Cytotoxic activities of Leptospira interrogans hemolysin SphH as a pore-forming protein on mammalian cells

Design and evaluation of potent multiepitope broad spectrum DNA and protein vaccine candidates against leptospirosis

Leptospirosis is a widespread zoonotic disease that causes severe health complications with no approved vaccine which provide broad range protection. In this study, we have focused on LruC protein from the outer membrane of Leptospira spp. LruC protein has been considered as promising target for vaccine due to its immunogenicity and conservancy. We have identified total 13 conserved B-cell, CTL, and HTL epitopes from 22 different pathogenic Leptospira species and serovars, which were linked with 4 linkers and 3 adjuvants (HBHA, CTB, TLR4) to design 36 multiepitope vaccine constructs to study the effect of different components on vaccine effectiveness. The antigenicity, immunogenicity, and non-allergenicity of the constructs were confirmed through computational analyses. Physico-chemical properties, secondary structure, and tertiary models of the vaccine constructs were predicted and validated. Molecular docking studies were conducted with Toll-like receptors (TLR2, TLR4) to assess binding affinity, identifying three top vaccine candidates (HBHA-construct 6, CTB-construct 9, and TLR4-construct 12) for further investigation. Further, these candidates were successfully cloned into pVAX1 and pET30a vectors to prepare DNA and protein vaccines, respectively. Moreover, these multiepitope vaccines were tested in mice models to assess its immunogenicity. ELISA performed with antisera against vaccine antigen, as well as crude extract of pathogenic Leptospira species showed significant IgG responses, particularly in protein vaccines. Flow cytometry revealed increased IFN-γ producing CD4+ and CD8+ T cells, especially in the TLR4-adjuvanted vaccine groups. The microscopic agglutination test further confirmed the specificity of the antibody response to Leptospira serovars. Overall, this study demonstrates the potential of these multiepitope vaccine constructs in eliciting a robust immune response, laying the foundation for future challenge study and preclinical evaluation.

Trends and advances in Leptospira, a bibliometric analysis

Background

Leptospirosis is an acute zoonotic disease caused by pathogenic Leptospira, primarily transmitted to humans through contact with water or soil contaminated by the bacteria. It is globally distributed, with heightened prevalence in tropical regions. While prior studies have examined the pathophysiology, epidemiology, and risk factors of leptospirosis, few have explored trends and emerging topics in the field. This study applies bibliometric analysis to generate a visual knowledge map, identifying research hotspots and forecasting future trends in leptospirosis investigations.

Methods

Data were extracted from the Web of Science Core Collection (WOSCC), encompassing all publications up to May 1, 2024. CiteSpace and VOSViewer software were used to analyze annual publication trends, as well as contributions from countries, institutions, journals, authors, references, and keywords, thereby pinpointing current research priorities and potential future directions.

Results

A total of 5,244 articles were included, sourced from 4,716 institutions, 955 journals, and 156 countries or regions. The United States led with 1,315 publications and had the most significant influence in the field. "PLOS Neglected Tropical Diseases" published the highest number of articles (166), while "Infection and Immunity" garnered the most citations (6,591). Prominent research areas included restriction endonucleases, monoclonal antibodies, outer membrane proteins, water environments, detection methods, and antimicrobial agents. Research focus has shifted from early genomic and antigenic studies to investigations into outer membrane protein functions and environmental persistence, culminating in recent advances in molecular mechanisms and diagnostic technology development.

Conclusion

This bibliometric analysis provides a comprehensive snapshot of leptospirosis research, emphasizing collaborations and impact among authors, countries, institutions, and journals. It offers valuable insights into ongoing trends and serves as a reference for future collaboration and research opportunities in the field.

Acute leptospirosis in horses: A retrospective study of 11 cases (2015-2023)

BACKGROUND

Reports of leptospirosis in horses are limited.

OBJECTIVES

To describe the clinical and diagnostic findings of acute systemic leptospirosis in horses.

ANIMALS

Eleven client-owned horses presented to an equine hospital because of acute onset of disease between 2015 and 2023.

METHODS

Retrospective case series. Horses diagnosed with leptospirosis by 1 or more of urine PCR, serologic microscopic agglutination test (MAT), and histopathology.

RESULTS

Common clinical signs included lethargy (10), anorexia (10), fever (9), tachypnea (9), abnormal lung sounds (9), and epistaxis (6). Acute kidney injury was present in all cases. Evidence of pulmonary hemorrhage and liver disease was found in 8 (73%) and 6 (55%) horses, respectively. In 6 (55%) horses, kidneys, lungs, and liver were affected. Urine quantitative polymerase chain reaction for detection of pathogenic Leptospira spp. was positive in 6 (55%) cases. On serology Leptospira interrogans serovar Australis, Autumnalis, and Bratislava accounted for 86% of all titers ≥1 : 800. Overall case fatality rate was 4/11 (36%). Main findings on necropsy were tubular necrosis, interstitial nephritis, hemorrhage in the alveoli, pulmonary edema, periportal hepatitis and necrosis, cholestasis, and cholangitis.

CONCLUSIONS AND CLINICAL IMPORTANCE

Leptospirosis should be considered as a differential diagnosis in horses with evidence of acute systemic inflammation and acute renal injury, epistaxis, or hepatic disease. For increased likelihood of identifying positive cases, both MAT serology and urine PCR should be performed.

Story of Pore-Forming Proteins from Deadly Disease-Causing Agents to Modern Applications with Evolutionary Significance

Animal venoms are a complex mixture of highly specialized toxic molecules. Among them, pore-forming proteins (PFPs) or toxins (PFTs) are one of the major disease-causing toxic elements. The ability of the PFPs in defense and toxicity through pore formation on the host cell surface makes them unique among the toxin proteins. These features made them attractive for academic and research purposes for years in the areas of microbiology as well as structural biology. All the PFPs share a common mechanism of action for the attack of host cells and pore formation in which the selected pore-forming motifs of the host cell membrane-bound protein molecules drive to the lipid bilayer of the cell membrane and eventually produces water-filled pores. But surprisingly their sequence similarity is very poor. Their existence can be seen both in a soluble state and also in transmembrane complexes in the cell membrane. PFPs are prevalent toxic factors that are predominately produced by all kingdoms of life such as virulence bacteria, nematodes, fungi, protozoan parasites, frogs, plants, and also from higher organisms. Nowadays, multiple approaches to applications of PFPs have been conducted by researchers both in basic as well as applied biological research. Although PFPs are very devastating for human health nowadays researchers have been successful in making these toxic proteins into therapeutics through the preparation of immunotoxins. We have discussed the structural, and functional mechanism of action, evolutionary significance through dendrogram, domain organization, and practical applications for various approaches. This review aims to emphasize the PFTs to summarize toxic proteins together for basic knowledge as well as to highlight the current challenges, and literature gap along with the perspective of promising biotechnological applications for their future research.

Human leptospirosis: In search for a better vaccine

Leptospirosis is a neglected disease caused by bacteria of the genus Leptospira and is more prevalent in tropical and subtropical countries. This pathogen infects humans and other animals, responsible for the most widespread zoonosis in the world, estimated to be responsible for 60 000 deaths and 1 million cases per year. To date, commercial vaccines against human leptospirosis are available only in some countries such as Japan, China, Cuba and France. These vaccines prepared with inactivated Leptospira (bacterins) induce a short-term and serovar-specific immune response, with strong adverse side effects. To circumvent these limitations, several research groups are investigating new experimental vaccines in order to ensure that they are safe, efficient, and protect against several pathogenic Leptospira serovars, inducing sterilizing immunity. Most of these protocols use attenuated cultures, preparations after LPS removal, recombinant proteins or DNA from pathogenic Leptospira spp. The aim of this review was to highlight several promising vaccine candidates, considering their immunogenicity, presence in different pathogenic Leptospira serovars, their role in virulence or immune evasion and other factors.

