture of mDCs with autologous lymphocytes induced an increase in regulatory T (Treg) cell frequency in MLSA-stimulated cultures, showing that M. leprae constituents may play opposite roles that may possibly be related to the dubious effect of IDO-1 in the different clinical forms of disease. Our data show that M. leprae and its fractions are able to differentially modulate the activity and functionality of IDO-1 in mDCs by a pathway that involves TLR2, suggesting that this enzyme may play an important role in leprosy immunopathogenesis.

Oct-6 transcriptional factor a possible biomarker for leprosy diagnosis.

Leprosy is an infectious disease caused by Mycobacterium leprae that affects the skin and nerves. The nerve damage in leprosy may be related to alterations in transcriptional factors, such as Krox-20, Oct-6, Sox-10. Thirty skin biopsies in leprosy patients and 15 non-leprosy skin biopsies were evaluated using RT-qPCR to assess Krox-20, Oct-6, and Sox-10 and these data was related with S-100 immunohistochemistry. Changes in gene expression were observed in the skin and dermal nerves of leprosy patients in Oct-6 and Sox-10. When comparing Oct-6 with S-100 IHC as diagnostic tests for leprosy, Oct-6 showed a sensitivity of 73.3%, and specificity of 100%, while S-100 IHC showed a sensitivity of 96.6% and specificity of 100%. Our data suggest Oct-6 could be an auxiliary biomarker specific to detecting changes in dermal nerves in leprosy and thus useful to health workers and pathologists with no expertise to observe nerve injuries in leprosy.

The function of peroxisome proliferator-activated receptors PPAR-γ and PPAR-δ in Mycobacterium leprae-induced foam cell formation in host macrophages.

Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae). In lepromatous leprosy (LL), skin macrophages, harboring extensive bacterial multiplication, gain a distinctive foamy appearance due to increased intracellular lipid load. To determine the mechanism by which M. leprae modifies the lipid homeostasis in host cells, an in vitro M. leprae infection system, using human macrophage precursor THP-1 cells and M. leprae prepared from the footpads of nude mice, was employed. RNA extracted from skin smear samples of patients was used to investigate host gene expressions before and after multidrug therapy (MDT). We found that a cluster of peroxisome proliferator-activated receptor (PPAR) target genes associated with adipocyte differentiation were strongly induced in M. leprae-infected THP-1 cells, with increased intracellular lipid accumulation. PPAR-δ and PPAR-γ expressions were induced by M. leprae infection in a bacterial load-dependent manner, and their proteins underwent nuclear translocalization after infection, indicating activation of PPAR signaling in host cells. Either PPAR-δ or PPAR-γ antagonist abolished the effect of M. leprae to modify host gene expressions and inhibited intracellular lipid accumulation in host cells. M. leprae-specific gene expressions were detected in the skin smear samples both before and after MDT, whereas PPAR target gene expressions were dramatically diminished after MDT. These results suggest that M. leprae infection activates host PPAR signaling to induce an array of adipocyte differentiation-associated genes, leading to accumulation of intracellular lipids to accommodate M. leprae parasitization. Certain PPAR target genes in skin lesions may serve as biomarkers for monitoring treatment efficacy.

Elevated IL-6R on CD4+ T cells promotes IL-6 driven Th17 cell responses in patients with T1R leprosy reactions.

Th17 cells play vital role during pathogenesis of leprosy reactions. Previously, we have reported that IL-23 is involved in Th17 cells differentiation. Subsequently, our group also showed that IL-6 induces Th17 cell differentiation along with TGF-ß in leprosy reactions. Here, we next asked the question that whether IL-6 or IL-23 induced Th17 cells are different in nature? In this study, Type 1 Reactions (T1R) showed significantly (p < 0.001) higher percentage of IL-17A producing CD4+IL6R+ T cells as compared to non-reaction (NR) patients. Furthermore, recombinant IL-6, IL-23 and TGF-ß promoted IL-17A secretion by CD4+IL6R+ T cells. Subsequently, IL-6R and IL-23R blocking experiments showed significantly (p < 0.002) down regulated IL-17A in T1R reaction as compared to NR leprosy patients. The present study for the first time establishes that pathogenic Th17 cells produce IL-17 in an IL-6 dependent manner in leprosy T1R reactions. Thus, present approaches that specifically target Th17 cells and/or the cytokines that promote their development, such as IL-6, TGF-ß and IL-23A may provide more focused treatment strategies for the management of Mycobacterium leprae and its reactions.

