Mononuclear-macrophages but not neutrophils act as major infiltrating anti-leptospiral phagocytes during leptospirosis

Non-purulent myositis caused by direct invasion of skeletal muscle tissue by Leptospira in a hamster model

Myalgia is a common symptom of Leptospira infection in humans. Autopsies have reported that muscle tissue shows degeneration and necrosis of the myofibers and infiltration of inflammatory cells composed mainly of macrophages and lymphocytes. It remains unclear whether Leptospira directly infects the muscle and how the infiltrating inflammatory cells are involved in muscle fiber destruction. This study evaluated the relationship between histopathological changes and leptospiral localization in the muscle tissue of a hamster model. The influence of macrophages in skeletal muscle injury was also investigated, using selective depletion of macrophages by administration of liposomal clodronate. Hamsters infected subcutaneously with Leptospira interrogans serovar Manilae strain UP-MMC-SM showed myositis of the thighs adjacent to the inoculated area beginning at 6 days post-infection. The myositis was non-purulent and showed sporadic degeneration and necrosis of muscle fibers. The degeneration of myofibers was accompanied by aggregations of macrophages. Immunofluorescence staining revealed leptospires surrounding the damaged muscle fibers. Subcutaneous injection of formalin-killed Leptospira or intraperitoneal injection of live Leptospira caused no myositis in hamster thighs. Liposomal clodronate treatment in infected hamsters reduced macrophage infiltration in muscle tissue without impacting bacterial clearance. Muscle necrosis was still observed in the infected hamsters treated with liposomal clodronate, and there was no significant change in serum creatine kinase levels compared to those in animals treated with liposomes alone. Our findings suggest that leptospiral invasion of muscle tissue from an inoculation site leads to the destruction of muscle fibers and causes non-purulent myositis, whereas the infiltrating macrophages contribute less to muscle destruction.

Correction: Mononuclear-macrophages but not neutrophils act as major infiltrating anti-leptospiral phagocytes during leptospirosis

[This corrects the article DOI: 10.1371/journal.pone.0181014.].

Leptospirosis kidney disease: Evolution from acute to chronic kidney disease

Leptospirosis is a neglected bacterial disease caused by leptospiral infection that carries a substantial mortality risk in severe cases. Research has shown that acute, chronic, and asymptomatic leptospiral infections are closely linked to acute and chronic kidney disease (CKD) and renal fibrosis. Leptospires affect renal function by infiltrating kidney cells via the renal tubules and interstitium and surviving in the kidney by circumventing the immune system. The most well-known pathogenic molecular mechanism of renal tubular damage caused by leptospiral infection is the direct binding of the bacterial outer membrane protein LipL32 to toll-like receptor-2 expressed in renal tubular epithelial cells (TECs) to induce intracellular inflammatory signaling pathways. These pathways include the production of tumor necrosis factor (TNF)-α and nuclear factor kappa activation, resulting in acute and chronic leptospirosis-related kidney injury. Few studies have investigated the relationship between acute and chronic renal diseases and leptospirosis and further evidence is necessary. In this review, we intend to discuss the roles of acute kidney injury (AKI) to/on CKD in leptospirosis. This study reviews the molecular pathways underlying the pathogenesis of leptospirosis kidney disease, which will assist in concentrating on potential future research directions.

Internalization of Leptospira interrogans via diverse endocytosis mechanisms in human macrophages and vascular endothelial cells

Leptospirosis, one of the leading global causes of morbidity and mortality, is an emerging public health problem, particularly in large urban centers of developing countries. Leptospirosis results from infection with an organism belonging to the Leptospira genus L. interrogans. The extensive invasive ability has previously been documented, however a mechanism that describes how the organism is internalized by human macrophages and transmigrates through human blood vessel remains poorly understood. In the present study, we utilized a human macrophage and vascular endothelial cell line to study the diverse invasive mechanisms by which L. interrogans infections occur. We found that THP-1 and HUVEC had a diverse expression of cell receptors and L. interrogans entered THP-1 and HUVEC by different pathways. In the macrophage model cell line, ITGB1/FAK-signaling mediated microfilament dependent endocytosis with lysosome fusion, whereas ITGB1/CAV-1/PI3K-signaling mediated microfilament dependent endocytosis and transcytosis without lysosome fusion in the endothelial cell model. Shedding of pathogenic leptospires from HUVEC displayed higher viability than those from THP-1. The monolayer of HUVEC maintained integrity during the infection, while 3D imaging showed that leptospires were transmigrated both intra- and intercellularly. These results indicate that endocytosis of leptospires in human macrophages and human vascular endothelial cells are quite different, macrophages are responsible for eliminating leptospires in the human body during the infection while vascular endothelial cells facilitate dissemination of leptospires from blood vessels into target organs where they cause injury.

Leptospirosis is a zoonotic bacterial disease which causes 1.03 million cases and 58,900 deaths each year. Human infections occur when the primary reservoir hosts, such as rodents, contaminate food and water with leptospires. Unlike other bacterial pathogens, leptospires invade the human body through mucosal barriers and enter the bloodstream, which can result in septicemia. Left untreated, leptospirosis can spread into multiple organs and tissues such as lungs, liver and kidneys. Pathological features of this disease include high fever, myalgia, lymphadenectasis, hemorrhaging and jaundice. Human macrophages and vascular endothelial cells play important roles in eliminating and preventing the transmission of this pathogen. We speculated that leptospires could be neutralized in macrophages and subsequently transported by vascular endothelial cells throughout the human body. In this research, the diverse mechanisms of human macrophages and vascular endothelial cells infected by leptospires were explored. Our findings can be used to improve the treatment, prevention, and supervision regarding leptospire transmission and infection.

