Gene expression profiles of immune mediators and histopathological findings in animal models of leptospirosis: comparison between susceptible hamsters and resistant mice

Hamster and mouse CD25+CD4+ T cell responses to the C-terminal of leptospiral Ig-like protein A

Leptospirosis is a major public health problem in humans and animals worldwide. The variable carboxy-terminal domain 7-13 of LigA (LigAc) is currently the most promising immunogen for the leptospirosis subunit vaccine. Its protective evidence was investigated in susceptible hamsters whose immunity was mostly based on the knowledge of resistant mice. The difference in immunity of these two animals might be an obstacle to successful vaccine development. The protective immunity induced by LigAc was reported to be specific antibodies while T-cell-mediated immunity has never been investigated. We reported for the first time that hamsters and mice gave dissimilar T-cell responses. Mice and hamsters were divided into 3 groups: an adjuvant plus recombinant LigAc (rLigAc) immunized, an adjuvant-injected, and a negative control group. Immunizations were done three times at 2-week intervals. The rLigAc-specific IgG antibody titers in rLigAc immunized mice and hamsters were significantly higher than in the control groups but no significant difference between the animals. The percentages of hamster CD4+ T cells were significantly higher than those of mice. Mouse CD25+CD4+ T cells responded to rLigAc significantly higher than hamsters. Interestingly, the rLigAc significantly reduced the percentage of IFN-γ+CD4+ cells in mice (≅30 %) and more decrease (≅70 %) was found in hamsters. Remarkably, it also reduced considerably hamster IL-4+CD4+ T cells (≅80 %) but an extremely low decrease in mice (≅20 %). Our result indicated that mice and hamsters gave different responses to leptospiral antigens which might be the possible key that plays a role in the outcome of disease.

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.

In silico prediction and experimental evaluation of LIP3228 of pathogenic Leptospira as a potential subunit vaccine target against leptospirosis

A protein subunit vaccine comprising conserved surface-exposed outer membrane proteins (SE-OMPs) is considered a promising platform for leptospirosis vaccine. The search for novel vaccine candidates that confer high protective efficacy against leptospirosis is ongoing. The LIP3228 protein was previously identified as a conserved and abundant SE-OMP with the potential to serve as an effective vaccine candidate. However, it is crucial to explore the immunological properties of this vaccine antigen before proceeding with animal experiments. This study aimed to assess the immunological characteristics of LIP3228 through in silico prediction and to validate its immunogenicity and protective efficacy in a hamster model of acute leptospirosis. The LIP3228 vaccine candidate was predicted in silico to be immunogenic, with strong binding B-cell and T-cell epitopes. In the immune simulator, it demonstrated stable interactions with Toll-like receptors 2 (TLR2) and 4 (TLR4) and induced immune responses, potentially stimulating host immune responses in vivo. The animal experiment showed that immunization with recombinant LIP3228 protein, formulated with AddaVax adjuvant, induced high and specific IgG responses in hamsters, with IgG2 being the predominant subclass. Although no significant improvement in survival was observed compared to the negative control after a homologous challenge with virulent leptospires, the vaccinated hamsters showed a reduction in histopathological changes and severity of lesions in target organs compared to unvaccinated hamsters. These results suggest that the immunoinformatic prediction is effective in predicting immunogenicity but not protective efficacy. Therefore, LIP3228 could be considered a potential vaccine candidate for mitigating severe tissue damage. These findings may have significant implications for the development of subunit vaccines in the future.

Astragalus polysaccharides protects against acute leptospirosis by glycolysis-depended priming effect

Leptospirosis, caused by pathogenic leptospira, is a neglected infectious disease that causes acute kidney injury, bleeding disorders, and even death. People can become infected with leptospirosis when they travel into epidemic areas. Except for vaccines and antibiotics, there are few reports of other drugs about prevention of leptospirosis. In this study, we show that the natural molecular compound, astragalus polysaccharides (APS), prevents against acute leptospirosis in hamsters. Pretreatment with APS improved the survival rate of hamsters with more minor organ damage and lower leptospira burden. After pretreatment with APS, the expression levels of leptospira-induced TLR2, TLR4, and TNF-α were enhanced. The priming effect of APS was studied in vitro. The data showed that leptospira-induced expressions of TNF-α and IL-1β were higher in APS-primed peritoneal macrophage, with enhanced glucose consumption and lactate production. Transcriptomic analysis revealed that pretreatment with APS down regulated respiratory chain and mitochondrial function, up regulated glycolysis related gene expressions. After pretreatment with glycolysis inhibitor (2-DG), the priming effect of APS in leptospira infection was inhibited. Our results indicated that pretreatment with natural molecular compound, APS, protected against acute leptospirosis in hamsters by priming effect through enhanced glycolysis.

Pulmonary haemorrhage as the earliest sign of severe leptospirosis in hamster model challenged with Leptospira interrogans strain HP358

Background

Severe leptospirosis is challenging as it could evolve rapidly and potentially fatal if appropriate management is not performed. An understanding of the progression and pathophysiology of Leptospira infection is important to determine the early changes that could be potentially used to predict the severe occurrence of leptospirosis. This study aimed to understand the kinetics pathogenesis of Leptospira interrogans strain HP358 in the hamster model and identify the early parameters that could be used as biomarkers to predict severe leptospirosis.

Methodology/Principal findings

Male Syrian hamsters were infected with Leptospira interrogans strain HP358 and euthanized after 24 hours, 3, 4, 5, 6 and 7 days post-infection. Blood, lungs, liver and kidneys were collected for leptospiral detection, haematology, serum biochemistry and differential expression of pro- and anti-inflammatory markers. Macroscopic and microscopic organ damages were investigated. Leptospira interrogans strain HP358 was highly pathogenic and killed hamsters within 6–7 days post-infection. Pulmonary haemorrhage and blood vessel congestion in organs were noticed as the earliest pathological changes. The damages in organs and changes in biochemistry value were preceded by changes in haematology and immune gene expression.

Conclusion/Significance

This study deciphered haemorrhage as the earliest manifestation of severe leptospirosis and high levels of IL-1β, CXCL10/IP-10, CCL3/MIP-α, neutrophils and low levels of lymphocytes and platelets serve as a cumulative panel of biomarkers in severe leptospirosis.

As the severe form of leptospirosis could progress rapidly and be potentially fatal if not treated earlier, deciphering the pathophysiology kinetics of infection is crucial to determine the parameters of disease severity. To understand this, we challenged hamsters with the highly virulent Leptospira interrogans strain HP358. Pulmonary haemorrhage was observed as the earliest pathological change followed by liver and kidneys damages. The increased expression of IL-1β, CXCL10/IP-10, CCL3/MIP-α, high neutrophils and low lymphocytes and platelets production observed in the present study indicate that these parameters could serve as a cumulative panel of biomarkers in severe leptospirosis.

IL-10 Deficiency Protects Hamsters from Leptospira Infection

Leptospirosis is a global zoonotic disease with outcomes ranging from subclinical infection to fatal Weil's syndrome. In addition to antibiotics, some immune activators have shown protective effects against leptospirosis. However, the unclear relationship between Leptospira and cytokines has limited the development of antileptospiral immunomodulators. In this study, the particular role of interleukin-10 (IL-10) in leptospirosis was explored by using IL-10-defective (IL-10-/-) hamsters. After Leptospira infection, an improved survival rate, reduced leptospiral burden, and alleviation of organ lesions were found in IL-10-/- hamsters compared with wild-type (WT) hamsters. In addition, the levels of expression of the IL-1β, IL-6, and tumor necrosis factor alpha (TNF-α) genes and the level of nitric oxide (NO) were higher in IL-10-/- hamsters than in WT hamsters. Our results indicate that IL-10 deficiency protects hamsters from Leptospira infection.

Emergency vaccine immunization protects hamsters against acute leptospirosis

Leptospirosis, caused by pathogenic Leptospira, is a global critical zoonotic disease in terms of mortality and morbidity. Vaccines are often used to prevent leptospirosis. However, few studies have reported the therapeutic effect of a vaccine against Leptospira infection. This study demonstrates the efficacy of the emergency vaccine immunization against acute leptospirosis in hamsters. Treatment with a whole-cell vaccine (Leptospira interrogans serovar Lai) at 24 h post-infection improved the survival rate of hamsters with lower leptospiral burden and minor pathological damage to organs. The vaccine also protected against multiple Leptospira serotypes acute infection. However, the protective effect of the vaccines was lost when beginning treatment at 36 h or 48 h post-infection. These results indicated that vaccines could treat acute leptospirosis in hamsters, but only if immunization is within 24 h after infection.

