Pathogenic Leptospira spp. shed in the urine of reservoir hosts into freshwater can be transmitted to a susceptible host through skin abrasions or mucous membranes causing leptospirosis. The infection process involves the ability of leptospires to adhere to cell surface and extracellular matrix components, a crucial step for dissemination and colonization of host tissues. Therefore, the elucidation of novel mediators of host-pathogen interaction is important in the discovery of virulence factors involved in the pathogenesis of leptospirosis. In this study, we assess the functional roles of transmembrane outer membrane proteins OmpL36 (LIC13166), OmpL37 (LIC12263), and OmpL47 (LIC13050), which we recently identified on the leptospiral surface. We determine the capacity of these proteins to bind to host tissue components by enzyme-linked immunosorbent assay. OmpL37 binds elastin preferentially, exhibiting dose-dependent, saturating binding to human skin (Kd, 104±19 nM) and aortic elastin (Kd, 152±27 nM). It also binds fibrinogen (Kd, 244±15 nM), fibrinogen fragment D (Kd, 132±30 nM), plasma fibronectin (Kd, 359±68 nM), and murine laminin (Kd, 410±81 nM). The binding to human skin elastin by both recombinant OmpL37 and live Leptospira interrogans is specifically enhanced by rabbit antiserum for OmpL37, suggesting the involvement of OmpL37 in leptospiral binding to elastin and also the possibility that host-generated antibodies may promote rather than inhibit the adherence of leptospires to elastin-rich tissues. Further, we demonstrate that OmpL37 is recognized by acute and convalescent leptospirosis patient sera and also by Leptospira-infected hamster sera. Finally, OmpL37 protein is detected in pathogenic Leptospira serovars and not in saprophytic Leptospira. Thus, OmpL37 is a novel elastin-binding protein of pathogenic Leptospira that may be promoting attachment of Leptospira to host tissues.
Leptospirosis is a potentially fatal disease in humans and livestock caused by Leptospira bacteria. Effective antibiotic treatment depends on timely, accurate diagnosis. However, current diagnostic and vaccine options are limited by their specificity for the lipid-sugar coat of leptospires, which varies among 200 serum-reactive groups. We aim to understand how leptospires infect a host, and in turn, to develop broadly effective diagnostic and immunization products. We recently described OmpL37, a new protein on the surface of leptospires. Here, we show it is made by pathogenic strains, suggesting it can be a target for detecting and protecting against a wide range of Leptospira. Moreover, leptospirosis patients and hamsters infected with leptospires make antibodies against OmpL37. Purified OmpL37 binds host proteins, including human elastin, fibrinogen, fibronectin, and mouse laminin. Although other leptospiral proteins bind multiple host proteins, OmpL37 has novel preferential affinity for skin and aorta elastin, suggesting a role in a common route of transmission through abraded skin and exposed blood vessels. Indeed, OmpL37 binding and leptospiral attachment to elastin are both enhanced by OmpL37 antiserum, further implicating a possible role for OmpL37 during infection. Thus, OmpL37 may mediate host attachment and has potential clinical application with a broad range of Leptospira.
Leptospira (L.) interrogans are bacteria responsible for a worldwide reemerging zoonosis. Some animals asymptomatically carry L. interrogans in their kidneys and excrete bacteria in their urine, which contaminates the environment. Humans are infected through skin contact with leptospires and develop mild to severe leptospirosis. Previous attempts to construct fluorescent or bioluminescent leptospires, which would permit in vivo visualization and investigation of host defense mechanisms during infection, have been unsuccessful. Using a firefly luciferase cassette and random transposition tools, we constructed bioluminescent chromosomal transformants in saprophytic and pathogenic leptospires. The kinetics of leptospiral dissemination in mice, after intraperitoneal inoculation with a pathogenic transformant, was tracked by bioluminescence using live imaging. For infective doses of 106 to 107 bacteria, we observed dissemination and exponential growth of leptospires in the blood, followed by apparent clearance of bacteria. However, with 2×108 bacteria, the septicemia led to the death of mice within 3 days post-infection. In surviving mice, one week after infection, pathogenic leptospires reemerged only in the kidneys, where they multiplied and reached a steady state, leading to a sustained chronic renal infection. These experiments reveal that a fraction of the leptospiral population escapes the potent blood defense, and colonizes a defined number of niches in the kidneys, proportional to the infective dose. Antibiotic treatments failed to eradicate leptospires that colonized the kidneys, although they were effective against L. interrogans if administered before or early after infection. To conclude, mice infected with bioluminescent L. interrogans proved to be a novel model to study both acute and chronic leptospirosis, and revealed that, in the kidneys, leptospires are protected from antibiotics. These bioluminescent leptospires represent a powerful new tool to challenge mice treated with drugs or vaccines, and test the survival, dissemination, and transmission of leptospires between environment and hosts.