Implication of the IL-10-Expression Signature in the Pathogenicity of Leptospira-Infected Macrophages

Leptospirosis, an emerging infectious disease caused by pathogenic Leptospira spp., occurs in ecoregions with heavy rainfall and has public health implications. Macrophages are the major anti-Leptospira phagocytes that infiltrate the kidneys during renal leptospirosis, which is caused by leptospires residing in the renal tubules. The pathogenicity of Leptospira spp. in immune effector cells such as macrophages is not well understood. To evaluate this pathogenesis, we characterized and compared the transcriptome-wide alterations in macrophages infected with pathogenic and nonpathogenic Leptospira spp. Using transcriptome data and quantitative reverse transcription PCR analysis, at 2 h postinfection, the hypoxia-inducible factor-1α-dependent glycolysis pathway was implicated in pathogenic Leptospira-infected macrophages but not in nonpathogenic leptospiral infections. Immune-related biological processes were mostly activated in pathogenic Leptospira-infected macrophages, and flow cytometry investigations revealed that classically activated macrophages represent the predominant polarization status. At 24 h after infection, biological pathways associated with interleukin-10, IL-10, signaling the induction of macrophage tolerance, as well as higher levels of IL-10 mRNA and protein expression, were observed in nonpathogenic Leptospira-infected macrophages compared to in pathogenic leptospiral infection. Following leptospiral infection of macrophages, strong IL-10-expressing transcriptome signatures were observed following nonpathogenic leptospiral infection. The transcriptional programs generated in Leptospira-infected macrophages revealed an inflammatory milieu following the production of a critical anti-inflammatory cytokine, IL-10, which is implicated in controlling the pathogenicity of activated macrophages. These findings imply that IL-10-mediated anti-inflammatory responses and tolerance in activated macrophages induced by nonpathogenic Leptospira spp. infection reduce inflammation and tissue damage, thus providing a potential therapeutic target for leptospirosis. IMPORTANCE Activation of macrophages by Leptospira spp. infection is thought to be involved in the pathogenesis of leptospirosis. To evaluate the innate macrophage responses to Leptospira spp., specifically pathogenic versus nonpathogenic Leptospira spp., we characterized the entire transcriptome-wide alterations in infected macrophages. We showed that hypoxia-inducible factor-1α and immune-related pathways are activated in pathogenic leptospiral-infected macrophages. We confirmed the significantly high levels of IL-10-expressing signatures and tolerance in activated macrophages caused by nonpathogenic Leptospira infection. Furthermore, nonpathogenic leptospiral infections attenuated macrophage activation responses. These findings suggest a potential therapeutic strategy for the immune microenvironment caused by macrophage activation driven by IL-10 overexpression, which may contribute to regulating inflammation in leptospirosis.

Gut microbiota involved in leptospiral infections

Leptospirosis is a re-emerging zoonotic disease worldwide. Intestinal bleeding is a common but neglected symptom in severe leptospirosis. The regulatory mechanism of the gut microbiota on leptospirosis is still unclear. In this study, we found that Leptospira interrogans infection changed the composition of the gut microbiota in mice. Weight loss and an increased leptospiral load in organs were observed in the gut microbiota-depleted mice compared with those in the control mice. Moreover, fecal microbiota transplantation (FMT) to the microbiota-depleted mice reversed these effects. The phagocytosis response and inflammatory response in bone marrow-derived macrophages and thioglycolate-induced peritoneal macrophages were diminished in the microbiota-depleted mice after infection. However, the phagocytosis response and inflammatory response in resident peritoneal macrophage were not affected in the microbiota-depleted mice after infection. The diminished macrophage disappearance reaction (bacterial entry into the peritoneum acutely induced macrophage adherence to form local clots and out of the fluid phase) led to an increased leptospiral load in the peritoneal cavity in the microbiota-depleted mice. In addition, the impaired capacity of macrophages to clear leptospires increased leptospiral dissemination in Leptospira-infected microbiota-depleted mice. Our study identified the microbiota as an endogenous defense against L. interrogans infection. Modulating the structure and function of the gut microbiota may provide new individualized preventative strategies for the control of leptospirosis and related spirochetal infections.

A Three-Dimensional Lung Cell Model to Leptospira Virulence Investigations

Leptospirosis is a worldwide zoonosis and a serious public health threat in tropical and subtropical areas. The etiologic agents of leptospirosis are pathogenic spirochetes from the genus Leptospira. In severe cases, patients develop a pulmonary hemorrhage that is associated with high fatality rates. Several animal models were established for leptospirosis studies, such as rodents, dogs, and monkeys. Although useful to study the relationship among Leptospira and its hosts, the animal models still exhibit economic and ethical limitation reasons and do not fully represent the human infection. As an attempt to bridge the gap between animal studies and clinical information from patients, we established a three-dimensional (3-D) human lung cell culture for Leptospira infection. We show that Leptospira is able to efficiently infect the cell lung spheroids and also to infiltrate in deeper areas of the cell aggregates. The ability to infect the 3-D lung cell aggregates was time-dependent. The 3-D spheroids infection occurred up to 120 h in studies with two serovars, Canicola and Copenhageni. We standardized the number of bacteria in the initial inoculum for infection of the spheroids and we also propose two alternative culture media conditions. This new approach was validated by assessing the expression of three genes of Leptospira related to virulence and motility. The transcripts of these genes increased in both culture conditions, however, in higher rates and earlier times in the 3-D culture. We also assessed the production of chemokines by the 3-D spheroids before and after Leptospira infection, confirming induction of two of them, mainly in the 3-D spheroids. Chemokine CCL2 was expressed only in the 3-D cell culture. Increasing of this chemokine was observed previously in infected animal models. This new approach provides an opportunity to study the interaction of Leptospira with the human lung epithelium in vitro.