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.

Genomic Association between SNP Markers and Diseases in the "Curraleiro Pé-Duro" Cattle

Susceptibility to diseases is inherited and can be transmitted between populations. Single-nucleotide polymorphism (SNPs) in genes related to immune response is associated with diseases in cattle. This study investigated SNPs in the genomic region of cytokines in 702 samples of Curraleiro Pé-Duro cattle and associated them with the occurrence of antibodies in brucellosis, leptospirosis, neosporosis, leukosis, infectious bovine rhinotracheitis (IBR), and bovine viral diarrhea (BVD) tests. DNA samples were evaluated by the kompetitive allele-specific polymerase chain reaction (KASP) method to identify polymorphisms. The gametic phase and SNP haplotypes were determined with the help of PHASE 2.1.1 software. Haplotypes were associated with serological results against Brucella abortus, Leptospira sp., Neospora caninum, leukosis, infectious rhinotracheitis, and BVD using univariate analysis followed by logistic regression. Haplotype 2 of TLR2 was present in 70% of the animals that tested positive for N. caninum infection. Haplotypes of TLR10 and TLR6 and IL10RA were more common in seronegative animals. Haplotypes related to the gene IL10RA were associated with animals negative to all infections. Curraleiro Pé-Duro cattle presented polymorphisms related to resistance to bacterial, viral, and N. caninum infections.

Immune-enhanced effect of Iris polysaccharide is protective against leptospirosis

Leptospirosis, caused by pathogenic Leptospira species, is an essential but neglected zoonosis. There are more than 300 serovars of pathogenic Leptospira, while inactivated bacteria offers only short-term serovar-specific protection. Leptospirosis treatment is mainly dependent on the use of antibiotics. However, the side effects of antibiotics and the risk of antibiotic resistance remain major problems. Thus, alternative agents which are fewer side effects on humans and efficient in leptospirosis would be welcome. Many studies have reported that polysaccharides could be used as immunostimulants in treating infection and cancer. In this study, we examined the protective effect of polysaccharides isolated from Iris against leptospirosis. To our knowledge, it is the first time to report Iris polysaccharides (IP) as an immunostimulant in treating infection. The results showed that IP treatment significantly increased the survival rate of hamsters challenged by a lethal dose of leptospires. Besides, the tissue injury and leptospiral load were reduced in IP-treated infection group compared with the untreated infection group at 4 days post-infection (p.i.). Intriguingly, IP treatment sustained intense immune response at 4 days p.i. analyzed by qPCR. The results exhibited that the gene expression of TLR2 and TLR4 was significantly increased in the group coinjected with IP and leptospires than in the infected controls. And the expression of IL-1β and TNF-α were also up-regulated after IP treatment, except the expression of IL-1β in the kidney. Our results not only broaden the medicinal value of Iris, but also provide a competent candidate for the control of Leptospira infection.

Transcriptomic signatures of exacerbated progression in leptospirosis subclinical chronic kidney disease with secondary nephrotoxic injury

High-incidence regions of leptospirosis caused by Leptospira spp. coincide with chronic kidney disease. This study investigated whether asymptomatic leptospirosis is an emerging culprit that predisposes to progressive chronic kidney disease when superimposed on secondary nephrotoxic injury. Kidney histology/function and whole transcriptomic profiles were evaluated for Leptospira-infected C57/BL6 mice with adenine-induced kidney injury. The extent of tubulointerstitial kidney lesions and expression of inflammation/fibrosis genes in infected mice with low-dose (0.1%) adenine, particularly in high-dose (0.2%) adenine-fed superimposed on Leptospira-infected mice, were significantly increased compared with mice following infection or adenine diet alone, and the findings are consistent with renal transcriptome analysis. Pathway enrichment findings showed that integrin-β- and fibronectin-encoding genes had distinct expression within the integrin-linked kinase-signaling pathway, which were upregulated in 0.2% adenine-fed Leptospira-infected mice but not in 0.2% adenine-fed mice, indicating that background subclinical Leptospiral infection indeed enhanced subsequent secondary nephrotoxic kidney injury and potential pathogenic molecules associated with secondary nephrotoxic leptospirosis. Comparative analysis of gene expression patterns with unilateral ureteric obstruction-induced mouse renal fibrosis and patients with chronic kidney disease showed that differentially expressed orthologous genes such as hemoglobin-α₂, PDZ-binding kinase, and DNA topoisomerase II-α were identified in infected mice fed with low-dose and high-dose adenine, respectively, revealing differentially expressed signatures identical to those found in the datasets and may serve as markers of aggravated kidney progression. This study indicates that background subclinical leptospirosis, when subjected to various degrees of subsequent secondary nephrotoxic injury, may predispose to exacerbated fibrosis, mimicking the pathophysiological process of progressive chronic kidney disease.NEW & NOTEWORTHY Leptospira-infected mice followed by secondary nephrotoxic injury exacerbated immune/inflammatory responses and renal fibrosis. Comparison with the murine model revealed candidates involved in the progression of renal fibrosis in chronic kidney disease (CKD). Comparative transcriptome study suggests that secondary nephrotoxic injury in Leptospira-infected mice recapitulates the gene expression signatures found in CKD patients. This study indicates that secondary nephrotoxic injury may exacerbate CKD in chronic Leptospira infection implicating in the progression of CKD of unknown etiology.

Anti-Leptospira immunoglobulin profiling in mice reveals strain specific IgG and persistent IgM responses associated with virulence and renal colonization

Leptospira interrogans is a pathogenic spirochete responsible for leptospirosis, a neglected, zoonotic reemerging disease. Humans are sensitive hosts and may develop severe disease. Some animal species, such as rats and mice can become asymptomatic renal carriers. More than 350 leptospiral serovars have been identified, classified on the basis of the antibody response directed against the lipopolysaccharide (LPS). Similarly to whole inactivated bacteria used as human vaccines, this response is believed to confer only short-term, serogroup-specific protection. The immune response of hosts against leptospires has not been thoroughly studied, which complicates the testing of vaccine candidates. In this work, we studied the immunoglobulin (Ig) profiles in mice infected with L. interrogans over time to determine whether this humoral response confers long-term protection after homologous challenge six months post-infection. Groups of mice were injected intraperitoneally with 2×10⁷ leptospires of one of three pathogenic serovars (Manilae, Copenhageni or Icterohaemorrhagiae), attenuated mutants or heat-killed bacteria. Leptospira-specific immunoglobulin (IgA, IgM, IgG and 4 subclasses) produced in the first weeks up to 6 months post-infection were measured by ELISA. Strikingly, we found sustained high levels of IgM in mice infected with the pathogenic Manilae and Copenhageni strains, both colonizing the kidney. In contrast, the Icterohaemorrhagiae strain did not lead to kidney colonization, even at high dose, and triggered a classical IgM response that peaked at day 8 post-infection and disappeared. The virulent Manilae and Copenhageni serovars elicited high levels and similar profiles of IgG subclasses in contrast to Icterohaemorrhagiae strains that stimulated weaker antibody responses. Inactivated heat-killed Manilae strains elicited very low responses. However, all mice pre-injected with leptospires challenged with high doses of homologous bacteria did not develop acute leptospirosis, and all antibody responses were boosted after challenge. Furthermore, we showed that 2 months post-challenge, mice pre-infected with the attenuated M895 Manilae LPS mutant or heat-killed bacterin were completely protected against renal colonization. In conclusion, we observed a sustained IgM response potentially associated with chronic leptospiral renal infection. We also demonstrated in mice different profiles of protective and cross-reactive antibodies after L. interrogans infection, depending on the serovar and virulence of strains.