Leptospirosis is a worldwide neglected disease caused by the pathogenic bacterium named Leptospira interrogans. Some rodents, such as rats, do not get sick from leptospirosis and constitute a reservoir. They carry leptospires in their kidneys and excrete the bacteria in the environment. L. interrogans are mobile and penetrate their hosts through abraded skin or mucosa. Infected humans may develop mild to severe leptospirosis, potentially leading to death. Leptospires are difficult to cultivate and to genetically manipulate, impairing the study of leptospirosis. Here, we constructed bioluminescent leptospires, and monitored infection in live mice by tracking bioluminescence. In the first days after infection, a rapid dissemination and growth of bacteria was observed in the blood circulation, followed around one week after the infection by their apparent disappearance. However, the leptospires reemerged and multiplied in the kidneys, to reach sustained levels three weeks after infection. The use of antibiotics showed that antibiotic-susceptible L. interrogans are very difficult to eradicate once they are settled in the kidneys. Mice infected with bioluminescent leptospires represent a pertinent model to study leptospirosis. These bioluminescent leptospires are novel tools that will be useful to test the efficacy of treatments or vaccines against leptospirosis.
Leptospirosis is a zoonosis of multisystem involvement caused by pathogenic strains of the genus Leptospira. In the last few years, intensive studies aimed at the development of a vaccine have provided important knowledge about the nature of the immunological mechanisms of the host. The purpose of this study was to analyze the immune responses to two recombinant proteins, MPL17 and MPL21 (encoded by the genes LIC10765 and LIC13131, respectively) of Leptospira interrogans serovar Copenhageni in individuals during infection. The recombinant proteins were expressed in Escherichia coli as six-His tag fusion proteins and were purified from the soluble bacterial fraction by affinity chromatography with Ni2+-charged resin. The recombinant proteins were used to evaluate their ability to bind to immunoglobulin G (IgG) (and IgG subclass) or IgM antibodies in serum samples from patients in the early and convalescent phases of leptospirosis (n = 52) by enzyme-linked immunosorbent assays. The prevalences of total IgG antibodies against MPL17 and MPL21 were 38.5% and 21.2%, respectively. The titers achieved with MPL17 were statistically significantly higher than those obtained by the reference microscopic agglutination test. The specificity of the assay was estimated to be 95.5% for MPL17 and 80.6% for MPL21 when serum samples from individuals with unrelated febrile diseases and control healthy donors were tested. The proteins are conserved among Leptospira strains that cause human and animal diseases. MPL17 and MPL21 are most likely new surface proteins of leptospires, as revealed by liquid-phase immunofluorescence assays with living organisms. Our results demonstrate that these recombinant proteins are highly immunogenic and, when they are used together, might be useful as a means of diagnosing leptospirosis.
Leptospirosis is a global zoonotic disease caused by different Leptospira species, such as Leptospira interrogans, that colonize the renal tubules of wild and domestic animals. Thus far, attempts to develop effective leptospirosis vaccines, both for humans and animals, have failed to induce immune responses capable of conferring protection and simultaneously preventing renal colonization. In this study, we evaluated the protective immunity induced by subunit vaccines containing seven different recombinant Leptospira interrogans outer membrane proteins, including the carboxy-terminal portion of the immunoglobulinlike protein A (LigAC) and six novel antigens, combined with aluminum hydroxide (alum) or Salmonella flagellin (FliC) as adjuvants. Hamsters vaccinated with the different formulations elicited high antigen-specific antibody titers. Immunization with LigAC, either with alum or flagellin, conferred protective immunity but did not prevent renal colonization. Similarly, animals immunized with LigAC or LigAC coadministered with six leptospiral proteins with alum adjuvant conferred protection but did not reduce renal colonization. In contrast, immunizing animals with the pool of seven antigens in combination with flagellin conferred protection and significantly reduced renal colonization by the pathogen. The present study emphasizes the relevance of antigen composition and added adjuvant in the efficacy of antileptospirosis subunit vaccines and shows the complex relationship between immune responses and renal colonization by the pathogen.