Inflammatory Signatures of Pathogenic and Non-Pathogenic Leptospira Infection in Susceptible C3H-HeJ Mice

The exact global impact of leptospirosis is unknown due to inadequate surveillance systems in place in most low-income countries. In this study, we analyzed the differences in mouse inflammatory signatures involved in pathogenic versus non-pathogenic Leptospira recognition at 24h and 72h post infection. Injection of C3H-HeJ mice with non-pathogenic L. biflexa increased circulation of a few chemokines (5/21, 24%) without secretion of cytokines in blood that resulted in engagement of resident macrophages, dendritic cells, neutrophils and NK cells without engagement of T cells. In contrast, pathogenic L. interrogans induced circulation of a much higher panel of chemokines (18/21, 86%) and pro- and anti-inflammatory cytokines (11/19, 58%) in blood with a resulting signaling cascade leading to engagement of macrophages, dendritic cells, monocytes, NK cells and T cells without engagement of neutrophils. Although neutrophils do not appear to be engaged, a considerable number of chemokines that recruit other granulocytes such as eosinophils and basophils were also increased at 72h post infection with L. interrogans. Overall, the data suggest that prevention of dissemination of L. biflexa is associated with an early engagement of the innate immune response characterized by upregulation of a few chemokines that results in an efficacious phagocytic response without an overwhelming increase of pro-inflammatory cytokines. However, when macrophages fail to clear a pathogenic serovar such as L. interrogans, the adaptive response (T cells) is engaged to help out, but the resulting chemo-cytokine storm mediates a robust but non-resolving inflammatory response to pathogenic Leptospira that results in dissemination, kidney colonization, pathology and disease.

Scavenger receptor A1 participates in uptake of Leptospira interrogans serovar Autumnalis strain 56606v and inflammation in mouse macrophages

Leptospirosis, caused by pathogenic Leptospira species, has emerged as a widespread zoonotic disease worldwide. Macrophages mediate the elimination of pathogens through phagocytosis and cytokine production. Scavenger receptor A1 (SR-A1), one of the critical receptors mediating this process, plays a complicated role in innate immunity. However, the role of SR-A1 in the immune response against pathogenic Leptospira invasion is unknown. In the present study, we found that SR-A1 is an important nonopsonic phagocytic receptor on murine macrophages for Leptospira. However, intraperitoneal injection of leptospires into WT mice presented with more apparent jaundice, subcutaneous hemorrhaging, and higher bacteria burdens in blood and tissues than that of SR-A1^-/- mice. Exacerbated cytokine and inflammatory mediator levels were also observed in WT mice and higher recruited macrophages in the liver than those of SR-A1^-/- mice. Our findings collectively reveal that although beneficial in the uptake of Leptospira by macrophage, SR-A1 might be exploited by Leptospira to modulate inflammatory activation and increase the susceptibility of infection in the host. These results provide our new insights into the innate immune response during early infection by L. interrogans.

The pre-activated immune response induced by LPS protects host from leptospirosis

Leptospirosis is an important global zoonosis caused by pathogenic Leptospira. It is estimated that more than 1 million people are infected by Leptospira each year, and the death toll is about 60,000. Some studies showed that delayed immune response was associated with severe leptospirosis, and TLR4 was very important in the control of leptospirosis. In this study, we aimed to explore the effect of the classical activator (LPS) of TLR4 on leptospirosis in susceptible and resistant hosts. The results showed that LPS pretreatment increased the survival rate of hamsters to 80%. And LPS pre-treatment also significantly reduced the leptospiral load and alleviated the pathological injury in organs of hamsters and mice. The result detected by ELISA in mice showed that the levels of TNF-α and IL-1β were increased in the LPS-treated group compared to the control group before infection. However, two days after infection, the level of cytokines in LPS group was down-regulated compared with that in control group. In addition, in vitro results showed that LPS pre-treatment enhanced the phagocytosis and bactericidal ability of macrophages on Leptospira. Collectively, our results indicated that the pre-activated immune response induced by LPS enhanced the ability of host against leptospirosis.

Phagocyte Escape of Leptospira: The Role of TLRs and NLRs

The spirochetal bacteria Leptospira spp. are causative agents of leptospirosis, a globally neglected and reemerging zoonotic disease. Infection with these pathogens may lead to an acute and potentially fatal disease but also to chronic asymptomatic renal colonization. Both forms of disease demonstrate the ability of leptospires to evade the immune response of their hosts. In this review, we aim first to recapitulate the knowledge and explore the controversial data about the opsonization, recognition, intracellular survival, and killing of leptospires by scavenger cells, including platelets, neutrophils, macrophages, and dendritic cells. Second, we will summarize the known specificities of the recognition or escape of leptospire components (the so-called microbial-associated molecular patterns; MAMPs) by the pattern recognition receptors (PRRs) of the Toll-like and NOD-like families. These PRRs are expressed by phagocytes, and their stimulation by MAMPs triggers pro-inflammatory cytokine and chemokine production and bactericidal responses, such as antimicrobial peptide secretion and reactive oxygen species production. Finally, we will highlight recent studies suggesting that boosting or restoring phagocytic functions by treatments using agonists of the Toll-like or NOD receptors represents a novel prophylactic strategy and describe other potential therapeutic or vaccine strategies to combat leptospirosis.