Analysis of HLA-G protein expression in leprosy.

The aim of this study was to evaluate the expression of human leukocyte antigen G (HLA-G) in leprosy. Biopsy and serum samples were collected from 18 patients presenting with leprosy and from healthy controls. Samples were analyzed using immunohistochemistry and ELISA techniques. HLA-G expression was observed in biopsy samples of all patients. The healthy control samples were consistently negative for HLA-G expression. Control plasma samples displayed significantly higher HLA-G expression than those from the patients (p < 0.01). These results are the first demonstration of the expression of HLA-G in leprosy.

Notch Signaling Pathway Expression in the Skin of Leprosy Patients: Association With Skin and Neural Damage.

Introduction: Leprosy is an infectious disease caused by Mycobacterium leprae, a debilitating disease that affects the skin and peripheral nerves. It is possible that tissue changes during infection with leprosy are related to alterations in the activity of the Notch signaling pathway, an innate signaling pathway in the physiology of the skin and peripheral nerves. Methods: This is a descriptive observational study. Thirty skin biopsies from leprosy patients and 15 from individuals with no history of this disease were evaluated. In these samples, gene expressions of cellular components associated with the Notch signaling pathway, Hes-1, Hey-1, Runx-1 Jagged-1, Notch-1, and Numb, were evaluated using q-PCR, and protein expression was evaluated using immunohistochemistry of Runx-1 and Hes-1. Results: Changes were observed in the transcription of Notch signaling pathway components; Hes-1 was downregulated and Runx-1 upregulated in the skin of infected patients. These results were confirmed by immunohistochemistry, where reduction of Hes-1 expression was found in the epidermis, eccrine glands, and hair follicles. Increased expression of Runx-1 was found in inflammatory cells in the dermis of infected patients; however, it is not related to tissue changes. With these results, a multivariate analysis was performed to determine the causes of transcription factor Hes-1 reduction. It was concluded that tissue inflammation was the main cause. Conclusions: The tissue changes found in the skin of infected patients could be associated with a reduction in the expression of Hes-1, a situation that would promote the survival and proliferation of M. leprae in this tissue.

Population Pharmacokinetic Model to Assess the Impact of Disease State on Thalidomide Pharmacokinetics.

A population pharmacokinetic (PPK) model to describe the pharmacokinetics of thalidomide in different patient populations was developed using data pooled from healthy subjects and patients with Hansen's disease, human immunodeficiency virus (HIV), and multiple myeloma (MM). The analysis data set had a total of 164 evaluable subjects who received various doses (50 to 400 mg) of oral thalidomide in single- and/or multiple-dose regimens. The plasma thalidomide concentrations were adequately described by a linear 1-compartment PPK model with first-order absorption and first-order elimination. Inclusion of MM as a covariate on apparent clearance (CL/F) accounted for 4.4% of the interindividual variability (IIV) of CL/F. Body weight as a covariate on CL/F and apparent volume of distribution (V/F) also improved model fitting slightly, accounting for 7.2% and 20% of IIV, respectively. Although inclusion of body weight and MM as covariates of CL/F and body weight on V/F improved the goodness of fit of the model in a statistically significant manner, the impact of this difference in CL/F is not considered clinically relevant. Other factors such as age, sex, race, creatinine clearance, and alanine transaminase had no effect on thalidomide pharmacokinetics. MM, HIV, and Hansen's disease have no clinically relevant effect on thalidomide disposition relative to healthy volunteers.

Expression of NLRP3 inflammasome in leprosy indicates immune evasion of Mycobacterium leprae

BACKGROUND Leprosy is an infectious-contagious disease caused by Mycobacterium leprae that remain endemic in 105 countries. This neglected disease has a wide range of clinical and histopathological manifestations that are related to the host inflammatory and immune responses. More recently, the inflammasome has assumed a relevant role in the inflammatory response against microbiological agents. However, the involvement of inflammasome in leprosy remains poorly understood. OBJECTIVES The aim is to associate biomarkers of inflammasome with the different immunopathological forms of leprosy. METHODS We performed an observational, cross-sectional, and comparative study of the immunophenotypic expression of inflammasome-associated proteins in immunopathological forms of leprosy of 99 skin lesion samples by immunohistochemistry. The intensity and percentage of NLRP3, Caspase-1, Caspases-4/5, interleukin-1β and interleukin-18 immunoreactivities in the inflammatory infiltrate of skin biopsies were evaluated. FINDINGS Strong expression of NLRP3 and inflammatory Caspases-4/5 were observed in lepromatous leprosy (lepromatous pole). In addition, were observed low expression of caspase-1, interleukin-1β, and interleukin-18 in tuberculoid and lepromatous leprosy. The interpolar or borderline form showed immunophenotype predominantly similar to the lepromatous pole. MAIN CONCLUSIONS Our results demonstrate that the NLRP3 inflammasome is inactive in leprosy, suggesting immune evasion of M. leprae.