Leptospira interrogans is a pathogenic spirochete responsible for leptospirosis, a neglected zoonotic reemerging disease. The immune response of hosts against these bacteria has not been thoroughly studied. Here, we studied over 6 months the antibody profiles in mice infected with L. interrogans and determined whether this humoral response confers long-term protection after homologous challenge six months after primary infection. Groups of mice were infected intraperitoneally with 2×10⁷ bacteria of one of three different pathogenic serovars (Manilae, Copenhageni and Icterohaemorrhagiae) and some corresponding attenuated avirulent mutants. We measured by ELISA each type of Leptospira-specific immunoglobulin (Ig) (IgA, IgM, IgG and 4 subclasses) produced in the first weeks up to 6 months post-infection and studied their cross-reactivities among serovars. We showed different profiles of antibody response after L. interrogans challenge in mice, depending on the serovar and virulence of strains. However, all infected mice, including the ones harboring low antibody levels, like mice vaccinated with an inactivated, heat-killed strain, were protected against leptospirosis after challenge. Notably, we also showed an unusual sustained IgM response associated with chronic leptospiral colonization. Altogether, this long-term immune protection is different from what is known in humans and warrants further investigation.

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.

Chemokine expression profiles in liver and kidney of mice with different susceptibilities to leptospirosis

Leptospirosis is a global disease that affects humans and animals, impacting public health and the economy. The symptoms caused by Leptospira infection can vary from mild to severe, affecting liver, lungs, and kidneys. The host-pathogen interaction in leptospirosis is still poorly understood, but there is evidence for the role of the host immune response in the pathogenesis. Chemokines are a family of structurally-related low-molecular-mass proteins (8-14 kDa) that signal the recruitment of leukocytes. In this study the profile of 22 chemokines were evaluated in liver and kidney of three mice strains with different phenotypes of susceptibility to leptospirosis. We extended our previously reported observations showing that expression of chemokines with homeostatic function, activation and chemotaxis of leukocytes are essential to modulate and to induce resistance to leptospirosis. Our findings support that an early induction of CXC chemokines in resistant BALB/c mice can be associated with the control of the infection. The correlation of chemokine expression between liver and kidney observed in BALB/c suggests that a balance of chemokine induction in the organs may contribute to resistance to 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.

Potential use of a canine whole blood culture system to evaluate the immune response to Leptospira

In susceptible hosts, protection from Leptospira infection is mediated by the innate immune response at the point of entry and humoral immunity. Thus, identifying and segregating the initial host response at the representative host-pathogen interface is needed to understand the typical outcomes of Leptospira infection, clearance, persistence, or disease. An in vitro whole blood culture system to study the overall immune response using pathogenic and non-pathogenic Leptospira strains was explored in this study. Using an ELISA, increased IL-8, TNF alpha, and IL-1 in blood samples stimulated with pathogenic and nonpathogenic Leptospira compared to unstimulated controls were detected. In RT² Profiler PCR Array assays, consistent upregulation of 22 genes and downregulation of 25 genes were observed. Few of the notable upregulated genes included BPI, CCL3, CXCL2, IL-6, IL-8, TLR1, TLR2, TLR6, and TNF and downregulated genes included, LBP, LYZ, MPO, MYD88. IFNβ was upregulated in samples treated with pathogenic Leptospira and IL-1β was upregulated in samples treated with nonpathogenic Leptospira. Toll- like Receptor signaling and expression of pattern recognition receptors were two of the five prominent canonical pathways observed. Individual deconvolution of each of the specific and significant pathways observed in this study may improve the understanding of the pathogenesis of this important zoonotic agent. The use of this system in conjunction with whole transcriptome analysis in a larger population, may unveil the robust nature of host/Leptospira interaction.

Escape of TLR5 Recognition by Leptospira spp.: A Rationale for Atypical Endoflagella

Leptospira (L.) interrogans are invasive bacteria responsible for leptospirosis, a worldwide zoonosis. They possess two periplasmic endoflagellae that allow their motility. L. interrogans are stealth pathogens that escape the innate immune recognition of the NOD-like receptors NOD1/2, and the human Toll-like receptor (TLR)4, which senses peptidoglycan and lipopolysaccharide (LPS), respectively. TLR5 is another receptor of bacterial cell wall components, recognizing flagellin subunits. To study the contribution of TLR5 in the host defense against leptospires, we infected WT and TLR5 deficient mice with pathogenic L. interrogans and tracked the infection by in vivo live imaging of bioluminescent bacteria or by qPCR. We did not identify any protective or inflammatory role of murine TLR5 for controlling pathogenic Leptospira. Likewise, subsequent in vitro experiments showed that infections with different live strains of L. interrogans and L. biflexa did not trigger TLR5 signaling. However, unexpectedly, heat-killed bacteria stimulated human and bovine TLR5, but did not, or barely induced stimulation via murine TLR5. Abolition of TLR5 recognition required extensive boiling time of the bacteria or proteinase K treatment, showing an unusual high stability of the leptospiral flagellins. Interestingly, after using antimicrobial peptides to destabilize live leptospires, we detected TLR5 activity, suggesting that TLR5 could participate in the fight against leptospires in humans or cattle. Using different Leptospira strains with mutations in the flagellin proteins, we further showed that neither FlaA nor Fcp participated in the recognition by TLR5, suggesting a role for the FlaB. FlaB have structural homology to Salmonella FliC, and possess conserved residues important for TLR5 activation, as shown by in silico analyses. Accordingly, we found that leptospires regulate the expression of FlaB mRNA according to the growth phase in vitro, and that infection with L. interrogans in hamsters and in mice downregulated the expression of the FlaB, but not the FlaA subunits. Altogether, in contrast to different bacteria that modify their flagellin sequences to escape TLR5 recognition, our study suggests that the peculiar central localization and stability of the FlaB monomers in the periplasmic endoflagellae, associated with the downregulation of FlaB subunits in hosts, constitute an efficient strategy of leptospires to escape the TLR5 recognition and the induced immune response.

Leptospirosis in cats: Current literature review to guide diagnosis and management

GLOBAL IMPORTANCE

Leptospirosis is the most widespread zoonosis worldwide. Mammals (eg, rats, horses, cows, pigs, dogs, cats and aquatic species, such as sea lions and northern elephant seals) can all be infected by leptospires. Infection in animals occurs through contact with urine or water contaminated with the bacteria. In people, the disease is acquired mainly from animal sources or through recreational activities in contaminated water.

PRACTICAL RELEVANCE

Literature on the clinical presentation of leptospirosis in cats is scarce, although it has been demonstrated that cats are susceptible to infection and are capable of developing antibodies. The prevalence of antileptospiral antibodies in cats varies from 4% to 33.3% depending on the geographical location. Urinary shedding of leptospires in naturally infected cats has been reported, with a prevalence of up to 68%. Infection in cats has been associated with the consumption of infected prey, especially rodents. Thus, outdoor cats have a higher risk of becoming infected.

CLINICAL CHALLENGES

Clinical presentation of this disease in cats is rare and it is not known what role cats have in the transmission of leptospirosis. Ongoing work is needed to characterise feline leptospirosis.

AUDIENCE

This review is aimed at all veterinarians, both general practitioners who deal with cats on a daily basis in private practice, as well as feline practitioners, since both groups face the challenge of diagnosing and treating infectious and zoonotic diseases.

EVIDENCE BASE

The current literature on leptospirosis in cats is reviewed. To date, few case reports have been published in the field, and information has mostly been extrapolated from infections in people and dogs. This review is expected to serve as a guide for the diagnosis and management of the disease in cats.

Increased inflammation with crude E. coli LPS protects against acute leptospirosis in hamsters

Leptospirosis is a worldwide zoonotic disease that causes acute kidney injury, liver disease, bleeding disorders, and even death. Treatment of the disease is largely dependent on the use of antibiotics, but recent studies on pathogenesis of leptospirosis have shown that immunomodulation may also be an effective treatment for this disease. Since the delay in inflammation correlates with higher pathogenicity of leptospira, we studied the effect of inducing inflammation on leptospirosis by using TLR4 activator LPS. In accordance with our hypothesis, treatment with LPS protected against leptospirosis by enhancing the inflammatory response in hamsters. The gene expression levels of TLR2, TLR4, NLRP3 and inflammatory factors were higher in LPS-treated group during leptospira infection in hamsters. Although the levels of NO and iNOS were higher in LPS-treated group than in Leptospira-infected group, the protective effect induced by LPS is iNOS-independent. Treatment with LPS induced higher anti-leptospira IgG level than infection with leptospira alone. Then, expressions of costimulatory molecules and maturation markers were analysed. The data showed that treatment with LPS enhanced the expression of CD40, CD80 and CD86. Our results indicate that increased inflammation induced by LPS derived from Escherichia coli (E. coli) protects against leptospirosis in hamsters.