Plasma Osteopontin Levels is Associated with Biochemical Markers of Kidney Injury in Patients with Leptospirosis

Leptospirosis becomes severe, with a fatality rate of >10%, and manifests as severe lung injury accompanied by acute kidney injury. Using urine and blood samples of 112 patients with leptospirosis, osteopontin (OPN), galectin-9 (Gal-9) and other kidney-related biomarkers were measured to understand the pathological and diagnostic roles of OPN and Gal-9 in leptospirosis. Plasma levels of full-length (FL)-OPN (pFL-OPN) (p < 0.0001), pFL-Gal-9(p < 0.0001) and thrombin-cleaved OPN (p < 0.01) were significantly higher in patients with leptospirosis than in healthy controls (n = 30), as were levels of several indicators of renal toxicity: serum cystatin C (p < 0.0001), urine N-acetyl-β-glucosaminidase (NAG)/creatinine (p < 0.05), and urine clusterin/creatinine (p < 0.05). pFL-Gal-9 levels were negatively correlated with pFL-OPN levels (r = −0.24, p < 0.05). pFL-OPN levels were positively correlated with serum cystatin C (r = 0.41, p < 0.0001), urine NAG/creatinine (r = 0.35, p < 0.001), urine clusterin/creatinine (r = 0.33, p < 0.01), and urine cystatin C/creatinine (r = 0.33, p < 0.05) levels. In a group of patients with abnormally high creatinine levels, significantly higher levels of serum cystatin C (p < 0.0001) and pFL-OPN (p < 0.001) were observed. Our results demonstrate that pFL-OPN reflect kidney injury among patients with leptospirosis.

Leptospirosis is an invasive infectious and systemic inflammatory disease

Pathogenic Leptospira species are the causative agents of leptospirosis, a world-spreading zoonotic infectious disease. The pathogens possess a powerful invasiveness by invading human body through mucosal/skin barriers, rapid entry into bloodstream to cause septicemia, diffusion from bloodstream into internal organs and tissues to cause aggravation of disease, and discharge from urine through renal tubules to form natural infectious sources. Leptospirosis patients present severe inflammatory symptoms such as high fever, myalgia and lymphadenectasis. Hemorrhage and jaundice are the pathological features of this disease. Previous studies revealed that some outer membrane proteins of Leptospira interrogans, the most important pathogenic Leptospira species, acted as adherence factors to binding to receptor molecules (fibronectin, laminin and collagens) in extracellular matrix of host cells. Collagenase, metallopeptidases and endoflagellum contributed to the invasiveness of L. interrogans. Except for lipopolysaccharide, multiple hemolysins of L. interrogans displayed a powerful ability to induce pro-inflammatory cytokines and hepatocyte apoptosis. vWA and platelet activating factor acetylhydrolase-like proteins from L. interrogans could induce severe pulmonary hemorrhage in mice. L. interrogans utilized cellular endocytic recycling and vesicular transport systems for intracellular migration and transcellular transport. All the research achievements are helpful for further understanding the virulence of pathogenic Leptospira species and pathogenesis of leptospirosis.

Heparin-Binding Protein Release Is Strongly Induced by Leptospira Species and Is a Candidate for an Early Diagnostic Marker of Human Leptospirosis

BACKGROUND

Leptospirosis, caused by spirochetes of the genus Leptospira, is one of the most widespread zoonoses worldwide. Efficient diagnostic methods for early diagnosis of leptospirosis are still lacking, and acute disease presents with nonspecific symptomatology and is often misdiagnosed. The leptospires pathogenic processes and virulence mechanisms remain virtually unknown. In severe infections, hemostatic impairment is frequently observed, and pathophysiological complications often develop when the host response is modulated by the pathogen. The neutrophil heparin-binding protein (HBP) is an inflammatory mediator and potent inducer of vascular leakage.

RESULTS

In this study, we found that leptospires and their secreted products induce the release of HBP from stimulated neutrophils through a controlled degranulation mechanism. We acknowledged 2 leptospiral proteins as able to induce HBP degranulation. These findings have clinical implications, as high levels of HBP were detected in serum from patients with leptospirosis, especially at the early phase of the disease.

CONCLUSION

In conclusion, we describe a new mechanism by which the leptospirosis pathophysiological complications may arise, such as vascular leakage and edema formation. We also propose HBP as a new early screening biomarker for human leptospirosis.

Survival Tests for Leptospira spp

Measuring viability is an important and necessary assessment in studying microorganisms. Several methods can be applied to Leptospira spp., each with advantages and inconveniencies. Here, we describe the traditional colony-forming unit method, together with two other methods based, respectively, on the reducing capacity of live cells (Alamar Blue^® Assay) and differential staining of live and dead cells (LIVE/DEAD BacLight^®). The Alamar Blue^® Assay uses the blue reagent resazurin, which can be reduced into the pink reagent resorufin by live cell oxidoreductases. Production of resorufin can be quantified by absorbance or fluorescence reading. The LIVE/DEAD BacLight^® assay uses a mixture of two nucleic acid dyes (Syto9 and propidium iodide) that differentially penetrate and stain nucleic acid of cells with decreased membrane integrity. The colony-forming unit method is labor-intensive but the most sensitive and linear method. The two other methods are not laborious and well-adapted to high-throughput studies, but the range of detection and linearity are limited.

Transbronchial Invasion and Proliferation of Leptospira interrogans in Lung without Inflammatory Cell Infiltration in a Hamster Model

Leptospirosis caused by pathogenic Leptospira is one of the most common zoonoses in the world. It is believed that humans become infected with it mainly through their skin and mucous membranes by contact with water or soil that is contaminated with urine excreted from infected animals. Recently, outbreaks have frequently occurred in the tropics, especially after flooding, but how leptospires cause mass infection remains poorly understood. In this study, we injected leptospires into the tracheas of hamsters under direct view and prove for the first time that leptospires can infect through the respiratory tract. We determined that a 50% lethal dose (LD₅₀) of the Leptospira interrogans strain UP-MMC-SM (L495) for hamsters in transtracheal infection was 3.2 × 10² cells. The results of culture, macroscopic findings, and histopathological analysis suggested that intratracheally injected leptospires invaded the lung tissue, proliferated in the collagen-rich stroma adjacent to the bronchus and blood vessels, and then spread throughout the body via the bloodstream. In the lung, leptospires continuously infiltrated the alveolar wall without inflammatory cell infiltration, spread throughout the lung, and finally caused pulmonary hemorrhage. Our results revealed that the respiratory tract might be a portal of entry for leptospires. We speculate that some cases of leptospirosis might be caused by transbronchial infection from inhaling infectious aerosols containing leptospires during floods. Leptospira was also confirmed to be a unique pathogen that invades through the bronchus, proliferates in the collagen-rich lung stroma, and spreads through the alveolar interstitium throughout the lung without causing pneumonia.