Intracellular Mycobacterium leprae Utilizes Host Glucose as a Carbon Source in Schwann Cells.

New approaches are needed to control leprosy, but understanding of the biology of the causative agent Mycobacterium leprae remains rudimentary, principally because the pathogen cannot be grown in axenic culture. Here, we applied 13C isotopomer analysis to measure carbon metabolism of M. leprae in its primary host cell, the Schwann cell. We compared the results of this analysis with those of a related pathogen, Mycobacterium tuberculosis, growing in its primary host cell, the macrophage. Using 13C isotopomer analysis with glucose as the tracer, we show that whereas M. tuberculosis imports most of its amino acids directly from the host macrophage, M. leprae utilizes host glucose pools as the carbon source to biosynthesize the majority of its amino acids. Our analysis highlights the anaplerotic enzyme phosphoenolpyruvate carboxylase required for this intracellular diet of M. leprae, identifying this enzyme as a potential antileprosy drug target.IMPORTANCE Leprosy remains a major problem in the world today, particularly affecting the poorest and most disadvantaged sections of society in the least developed countries of the world. The long-term aim of research is to develop new treatments and vaccines, and these aims are currently hampered by our inability to grow the pathogen in axenic culture. In this study, we probed the metabolism of M. leprae while it is surviving and replicating inside its primary host cell, the Schwann cell, and compared it to a related pathogen, M. tuberculosis, replicating in macrophages. Our analysis revealed that unlike M. tuberculosis, M. leprae utilized host glucose as a carbon source and that it biosynthesized its own amino acids, rather than importing them from its host cell. We demonstrated that the enzyme phosphoenolpyruvate carboxylase plays a crucial role in glucose catabolism in M. leprae Our findings provide the first metabolic signature of M. leprae in the host Schwann cell and identify novel avenues for the development of antileprosy drugs.

Lucio phenomenon mimicking antiphospholipid syndrome: The occurrence of antiphospholipid antibodies in a leprosy patient.

Lucio phenomenon is an atypical reaction of leprosy, characterized by vasculitic lesions that can mimic antiphospholipid syndrome (APS) clinically. Distinguishing the two can be difficult as antiphospholipid autoantibodies may be present in patients with leprosy. We report on a 32-year-old female patient presenting with a sudden onset of fever, hemorrhagic bullae, and skin necrosis on her lower legs. She was treated for APS due to the presence of antiphospholipid antibodies but had an inadequate response. A skin biopsy revealed thrombotic vasculopathy and necrotizing vasculitis associated with aggregation of foam cells in the perivascular area and subcutis, with acid-fast bacilli in the histiocytes and blood vessel walls. Direct immunofluorescence showed IgM, C3, and fibrinogen deposition in the superficial and deep dermal blood vessels. The pathology confirmed the diagnosis of Lucio phenomenon, and appropriate therapy was given. It is essential to evaluate the patient comprehensively, including clinical, serological, and pathological aspects, to obtain the correct diagnosis.

Immunohistochemical characterization of the M4 macrophage population in leprosy skin lesions.

BACKGROUND: Since macrophages are one of the major cell types involved in the Mycobacterium leprae immune response, roles of the M1 and M2 macrophage subpopulations have been well defined. However, the role of M4 macrophages in leprosy or other infectious diseases caused by mycobacteria has not yet been clearly characterized. This study aimed to investigate the presence and potential role of M4 macrophages in the immunopathology of leprosy. METHODS: We analyzed the presence of M4 macrophage markers (CD68, MRP8, MMP7, IL-6, and TNF-α) in 33 leprosy skin lesion samples from 18 patients with tuberculoid leprosy and 15 with lepromatous leprosy by immunohistochemistry. RESULTS: The M4 phenotype was more strongly expressed in patients with the lepromatous form of the disease, indicating that this subpopulation is less effective in the elimination of the bacillus and consequently is associated with the evolution to one of the multibacillary clinical forms of infection. CONCLUSION: M4 macrophages are one of the cell types involved in the microbial response to M. leprae and probably are less effective in controlling bacillus replication, contributing to the evolution to the lepromatous form of the disease.