Cellular Pathophysiology of Leptospirosis: Role of Na/K-ATPase

Inada and Ido identified Leptospira sp. as the pathogen responsible for Weil's Disease in 1915. Later, it was confirmed that Leptospira causes leptospirosis. The host microorganism's interaction at the cellular level remained misunderstood for many years. Although different bacterial components have been isolated and purified, the complexity of the molecular interactions between these components and the host and the molecular mechanisms responsible for the systemic dysfunctions still needs to be fully unveiled. Leptospirosis affects virtually all animal species. Its cellular pathophysiology must involve a ubiquitous cellular mechanism in all eukaryotes. Na/K-ATPase is the molecular target of the leptospiral endotoxin (glycolipoprotein-GLP). Na/K-ATPase dysfunctions on different types of cells give rise to the organ disorders manifested in leptospirosis. Concomitantly, the development of a peculiar metabolic disorder characterized by dyslipidemia, with increased levels of circulating free fatty acids and an imbalance in the fatty acid/albumin molar ratio, triggers events of cellular lipotoxicity. Synergistically, multiple molecular stimuli are prompted during the infection, activating inflammasomes and Na/K-ATPase signalosome, leading to pro-inflammatory and metabolic alterations during leptospirosis. Leptospirosis involves diverse molecular mechanisms and alteration in patient inflammatory and metabolic status. Nonetheless, Na/K-ATPase is critical in the disease, and it is targeted by GLP, its components, and other molecules, such as fatty acids, that inhibit or trigger intracellular signaling through this enzyme. Herein, we overview the role of Na/K-ATPase during leptospirosis infection as a potential therapeutic target or an indicator of disease severity.

Generation of an RNA aptamer against LipL32 of Leptospira isolated by Tripartite-hybrid SELEX coupled with in-house Python-aided unbiased data sorting

Leptospirosis is a potentially life-threatening zoonosis caused by pathogenic Leptospira. The major hurdle of the diagnosis of Leptospirosis lies in the issues associated with current methods of detection, which are time-consuming, tedious and the need for sophisticated, special equipments. Restrategizing the diagnostics of Leptospirosis may involve considerations of the direct detection of the outer membrane protein, which can be faster, cost-saving and require fewer equipments. One such promising marker is LipL32, which is an antigen with high amino acid sequence conservation among all the pathogenic strains. In this study, we endeavored to isolate an aptamer against LipL32 protein via a modified SELEX strategy known as tripartite-hybrid SELEX, based on 3 different partitioning strategies. In this study, we also demonstrated the deconvolution of the candidate aptamers by using in-house Python-aided unbiased data sorting in examining multiple parameters to isolate potent aptamers. We have successfully generated an RNA aptamer against LipL32 of Leptospira, LepRapt-11, which is applicable in a simple direct ELASA for the detection of LipL32. LepRapt-11 can be a promising molecular recognition element for the diagnosis of leptospirosis by targeting LipL32.

Sph2(176-191) and Sph2(446-459): Identification of B-Cell Linear Epitopes in Sphingomyelinase 2 (Sph2), Naturally Recognized by Patients Infected by Pathogenic Leptospires

Sphingomyelin is a major constituent of eukaryotic cell membranes, and if degraded by bacteria sphingomyelinases may contribute to the pathogenesis of infection. Among Leptospira spp., there are five sphingomyelinases exclusively expressed by pathogenic leptospires, in which Sph2 is expressed during natural infections, cytotoxic, and implicated in the leptospirosis hemorrhagic complications. Considering this and the lack of information about associations between Sph2 and leptospirosis severity, we use a combination of immunoinformatics approaches to identify its B-cell epitopes, evaluate their reactivity against samples from leptospirosis patients, and investigate the role of antibodies anti-Sph2 in protection against severe leptospirosis. Two B-cell epitopes, Sph2_(176-191) and Sph2_(446-459), were predicted in Sph2 from L. interrogans serovar Lai, presenting different levels of identity when compared with other pathogenic leptospires. These epitopes were recognized by about 40% of studied patients with a prevalence of IgG antibodies against both Sph2_(176-191) and Sph2_(446-459). Remarkably, just individuals with low reactivity to Sph2_(176-191) presented clinical complications, while high responders had only mild symptoms. Therefore, we identified two B-cell linear epitopes, recognized by antibodies of patients with leptospirosis, that could be further explored in the development of multi-epitope vaccines against leptospirosis.

In silico prediction of molecular mechanisms of toxicity mediated by the leptospiral PF07598 gene family-encoded virulence-modifying proteins

Mechanisms of leptospirosis pathogenesis remain unclear despite the identification of a number of potential leptospiral virulence factors. We recently demonstrated potential mechanisms by which the virulence-modifying (VM) proteins-defined as containing a Domain of Unknown function (DUF1561), encoded by the PF07598 gene family-found only in group 1 pathogenic Leptospira-might mediate the clinical pathogenesis of leptospirosis. VM proteins belongs to classical AB toxin paradigm though have a unique AB domain architecture, unlike other AB toxins such as diphtheria toxin, pertussis toxin, shiga toxin, or ricin toxin which are typically encoded by two or more genes and self-assembled into a multi-domain holotoxin. Leptospiral VM proteins are secreted R-type lectin domain-containing exotoxins with discrete N-terminal ricin B-like domains involved in host cell surface binding, and a C-terminal DNase/toxin domain. Here we use the artificial intelligence-based AlphaFold algorithm and other computational tools to predict and elaborate on details of the VM protein structure-function relationship. Comparative AlphaFold and CD-spectroscopy defined the consistent secondary structure (Helix and ß-sheet) content, and the stability of the functional domains were further supported by molecular dynamics simulation. VM proteins comprises distinctive lectic family (QxW)₃ motifs, the Mycoplasma CARDS toxin (D3 domain, aromatic patches), C-terminal similarity with mammalian DNase I. In-silico study proposed that Gln412, Gln523, His533, Thr59 are the high binding energy or ligand binding residues plausibly anticipates in the functional activities. Divalent cation (Mg⁺²-Gln412) and phosphate ion (PO₄]^-3-Arg615) interaction further supports the functional activities driven by C-terminal domain. Computation-driven structure-function studies of VM proteins will guide experimentation towards mechanistic understandings of leptospirosis pathogenesis, which underlie development of new therapeutic and preventive measures for this devastating disease.

Leptospiral sphingomyelinase Sph2 as a potential biomarker for diagnosis of leptospirosis

Leptospirosis is an underestimated infectious tropical disease caused by the spirochetes belonging to the genus Leptospira. Leptospirosis is grossly underdiagnosed due to its myriad symptoms, varying from mild febrile illness to severe haemorrhage. Laboratory tests for leptospirosis is an extremely important and potent way for disease diagnosis, as the clinical manifestations are very similar to other febrile diseases. Currently available diagnostic techniques are time-consuming, require expertise and sophisticated instruments, and cannot identify the disease at an early phase of infection. Early diagnosis of leptospirosis is the need of the hour while considering the severe complications after the infection and the rate of mortality after misdiagnosis. Secretion of Leptospira-specific sphingomyelinases in leptospirosis patient's urine within a few days of the onset of infection is quite common and is a virulence factor present only in pathogenic Leptospira species. Herein, the structural and functional importance of leptospiral sphingomyelinase Sph2 in leptospirosis pathogenesis, as well as the potential of screening urinary Sph2 for diagnosis and the scope for developing a rapid and easily affordable point-of-care test for urinary leptospiral sphingomyelinase Sph2 as an alternative to current diagnostic methods are discussed.