Leptospirosis is a zoonotic disease caused by pathogenic spirochetes of
theLeptospira genus. Vaccination with bacterins has severe
limitations. Here, we evaluated the N-terminal region of the leptospiral
immunoglobulin-like B protein (LigBrep) as a vaccine candidate against leptospirosis
using immunisation strategies based on DNA prime-protein boost, DNA vaccine, and
subunit vaccine. Upon challenge with a virulent strain ofLeptospira
interrogans, the prime-boost and DNA vaccine approaches induced
significant protection in hamsters, as well as a specific IgG antibody response and
sterilising immunity. Although vaccination with recombinant fragment of LigBrep also
produced a strong antibody response, it was not immunoprotective. These results
highlight the potential of LigBrep as a candidate antigen for an effective vaccine
against leptospirosis and emphasise the use of the DNA prime-protein boost as an
important strategy for vaccine development.
leptospirosis; Leptospira; LigBrep; subunit vaccine; DNA vaccine; prime-boost
The leptospiral LigA protein consists of 13 bacterial immunoglobulin-like (Big) domains and is the only purified recombinant subunit vaccine that has been demonstrated to protect against lethal challenge by a clinical isolate of Leptospira interrogans in the hamster model of leptospirosis. We determined the minimum number and location of LigA domains required for immunoprotection. Immunization with domains 11 and 12 was found to be required but insufficient for protection. Inclusion of a third domain, either 10 or 13, was required for 100% survival after intraperitoneal challenge with Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130. As in previous studies, survivors had renal colonization; here, we quantitated the leptospiral burden by qPCR to be 1.2×103 to 8×105 copies of leptospiral DNA per microgram of kidney DNA. Although renal histopathology in survivors revealed tubulointerstitial changes indicating an inflammatory response to the infection, blood chemistry analysis indicated that renal function was normal. These studies define the Big domains of LigA that account for its vaccine efficacy and highlight the need for additional strategies to achieve sterilizing immunity to protect the mammalian host from leptospiral infection and its consequences.
Leptospirosis is the most widespread bacterial infection transmitted to humans from host animals that harbor the bacteria in their kidneys. Human infections caused by the bacterium, Leptospira interrogans, frequently result in a life-threatening illness characterized by jaundice and kidney failure. Vaccines are urgently needed to prevent leptospirosis in populations at risk. The leptospiral protein, LigA, is a promising vaccine candidate because it is the first purified protein to be shown to protect animals from fatal leptospirosis. The goal of this study was to determine which of LigA's 13 domains are required for the protective effect. Immunization with domains 11 and 12 was found to be required, but was insufficient, for protection. A third domain, either 10 or 13, was required for 100% survival. As in previous studies, residual bacteria were cultured from the kidneys of survivors. However, in contrast to previous studies, we determined the amount of bacterial DNA in the kidneys as a measure of vaccine efficacy. We also examined the kidneys microscopically for signs of damage and measured blood chemistries to assess kidney function. These are important steps towards developing vaccines that provide protection from kidney damage and infection.
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.
Leptospiral immunoglobulin-like (Lig) proteins are of great interest due to their ability to act as mediators of pathogenesis, serodiagnostic antigens, and immunogens. Purified recombinant LigA protein is the most promising subunit vaccine candidate against leptospirosis reported to date, however, as purified proteins are weak immunogens the use of a potent adjuvant is essential for the success of LigA as a subunit vaccine. In the present study, we compared xanthan pv. pruni (strain 106), aluminium hydroxide (alhydrogel), and CpG ODN as adjuvants in a LigA subunit vaccine preparation. Xanthan gum is a high molecular weight extracellular polysaccharide produced by fermentation of Xanthomonas spp., a plant-pathogenic bacterium genus. Preparations containing xanthan induced a strong antibody response comparable to that observed when alhydrogel was used. Upon challenge with a virulent strain of L. interrogans serovar Copenhageni, significant protection (Fisher test, P < 0.05) was observed in 100%, 100%, and 67% of hamsters immunized with rLigANI-xanthan, LigA-CpG-xanthan, and rLigANI-alhydrogel, respectively. Furthermore, xanthan did not cause cytotoxicity in Chinese hamster ovary (CHO) cells in vitro. The use of xanthan as an adjuvant is a novel alternative for enhancing the immunogenicity of vaccines against leptospirosis and possibly against other pathogens.