Mast cell heterogeneity and anti-inflammatory annexin A1 expression in leprosy skin lesions.

Mast cells (MCs) have important immunoregulatory roles in skin inflammation. Annexin A1 (ANXA1) is an endogenous anti-inflammatory protein that can be expressed by mast cells, neutrophils, eosinophils, monocytes, epithelial and T cells. This study investigated MCs heterogeneity and ANXA1 expression in human dermatoses with special emphasis in leprosy. Sixty one skin biopsies from 2 groups were investigated: 40 newly diagnosed untreated leprosy patients (18 reaction-free, 11 type 1 reaction/T1R, 11 type 2 reaction/T2R); 21 patients with other dermatoses. Tryptase/try+ and chymase/chy + phenotypic markers and toluidine blue stained intact/degranulated MC counts/mm2 were evaluated. Try+/chy+ MCs and ANXA1 were identified by streptavidin-biotin-peroxidase immunostaining and density was reported. In leprosy, degranulated MCs outnumbered intact ones regardless of the leprosy form (from tuberculoid/TT to lepromatous/LL), leprosy reactions (reactional/reaction-free) and type of reaction (T1R/T2R). Compared to other dermatoses, leprosy skin lesions showed lower numbers of degranulated and intact MCs. Try+ MCs outnumbered chy+ in leprosy lesions (reaction-free/reactional, particularly in T2R), but not in other dermatoses. Compared to other dermatoses, ANXA1 expression, which is also expressed in mast cells, was higher in the epidermis of leprosy skin lesions, independently of reactional episode. In leprosy, higher MC degranulation and differential expression of try+/chy+ subsets independent of leprosy type and reaction suggest that the Mycobacterium leprae infection itself dictates the inflammatory MCs activation in skin lesions. Higher expression of ANXA1 in leprosy suggests its potential anti-inflammatory role to maintain homeostasis preventing tissue and nerve damage.

Aryl Hydrocarbon Receptor Controls Monocyte Differentiation into Dendritic Cells versus Macrophages.

After entering tissues, monocytes differentiate into cells that share functional features with either macrophages or dendritic cells (DCs). How monocyte fate is directed toward monocyte-derived macrophages (mo-Macs) or monocyte-derived DCs (mo-DCs) and which transcription factors control these differentiation pathways remains unknown. Using an in vitro culture model yielding human mo-DCs and mo-Macs closely resembling those found in vivo in ascites, we show that IRF4 and MAFB were critical regulators of monocyte differentiation into mo-DCs and mo-Macs, respectively. Activation of the aryl hydrocarbon receptor (AHR) promoted mo-DC differentiation through the induction of BLIMP-1, while impairing differentiation into mo-Macs. AhR deficiency also impaired the in vivo differentiation of mouse mo-DCs. Finally, AHR activation correlated with mo-DC infiltration in leprosy lesions. These results establish that mo-DCs and mo-Macs are controlled by distinct transcription factors and show that AHR acts as a molecular switch for monocyte fate specification in response to micro-environmental factors.

Response of iNOS and its relationship with IL-22 and STAT3 in macrophage activity in the polar forms of leprosy.

Leprosy is a chronic granulomatous infection that manifests as different clinical forms related to the immunological response. The aim of the study was to evaluated the response of IL-22, STAT3, CD68 and iNOS in leprosy skin lesions. The mean number IL-22 positive cells was 12.12±1.90cells/field in the TT form and 31.31±2.91cells/field in the LL form. STAT3 positive cells was 5.29±1.96 cells/field in the TT form, while this number was 11.13±3.48cells/field in the LL form. The mean number of CD68 positive cells was 25.18±6.21cells/field in the TT form and 62.81±8.13cells/field in the LL form. Quantitative analysis of iNOS revealed a significant difference, with the mean number of cells expressing the enzyme being 30.24±2.88cells/field in the TT form compared to 35.44±4.69cells/field in the LL form. Linear correlations in lesions of TT patients showed a moderate positive correlations between CD68 and iNOS, STAT3 and Inos, IL-22 and STAT3, and IL-22 and iNOS. Our results demonstrate that these factors can act synergistically to induce a microbicidal activity in the population of macrophages in the leprosy lesions.