Characterization of a virulence-modifying protein of Leptospira interrogans identified by shotgun phage display

Pathogenic species of Leptospira are etiologic agents of leptospirosis, an emerging zoonotic disease of worldwide extent and endemic in tropical regions. The growing number of identified leptospiral species sheds light to their genetic diversity and unique virulence mechanisms, many of them still remain unknown. Toxins and adhesins are important virulence factors in several pathogens, constituting promising antigens for the development of vaccines with cross-protection and long-lasting effect against leptospirosis. For this aim, we used the shotgun phage display technique to unravel new proteins with adhesive properties. A shotgun library was constructed using fragmented genomic DNA from Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130 and pG8SAET phagemid vector. Selection of phages bearing new possible cell-binding antigens was performed against VERO cells, using BRASIL biopanning methodology. Analysis of selected clones revealed the hypothetical protein LIC10778, a potentially exposed virulence factor that belongs to the virulence-modifying (VM) protein family (PF07598), composed of 13 members in the leptospiral strain Fiocruz L1-130. Prediction of LIC10778 tertiary structure indicates that the protein contains a cellular-binding domain (N-terminal portion) and an unknown domain of no assigned activity (C-terminal portion). The predicted N-terminal domain shared structural similarities with the cell-binding and internalization domain of toxins like Ricin and Abrin, as well as to the Community-Acquired Respiratory Distress Syndrome (CARDS) toxin in Mycoplasma pneumoniae. Interestingly, recombinant portions of the N-terminal region of LIC10778 protein showed binding to laminin, collagens I and IV, vitronectin, and plasma and cell fibronectins using overlay blotting technique, especially regarding the binding site identified by phage display. These data validate our preliminary phage display biopanning and support the predicted three-dimensional models of LIC10778 protein and other members of PF07598 protein family, confirming the identification of the N-terminal cell-binding domains that are similar to ricin-like toxins. Moreover, fluorescent fused proteins also confirmed that N-terminal region of LIC10778 is capable of binding to VERO and A549 cell lines, further highlighting its virulence role during host-pathogen interaction in leptospirosis probably mediated by its C-terminal domain. Indeed, recent results in the literature confirmed this assumption by demonstrating the cytotoxicity of a closely related PF07598 member.

Pathogenic Leptospira Evolved a Unique Gene Family Comprised of Ricin B-Like Lectin Domain-Containing Cytotoxins

Leptospirosis is a globally important neglected zoonotic disease. Previous data suggest that a family of virulence-modifying (VM) proteins (PF07598) is a distinctive feature of group I pathogenic Leptospira that evolved as important virulence determinants. Here, we show that one such VM protein, LA3490 (also known as Q8F0K3), is expressed by Leptospira interrogans serovar Lai, as a secreted genotoxin that is potently cytotoxic to human cells. Structural homology searches using Phyre2 suggested that VM proteins are novel R-type lectins containing tandem N-terminal ricin B-chain-like β-trefoil domains. Recombinant LA3490 (rLA3490) and an N-terminal fragment, t3490, containing only the predicted ricin B domain, bound to the terminal galactose and N-acetyl-galactosamine residues, asialofetuin, and directly competed for asialofetuin-binding sites with recombinant ricin B chain. t3490 alone was sufficient for binding, both to immobilized asialofetuin and to the HeLa cell surface but was neither internalized nor cytotoxic. Treatment of HeLa cells with rLA3490 led to cytoskeleton disassembly, caspase-3 activation, and nuclear fragmentation, and was rapidly cytolethal. rLA3490 had DNase activity on mammalian and bacterial plasmid DNA. The combination of cell surface binding, internalization, nuclear translocation, and DNase functions indicate that LA3490 and other VM proteins evolved as novel forms of the bacterial AB domain-containing toxin paradigm.

[Role of systemic infections in canine kidney diseases]

Kidney diseases represent a common problem as well as a frequent cause of death in dogs. Infectious agents may be responsible for glomerulopathies and acute kidney injuries. Many infections commonly associated with the development of immune complex glomerulonephritis in central and southern Europe are important as travel-associated diseases in Germany. These include leishmaniosis, dirofilariosis, and ehrlichiosis. Rarely, anaplasmosis, hepatozoonosis, Lyme disease as well as babesiosis caused by small Babesia spp. are detected as cause of canine immune complex glomerulonephritis in Germany. Leptospirosis, canine infectious hepatitis, and babesiosis caused by large Babesia spp. may be responsible for the development of acute kidney injuries associated with tubulointerstitial nephritis. Therefore, further diagnostics aiming at identifying potentially causative infectious agents in dogs with renal disease is important for both prognosis and therapy of the patient.

Revisiting the Development of Vaccines Against Pathogenic Leptospira: Innovative Approaches, Present Challenges, and Future Perspectives

Human vaccination against leptospirosis has been relatively unsuccessful in clinical applications despite an expressive amount of vaccine candidates has been tested over years of research. Pathogenic Leptospira encompass a great number of serovars, most of which do not cross-react, and there has been a lack of genetic tools for many years. These obstacles have hampered the understanding of the bacteria's biology and, consequently, the identification of an effective antigen. Thus far, many approaches have been used in an attempt to find a cost-effective and broad-spectrum protective antigen(s) against the disease. In this extensive review, we discuss several strategies that have been used to develop an effective vaccine against leptospirosis, starting with Leptospira-inactivated bacterin, proteins identified in the genome sequences of pathogenic Leptospira, including reverse vaccinology, plasmid DNA, live vaccines, chimeric multi-epitope, and toll- and nod-like receptors agonists. This overview should be able to guide scientists working in the field to select potential antigens and to choose the appropriate formulation to administer the candidates.

A Review on Host-Leptospira Interactions: What We Know and Future Expectations

Leptospirosis is a widespread zoonosis caused by pathogenic Leptospira spp. It is considered a neglected infectious disease of human and veterinary concern. Our group has been investigating proteins annotated as hypothetical, predicted to be located on the leptospiral surface. Because of their location, these proteins may have the ability to interact with various host components, which could allow establishment of the infection. These proteins act as adherence factors by binding to host receptor molecules, such as the extracellular matrix (ECM) components laminin and glycosaminoglycans to help bacterial colonization. Leptospira also interacts with the host fibrinolytic system, which has been demonstrated to be a powerful tool for invasion mechanisms. The interaction with fibrinogen and thrombin has been shown to reduce fibrin clot formation. Additionally, the degradation of coagulation cascade components by secreted proteases or by acquired surface plasmin could also play a role in reducing clot formation, hence facilitating dissemination during infection. Interaction with host complement system regulators also plays a role in helping bacteria to evade the immune system, facilitating invasion. Interaction of Leptospira to cell receptors, such as cadherins, can contribute to investigate molecules that participate in virulence. To achieve a better understanding of the host-pathogen interaction, leptospiral mutagenesis tools have been developed and explored. This work presents several proteins that mediate binding to components of the ECM, plasma, components of the complement system and cells, to gather research achievements that can be helpful in better understanding the mechanisms of leptospiral-host interactions and discuss genetic manipulation for Leptospira spp. aimed at protein function validation.

In vivo and in silico Virulence Analysis of Leptospira Species Isolated From Environments and Rodents in Leptospirosis Outbreak Areas in Malaysia

The zoonotic disease leptospirosis is caused by pathogenic species of the genus Leptospira. With the advancement of studies in leptospirosis, several new species are being reported. It has always been a query, whether Leptospira species, serovars, and strains isolated from different geographical locations contribute to the difference in the disease presentations and severity. In an epidemiological surveillance study performed in Malaysia, we isolated seven novel intermediate and saprophytic species (Leptospira semungkisensis, Leptospira fletcheri, Leptospira langatensis, Leptospira selangorensis, Leptospira jelokensis, Leptospira perdikensis, Leptospira congkakensis) from environments and three pathogenic species from rodents (Leptospira borgpetersenii strain HP364, Leptospira weilii strain SC295, Leptospira interrogans strain HP358) trapped in human leptospirosis outbreak premises. To evaluate the pathogenic potential of these isolates, we performed an in vivo and in silico virulence analysis. Environmental isolates and strain HP364 did not induce any clinical manifestations in hamsters. Strain SC295 caused inactivity and weight loss with histopathological changes in kidneys, however, all hamsters survived until the end of the experiment. Strain HP358 showed a high virulent phenotype as all infected hamsters died or were moribund within 7 days postinfection. Lungs, liver, and kidneys showed pathological changes with hemorrhage as the main presentation. In silico analysis elucidated the genome size of strain HP358 to be larger than strains HP364 and SC295 and containing virulence genes reported in Leptospira species and a high number of specific putative virulence factors. In conclusion, L. interrogans strain HP358 was highly pathogenic with fatal outcome. The constituent of Leptospira genomes may determine the level of disease severity and that needs further investigations.