Influence of breed on the clinical and hemato-biochemical parameters in sheep experimentally infected with Leptospira sp

Early diagnosis of leptospirosis may aid in a favorable prognosis in infected animals, but there are few reports of clinical and hematochemical changes in the ovine species, nor whether the breed exerts any influence on the response to infection. Thus, the objective of the present study was to evaluate the clinical, biochemical and hematological alterations in Santa Inês and crossbred ewes challenged with Leptospira interrogans serogroup Pomona serovar Kennewicki. Twenty-four sheep were used in this experiment, 12 crossbred (group A) and 12 Santa Inês (group B). In each group, sheep were conjunctivally and intraperitoneally challenged. During 60 days post-infection the ewes were evaluated for the presentation of clinical signs and the blood was collected for hemogram and serum biochemistry. Concentration of urea and creatinine; serum aspartate aminotransferase activity (AST); gamma-glutamyltransferase (GGT); total protein and albumin; total bilirubin, direct and indirect were analyzed. The urine of these sheep was collected for urinalysis. Only two Santa Inês sheep showed blood in the urine. Clinical signs implicated in Leptospira sp. infection were not identified. Some sheep had anemia, especially crossbred. However, anemia may be attributed to the more effective cellular response that has been identified in crossbred animals. Only one animal presented leukocytosis with neutrophilia, while 11 presented atypical leukopenia, especially those of the Santa Inês breed. There was a decrease in total protein and albumin, as well as the increase in gammaglutamyltranspeptidase (GGT), especially in Santa Inês sheep. The level of aspartate aminotransferase (AST) remained within the normal range for the species. A significant increase (p < 0.05) in conjugated bilirubin levels in challenged animals was detected. Only one sheep intraperitoneally challenged presented a high level of urea in the blood, but the creatinine level remained within the normal range. The intraperitoneal route was responsible for more significant changes (p < 0.05) in the hemogram and biochemistry when compared to the conjunctival route. The results indicate that crossbred sheep have a more efficient cellular response than Santa Inês sheep, which may confer a greater resistance to infection. Clinical signs are not good parameters to follow the development of leptospirosis in crossbred and Santa Inês breed. Hematological and biochemical analyzes were useful in the detection of anemia and possible liver changes caused by leptospirosis. The intraperitoneal route was able to cause more conclusive alterations of the analyzed parameters, however, it is possible that the alterations caused by the conjunctival route reproduce in a more faithful way what happens in a natural situation of infection.

Elevated Activation of Neutrophil Toll-Like Receptors in Patients with Acute Severe Leptospirosis: An Observational Study

Leptospirosis is the leading cause of zoonotic morbidity and mortality globally, yet little is known about the immune mechanisms that may contribute to pathogenesis and severe disease. Although neutrophils are a key component of early immune responses to infection, they have been associated with tissue damage and inflammation in some febrile infections. To assess whether neutrophils contribute to the pathogenesis observed in severe leptospirosis, we quantitated levels of neutrophil activation markers in patients with varying disease severities. Hospitalized leptospirosis patients had significantly higher levels of toll-like receptors 2 and 4 (TLR2 and TLR4, respectively) on peripheral neutrophils than healthy controls, with the highest levels detected in patients with organ dysfunction. We observed no significant differences in other neutrophil baseline activation markers (CD62L and CD11b) or activation capacity (CD62L and CD11b levels following stimulation), regardless of disease severity. Our results provide preliminary evidence supporting the hypothesis that higher initial bacterial loads or inadequate or delayed neutrophil responses, rather than TLR-driven inflammation, may drive severe disease outcomes.

Next-generation sequencing predicts interaction network between miRNA and target genes in lipoteichoic acid-stimulated human neutrophils

Toll-like receptors (TLRs), which are a class of pattern-recognition receptors, can sense specific molecules of pathogens and then activate immune cells, such as neutrophils. The regulation of TLR signaling in immune cells has been investigated by various studies. However, the interaction of TLR signaling-activated microRNAs (miRNAs) and genes has not been well investigated in a specific type of immune cells. In the present study, neutrophils were isolated from peripheral blood of a healthy donor, and then treated for 16 h with Staphylococcus aureus lipoteichoic acid (LTA), which is an agonist of TLR2. The miRNA and mRNA expression profiles were analyzed via next-generation sequencing and bioinformatics approaches. A total of 290 differentially expressed genes between LTA-treated and vehicle-treated neutrophils were identified. Gene ontology analysis revealed that various biological processes and pathways, including inflammatory responses, defense response, positive regulation of cell migration, motility, and locomotion, and cell surface receptor signaling pathway, were significantly enriched. In addition, 38 differentially expressed miRNAs were identified and predicted to be involved in regulating signal transduction and cell communication. The interaction of 4 miRNAs (hsa-miR-34a-5p, hsa-miR-34c-5p, hsa-miR-708-5p, and hsa-miR-1271-5p) and 5 genes (MET, CACNB3, TNS3, TTYH3, and HBEGF) was proposed to participate in the LTA-induced signaling network. The present findings may provide novel information for understanding the detailed expression profiles and potential networks between miRNAs and their target genes in LTA-stimulated healthy neutrophils.