Endothelium adhesion molecules ICAM-1, ICAM-2, VCAM-1 and VLA-4 expression in leprosy.

Leprosy triggers a complex relationship between the pathogen and host immune response. Endothelium plays an important role in this immune response by directly influencing cell migration to infected tissues. The objective of this work is to investigate the possible role of endothelium in M. leprae infection, correlating the characteristics of endothelial markers with the expression pattern of cytokines. Thirty-six skin biopsy samples were cut into 5-µm thick sections and stained with hematoxylin-eosin and Ziehl-Neelsen for morphological analysis and then submitted to immunohistochemical analysis using monoclonal antibodies against ICAM-1, ICAM-2, VCAM-1, and VLA-4. Immunostaining for ICAM-1 showed a significantly larger number of stained endothelial cells in the tuberculoid leprosy (9.92 ± 1.11 cells/mm2) when compared to lepromatous samples (5.87 ± 1.01 cells/mm2) and ICAM-2 revealed no significant difference in the number of endothelial cells expressing this marker between the tuberculoid (13.21 ± 1.27 cells/mm2) and lepromatous leprosy (14.3 ± 1.02 cells/mm2). VCAM-1-immunostained showed 18.28 ± 1.46/mm2 cells in tuberculoid leprosy and 10.67 ± 1.25 cells/mm2 in the lepromatous leprosy. VLA-4 exhibited 22.46 ± 1.38 cells/mm2 in the tuberculoid leprosy 16.04 ± 1.56 cells/mm2 in the lepromatous leprosy. Samples with characteristics of the tuberculoid leprosy exhibited a larger number of cells stained with ICAM-1, VCAM-1 and VLA-4, demonstrating the importance of these molecules in the migration and selection of cells that reach the inflamed tissue.

The involvement of endothelial mediators in leprosy.

Leprosy is a chronic infectious disease that requires better understanding since it continues to be a significant health problem in many parts of the world. Leprosy reactions are acute inflammatory episodes regarded as the central etiology of nerve damage in the disease. The activation of endothelium is a relevant phenomenon to be investigated in leprosy reactions. The present study evaluated the expression of endothelial factors in skin lesions and serum samples of leprosy patients. Immunohistochemical analysis of skin samples and serum measurements of VCAM-1, VEGF, tissue factor and thrombomodulin were performed in 77 leprosy patients and 12 controls. We observed significant increase of VCAM-1 circulating levels in non-reactional leprosy (p = 0.0009). The immunostaining of VEGF and tissue factor was higher in endothelium of non-reactional leprosy (p = 0.02 for both) than healthy controls. Patients with type 1 reaction presented increased thrombomodulin serum levels, compared with non-reactional leprosy (p = 0.02). In type 2 reaction, no significant modifications were observed for the endothelial factors investigated. The anti-inflammatory and antimicrobial activities of the endotfhelial factors may play key-roles in the pathogenesis of leprosy and should be enrolled in studies focusing on alternative targets to improve the management of leprosy and its reactions.

The involvement of endothelial mediators in leprosy

Leprosy is a chronic infectious disease that requires better understanding since it continues to be a significant health problem in many parts of the world. Leprosy reactions are acute inflammatory episodes regarded as the central etiology of nerve damage in the disease. The activation of endothelium is a relevant phenomenon to be investigated in leprosy reactions. The present study evaluated the expression of endothelial factors in skin lesions and serum samples of leprosy patients. Immunohistochemical analysis of skin samples and serum measurements of VCAM-1, VEGF, tissue factor and thrombomodulin were performed in 77 leprosy patients and 12 controls. We observed significant increase of VCAM-1 circulating levels in non-reactional leprosy (p = 0.0009). The immunostaining of VEGF and tissue factor was higher in endothelium of non-reactional leprosy (p = 0.02 for both) than healthy controls. Patients with type 1 reaction presented increased thrombomodulin serum levels, compared with non-reactional leprosy (p = 0.02). In type 2 reaction, no significant modifications were observed for the endothelial factors investigated. The anti-inflammatory and antimicrobial activities of the endotfhelial factors may play key-roles in the pathogenesis of leprosy and should be enrolled in studies focusing on alternative targets to improve the management of leprosy and its reactions.