The role of leptospiremia and specific immune response in severe leptospirosis

Leptospirosis can cause a high mortality rate, especially in severe cases. This multicenter cross-sectional study aimed to examine both host and pathogen factors that might contribute to the disease severity. A total of 217 leptospirosis patients were recruited and divided into two groups of non-severe and severe. Severe leptospirosis was defined by a modified sequential organ failure assessment (mSOFA) score of more than two or needed for mechanical ventilation support or had pulmonary hemorrhage or death. We found that leptospiremia, plasma neutrophil gelatinase-associated lipocalin (pNGAL), and interleukin 6 (IL-6) at the first day of enrollment (day 1) and microscopic agglutination test (MAT) titer at 7 days after enrollment (days 7) were significantly higher in the severe group than in the non-severe group. After adjustment for age, gender, and the days of fever, there were statistically significant associations of baseline leptospiremia level (OR 1.70, 95% CI 1.23–2.34, p = 0.001), pNGAL (OR 9.46, 95% CI 4.20–21.33, p < 0.001), and IL-6 (OR 2.82, 95% CI 1.96–4.07, p < 0.001) with the severity. In conclusion, a high leptospiremia, pNGAL, and IL-6 level at baseline were associated with severe leptospirosis.

Characterization of a Novel Peptide from Pathogenic Leptospira and Its Cytotoxic Effect

Leptospirosis is a zoonotic infectious disease caused by pathogenic Leptospira species. Virulence proteins have been shown to be key determinants of the pathogenesis of pathogenic Leptospira. A specific peptide at a mass-to-charge ratio of 7000 Da was identified in Leptospira whole cells using matrix-assisted laser/desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. This peptide was specifically present in pathogenic Leptospira and in clinical isolates. We report here the characterization of this specific peptide using a proteomics approach. This peptide was significantly matched to a hypothetical conserved L. interrogans protein (LA2458) with a calculated molecular weight of 7140.136 Da containing a tellurite-resistance domain at its C terminus (TerB-C). The amino acid sequences revealed the presence of hydrophobic transmembrane portions and two linear B-cell epitopes. Despite its low abundance, this synthetic peptide demonstrated dose-dependent cytotoxicity toward African green monkey kidney (Vero) cells via the apoptosis pathway. The concentration of the peptide 100 µM induced about 50% of cell death after a 24 h exposure. This peptide could be useful for the diagnosis of leptospirosis and the study of pathogenesis.

Cytotoxicity of the 42 kDa SMase C sphingomyelinase secreted by Leptospira interrogans serovar Pomona on Vero cells

Sphingomyelinases produced by the pathogenic members of the genus Leptospira are implicated in the haemorrhagic manifestations seen in the severe form of leptospirosis. With multiple sphingomyelinase genes present in the genome of pathogenic Leptospira, much remains to be understood about these molecules. They include factors regulating their expression, post-translational modifications, and release of the biologically active forms of these molecules. In this study, serovar Pomona was chosen as it is reported to express high levels of sphingomyelinase that explained the haemolytic activity seen in experimental animals infected with this pathogen. Here, we demonstrate the cytotoxicity of a 42 kDa sphingomyelinase secreted by Leptospira interrogans serovar Pomona strain Pomona upon infecting Vero cells. This sphingomyelinase detected using specific anti-sphingomyelinase antibodies, exhibited haemolytic and sphingomyelinase activities that caused host-cell damage evident from the confocal images and scanning electron micrographs. The implications of these findings and the detection of a 42 kDa sphingomyelinase in the urine of human patients with leptospirosis in our earlier study is discussed with an emphasis on the potential of these sphingomyelinases as candidate markers for the early diagnosis of 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.

Raised levels of Il-6, Il-17a, and Il-22 in fatal leptospirosis

Clinical manifestations of leptospirosis range from mild, common cold-like illness, to a life-threatening condition. The host immune response has been hypothesized to play a major role in leptospirosis outcome. Increased levels of inflammatory mediators, such as cytokines, may promote tissue damage that lead to increased disease severity. The question is whether cytokines levels may predict the outcome of leptospirosis and guide patient management. This study aimed to assess the association between Th1-, Th2-, and Th17-related cytokines with the clinical outcome of patients with leptospirosis. Different cytokine levels were measured in fifty-two plasma samples of hospitalized patients diagnosed with leptospirosis in Malaysia (January 2016-December 2017). Patients were divided into two separate categories: survived (n = 40) and fatal outcome (n = 12). Nineteen plasma samples from healthy individuals were obtained as controls. Cytokine quantification was performed using Simple Plex™ assays from ProteinSimple (San Jose, CA, USA). Measurements were done in triplicate and statistical analysis was performed using GraphPad software and SPSS v20. IL-6 (p = 0.033), IL-17A (p = 0.022), and IL-22 (p = 0.046) were significantly elevated in fatal cases. IL-17A concentration (OR 1.115; 95% CI 1.010-1.231) appeared to be an independent predictor of fatality of leptospirosis. Significantly higher levels of TNF-α (p ≤ 0.0001), IL-6 (p ≤ 0.0001), IL-10 (p ≤ 0.0001), IL-12 (p ≤ 0.0001), IL17A (p ≤ 0.0001), and IL-18 (p ≤ 0.0001) were observed among leptospirosis patients in comparison with healthy controls. Our study shows that certain cytokine levels may serve as possible prognostic biomarkers in leptospirosis patients.

Historical Review of Leptospirosis in the Korea (1945 - 2015)

Leptospirosis is a widespread worldwide zoonosis. Human leptospirosis was first identified in the Korea in 1984 as the cause of “epidemic pulmonary hemorrhagic fever of unknown etiology” that occurred sporadically or in outbreaks. The major outbreaks, leading to some deaths, mainly involved rice field farmers who worked in wet and muddy rice paddies following floods or heavy rainfalls. Leptospirosis was designated a nationally notifiable disease in 1987. The Korean government introduced a supplementary immunization program to control the disease from 1988 to 1997, which provided people at risk in endemic areas with the inactivated vaccine prepared from a local strain Leptospira interrogans serovar Lai. In addition, the continuous promotion of education and awareness in the media played a role in improving personal hygiene management. Since then, the reported incidence of leptospirosis has been low. Leptospirosis is currently considered in the differential diagnosis of acute febrile illnesses occurring in fall. This study historically reviews clinical and epidemiological publications, scientific reports, and public health policies for recognition, identification, and infection control of human leptospirosis in the Korea.

Immuno-informatics based approaches to design a novel multi epitope-based vaccine for immune response reinforcement against Leptospirosis

Leptospirosis is known as a zoonotic disease of global importance originated from infection with the spirochete bacterium Leptospira. Although several leptospirosis vaccines have been tested, the vaccination is relatively unsuccessful in clinical application despite decades of research. Therefore, this study was conducted to construct a novel multi-epitope based vaccine against leptospirosis by using Hap1, LigA, LAg42, SphH and HSP58 antigens. T cell and IFN gamma epitopes were predicted from these antigens. In addition, to induce strong CD4⁺ helper T lymphocytes (HTLs) responses, Pan HLA DR-binding epitope (PADRE) and helper epitopes selected from Tetanus toxin fragment C (TTFrC) were applied. Moreover, for boosting immune response, Heparin-Binding Hemagglutinin (HBHA), a novel TLR4 agonist was added to the construct as an adjuvant. Finally, selected epitopes were linked together using EAAAK, GPGPG, AAY and HEYGAEALERAG linkers. Based on the predicted epitopes, a multi-epitope vaccine was construct with 490 amino acids. Physico-chemical properties, secondary and tertiary structures, stability, intrinsic protein disorder, solubility, and allergenicity of this vaccine construct were assessed by applying immunoinformatics analyses. A soluble, and non-allergic protein with a molecular weight of 53.476 kDa was obtained. Further analyses validated the stability of the chimeric protein and the predicted epitopes in the chimeric vaccine indicated strong potential to induce B-cell and T-cell mediated immune response. Therefore, immunoinformatics analysis showed that the modeled multi-epitope vaccine can properly stimulate the both T and B cells immune responses and could potentially be used for prophylactic or therapeutic usages.