Leptospira interrogans is the etiological agent of leptospirosis, a zoonotic disease of human and veterinary concern. The identification of novel proteins that mediate host-pathogen interactions is important for understanding the bacterial pathogenesis as well as to identify protective antigens that would help fight the disease. We describe in this work the cloning, expression, purification and characterization of three predicted leptospiral membrane proteins, LIC10258, LIC12880 (Lp30) and LIC12238. We have employed Escherichia coli BL21 (SI) strain as a host expression system. Recently, we have identified LIC12238 as a plasminogen (PLG)-binding receptor. We show now that Lp30 and rLIC10258 are also PLG-receptors of Leptospira, both exhibiting dose-dependent and saturating binding (KD, 68.8±25.2 nM and 167.39±60.1 nM, for rLIC10258 and rLIC12880, respectively). In addition, LIC10258, which is a novel OmpA-like protein, binds laminin and plasma fibronectin ECM molecules and hence, it was named Lsa66 (Leptospiral surface adhesin of 66 kDa). Binding of Lsa66 to ECM components was determined to be specific, dose-dependent and saturable, with a KD of 55.4±15.9 nM to laminin and of 290.8±11.8 nM to plasma fibronectin. Binding of the recombinant proteins to PLG or ECM components was assessed by using antibodies against each of the recombinant proteins obtained in mice and confirmed by monoclonal anti-polyhistidine antibodies. Lsa66 caused partial inhibition on leptospiral adherence to immobilized ECM and PLG. Moreover, this adhesin and rLIC12238 are recognized by antibodies in serum samples of confirmed leptospirosis cases. Thus, Lsa66 is a novel OmpA-like protein with dual activity that may promote the attachment of Leptospira to host tissues and may contribute to the leptospiral invasion. To our knowledge, this is the first leptospiral protein with ECM and PLG binding properties reported to date.
Background. Leptospira species cause leptospirosis, a zoonotic disease found worldwide. Current vaccines against leptospirosis provide protection only against closely related serovars.
Methods. We evaluated an attenuated transposon mutant of Leptospira interrogans serovar Manilae (M1352, defective in lipopolysaccharide biosynthesis) as a live vaccine against leptospirosis. Hamsters received a single dose of vaccine and were challenged with the homologous serovar (Manilae) and a serologically unrelated heterologous serovar (Pomona). Comparisons were made with killed vaccines. Potential cross-protective antigens against leptospirosis were investigated.
Results. Live M1352 vaccine induced superior protection in hamsters against homologous challenge. The live vaccine also stimulated cross-protection against heterologous challenge, with 100% survival (live M1352) versus 40% survival (killed vaccine). Hamsters receiving either vaccine responded to the dominant membrane proteins LipL32 and LipL41. Hamsters receiving the live vaccine additionally recognized LA3961/OmpL36 (unknown function), Loa22 (OmpA family protein, recognized virulence factor), LA2372 (general secretory protein G), and LA1939 (hypothetical protein). Manilae LigA was recognized by M1352 vaccinates, whereas LipL36 was detected in Pomona.
Conclusion. This study demonstrated that a live, attenuated vaccine can stimulate cross-protective immunity to L. interrogans and has identified antigens that potentially confer cross-protection against leptospirosis.