Phagocytosis of Leptospira by leukocytes from mice with different susceptibility to leptospirosis and possible role of chemokines

Background

Leptospirosis is a widespread zoonosis caused by pathogenic prokaryotic microbes of the genus Leptospira. Although there are several reports in the literature, host-pathogen interaction is still poorly understood. The role of chemokine expression is important on the chemotaxis, activation and regulation of immune cells. Recent studies have shown that their expression profiles play an important role on the severity of leptospirosis outcome. We evaluated the phagocytosis of Leptospira by spleens cells from C3H/HeJ, C3H/HePas and BALB/c mouse strains, respectively susceptible, intermediate and resistant to leptospirosis, and by RAW 264.7 macrophages. Besides, we evaluated the effects of CCL2 treatment on the phagocytosis. The cells were incubated with or without CCL2 chemokine, and infected with virulent L. interrogans sv Copenhageni. Cells and culture supernatants were collected for subsequent analysis.

Results

The number of leptospires was higher in BALB/c cells, CCL2 pre-treated or only infected groups, when compared to C3H/HeJ and C3H/HePas cells. Indeed, CCL2 activation did not interfere in the phagocytosis of Leptospira. Expression of chemokines CXCL5 and CCL8 levels were significantly inhibited in infected BALB/c cells when compared to the non-infected control.

Conclusions

Higher ability to phagocytosis and early modulation of some chemokines correlated with the resistance to leptospirosis disease. Exposure to CCL2 did not interfere on phagocytosis of Leptospira in our experimental conditions, but acted in the modulation of chemokines expression during Leptospira infection.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1371-9) contains supplementary material, which is available to authorized users.

Leptospira species promote a pro-inflammatory phenotype in human neutrophils

Leptospirosis is a global zoonosis caused by pathogenic Leptospira. Neutrophils are key cells against bacterial pathogens but can also contribute to tissue damage. Because the information regarding the role of human neutrophils in leptospirosis is scant, we comparatively analysed the human neutrophil's response to saprophytic Leptospira biflexa serovar Patoc (Patoc) and the pathogenic Leptospira interrogans serovar Copenhageni (LIC). Both species triggered neutrophil responses involved in migration, including the upregulation of CD11b expression, adhesion to collagen, and the release of IL-8. In addition, both species increased levels of pro-inflammatory IL-1β and IL-6 associated with the inflammasome and NFκB pathway activation and delayed neutrophil apoptosis. LIC was observed on the neutrophil surface and not phagocytized. In contrast, Patoc generated intracellular ROS associated with its uptake. Neutrophils express the TYRO3, AXL, and MER receptor protein tyrosine kinases (TAM), but only LIC selectively increased the level of AXL. TLR2 but not TLR4-blocking antibodies abrogated the IL-8 secretion triggered by both Leptospira species. In summary, we demonstrate that Leptospira species trigger a robust neutrophil activation and pro-inflammatory response. These findings may be useful to find new diagnostic markers and therapeutic strategies against leptospirosis.

The monocytosis during human leptospirosis is associated with modest immune cell activation states

Leptospirosis is a life-threatening zoonotic disease and it has been hypothesized that the innate immune system fails to control the infection through ill-characterized mechanisms. The aim of this observational study was to better evaluate the activation processes of monocytes at the early stage of the disease. Blood samples were taken from healthy donors (n = 37) and patients hospitalized for either non-severe (n = 25) or severe (n = 32) leptospirosis. Monocyte cell counts and phenotypes were assessed by flow cytometry. We analysed the expression of several cell activation markers: CD14, CD16, HLA-DR, CD69, TLR2, TLR4, CD11b and CD11c. Although monocyte values at admittance were not significantly different from controls, patients experienced significant monocytosis at 1.33 × 10⁹/L (p < 0.0001 compared to controls: 0.56 × 10⁹/L) during their hospital stay. This monocytosis observed during hospital stay was correlated to several surrogate markers of organ injury. Non-classical (CD14-CD16+) and intermediate (CD14+CD16+) monocyte subsets increased compared to controls (p < 0.05). Accordingly, classical monocyte subset (CD14+CD16-) showed decreased percentages (p < 0.0001). Levels of several cell surface activation molecules were decreased: HLA-DR involved in MHC class II antigen presentation, integrins CD11b and CD11c implicated in phagocytosis and cell recruitment (p < 0.0001). None of these parameters had a prognostic value. Results from this study showed that during acute human leptospirosis, patients experienced monocytosis with a switch toward an inflammation-related phenotype contrasted by low expression levels of markers implicated in monocyte function.

Haemolysin Sph2 of Leptospira interrogans induces cell apoptosis via intracellular reactive oxygen species elevation and mitochondrial membrane injury

Leptospira interrogans causes widespread leptospirosis in humans and animals, with major symptoms of jaundice and haemorrhage. Sph2, a member of the sphingomyelinase haemolysins, is an important virulence factor for leptospire. In this study, the function and mechanism of Sph2 in the pathogenesis of leptospirosis were investigated to further understand the pathogenesis of leptospire. Real-time PCR analysis of expression levels during cell invasion showed that sph2 gene expression was transiently induced in human umbilical vein endothelial cells (HUVECs), human embryo liver cells (L02), and human epithelial lung cells (L132), with expression levels reaching a peak after 45 min of infection. Further functional analysis of recombinant Sph2 (rSph2) by LDH assays and confocal microscopy showed that rSph2 can be internalised by cells both by causing cell membrane damage and by a damage-independent clathrin-mediated endocytosis pathway. Subsequently, rSph2 is able to translocate to mitochondria, which led to an increase in the levels of reactive oxygen species (ROS) and a decrease of the mitochondrial membrane potential (ΔΨ_m ). Further flowcytometry analyses after rSph2 exposure showed that 28.7%, 31%, and 27.3% of the HUVEC, L02, and L132 cells, respectively, became apoptotic. Because apoptosis could be decreased with the ROS inhibitor N-acetyl cysteine, these experiments suggested that rSph2 triggers apoptosis through mitochondrial membrane damage and ROS elevation. The ability of leptospiral haemolysin rSph2 to cause apoptosis likely contributes to the pathogenesis of leptospirosis.