Leptospirosis in human: Biomarkers in host immune responses

Leptospirosis remains one of the most widespread zoonotic diseases caused by spirochetes of the genus Leptospira, which accounts for high morbidity and mortality globally. Leptospiral infections are often found in tropical and subtropical regions, with people exposed to contaminated environments or animal reservoirs are at high risk of getting the infection. Leptospirosis has a wide range of clinical manifestations with non-specific signs and symptoms and often misdiagnosed with other acute febrile illnesses at early stage of infection. Despite being one of the leading causes of zoonotic morbidity worldwide, there is still a gap between pathogenesis and human immune responses during leptospiral infection. It still remains obscure whether the severity of the infection is caused by the pathogenic properties of the Leptospira itself, or it is a consequence of imbalance host immune factors. Hence, in this review, we seek to summarize the past and present milestone findings on the biomarkers of host immune response aspects during human leptospiral infection, including cytokine and other immune mediators. A profound understanding of the interlink between virulence factors and host immune responses during human leptospirosis is imperative to identify potential biomarkers for diagnostic and prognostic applications as well as designing novel immunotherapeutic strategies in future.

Bacterial Sphingomyelinases and Phospholipases as Virulence Factors

Bacterial sphingomyelinases and phospholipases are a heterogeneous group of esterases which are usually surface associated or secreted by a wide variety of Gram-positive and Gram-negative bacteria. These enzymes hydrolyze sphingomyelin and glycerophospholipids, respectively, generating products identical to the ones produced by eukaryotic enzymes which play crucial roles in distinct physiological processes, including membrane dynamics, cellular signaling, migration, growth, and death. Several bacterial sphingomyelinases and phospholipases are essential for virulence of extracellular, facultative, or obligate intracellular pathogens, as these enzymes contribute to phagosomal escape or phagosomal maturation avoidance, favoring tissue colonization, infection establishment and progression, or immune response evasion. This work presents a classification proposal for bacterial sphingomyelinases and phospholipases that considers not only their enzymatic activities but also their structural aspects. An overview of the main physiopathological activities is provided for each enzyme type, as are examples in which inactivation of a sphingomyelinase- or a phospholipase-encoding gene impairs the virulence of a pathogen. The identification of sphingomyelinases and phospholipases important for bacterial pathogenesis and the development of inhibitors for these enzymes could generate candidate vaccines and therapeutic agents, which will diminish the impacts of the associated human and animal diseases.

Comparative analyses of transport proteins encoded within the genomes of Leptospira species

Select species of the bacterial genus Leptospira are causative agents of leptospirosis, an emerging global zoonosis affecting nearly one million people worldwide annually. We examined two Leptospira pathogens, Leptospira interrogans serovar Lai str. 56601 and Leptospira borgpetersenii serovar Hardjo-bovis str. L550, as well as the free-living leptospiral saprophyte, Leptospira biflexa serovar Patoc str. 'Patoc 1 (Ames)'. The transport proteins of these leptospires were identified and compared using bioinformatics to gain an appreciation for which proteins may be related to pathogenesis and saprophytism. L. biflexa possesses a disproportionately high number of secondary carriers for metabolite uptake and environmental adaptability as well as an increased number of inorganic cation transporters providing ionic homeostasis and effective osmoregulation in a rapidly changing environment. L. interrogans and L. borgpetersenii possess far fewer transporters, but those that they all have are remarkably similar, with near-equivalent representation in most transporter families. These two Leptospira pathogens also possess intact sphingomyelinases, holins, and virulence-related outer membrane porins. These virulence-related factors, in conjunction with decreased transporter substrate versatility, indicate that pathogenicity arose in Leptospira correlating to progressively narrowing ecological niches and the emergence of a limited set of proteins responsible for host invasion. The variability of host tropism and mortality rates by infectious leptospires suggests that small differences in individual sets of proteins play important physiological and pathological roles.

Role of sph2 Gene Regulation in Hemolytic and Sphingomyelinase Activities Produced by Leptospira interrogans

Pathogenic members of the genus Leptospira are the causative agents of leptospirosis, a neglected disease of public and veterinary health concern. Leptospirosis is a systemic disease that in its severest forms leads to renal insufficiency, hepatic dysfunction, and pulmonary failure. Many strains of Leptospira produce hemolytic and sphingomyelinase activities, and a number of candidate leptospiral hemolysins have been identified based on sequence similarity to well-characterized bacterial hemolysins. Five of the putative hemolysins are sphingomyelinase paralogs. Although recombinant forms of the sphingomyelinase Sph2 and other hemolysins lyse erythrocytes, none have been demonstrated to contribute to the hemolytic activity secreted by leptospiral cells. In this study, we examined the regulation of sph2 and its relationship to hemolytic and sphingomyelinase activities produced by several L. interrogans strains cultivated under the osmotic conditions found in the mammalian host. The sph2 gene was poorly expressed when the Fiocruz L1-130 (serovar Copenhageni), 56601 (sv. Lai), and L495 (sv. Manilae) strains were cultivated in the standard culture medium EMJH. Raising EMJH osmolarity to physiological levels with sodium chloride enhanced Sph2 production in all three strains. In addition, the Pomona subtype kennewicki strain LC82-25 produced substantially greater amounts of Sph2 during standard EMJH growth than the other strains, and sph2 expression increased further by addition of salt. When 10% rat serum was present in EMJH along with the sodium chloride supplement, Sph2 production increased further in all strains. Osmotic regulation and differences in basal Sph2 production in the Manilae L495 and Pomona strains correlated with the levels of secreted hemolysin and sphingomyelinase activities. Finally, a transposon insertion in sph2 dramatically reduced hemolytic and sphingomyelinase activities during incubation of L. interrogans at physiologic osmolarity. Complementation of the mutation with the sph2 gene partially restored production of hemolytic and sphingomyelinase activities. These results indicate that the sph2 gene product contributes to the hemolytic and sphingomyelinase activities secreted by L. interrogans and most likely dominates those functions under the culture condition tested.

The spirochete Leptospira causes leptospirosis, a potentially deadly disease of humans and animals. Candidate factors that promote infection include hemolysins encoded by several leptospiral genes. Hemolysins rupture red blood cells in vitro. Some hemolysins are sphingomyelinases, which target sphingomyelin in the host cell membrane. Hemolysins have the potential to disrupt organ function during infection. It is not known which hemolysins and sphingomyelinases are responsible for the hemolytic and sphingomyelinase activities secreted by L. interrogans. We found that the production of hemolytic activity is regulated and is tied to expression of sph2, which encodes a hemolysin with sphingomyelinase, cytotoxic, and fibronectin-binding activities. Hemolytic and sphingomyelinase activities and sph2 expression were higher when the osmolarity of the culture medium was raised to the level found in the mammalian host. Similarly, sph2 expression was substantially higher in an L. interrogans strain that secreted large amounts of hemolytic and sphingomyelinase activities than in a strain that generated negligible amounts. Most importantly, disruption of the sph2 gene eliminated hemolysin production and yielded substantially less sphingomyelinase than the wild-type strain. Our findings indicate that sph2 is a major contributor to the hemolytic and sphingomyelinase activities secreted by L. interrogans and that the hemolytic and sphingomyelinase activities measured in standard L. interrogans cultures may underestimate the levels produced during infection.

Comparative genomic analyses of transport proteins encoded within the genomes of Leptospira species

Select species of the bacterial genus Leptospira are causative agents of leptospirosis, an emerging global zoonosis affecting nearly one million people worldwide annually. We examined two Leptospira pathogens, Leptospira interrogans serovar Lai str. 56601 and Leptospira borgpetersenii serovar Hardjo-bovis str. L550, as well as the free-living leptospiral saprophyte, Leptospira biflexa serovar Patoc str. 'Patoc 1 (Ames)'. The transport proteins of these leptospires were identified and compared using bioinformatics to gain an appreciation for which proteins may be related to pathogenesis and saprophytism. L. biflexa possesses a disproportionately high number of secondary carriers for metabolite uptake and environmental adaptability as well as an increased number of inorganic cation transporters providing ionic homeostasis and effective osmoregulation in a rapidly changing environment. L. interrogans and L. borgpetersenii possess far fewer transporters, but those that they have are remarkably similar, with near-equivalent representation in most transporter families. These two Leptospira pathogens also possess intact sphingomyelinases, holins, and virulence-related outer membrane porins. These virulence-related factors, in conjunction with decreased transporter substrate versatility, indicate that pathogenicity was accompanied by progressively narrowing ecological niches and the emergence of a limited set of proteins responsible for host invasion. The variability of host tropism and mortality rates by infectious leptospires suggests that small differences in individual sets of proteins play important physiological and pathological roles.