Use of Golden Syrian Hamster as an Animal Model to Study Leptospirosis-Associated Immune Responses

Experimental infections greatly contribute to further deepen our knowledge of infectious diseases. In the case of leptospirosis, hamsters as well as gerbils and guinea pigs have been used as animal models of acute leptospirosis in studying the pathophysiology of the disease. Here we describe a typical Leptospira infection using golden Syrian hamsters. We will also present techniques we use to study the resulting bacterial burden and gene expression patterns in the host in order to decipher the innate immune response to leptospirosis.

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.

The preventable efficacy of β-glucan against leptospirosis

Leptospirosis, caused by pathogenic Leptospira species, has emerged as an important neglected zoonotic disease. Few studies have reported the preventable effects of immunoregulators, except for antibiotics, against leptospirosis. Generally, immunostimulatory agents are considered effective for enhancing innate immune responses. Many studies have found that beta-glucan (β-glucan) could be a potent and valuable immunostimulant for improving immune responses and controlling diseases. In this study, we investigated the preventable role of β-glucan against Leptospira infection in hamsters. First, β-glucan was administered 24 h prior to, during and after infection. The results showed that β-glucan increased the survival rate to 100%, alleviated tissue injury, and decreased leptospire loads in target organs. Additionally, we found using quantitative real-time PCR that application of β-glucan significantly enhanced the expression of Toll-like receptor (TLR) 2, interleukin (IL)-1β and iNOS at 2 dpi (days post infection) and reduced the increase of TLR2, IL-1β and iNOS induced by Leptospira at 5 dpi. Furthermore, to induce memory immunity, β-glucan was administered 5 days prior to infection. β-Glucan also significantly increased the survival rates and ameliorated pathological damage to organs. Moreover, we demonstrated that β-glucan-trained macrophages exhibited elevated expression of proinflammatory cytokines (IL-1β and IL-6) in vitro, indicating that β-glucan induces an enhanced inflammatory response against Leptospira infection. These results indicate that administration of β-glucan and other immunostimulants could be potential valuable options for the control of Leptospira infection.

Murine Renal Transcriptome Profiles Upon Leptospiral Infection: Implications for Chronic Kidney Diseases

Background

Leptospirosis caused by pathogenic Leptospira spp leads to kidney damage that may progress to chronic kidney disease. However, how leptospiral infections induced renal damage is unclear.

Methods

We apply microarray and next-generation sequencing technologies to investigate the first murine transcriptome-wide, leptospires-mediated changes in renal gene expression to identify biological pathways associated with kidney damage.

Results

Leptospiral genes were detected in renal transcriptomes of mice infected with Leptospira interrogans at day 28 postinfection, suggesting colonization of leptospires within the kidney with propensity of chronicity. Comparative differential gene expression and pathway analysis were investigated in renal transcriptomes of mice infected with pathogens and nonpathogens. Pathways analysis showed that Toll-like receptor signaling, complements activation, T-helper 1 type immune response, and T cell-mediated immunity/chemotaxis/proliferation were strongly associated with progressive tubulointerstitial damage caused by pathogenic leptospiral infection. In addition, 26 genes related with complement system, immune function, and cell-cell interactions were found to be significantly up-regulated in the L interrogans-infected renal transcriptome.

Conclusions

Our results provided comprehensive knowledge regarding the host transcriptional response to leptospiral infection in murine kidneys, particularly the involvement of cell-to-cell interaction in the immune response. It would provide valuable resources to explore functional studies of chronic renal damage caused by leptospiral infection.

Interaction of Leptospira with the Innate Immune System

Innate immunity encompasses immediate host responses that detect and respond to microbes. Besides recognition by the complement system (see the chapter by A. Barbosa, this volume), innate immunity concerns cellular responses. These are triggered through recognition of conserved microbial components (called MAMPs) by pattern recognition receptors (PRRs), leading, through secretion of cytokines, antimicrobial peptides, and immune mediators, to cellular recruitment and phagocytosis. Leptospira spp. are successful zoonotic pathogenic bacteria that obviously overcome the immune system of their hosts. The first part of this chapter summarizes what is known about leptospires recognition and interaction with phagocytes and other innate immune cells, and the second part describes specific interactions of leptospiral MAMPs with PRRs from the TLR and NLR families. On the one hand, pathogenic leptospires appear to escape macrophage and neutrophil phagocytosis. On the other hand, studies about PRR sensing of leptospires remain very limited, but suggest that pathogenic leptospires escape some of the PRRs in a host-specific manner, due to peculiar cell wall specificities or post-translational modifications that may impair their recognition. Further studies are necessary to clarify the mechanisms and consequences of leptospiral escape on phagocytic functions and hopefully give clues to potential therapeutic strategies aimed at restoring the defective activation of PRRs by pathogenic Leptospira spp.

Bio-accessible milk casein derived tripeptide (LLY) mediates overlapping anti- inflammatory and anti-oxidative effects under cellular (Caco-2) and in vivo milieu

Inflammation and oxidative stress are closely linked patho-physiological processes which occur concurrently in many diseased conditions. Recently, interdependence between these two processes explains the antioxidant paradox associated with failure to select appropriate agents required for prevention of diseases known to be induced by oxidative stress. Present study established the overlapping anti-inflammatory and anti-oxidative potential along with bio-accessibility of milk casein derived tripeptide (LLY). Tripeptide exhibited anti-inflammatory response under ex vivo conditions by suppressing (P<.01) mice splenocytes proliferation and modulating their cytokines (IFN-γ, IL-10 and TGF-β) with improved phagocytosis of peritoneal macrophages. Conversely, tripeptide displayed extraordinary radical scavenging ability and cellular anti-oxidative potential using chemical assays and H₂O₂ induced oxidative stress model on Caco-2 cells. Under cellular assessment, on one hand tripeptide inhibited (P<.01) intracellular ROS generation and reduced MDA and protein carbonyls but on the other also increased (P<.01) the activity of anti-oxidative enzyme, catalase without much effect on SOD and GPx. This anti-oxidative potential was further established by studying relative expression of genes (Nrf-2 and Keap1) and Nrf-2 nuclear translocation associated with anti-oxidative signaling in Caco-2 cells. Bio-accessibility of tripeptide and its intact transport across Caco-2 cell monolayer was also found to be 1.72±0.22% through PepT1 mediated transport mechanism. Besides, tripeptide displayed strong anti-oxidative and anti-inflammatory potential under in vivo conditions in mice against ethanol induced oxidative stress by elevating (P<.01) liver GSH content and by decreasing (P<.01) the activities of anti-oxidative enzymes, MDA along with reduced expression of CYP2E1, PPAR-α, TNF-α and COX-2 genes than ethanol control.

Leptospirosis Pathophysiology: Into the Storm of Cytokines

Leptospirosis is a neglected tropical zoonosis caused by pathogenic spirochetes of the genus Leptospira. Infected reservoir animals, typically mice and rats, are asymptomatic, carry the pathogen in their renal tubules, and shed pathogenic spirochetes in their urine, contaminating the environment. Humans are accidental hosts of pathogenic Leptospira. Most human infections are mild or asymptomatic. However, 10% of human leptospirosis cases develop into severe forms, including high leptospiremia, multi-organ injuries, and a dramatically increased mortality rate, which can relate to a sepsis-like phenotype. During infection, the triggering of the inflammatory response, especially through the production of cytokines, is essential for the early elimination of pathogens. However, uncontrolled cytokine production can result in a cytokine storm process, followed by a state of immunoparalysis, which can lead to sepsis and associated organ failures. In this review, the involvement of cytokine storm and subsequent immunoparalysis in the development of severe leptospirosis in susceptible hosts will be discussed. The potential contribution of major pro-inflammatory cytokines in the development of tissue lesions and systemic inflammatory response, as well as the role of anti-inflammatory cytokines in contributing to the onset of a deleterious immunosuppressive cascade will also be examined. Data from studies comparing susceptible and resistant mouse models will be included. Lastly, a concise discussion on the use of cytokines for therapeutic purposes or as biomarkers of leptospirosis severity will be provided.