Leptospira interrogans outer membrane protein LipL21 is a potent inhibitor of neutrophil myeloperoxidase

Leptospirosis is a widespread zoonotic and neglected infectious disease of human and veterinary concern that is caused by pathogenic Leptospira species. After entrance in the host, pathogenic leptospires evade the host natural defense mechanisms in order to propagate and disseminate to multiple organs. Myeloperoxidase is an enzyme stored in neutrophils azurophilic granules, and is released upon neutrophil activation to produce mainly hypochlorous acid, a strong oxidant and potent antimicrobial agent. In the present investigation, we studied the modulation of myeloperoxidase activity by L. interrogans serovar Copenhageni. We show that leptospires and their culture supernatants are able to inhibit both peroxidase and chlorination activities of myeloperoxidase, without interfering with neutrophil degranulation. By leptospiral outer membrane protein extraction and fractionation, we identified the proteins LipL21 and LipL45 as myeloperoxidase inhibitors, constituting new Leptospira virulence factors. Accordingly, we propose a function for the protein LipL21, one of the most expressed leptospiral outer membrane proteins. Our results show a novel innate immune evasion mechanism by which leptospires interfere with the host response in order to cope with the host oxidative stress and efficiently achieve dissemination and colonization.

A novel Fas-binding outer membrane protein and lipopolysaccharide of Leptospira interrogans induce macrophage apoptosis through the Fas/FasL-caspase-8/-3 pathway

Leptospira interrogans is the major causative agent of leptospirosis, an emerging, globally spreading zoonotic infectious disease. The pathogen induces macrophage apoptosis, but the molecular basis and mechanism remain unknown. In the present study, we found that L. interrogans caused apoptosis of phagocytosis-inhibited macrophages, and the product of the L. interrogans LB047 gene (Lep-OMP047) was the unique protein captured by mouse and human Fas proteins. The recombinant expressed Lep-OMP047 (rLep-OMP047) strongly bound mouse and human Fas proteins with equilibrium association constant (K_D) values of 5.20 × 10⁻⁶ to 2.84 × 10⁻⁹ M according to surface plasmon resonance measurement and isothermal titration calorimetry. Flow-cytometric examination showed that 5 μg rLep-OMP047 or 1 μg lipopolysaccharide of L. interrogans (Lep-LPS) caused 43.70% or 21.90% early apoptosis in mouse J774A.1 macrophages and 28.41% or 15.80% for PMA-differentiated human THP-1 macrophages, respectively, but the apoptosis was blocked by Fas-antagonizing IgGs, Fas siRNAs, and caspase-8/-3 inhibitors. Moreover, Lep-OMP047 was significantly upregulated during infection of macrophages. Lep-LPS promoted the expression and cytomembrane translocation of Fas and FasL in macrophages. The JNK and p38 MAPK but not ERK signaling pathways, as well as the transcription factors c-Jun and ATF2 but not CHOP, mediated Lep-LPS-induced Fas/FasL expression and translocation. TLR2 but not TLR4 mediated Lep-LPS-induced JNK/p38 MAPK activation. Therefore, we demonstrated that a novel Fas-binding OMP and LPS of L. interrogans induce macrophage apoptosis through the Fas/FasL-caspase-8/-3 pathway.

Characterization of the microtranscriptome of macrophages infected with virulent, attenuated and saprophyte strains of Leptospira spp

Leptospirosis is a bacterial zoonosis, caused by Leptospira spp., that leads to significant morbidity and mortality worldwide. Despite considerable advances, much is yet to be discovered about disease pathogenicity. The influence of epigenetic mechanisms, particularly RNA-mediated post-transcriptional regulation of host immune response has been described following a variety of bacterial infections. The current study examined the microtranscriptome of macrophages J774A.1 following an 8h infection with virulent, attenuated and saprophyte strains of Leptospira. Microarray analysis revealed that 29 miRNAs were misregulated following leptospiral infection compared to control macrophages in a strain and virulence-specific manner. Pathway analysis for targets of these differentially expressed miRNAs suggests that several processes involved in immune response could be regulated by miRNAs. Our data provides the first evidence that host miRNAs are regulated by Leptospira infection in macrophages. A number of the identified miRNA targets participate in key immune response processes. We suggest that post-transcriptional regulation by miRNAs may play a role in host response to infection in leptospirosis.

Leptospirosis is a zoonotic disease, distributed worldwide, affecting millions of people each year, and leading to sixty thousand deaths per year. These bacteria are found in soil and water and are eliminated by the urine of rodents, their natural reservoir. Through skin contact, bacteria can be acquired, infecting the host. Infection process in leptospirosis is not completely understood and here we add another layer of disease regulation. Recent studies have shown that pathogens can modulate host response. Our current study examined the expression of microRNAs in murine macrophages following an 8h infection with virulent, attenuated and saprophyte strains of Leptospira. This study provides the first evidence that these post-transcriptional regulatory molecules, microRNAs, are modulated in macrophages in a species and virulence-specific manner, following infection with different strains of Leptospira spp. These microRNAs are involved in the regulation of inflammatory and antimicrobial responses in the host and could lead to the identification of biomarkers or therapeutic targets for this disease.