Immunohistochemical detection of IgM and IgG in lung tissue of dogs with leptospiral pulmonary haemorrhage syndrome (LPHS)

Leptospiral pulmonary haemorrhage syndrome (LPHS) is a severe form of leptospirosis. Pathogenic mechanisms are poorly understood. Lung tissues from 26 dogs with LPHS, 5 dogs with pulmonary haemorrhage due to other causes and 6 healthy lungs were labelled for IgG (n=26), IgM (n=25) and leptospiral antigens (n=26). Three general staining patterns for IgG/IgM were observed in lungs of dogs with LPHS with most tissues showing more than one staining pattern: (1) alveolar septal wall staining, (2) staining favouring alveolar surfaces and (3) staining of intra-alveolar fluid. Healthy control lung showed no staining, whereas haemorrhagic lung from dogs not infected with Leptospira showed staining of intra-alveolar fluid and occasionally alveolar septa. Leptospiral antigens were not detected. We conclude that deposition of IgG/IgM is demonstrable in the majority of canine lungs with naturally occurring LPHS, similar to what has been described in other species. Our findings suggest involvement of the host humoral immunity in the pathogenesis of LPHS and provide further evidence to support the dog as a natural disease model for human LPHS.

Comparative proteomic analysis of lung tissue from guinea pigs with leptospiral pulmonary haemorrhage syndrome (LPHS) reveals a decrease in abundance of host proteins involved in cytoskeletal and cellular organization

Leptospiral pulmonary haemorrhage syndrome (LPHS) is a particularly severe form of leptospirosis. LPHS is increasingly recognized in both humans and animals and is characterized by rapidly progressive intra-alveolar haemorrhage leading to high mortality. The pathogenic mechanisms of LPHS are poorly understood which hampers the application of effective treatment regimes. In this study a 2-D guinea pig proteome lung map was created and used to investigate the pathogenic mechanisms of LPHS. Comparison of lung proteomes from infected and non-infected guinea pigs via differential in-gel electrophoresis revealed highly significant differences in abundance of proteins contained in 130 spots. Acute phase proteins were the largest functional group amongst proteins with increased abundance in LPHS lung tissue, and likely reflect a local and/or systemic host response to infection. The observed decrease in abundance of proteins involved in cytoskeletal and cellular organization in LPHS lung tissue further suggests that infection with pathogenic Leptospira induces changes in the abundance of host proteins involved in cellular architecture and adhesion contributing to the dramatically increased alveolar septal wall permeability seen in LPHS.

BIOLOGICAL SIGNIFICANCE

The recent completion of the complete genome sequence of the guinea pig (Cavia porcellus) provides innovative opportunities to apply proteomic technologies to an important animal model of disease. In this study, the comparative proteomic analysis of lung tissue from experimentally infected guinea pigs with leptospiral pulmonary haemorrhage syndrome (LPHS) revealed a decrease in abundance of proteins involved in cellular architecture and adhesion, suggesting that loss or down-regulation of cytoskeletal and adhesion molecules plays an important role in the pathogenesis of LPHS. A publically available guinea pig lung proteome map was constructed to facilitate future pulmonary proteomics in this species.

RETRACTED: ChpK and MazF of the toxin-antitoxin modules are involved in the virulence of Leptospira interrogans during infection

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the corresponding author and the editorial office of Microbes and Infection. An independent reviewer of the retraction request was also appointed given that one of the authors is the Editor-in- Chief. For figure 1C, Lanes 1 and 2 appear to share some unexpected similarities, except for the bottom band, which also appear to be the band of interest. Sections of Figure 2C appear similar to sections of Figure 5D of a paper that had already appeared in Molecular Microbiology, volume 83, issue 5 (2012) 1006-1023. https://doi.org/10.1111/j.1365-2958.2012.07985.x. In figure 3A, Flow cytograms share identical/similar patterns highlighted in various colours. Peculiarly, some of these patterns can be seen as horizontal rotations of others along the axis that separates different quadrants. (ie red green & purple). Moreover, some quadrants appear to have very high densities of events that are suprisingly limited by quadrant gates (most noticeably quadrants B2 from the second column of panels. Figure 5A-B it was found that there were duplicated bands were produced. Figures 5C and 5D, it was found that bands across each individual gel appear identical. One of the conditions of submission of a paper for publication is that authors declare explicitly that the paper has not been previously published and is not under consideration for publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process”.

Immune responses to Leptospira infection: roles as biomarkers for disease severity

Various leptospiral components have been identified and shown to be involved in tissue destruction. In addition, immune responses to leptospires have been implicated in target organ damages in severe leptospirosis cases. Several inflammatory mediators were shown to be higher in susceptible animals than in resistant hosts. Moreover, cytokines/chemokines and serum proteins induced following Leptospira infection were suggested to be biomarkers for disease severity in human leptospirosis. This review focuses on the role of immune responses in the severity of leptospirosis. Studies in both animal models and humans are discussed.

Leptospira interrogans enolase is secreted extracellularly and interacts with plasminogen

Leptospira interrogans is the agent for leptospirosis, an important zoonosis in humans and animals across the globe. Surface proteins of invading pathogens, such as L. interrogans, are thought to be responsible for successful microbial persistence in vivo via interaction with specific host components. In particular, a number of invasive infectious agents exploit host proteolytic pathways, such as one involving plasminogen (Pg), which aid in efficient pathogen dissemination within the host. Here we show that L. interrogans serovar Lai binds host Pg and that the leptospiral gene product LA1951, annotated as enolase, is involved in this interaction. Interestingly, unlike in related pathogenic Spirochetes, such as Borrelia burgdorferi, LA1951 is not readily detectable in the L. interrogans outer membrane. We show that the antigen is indeed secreted extracellularly; however, it can reassociate with the pathogen surface, where it displays Pg-binding and measurable enzymatic activity. Hamsters infected with L. interrogans also develop readily detectable antibody responses against enolase. Taken together, our results suggest that the L. interrogans enolase has evolved to play a role in pathogen interaction with host molecules, which may contribute to the pathogenesis of leptospirosis.

Sphingomyelinase activity of Trichomonas vaginalis extract and subfractions

Trichomoniasis is one of the most common acute sexually transmitted curable diseases, and it is disseminated worldwide generating more than 170 million cases annually. Trichomonas vaginalis is the parasite that causes trichomoniasis and has the ability to destroy cell monolayers of the vaginal mucosa in vitro. Sphingomyelinases (SMase) are enzymes that catalyze the hydrolysis of sphingomyelin into ceramide and phosphorylcholine. Ceramide appears to be a second messenger lipid in programmed apoptosis, cell differentiation, and cell proliferation. Sphingomyelinase is probably a major source of ceramide in cells. Signal transduction mediated by ceramide leads cells to produce cytokine induced apoptosis during several inflammatory responses. SMase are also relevant toxins in several microorganisms. The main objective of this research is to identify SMase activity of T. vaginalis in the total extract (TE), P30, and S30 subfractions from brooked trophozoites. It was found that these fractions of T. vaginalis have SMase activity, which comes principally from P30 subfraction and was mainly type C. Enzymatic activity of SMase increased linearly with time and is pH dependent with two peaks by pH 5.5 and pH 7.5. The addition of manganese to the reaction mixture increased the SMase activity by 1.97.

In vivo gene expression and immunoreactivity of Leptospira collagenase

Pulmonary hemorrhage is an increasing cause of death of leptospirosis patients. Bacterial collagenase has been shown to be involved in lung hemorrhage induced by various infectious agents. According to Leptospira whole genome study, colA, a gene suggested to code for bacterial collagenase has been identified. We investigated colA gene expression in lung tissues of Leptospira infected hamsters. Golden Syrian Hamsters were injected intraperitoneally with Leptospira interrogans serovar Pyrogenes. The hamsters were sacrificed on days 3, 5 and 7 post-infection and lung tissues were collected for histological examination and RNA extraction. Lung pathologies including atelectasis and hemorrhage were observed. Expression of colA gene in lung tissues was demonstrated by both RT-PCR and real time PCR. In addition, ColA protein was cloned and the purified protein could react with sera from leptospirosis patients. Leptospira ColA protein may play a role in Leptospira survival or pathogenesis in vivo. Its reaction with leptospirosis sera suggests that this protein is immunogenic and could be another candidate for vaccine development.