LemA and Erp Y-like recombinant proteins from Leptospira interrogans protect hamsters from challenge using AddaVax™ as adjuvant

BACKGROUND

Recombinant subunit vaccines have been extensively evaluated as promising alternatives against leptospirosis. Here, we evaluated two proteins in formulations containing the adjuvant AddaVax™ as vaccine candidates for prevention and control of leptospirosis.

METHODS

Recombinant proteins rErp Y-like and rLemA were characterized by ELISA to assess their ability to bind extracellular matrix (ECM) components and fibrinogen. Groups of eight hamsters were immunized intramuscularly with rErp Y-like or rLemA mixed with a squalene-based adjuvant (AddaVax), and then vaccine efficacy was determined in terms of protection against a lethal challenge. The humoral immune response was determined by ELISA, and the evidence of sub-lethal infection was evaluated by histopathology and kidney culture.

RESULTS

rLemA protein binds laminin, fibrinogen, and collagen type IV, while rErp Y-like interacts with fibrinogen. Significant protection was achieved for rLemA and rErp Y-like vaccines, which showed 87.5% and 62.5% survivals, respectively. On day 28, the humoral immune response was significantly greater in the vaccine groups as compared to that in the control group, and the response was predominantly based on IgG2/3. The surviving animals showed negative results in culture isolation but presented with tissue lesions in the lungs and kidneys.

CONCLUSION

Cumulatively, our findings suggest that LemA and Erp Y-like proteins act as adhesins and are able to protect against mortality, but not against tissue lesions. Moreover, AddaVax is a novel adjuvant with potential for improving the immunogenicity of leptospiral vaccines.

Inbred Rats as a Model to Study Persistent Renal Leptospirosis and Associated Cellular Immune Responsiveness

Pathogenic species of Leptospira cause leptospirosis, a bacterial zoonotic disease with a global distribution affecting over one million people annually. Rats are regarded as one of the most significant reservoir hosts of infection for human disease, and in the absence of clinical signs of infection, excrete large numbers of organisms in their urine. A unique biological equilibrium exists between pathogenic leptospires and reservoir hosts of infection, but surprisingly, little is known concerning the host's cellular immune response that facilitates persistent renal colonization. To address this deficiency, we established and applied an immunocompetent inbred rat model of persistent renal colonization; leptospires were detected in urine of experimentally infected rats by 3 weeks post-infection and remained positive until 8 weeks post-infection. However, there was little, if any, evidence of inflammation in colonized renal tubules. At 8 weeks post-infection, a robust antibody response was detected against lipopolysaccharide and protein outer membrane (OM) components. Purified B and T cells derived from the spleen of infected and non-infected rats proliferated in response to stimulation with 0.5 μg of OM fractions of Leptospira, including CD4+ T cells, which comprised 40% of proliferating cells, compared to 25% in non-infected controls. However, analysis of gene expression did not determine which immunoregulatory pathways were activated. Lymphocytes purified from the lymph node draining the site of colonization, the renal lymph node, also showed an increase in percentage of proliferating B and T cells. However, in contrast to a phenotype of 40% CD4+ T cells in the spleen, the phenotype of proliferating T cells in the renal lymph node comprised 65% CD4+ T cells. These results confirm that the renal lymph node, the local lymphoid organ, is a dominant site containing Leptospira reactive CD4+ T cells and highlight the need to consider the local, vs. systemic, immune responses during renal colonization infection. The use of inbred immunocompetent rats provides a novel tool to further elucidate those pathophysiological pathways that facilitate the unique biological equilibrium observed in reservoir hosts of leptospirosis.

High level of IL-10 expression in the blood of animal models possibly relates to resistance against leptospirosis

Leptospirosis is a severe zoonosis which immunopathogenesis is poorly understood. We evaluated correlation between acute form of the disease and the ratio of the anti-inflammatory cytokine IL-10 to the pro-inflammatory TNF-α and IL-1β expression during the early phase of infection comparing resistant mice and susceptible hamsters infected with two different species of virulent Leptospira. The IL-10/TNF-α and IL-10/IL-1β expression ratios were higher in mouse compared to hamster independently of the Leptospira strain, suggesting a preponderant role of the host response and notably these cytokines in the clinical expression and survival to leptospirosis. Using an IL-10 neutralization strategy in Leptospira-infected mouse model, we also showed evidence of a possible role of this cytokine on host susceptibility, bacterial clearance and on regulation of cytokine gene expression.

Leptospira interrogans causes quantitative and morphological disturbances in adherens junctions and other biological groups of proteins in human endothelial cells

Pathogenic Leptospira transmits from animals to humans, causing the zoonotic life-threatening infection called leptospirosis. This infection is reported worldwide with higher risk in tropical regions. Symptoms of leptospirosis range from mild illness to severe illness such as liver damage, kidney failure, respiratory distress, meningitis, and fatal hemorrhagic disease. Invasive species of Leptospira rapidly disseminate to multiple tissues where this bacterium damages host endothelial cells, increasing vascular permeability. Despite the burden in humans and animals, the pathogenic mechanisms of Leptospira infection remain to be elucidated. The pathogenic leptospires adhere to endothelial cells and permeabilize endothelial barriers in vivo and in vitro. In this study, human endothelial cells were infected with the pathogenic L. interrogans serovar Copenhageni or the saprophyte L. biflexa serovar Patoc to investigate morphological changes and other distinctive phenotypes of host cell proteins by fluorescence microscopy. Among those analyzed, 17 proteins from five biological classes demonstrated distinctive phenotypes in morphology and/or signal intensity upon infection with Leptospira. The affected biological groups include: 1) extracellular matrix, 2) intercellular adhesion molecules and cell surface receptors, 3) intracellular proteins, 4) cell-cell junction proteins, and 5) a cytoskeletal protein. Infection with the pathogenic strain most profoundly disturbed the biological structures of adherens junctions (VE-cadherin and catenins) and actin filaments. Our data illuminate morphological disruptions and reduced signals of cell-cell junction proteins and filamentous actin in L. interrogans-infected endothelial cells. In addition, Leptospira infection, regardless of pathogenic status, influenced other host proteins belonging to multiple biological classes. Our data suggest that this zoonotic agent may damage endothelial cells via multiple cascades or pathways including endothelial barrier damage and inflammation, potentially leading to vascular hyperpermeability and severe illness in vivo. This work provides new insights into the pathophysiological mechanisms of Leptospira infection.

Doxycycline Attenuates Leptospira-Induced IL-1β by Suppressing NLRP3 Inflammasome Priming

Doxycycline (Dox), a semisynthetic antibiotic, has been reported to exert multiple immunomodulatory effects. Treatment with Dox has a satisfactory curative effect against leptospirosis. In addition to its antibacterial action, we supposed that Dox also modulated immune response in controlling leptospira infection. Using J774A.1 mouse macrophages, the effects of Dox on protein and mRNA levels of IL-1β and TNF-α were investigated after infection with live or sonicated Leptospira interrogans serovar Lai strain Lai (56601). Specifically, the level of IL-1β but not TNF-α was sharply decreased when treated with Dox in leptospira-infected macrophages. Western blot analysis showed that Dox suppressed the activation of leptospira-induced MAPK and NF-κB signaling pathways. Using NLRP3-deficient and NLRC4-deficient mice, the data showed that the expression of leptospira-induced IL-1β was mainly dependent on the presence of NLRP3 inflammasome in macrophages. Meanwhile, Dox suppressed leptospira-induced NLRP3 inflammasome priming with the upregulation of the Na/K-ATPase Pump β1 subunit. The inhibition effect of Dox on IL-1β was also conspicuous in cells with lipopolysaccharide and ATP stimulation. These results were confirmed in vivo, as peritoneal fluids of mice and organs of hamsters expressed less IL-1β after treatment of leptospiral infection with Dox. Our results indicated that Dox also modulated immune response to attenuate leptospira-induced IL-1β by suppressing p38, JNK, p65, and NLRP3 inflammasome priming.