Role of Murine Complement Component C5 in Acute in Vivo Infection by Pathogenic Leptospira interrogans

Leptospirosis is considered one of the most important zoonosis worldwide. The activation of the Complement System is important to control dissemination of several pathogens in the host. Only a few studies have employed murine models to investigate leptospiral infection and our aim in this work was to investigate the role of murine C5 during in vivo infection, comparing wild type C57BL/6 (B6 C5^+/+) and congenic C57BL/6 (B6 C5^−/−, C5 deficient) mice during the first days of infection. All animals from both groups survived for at least 8 days post-infection with pathogenic Leptospira interrogans serovar Kennewicki strain Fromm (LPF). At the third day of infection, we observed greater numbers of LPF in the liver of B6 C5^−/− mice when compared to B6 C5^+/+ mice. Later, on the sixth day of infection, the LPF population fell to undetectable levels in the livers of both groups of mice. On the third day, the inflammatory score was higher in the liver of B6 C5^+/+ mice than in B6 C5^−/− mice, and returned to normal on the sixth day of infection in both groups. No significant histopathological differences were observed in the lung, kidney and spleen from both infected B6 C5^+/+ than B6 C5^−/− mice. Likewise, the total number of circulating leukocytes was not affected by the absence of C5. The liver levels of IL-10 on the sixth day of infection was lower in the absence of C5 when compared to wild type mice. No significant differences were observed in the levels of several inflammatory cytokines when B6 C5^+/+ and B6 C5^−/− were compared. In conclusion, C5 may contribute to the direct killing of LPF in the first days of infection in C57BL/6 mice. On the other hand, other effector immune mechanisms probably compensate Complement impairment since the mice survival was not affected by the absence of C5 and its activated fragments, at least in the early stage of this infection.

Recent findings related to immune responses against leptospirosis and novel strategies to prevent infection

What are the new approaches and emerging ideas to prevent leptospirosis, a neglected bacterial re-emerging zoonotic disease? How do Leptospira interrogans escape the host defenses? We aim here to review and discuss the most recent literature that provides some answers to these questions, in particular data related to a better understanding of adaptive and innate immunity towards leptospires, and design of vaccines. This is an opinion paper, not a comprehensive review. We will try to highlight the new strategies and technologies boosting the search for drugs and vaccines. We will also address the bottlenecks and difficulties impairing the search for efficient vaccines and the many gaps in our knowledge of immunity against leptospirosis. Finally, we aim to delineate how Leptospira spp. escape the innate immune responses of Toll-Like receptors (TLR) and Nod-Like receptors (NLR). The rational use of TLR and NLR agonists as adjuvants could be key to design future vaccines against pathogenic leptospires.

A leptospiral AAA+ chaperone-Ntn peptidase complex, HslUV, contributes to the intracellular survival of Leptospira interrogans in hosts and the transmission of leptospirosis

Leptospirosis caused by Leptospira is a zoonotic disease of global importance but it is considered as an emerging or re-emerging infectious disease in many areas in the world. Until now, the mechanisms about pathogenesis and transmission of Leptospira remains poorly understood. As eukaryotic and prokaryotic proteins can be denatured in adverse environments and chaperone-protease/peptidase complexes degrade these harmful proteins, we speculate that infection may also cause leptospiral protein denaturation, and the HslU and HslV proteins of L. interrogans may compose a complex to degrade denatured proteins that enhances leptospiral survival in hosts. Here we show that leptospiral HslUV is an ATP-dependent chaperone-peptidase complex containing ATPase associated with various cellular activity (AAA+) and N-terminal nucleophile (Ntn) hydrolase superfamily domains, respectively, which hydrolyzed casein and chymotrypsin-like substrates, and this hydrolysis was blocked by threonine protease inhibitors. The infection of J774A.1 macrophages caused the increase of leptospiral denatured protein aggresomes, but more aggresomes accumulated in hslUV gene-deleted mutant. The abundant denatured leptospiral proteins are involved in ribosomal structure, flagellar assembly, two-component signaling systems and transmembrane transport. Compared to the wild-type strain, infection of cells in vitro with the mutant resulted in a higher number of dead leptospires, less leptospiral colony-forming units and lower growth ability, but also displayed a lower half lethal dose, attenuated histopathological injury and decreased leptospiral loading in lungs, liver, kidneys, peripheral blood and urine in hamsters. Therefore, our findings confirmed that HslUV AAA+ chaperone-Ntn peptidase complex of L. interrogans contributes to leptospiral survival in hosts and transmission of leptospirosis.

Bid-Induced Release of AIF/EndoG from Mitochondria Causes Apoptosis of Macrophages during Infection with Leptospira interrogans

Leptospirosis is a global zoonotic infectious disease caused by pathogenic Leptospira species. Leptospire-induced macrophage apoptosis through the Fas/FasL-caspase-8/3 pathway plays an important role in the survival and proliferation of the pathogen in hosts. Although, the release of mitochondrial apoptosis-inducing factor (AIF) and endonuclease G (EndoG) in leptospire-infected macrophages has been described, the mechanisms linking caspase and mitochondrion-related host-cell apoptosis has not been determined. Here, we demonstrated that leptospire-infection induced apoptosis through mitochondrial damages in macrophages. Apoptosis was caused by the mitochondrial release and nuclear translocation of AIF and/or EndoG, leading to nuclear DNA fragmentation. However, the mitochondrion-related CytC-caspase-9/3 pathway was not activated. Next, we found that the release and translocation of AIF and/or EndoG was preceded by the activation of the BH3-interacting domain death agonist (Bid). Furthermore, our data demonstrated that caspase-8 was activated during the infection and caused the activation of Bid. Meanwhile, high reactive oxygen species (ROS) trigged by the infection caused the dephosphorylation of Akt, which also activated Bid. In conclusion, Bid-mediated mitochondrial release of AIF and/or EndoG followed by nuclear translocation is a major mechanism of leptospire- induced apoptosis in macrophages, and this process is modulated by both caspase-8 and ROS-Akt signal pathways.