Leptospira and inflammation

Leptospirosis is an important zoonosis and has a worldwide impact on public health. This paper will discuss both the role of immunogenic and pathogenic molecules during leptospirosis infection and possible new targets for immunotherapy against leptospira components. Leptospira, possess a wide variety of mechanisms that allow them to evade the host immune system and cause infection. Many molecules contribute to the ability of Leptospira to adhere, invade, and colonize. The recent sequencing of the Leptospira genome has increased our knowledge about this pathogen. Although the virulence factors, molecular targets, mechanisms of inflammation, and signaling pathways triggered by leptospiral antigens have been studied, some questions are still unanswered. Toll-like receptors (TLRs) are the primary sensors of invading pathogens. TLRs recognize conserved microbial pattern molecules and activate signaling pathways that are pivotal to innate and adaptive immune responses. Recently, a new molecular target has emerged—the Na/K-ATPase—which may contribute to inflammatory and metabolic alteration in this syndrome. Na/K-ATPase is a target for specific fatty acids of host origin and for bacterial components such as the glycolipoprotein fraction (GLP) that may lead to inflammasome activation. We propose that in addition to TLRs, Na/K-ATPase may play a role in the innate response to leptospirosis infection.

Leptospiral outer membrane protein microarray, a novel approach to identification of host ligand-binding proteins

Leptospirosis is a zoonosis with worldwide distribution caused by pathogenic spirochetes belonging to the genus Leptospira. The leptospiral life cycle involves transmission via freshwater and colonization of the renal tubules of their reservoir hosts. Infection requires adherence to cell surfaces and extracellular matrix components of host tissues. These host-pathogen interactions involve outer membrane proteins (OMPs) expressed on the bacterial surface. In this study, we developed an Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130 OMP microarray containing all predicted lipoproteins and transmembrane OMPs. A total of 401 leptospiral genes or their fragments were transcribed and translated in vitro and printed on nitrocellulose-coated glass slides. We investigated the potential of this protein microarray to screen for interactions between leptospiral OMPs and fibronectin (Fn). This approach resulted in the identification of the recently described fibronectin-binding protein, LIC10258 (MFn8, Lsa66), and 14 novel Fn-binding proteins, denoted Microarray Fn-binding proteins (MFns). We confirmed Fn binding of purified recombinant LIC11612 (MFn1), LIC10714 (MFn2), LIC11051 (MFn6), LIC11436 (MFn7), LIC10258 (MFn8, Lsa66), and LIC10537 (MFn9) by far-Western blot assays. Moreover, we obtained specific antibodies to MFn1, MFn7, MFn8 (Lsa66), and MFn9 and demonstrated that MFn1, MFn7, and MFn9 are expressed and surface exposed under in vitro growth conditions. Further, we demonstrated that MFn1, MFn4 (LIC12631, Sph2), and MFn7 enable leptospires to bind fibronectin when expressed in the saprophyte, Leptospira biflexa. Protein microarrays are valuable tools for high-throughput identification of novel host ligand-binding proteins that have the potential to play key roles in the virulence mechanisms of pathogens.

Leptospiral hemolysins induce proinflammatory cytokines through Toll-like receptor 2-and 4-mediated JNK and NF-κB signaling pathways

BACKGROUND

Infection with pathogenic Leptospira species causes serious systemic inflammation in patients. Although a few leptospiral proinflammatory molecules have been identified, Leptospira likely encodes other unidentified strong inflammation stimulators. The pathogenic L. interrogans genome encodes numerous putative hemolysin genes. Since hemolysins from other bacteria can cause inflammatory reactions, we hypothesized that leptospiral hemolysins may function as proinflammatory stimulators that contribute to the strong inflammation associated with Leptospira infection.

METHODOLOGY/PRINCIPAL FINDINGS

We first used cytokine protein microarrays for systematic analysis of serum cytokine profiles in leptospirosis patients and leptospire-infected mice. We found that IL-1β, IL-6 and TNF-α were the main proinflammatory cytokines in the sera of both the patients and the mice. We then analyzed eight putative hemolysins in L. interrogans strain Lai. The results showed that five of them, Sph1, Sph2, Sph3, HlpA and TlyA were secreted and had hemolytic activity. More importantly, these five hemolysins induced the strong production of IL-1β, IL-6 and TNF-α in human and mouse macrophages (although a bit lower in the latter). Furthermore, blockade of TLR2 or TLR4 with either antibodies or inhibitors of the NF-κB or JNK signaling pathways significantly reduced the production of hemolysin-induced IL-1β, IL-6 and TNF-α. Macrophages isolated from TLR2-, TLR4-or double TLR2-and 4-deficient mice also confirmed that the leptospiral hemolysins that induce proinflammatory cytokines are both TLR2-and TLR4-dependent.

CONCLUSIONS/SIGNIFICANCE

Our findings demonstrate that L. interrogans secretes many hemolysins that function as powerful inducers of proinflammatory cytokines through both TLR2-and TLR4-dependent JNK and NF-κB pathways.

Aspectos anatomopatológicos da leptospirose em cães: 53 casos (1965-2011)

Os aspectos anatomopatológicos da leptospirose foram estudados em 53 cães que tiveram diagnóstico definitivo confirmado por imuno-histoquímica do tecido renal. Na necropsia, as principais lesões observadas incluíram icterícia (79,2%) e hemorragia (75,5%), principalmente no pulmão (56,6%). Alterações macroscópicas hepáticas (56,6%) e renais (50,9%) foram frequentes e caracterizavam-se principalmente por descolorações (30,2% e 32,1% respectivamente), acentuação do padrão lobular hepático (26,4%) e estriações brancas na superfície de corte dos rins (22,6%). Lesões extrarrenais de uremia ocorreram na metade dos casos (50,9%). Hepatomegalia (11,3%), nefromegalia (9,4%) e irregularidade da superfície capsular dos rins (3,8%) foram menos comuns. Na histologia dos rins (n=53), as lesões encontradas (98,1%) foram quase que exclusivamente agudas ou subagudas (96,2%) e caracterizavam-se por graus variados de nefrose tubular (86,8%) e nefrite intersticial não supurativa (60,4%), com evidente dissociação degenerativo-inflamatória. Na histologia do fígado (n=42), as lesões encontradas (97,6%) eram constituídas principalmente por dissociação dos cordões de hepatócitos (78,6%), colestase intra-canalicular (33,3%) e necrose hepática (31%). Lesões reativas, como hipertrofia das células de Kupffer, leucocitostase sinusoidal e infiltrado inflamatório mononuclear nos espaços porta, foram vistas em muitos casos (42,8%). Na histologia do pulmão (n=28), hemorragia (85,7%) e edema (57,1%) alveolares foram muito prevalentes. Neutrófilos e macrófagos nos espaços alveolares (35,7%) e neutrófilos no interior de pequenos vasos pulmonares (17,9%) também foram achados frequentes. Os resultados aqui demonstrados devem servir de alerta aos patologistas veterinários brasileiros, pois a apresentação anatomopatológica da leptospirose canina em nossa região (Região Central do Rio Grande do Sul, Brasil) não se modificou nos últimos 50 anos, mantendo-se semelhante àquela descrita internacionalmente até a década de 1980, mas muito diferente do que é atualmente reconhecido para os Estados Unidos, o Canadá e parte da Europa Ocidental. Recomendamos que os critérios histopatológicos para o diagnóstico da leptospirose canina devem incluir a presença concomitante de nefrite tubulointersticial aguda ou subaguda, hepatite reativa não específica e lesão alveolar difusa, incluindo hemorragia alveolar difusa com capilarite, em um cão que durante a necropsia demonstre icterícia, hemorragias e lesões extrarrenais de uremia na ausência de esplenomegalia.