A new model of self-resolving leptospirosis in mice infected with a strain of Leptospira interrogans serovar Autumnalis harboring LPS signaling only through TLR4

Leptospirosis is an emerging worldwide zoonosis caused by pathogenic Leptospira spp. Our understanding of leptospirosis pathogenesis and host immune response remains limited, while mechanistic studies are hindered by a lack of proper animal models and immunological reagents. Here we established a murine model of acute and self-resolving leptospirosis by infecting 10-week-old C57BL/6 mice with Leptospira interrogans serovar Autumnalis strain 56606v, with characteristic manifestations including jaundice as well as subcutaneous and pulmonary bleeding, but no kidney lesions. We also verified that the lipopolysaccharide (LPS) of strain 56606v signaled through a TLR4-dependent pathway in murine bone marrow-derived macrophages (BMDMs), rather than the previously reported TLR2. In addition, upon infection with Leptospira strain 56606v, TLR4^−/− C57BL/6 mice presented more severe jaundice and liver injury as well as higher bacterial loads than WT mice but milder pulmonary hemorrhaging. Molecular studies showed that leptospirosis-related bleeding coincides with the temporal kinetics of iNOS production, while jaundice and liver injury are probably due to insufficiently controlled bacterial loads in the liver. These results suggested that TLR4 is essential in mediating host leptospiral clearance and, to some extent, is associated with pulmonary and subcutaneous hemorrhage, probably through downstream inflammatory mediators, iNOS in particular. Overall, our murine model using immunocompetent mice might facilitate future studies into the pathogenesis of jaundice and bleeding in leptospirosis. Meanwhile, our study suggests the prospect of combining antibiotics and immunosuppressants in the treatment of severe leptospirosis presenting with pulmonary hemorrhage.

Il-10 deficient mice express IFN-γ mRNA and clear Leptospira interrogans from their kidneys more rapidly than normal C57BL/6 mice

Leptospira interrogans (L. interrogans), the causative agent of leptospirosis, is a widespread zoonotic spirochete that lives a dual lifestyle. L. interrogans infects mice, rats, and wildlife in a persistent and asymptomatic fashion, while also causing productive and acute infections in other mammals such as humans and hamsters. Infections in humans can be fatal, accompanied by a cytokine storm and shock-like symptoms. Production of IL-10 has been noted in both rodent and human infections which has led a number of investigators to hypothesize that IL-10 plays a role in the pathogenesis of this disease. To test this hypothesis we have compared bacteremia and the cytokine response of normal and IL-10 deficient C57Bl/6 mice following ip infection with L. interrogans. In normal mice bacterial 16s mRNA was detected in both lung and kidney tissues within a day after infection. Levels of 16s mRNA then dropped in both organs with complete elimination from the lung by day 3 but persistence in the kidney for 7days after infection. In contrast, in IL-10 deficient mice, the organism was eliminated more rapidly from the kidney. We found that infection of both control and IL-10 deficient mice produced similar levels of a number of pro-inflammatory cytokine mRNAs. On the other hand, IFN-γ mRNA was only induced in IL-10 deficient mice. These results support the hypothesis that L. interrogans ability to induce IL-10, which in turn prevents production of IFN-γ and inhibits T cell immunity, may contribute to the persistent growth of this microorganism in the murine kidney.

Low-dose norfloxacin and ciprofloxacin therapy worsen leptospirosis in hamster

Antibiotics play an important role in the treatment of leptospirosis. Many antibiotics at appropriate concentrations improved the survival rate and alleviated tissue injury, while, when dosing strategies fall below subtherapeutic levels, worse therapeutic effects are seen. In the present study, we investigated the efficacy of low-dose norfloxacin (10, 20 and 30 mg/kg) and ciprofloxacin (1, 2 and 5 mg/kg) against leptospirosis in a hamster model using Leptospira interrogans serovar Icterohaemorrhagiae. The histopathology and bacterial loads of target organs (liver, kidney and lung) were also studied by treatment with norfloxacin at the dose of 10 mg/kg in this model. Using RT-PCR, the expression of inflammatory factor IL-1β and TNF-α was analyzed by comparing the norfloxacin and untreated group. All untreated animals, serving as a negative control, displayed 50% survival rate, while hamsters treated with norfloxacin at the dose of 10 and 20 mg/kg and ciprofloxacin at the dose of 1 and 2 mg/kg showed a lower survival rate than the untreated group. Furthermore, norfloxacin at the dose of 10 mg/kg increased bacterial loads and aggravated tissue injury of target organs. The delayed induction of IL-1β and TNF-α was found in tissues of norfloxacin group. Our study indicates an increased risk associated with low-dose norfloxacin and ciprofloxacin in leptospirosis.

Toll-Like Receptor 2 Agonist Pam3CSK4 Alleviates the Pathology of Leptospirosis in Hamster

Leptospirosis, caused by pathogenic spirochetes, is a zoonotic disease of global importance. The detailed pathogenesis of leptospirosis is still unclear, which limits the ideal treatment of leptospirosis. In this study, we analyzed the expression of Toll-like receptor 2 (TLR2) and TLR4 in target organs of both resistant mice and susceptible hamsters after Leptospira interrogans serovar Autumnalis infection. TLR2 but not TLR4 transcripts in mouse organs contrasted with delayed induction and overexpression in hamster organs. Coinjection of leptospires and the TLR2 agonist Pam3CSK4 into hamsters improved their survival rate, alleviated tissue injury, and decreased the abundance of leptospires in target organs. The production of interleukin-10 (IL-10) from tissues was enhanced in hamsters of the group coinjected with leptospires and Pam3CSK4 compared with the leptospira-injected group. Similarly, IL-10 levels in TLR2-deficient mice were lower than those in wild-type mice. A high ratio of IL-10/tumor necrosis factor alpha (TNF-α) levels was found in both infected wild-type mice and hamsters coinjected with leptospires and Pam3CSK4. Moreover, TLR2-dependent IL-10 expression was detected in peritoneal macrophages after leptospira infection. Our data demonstrate that coinjection of leptospires and Pam3CSK4 alleviates the pathology of leptospirosis in hamsters; this effect may result from the enhanced expression of TLR2-dependent IL-10.

Cytokine and Chemokine Expression in Kidneys during Chronic Leptospirosis in Reservoir and Susceptible Animal Models

Leptospirosis is caused by pathogenic spirochetes of the genus Leptospira. Humans can be infected after exposure to contaminated urine of reservoir animals, usually rodents, regarded as typical asymptomatic carriers of leptospires. In contrast, accidental hosts may present an acute form of leptospirosis with a range of clinical symptoms including the development of Acute Kidney Injury (AKI). Chronic Kidney Disease (CKD) is considered as a possible AKI-residual sequela but little is known about the renal pathophysiology consequent to leptospirosis infection. Herein, we studied the renal morphological alterations in relation with the regulation of inflammatory cytokines and chemokines, comparing two experimental models of chronic leptospirosis, the golden Syrian hamster that survived the infection, becoming carrier of virulent leptospires, and the OF1 mouse, a usual reservoir of the bacteria. Animals were monitored until 28 days after injection with a virulent L. borgpetersenii serogroup Ballum to assess chronic infection. Hamsters developed morphological alterations in the kidneys with tubulointerstitial nephritis and fibrosis. Grading of lesions revealed higher scores in hamsters compared to the slight alterations observed in the mouse kidneys, irrespective of the bacterial load. Interestingly, pro-fibrotic TGF-β was downregulated in mouse kidneys. Moreover, cytokines IL-1β and IL-10, and chemokines MIP-1α/CCL3 and IP-10/CXCL-10 were significantly upregulated in hamster kidneys compared to mice. These results suggest a possible maintenance of inflammatory processes in the hamster kidneys with the infiltration of inflammatory cells in response to bacterial carriage, resulting in alterations of renal tissues. In contrast, lower expression levels in mouse kidneys indicated a better regulation of the inflammatory response and possible resolution processes likely related to resistance mechanisms.

The adaptor molecule Trif contributes to murine host defense during Leptospiral infection

Leptospirosis is a zoonotic disease and is caused by pathogenic species of the Leptospira genus, including Leptospira interrogans (L. interrogans). Humans, domestic and wild animals are susceptible to acute or chronic infection. The innate immune response is a critical defense mechanism against Leptospira interrogans, and has been investigated in mouse models. Murine Toll-like receptors (TLRs) have been shown to be key factors in sensing and responding to L. interrogans infection. Specifically, TLR2, TLR4 and the TLR adaptor molecule MyD88 are essential for host defense against L. interrogans; however, the role of the TLR adaptor molecule TIR-domain-containing adaptor-inducing interferon β (TRIF) in the response to L. interrogans has not been previously determined. In the present study, TRIF was found to play an important role during leptospiral infection. Following challenge with L. interrogans, Trif(-/-) mice exhibited delayed weight gain compared to wild-type mice. Moreover, Trif(-/-) mice exhibited an increase in L. interrogans burden in the kidneys, lungs, and blood at early time points (less than 7days post infection). Multiple components of the innate immune responses were dampened in response to leptospiral infection including transcription and production of cytokines, and the humoral response, which suggested that TRIF contributes to expression and production of cytokines important for the host defense against L. interrogans.

Expression Profile of Cytokines and Enzymes mRNA in Blood Leukocytes of Dogs with Leptospirosis and Its Associated Pulmonary Hemorrhage Syndrome

Background

Dogs with leptospirosis show similar organ manifestations and disease course as human patients, including acute kidney injury and pulmonary hemorrhage, making this naturally-occurring infection a good animal model for human leptospirosis. Expression patterns of cytokines and enzymes have been correlated with disease manifestations and clinical outcome in humans and animals. The aim of this study was to describe mRNA expression of pro- and anti-inflammatory mediators in canine leptospirosis and to compare it with other renal diseases to identify patterns characterizing the disease and especially its pulmonary form.

Methodology and Principal Findings

The mRNA abundance of cytokines (IL-1α, IL-1β, IL-8, IL-10, TNF-α, TGF-β) and enzymes (5-LO, iNOS) was measured prospectively in blood leukocytes from 34 dogs with severe leptospirosis and acute kidney injury, including 22 dogs with leptospirosis-associated pulmonary hemorrhages. Dogs with leptospirosis were compared to 14 dogs with acute kidney injury of other origin than leptospirosis, 8 dogs with chronic kidney disease, and 10 healthy control dogs. Canine leptospirosis was characterized by high 5-LO and low TNF-α expression compared to other causes of acute kidney injury, although the decreased TNF-α expression was also seen in chronic kidney disease. Leptospirosis-associated pulmonary hemorrhage was not characterized by a specific pattern, with only mild changes noted, including increased IL-10 and decreased 5-LO expression on some days in affected dogs. Fatal outcome from pulmonary hemorrhages was associated with low TNF-α, high IL-1β, and high iNOS expression, a pattern possibly expressed also in dogs with other forms of acute kidney injury.

Conclusion

The patterns of cytokine and enzyme expression observed in the present study indicate a complex pro- and anti-inflammatory response to the infection with leptospires. The recognition of these signatures may be of diagnostic and prognostic relevance for affected individuals and they may indicate options for newer therapies targeting the identified pathways.

Tissue apoptosis in mice infected with Leptospira interrogans serovar Icterohaemorrhagiae

BACKGROUND

This investigation aimed to evaluate the occurrence of some apoptotic features induced by Leptospira interrogans serovar Icterohaemorrhagiae infection in young BALB/c mice during 2, 4, 7, 10, 14 and 21 days post-infection (dpi).

METHODS

The animals were euthanized and lung, liver and kidneys were harvested to histopathology analysis and immunohistochemistry to caspase-3 antigen detection was performed.

RESULTS

Chromatin condensation in kidney and liver tissues, but not in lung tissue, was observed. Caspase-3 reactive cells, mainly characterized as renal epithelial cells, were detected in the days 14 and 21 at high levels when compared to days 2, 4 and 7 (p = 0.025; p < 0.05). Lung sections revealed caspase-3 labeled alveolar cells in 10 and 14 days post-infection was higher than observed at 7 days (p = 0.0497; p < 0.05). Liver sections demonstrated reactive cells at a highest level at 14 and 21 days post-infection when comparison to 2, 4, 7 and 10 days (p = 0.0069; p < 0.05).

CONCLUSIONS

Our results suggest that infection of L. interrogans induce in kidney, liver and lung an activation of apoptosis mediated by caspase-3 dependent pathway in later phases of infectious process.

Comparison of Bacterial Burden and Cytokine Gene Expression in Golden Hamsters in Early Phase of Infection with Two Different Strains of Leptospira interrogans

Leptospirosis, a zoonotic infection with worldwide prevalence, is caused by pathogenic spirochaetes of Leptospira spp., and exhibits an extremely broad clinical spectrum in human patients. Although previous studies indicated that specific serovars or genotypes of Leptospira spp. were associated with severe leptospirosis or its outbreak, the mechanism underlying the difference in virulence of the various Leptospira serotypes or genotypes remains unclear. The present study addresses this question by measuring and comparing bacterial burden and cytokine gene expression in hamsters infected with strains of two L. interrogans serovars Manilae (highly virulent) and Hebdomadis (less virulent). The histopathology of kidney, liver, and lung tissues was also investigated in infected hamsters. A significantly higher bacterial burden was observed in liver tissues of hamsters infected with serovar Manilae than those infected with serovar Hebdomadis (p < 0.01). The average copy number of the leptospiral genome was 1,302 and 20,559 in blood and liver, respectively, of hamsters infected with serovar Manilae and 1,340 and 4,896, respectively, in hamsters infected with serovar Hebdomadis. The expression levels of mip1alpha in blood; tgfbeta, il1beta, mip1alpha, il10, tnfalpha and cox2 in liver; and tgfbeta, il6, tnfalpha and cox2 in lung tissue were significantly higher in hamsters infected with serovar Manilae than those infected with serovar Hebdomadis (p < 0.05). In addition, infection with serovar Manilae resulted in a significantly larger number of hamsters with tnfalpha upregulation (p = 0.04). Severe distortion of tubular cell arrangement and disruption of renal tubules in kidney tissues and hemorrhage in lung tissues were observed in Manilae-infected hamsters. These results demonstrate that serovar Manilae multiplied more efficiently in liver tissues and induced significantly higher expression of genes encoding pro- and anti-inflammatory cytokines than serovar Hebdomadis even in tissues for which a significant difference in leptospiral load was not observed. In addition, our results suggest a serovar Manilae-specific mechanism responsible for inducing severe damage in kidneys and hemorrhage in lung.

Experimental Hamster Infection with a Strain of Leptospira borgpetersenii Ballum Isolated from a Reservoir Mouse in New Caledonia

Leptospirosis is a neglected zoonosis caused by pathogenic Leptospira. In this study, we characterized the virulence of isolate B3-13S obtained from a wild mouse (Mus musculus) captured in New Caledonia, subsequently identified as a bacterium belonging to the L. borgpetersenii serogroup Ballum. Hamsters were infected with an intraperitoneal injection of 2 × 10(8) bacteria, resulting in severe histopathological organ damages consistent with tissue lesions previously observed with other strains. Hamsters were also injected with 1 × 10(8) or 5 × 10(7) bacteria and animals that recovered showed renal carriage of leptospires in concentrations similar to the bacterial load quantified in mouse kidneys, with urinary shedding of bacteria up to 4 weeks postinfection. The serogroup Ballum is increasingly reported in human leptospirosis, and these results highlight the use of the B3-13S isolate for the development of models resulting in either severe acute or chronic forms of the infection, allowing for better characterization of its pathogenesis.