Structural analysis of the Leptospiral sphingomyelinases: in silico and experimental evaluation of Sph2 as an Mg-dependent sphingomyelinase

BACKGROUND

Leptospiral sphingomyelinases are candidate virulence factors present only in pathogenic Leptospira spp. Leptospira interrogans serovar Lai encodes Sph1, Sph2, Sph3, Sph4 and SphH. Except for Sph4, they all possess the exo-endo-phosphatase domain that groups them under the DNase I superfamily.

METHODS, RESULTS AND CONCLUSIONS

Modeling of exo-endo-phosphatase domains reveals high-level structural similarity of Sph2 with the crystal structure of SmcL and BC SMase sphingomyelinases from Listeria ivanovii and Bacillus cereus, respectively. A β-hairpin loop, essential for host cell membrane interaction, is absent in leptospiral sphingomyelinases. Instead, several aromatic amino acids were oriented outward from the surface of these molecules and formed clusters of hydrophobic regions that possibly enables the anchoring of these molecules into the host cell membrane, as demonstrated in Sph2 and Sph3. Sph2 is unique and possesses the Mg(++)-binding Glu53 residue in the metal-binding site and two His residues (His151 and His286) in the catalytic site. We demonstrate experimentally the Mg(++)-dependent hemolysis of erythrocytes by rSph2 and its ability to cleave sphingomyelin to ceramide. Anti-Sph2 antibodies neutralized the hemolytic activity of Sph2. In conclusion, we provide evidence showing that Sph2 is a Mg(++)-dependent hemolysin with both sphingomyelinase and hemolytic activities.

Multiple leptospiral sphingomyelinases (or are there?)

Culture supernatants of leptospiral pathogens have long been known to haemolyse erythrocytes. This property is due, at least in part, to sphingomyelinase activity. Indeed, genome sequencing reveals that pathogenic Leptospira species are richly endowed with sphingomyelinase homologues: five genes have been annotated to encode sphingomyelinases in Leptospira interrogans. Such redundancy suggests that this class of genes is likely to benefit leptospiral pathogens in their interactions with the mammalian host. Surprisingly, sequence comparison with bacterial sphingomyelinases for which the crystal structures are known reveals that only one of the leptospiral homologues has the active site amino acid residues required for enzymic activity. Based on studies of other bacterial toxins, we propose that leptospiral sphingomyelinase homologues, irrespective of their catalytic activity, may possess additional molecular functions that benefit the spirochaete. Potential secretion pathways and roles in pathogenesis are discussed, including nutrient acquisition, dissemination, haemorrhage and immune evasion. Although leptospiral sphingomyelinase-like proteins are best known for their cytolytic properties, we believe that a better understanding of their biological role requires the examination of their sublytic properties as well.

The emergence of severe pulmonary hemorrhagic leptospirosis: questions to consider

Since the 1980s, the incidence of severe pulmonary hemorrhage caused by Leptospira spp. infection has increased. The mild, non-specific symptoms or the more classical form of severe disease with hepatorenal manifestations, Weil's syndrome, predominate world-wide. However, several regions of the world have seen increases in numbers of patients with pulmonary hemorrhage attributed to leptospirosis. The reasons behind the emergence of this syndrome, which carries a high mortality rate, are not known. Several avenues for future research may shed light on the mechanisms involved in development of pulmonary hemorrhage, and inform targeted therapeutics to improve outcomes. Possibilities to consider include: (1) emergence of new bacterial strains, (2) acquisition of virulence traits by strains in the endemic regions, (3) changes in underlying health of the affected human populations, and (4) increased recognition of the syndrome and better record keeping by the medical and veterinary communities. Determining the causes of emerging clinical manifestations presents challenges and opportunities for potentially life-saving research into the pathogenesis of a number of infectious diseases, including leptospirosis.

InvA protein is a Nudix hydrolase required for infection by pathogenic Leptospira in cell lines and animals

Leptospirosis caused by pathogenic species of the genus Leptospira is a re-emerging zoonotic disease, which affects a wide variety of host species and is transmitted by contaminated water. The genomes of several pathogenic Leptospira species contain a gene named invA, which contains a Nudix domain. However, the function of this gene has never been characterized. Here, we demonstrated that the invA gene was highly conserved in protein sequence and present in all tested pathogenic Leptospira species. The recombinant InvA protein of pathogenic L. interrogans strain Lai hydrolyzed several specific dinucleoside oligophosphate substrates, reflecting the enzymatic activity of Nudix in Leptospira species. Pathogenic leptospires did not express this protein in media but temporarily expressed it at early stages (within 60 min) of infection of macrophages and nephric epithelial cells. Comparing with the wild type, the invA-deficient mutant displayed much lower infectivity and a significantly reduced survival rate in macrophages and nephric epithelial cells. Moreover, the invA-deficient leptospires presented an attenuated virulence in hamsters, caused mild histopathological damage, and were transmitted in lower numbers in the urine, compared with the wild-type strain. The invA revertant, made by complementing the invA-deficient mutant with the invA gene, reacquired virulence similar to the wild type in vitro and in vivo. The LD(50) in hamsters was 1000-fold higher for the invA-deficient mutant than for the invA revertant and wild type. These results demonstrate that the InvA protein is a Nudix hydrolase, and the invA gene is essential for virulence in pathogenic Leptospira species.

First report of an anti-tumor, anti-fungal, anti-yeast and anti-bacterial hemolysin from Albizia lebbeck seeds

A monomeric 5.5-kDa protein with hemolytic activity toward rabbit erythrocytes was isolated from seeds of Albizia lebbeck by using a protocol that involved ion-exchange chromatography on Q-Sepharose and SP-Sepharose, hydrophobic interaction chromatography on Phenyl-Sepharose, and gel filtration on Superdex 75. It was unadsorbed on both Q-Sepharose and SP-Sepharose, but adsorbed on Phenyl-Sepharose. Its hemolytic activity was fully preserved in the pH range 0-14 and in the temperature range 0-100 °C, and unaffected in the presence of a variety of metal ions and carbohydrates. The hemolysin reduced viability of murine splenocytes and inhibited proliferation of MCF-7 breast cancer cells and HepG2 hepatoma cells with an IC₅₀ of 0.21, 0.97, and 1.37 μM, respectively. It impeded mycelial growth in the fungi Rhizoctonia solani with an IC₅₀ of 39 μM but there was no effect on a variety of other filamentous fungi, including Fusarium oxysporum, Helminthosporium maydis, Valsa mali and Mycosphaerella arachidicola. Lebbeckalysin inhibited growth of Escherichia coli with an IC₅₀ of 0.52 μM.

Responses of human endothelial cells to pathogenic and non-pathogenic Leptospira species

Leptospirosis is a widespread zoonotic infection that primarily affects residents of tropical regions, but causes infections in animals and humans in temperate regions as well. The agents of leptospirosis comprise several members of the genus Leptospira, which also includes non-pathogenic, saprophytic species. Leptospirosis can vary in severity from a mild, non-specific illness to severe disease that includes multi-organ failure and widespread endothelial damage and hemorrhage. To begin to investigate how pathogenic leptospires affect endothelial cells, we compared the responses of two endothelial cell lines to infection by pathogenic versus non-pathogenic leptospires. Microarray analyses suggested that pathogenic L. interrogans and non-pathogenic L. biflexa triggered changes in expression of genes whose products are involved in cellular architecture and interactions with the matrix, but that the changes were in opposite directions, with infection by L. biflexa primarily predicted to increase or maintain cell layer integrity, while L. interrogans lead primarily to changes predicted to disrupt cell layer integrity. Neither bacterial strain caused necrosis or apoptosis of the cells even after prolonged incubation. The pathogenic L. interrogans, however, did result in significant disruption of endothelial cell layers as assessed by microscopy and the ability of the bacteria to cross the cell layers. This disruption of endothelial layer integrity was abrogated by addition of the endothelial protective drug lisinopril at physiologically relevant concentrations. These results suggest that, through adhesion of L. interrogans to endothelial cells, the bacteria may disrupt endothelial barrier function, promoting dissemination of the bacteria and contributing to severe disease manifestations. In addition, supplementing antibiotic therapy with lisinopril or derivatives with endothelial protective activities may decrease the severity of leptospirosis.