Leptospira interrogans reduces fibrin clot formation by modulating human thrombin activity via exosite I

Pathogenic bacteria of the genus Leptospira are the etiological agents of leptospirosis, a disease that affects humans and animals worldwide. Although there are an increasing number of studies on the biology of Leptospira, the mechanisms of pathogenesis are not yet understood. We report in this work that Leptospira interrogans FIOCRUZ L1-130 virulent, M20 culture attenuated and the saprophyte L. biflexa Patoc 1 strains do not bind prothrombin. Leptospiral binding to thrombin was detected with the virulent, followed by culture-attenuated M20, and practically none was observed with the saprophyte strain. The interaction of Leptospira with thrombin mostly occurs via exosite I, with a minor participation of catalytic site, as determined by employing the thrombin inhibitors hirugen, hirudin and argatroban. Leptospira interrogans binding to thrombin inhibits its catalytic activity reducing fibrin clot formation in thrombin-catalyzed reaction of fibrinogen. This inhibition was more efficient with the virulent FIOCRUZ L1-130 than with the M20 culture attenuated, while none was seen with the saprophyte strain, suggesting that this binding might be important for bacterial virulence. This is the first study reporting the binding of pathogenic Leptospira to thrombin promoting a decrease in fibrin clotting that could lead to hemorrhage, helping bacteria dissemination.

Host response to leptospira infection

Pathogenic Leptospira has the capacity to infect a broad range of mammalian hosts. Leptospirosis may appear as an acute, potentially fatal infection in accidental hosts, or progress into a chronic, largely asymptomatic infection in natural maintenance hosts. The course that Leptospira infection follows is dependent upon poorly understood factors, but is heavily influenced by both the host species and bacterial serovar involved in infection. Recognition of pathogen-associated molecular patterns (PAMPs) by a variety of host pattern recognition receptors (PRRs) activates the host immune system. The outcome of this response may result in bacterial clearance, limited bacterial colonization of a few target organs, principally the kidney, or induction of sepsis as the host succumbs to infection and dies. This chapter describes current knowledge of how the host recognizes Leptospira and responds to infection using innate and acquired immune responses. Aspects of immune-mediated pathology and pathogen strategies to evade the host immune response are also addressed.

Severity markers in severe leptospirosis: a cohort study

We aimed to evaluate parameters for their value as severity markers in hospitalized leptospirosis patients. We recruited 47 informed adult consenting patients and assessed a number of clinical, hematological, biochemical, and biological variables. Patients were sorted according to severity based on fatality or the requirement of mechanical ventilation or dialysis; the parameters studied were compared between groups on inclusion and the next day. Beside septic shock presentation or a high severity score (Simplified Acute Physiology Score; SAPS II), increased lactate, total bilirubin, lipase, and AST/ALT ratio or a decreased cytokines IL-10/TNF-α ratio were all significantly associated with severity. The gene expression of the IL-1 receptor antagonist IL-1ra, IL-1α, and the long pentraxin PTX-3 were also transcribed at higher levels in most severe cases. Patients could rapidly improve or deteriorate, highlighting the need for a new assessment the next day. Our results add to the limited body of knowledge about severity markers in leptospirosis. They also suggest that patients should be reassessed the next day before being possibly discharged from the hospital. Further studies are needed in order to confirm relevant and reliable prognostic parameters in leptospirosis that would be helpful for the purpose of triage.

Decay-accelerating factor 1 deficiency exacerbates leptospiral-induced murine chronic nephritis and renal fibrosis

Leptospirosis is a global zoonosis caused by pathogenic Leptospira, which can colonize the proximal renal tubules and persist for long periods in the kidneys of infected hosts. Here, we characterized the infection of C57BL/6J wild-type and Daf1^−/− mice, which have an enhanced host response, with a virulent Leptospira interrogans strain at 14 days post-infection, its persistence in the kidney, and its link to kidney fibrosis at 90 days post-infection. We found that Leptospira interrogans can induce acute moderate nephritis in wild-type mice and is able to persist in some animals, inducing fibrosis in the absence of mortality. In contrast, Daf1^−/− mice showed acute mortality, with a higher bacterial burden. At the chronic stage, Daf1^−/− mice showed greater inflammation and fibrosis than at 14 days post-infection and higher levels at all times than the wild-type counterpart. Compared with uninfected mice, infected wild-type mice showed higher levels of IL-4, IL-10 and IL-13, with similar levels of α-smooth muscle actin, galectin-3, TGF-β1, IL-17, IFN-γ, and lower IL-12 levels at 90 days post-infection. In contrast, fibrosis in Daf1^−/− mice was accompanied by high expression of α-smooth muscle actin, galectin-3, IL-10, IL-13, and IFN-γ, similar levels of TGF-β1, IL-12, and IL-17 and lower IL-4 levels. This study demonstrates the link between Leptospira-induced murine chronic nephritis with renal fibrosis and shows a protective role of Daf1.

Induction of boosted immune response in mice by leptospiral surface proteins expressed in fusion with DnaK

Leptospirosis is an important global disease of human and veterinary concern. Caused by pathogenic Leptospira, the illness was recently classified as an emerging infectious disease. Currently available veterinarian vaccines do not induce long-term protection against infection and do not provide cross-protective immunity. Several studies have suggested the use of DnaK as an antigen in vaccine formulation, due to an exceptional degree of immunogenicity. We focused on four surface proteins: rLIC10368 (Lsa21), rLIC10494, rLIC12690 (Lp95), and rLIC12730, previously shown to be involved in host-pathogen interactions. Our goal was to evaluate the immunogenicity of the proteins genetically fused with DnaK in animal model. The chosen genes were amplified by PCR methodology and cloned into pAE, an E. coli vector. The recombinant proteins were expressed alone or in fusion with DnaK at the N-terminus. Our results demonstrate that leptospiral proteins fused with DnaK have elicited an enhanced immune response in mice when compared to the effect promoted by the individual proteins. The boosted immune effect was demonstrated by the production of total IgG, lymphocyte proliferation, and significant amounts of IL-10 in supernatant of splenocyte cell cultures. We believe that this approach could be employed in vaccines to enhance presentation of antigens of Leptospira to professional immune cells.

A model system for studying the transcriptomic and physiological changes associated with mammalian host-adaptation by Leptospira interrogans serovar Copenhageni

Leptospirosis, an emerging zoonotic disease with worldwide distribution, is caused by spirochetes belonging to the genus Leptospira. More than 500,000 cases of severe leptospirosis are reported annually, with >10% of these being fatal. Leptospires can survive for weeks in suitably moist conditions before encountering a new host. Reservoir hosts, typically rodents, exhibit little to no signs of disease but shed large numbers of organisms in their urine. Transmission occurs when mucosal surfaces or abraded skin come into contact with infected urine or urine-contaminated water or soil. In humans, leptospires can cause a variety of clinical manifestations, ranging from asymptomatic or mild fever to severe icteric (Weil's) disease and pulmonary haemorrhage. Currently, little is known about how Leptospira persist within a reservoir host. Prior in vitro studies have suggested that leptospires alter their transcriptomic and proteomic profiles in response to environmental signals encountered during mammalian infection. However, no study has examined gene expression by leptospires within a mammalian host-adapted state. To obtain a more faithful representation of how leptospires respond to host-derived signals, we used RNA-Seq to compare the transcriptome of L. interrogans cultivated within dialysis membrane chambers (DMCs) implanted into the peritoneal cavities of rats with that of organisms grown in vitro. In addition to determining the relative expression levels of “core” housekeeping genes under both growth conditions, we identified 166 genes that are differentially-expressed by L. interrogans in vivo. Our analyses highlight physiological aspects of host adaptation by leptospires relating to heme uptake and utilization. We also identified 11 novel non-coding transcripts that are candidate small regulatory RNAs. The DMC model provides a facile system for studying the transcriptional and antigenic changes associated with mammalian host-adaption, selection of targets for mutagenesis, and the identification of previously unrecognized virulence determinants.

Leptospirosis, a global disease caused by the unusual bacterium Leptospira, is transmitted from animals to humans. Pathogenic species of Leptospira are excreted in urine from infected animals and can continue to survive in suitable environments before coming into contact with a new reservoir or accidental host. Leptospires have an inherent ability to survive a wide range of conditions encountered in nature during transmission and within mammals. However, we know very little about the regulatory pathways and gene products that promote mammalian host adaptation and enable leptospires to establish infection. In this study, we used a novel system whereby leptospires are cultivated in dialysis membrane chambers implanted into the peritoneal cavities of rats to compare the gene expression profiles of mammalian host-adapted and in vitro-cultivated organisms. In addition to providing a facile system for studying the transcriptional and physiologic changes leptospires undergo during mammalian infection, our data provide a rational basis for selecting new targets for mutagenesis.

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.