Leptospira is the etiologic agent of leptospirosis, a bacterial zoonosis distributed worldwide. Leptospiral lipopolysaccharide is a protective immunogen, but the extensive serological diversity of leptospires has inspired a search for conserved outer membrane proteins (OMPs) that may stimulate heterologous immunity. Previously, a global analysis of leptospiral OMPs (P. A. Cullen, S. J. Cordwell, D. M. Bulach, D. A. Haake, and B. Adler, Infect. Immun. 70:2311-2318, 2002) identified pL21, a novel 21-kDa protein that is the second most abundant constituent of the Leptospira interrogans serovar Lai outer membrane proteome. In this study, we identified the gene encoding pL21 and found it to encode a putative lipoprotein; accordingly, the protein was renamed LipL21. Southern hybridization analysis revealed the presence of lipL21 in all of the pathogenic species but in none of the saprophytic species examined. Alignment of the LipL21 sequence from six strains of Leptospira revealed 96 to 100% identity. When specific polyclonal antisera to recombinant LipL21 were used, LipL21 was isolated together with other known leptospiral OMPs by both Triton X-114 extraction and sucrose density gradient membrane fractionation. All nine strains of pathogenic leptospires investigated by Western blotting, whether culture attenuated or virulent, were found to express LipL21. In contrast, the expression of LipL21 or an antigenically related protein could not be detected in nonpathogenic L. biflexa. Infected hamster sera and two of eight human leptospirosis sera tested were found to react with recombinant LipL21. Native LipL21 was found to incorporate tritiated palmitic acid, consistent with the prediction of a lipoprotein signal peptidase cleavage site. Biotinylation of the leptospiral surface resulted in selective labeling of LipL21 and the previously known OMPs LipL32 and LipL41. These findings show that LipL21 is a surface-exposed, abundant outer membrane lipoprotein that is expressed during infection and conserved among pathogenic Leptospira species.
Leptospirosis is a worldwide zoonosis caused by pathogenic Leptospira. The whole-genome sequence of L. interrogans serovar Copenhageni together with bioinformatics tools represent a great opportunity to search for novel antigen candidates that could be used as subunit vaccine against leptospirosis. We focused on six genes encoding for conserved hypothetical proteins predicted to be exported to the outer membrane. The genes were amplified by PCR from Leptospira interrogans genomic DNA and were cloned and expressed in Escherichia coli. The recombinant proteins tagged with N-terminal hexahistidine were purified by metal-charged chromatography. The immunization of hamsters followed by challenge with lethal dose of virulent strain of Leptospira showed that the recombinant proteins Lsa21, Lsa66 and rLIC11030 elicited partial protection to animals. These proteins could be used combined or in a mixture with novel adjuvants in order to improve their effectiveness.
Leptospira interrogans; leptospirosis; recombinant protein; vaccine.
Leptospirosis is an important reemerging zoonosis, with more than half a million cases reported annually, and is caused by pathogenic Leptospira species. Development of a universal vaccine is one of the major strategic goals to overcome the disease burden of leptospirosis. In this study, a chimeric multi-epitope protein-based vaccine was designed and tested for its potency to induce a specific immune response and provide protection against L. interrogans infection.
The protein, containing four repeats of six T- and B-cell combined epitopes from the leptospiral outer membrane proteins, OmpL1, LipL32 and LipL21, was expressed and purified. Western blot analysis showed that the recombinant protein (named r4R) mainly expressed in a soluble pattern, and reacted with antibodies raised in rabbit against heat-killed Leptospira and in guinea pigs against the r4R vaccine. Microscopic agglutination tests showed that r4R antisera was immunological cross-reactive with a range of Chinese standard reference strains of Leptospira belonging to different serogroups. In guinea pigs, the r4R vaccine induced a Th1-biased immune response, as reflected by the IgG2a/IgG1 ratio and cytokine production of stimulated splenocytes derived from immunized animals. Finally, r4R-immunized guinea pigs showed increased survival of lethal Leptospira challenges compared with PBS-immunized animals and tissue damage and leptospiral colonization of the kidney were reduced.
The multi-epitope chimeric r4R protein is a promising antigen for the development of a universal cross-reactive vaccine against leptospirosis.
Electronic supplementary material
The online version of this article (doi:10.1186/s12866-016-0852-y) contains supplementary material, which is available to authorized users.
Leptospira; Outer membrane protein; Multi-epitope; Vaccine; Cross protection
Effort has been made to identify protective antigens in order to develop a recombinant vaccine against leptospirosis. Several attempts failed to conclusively demonstrate efficacy of vaccine candidates due to the lack of an appropriate model of lethal leptospirosis. The purposes of our study were: (i) to test the virulence of leptospiral isolates from Brazil, which are representative of important serogroups that cause disease in humans and animals; and (ii) to standardize the lethal dose 50% (LD50) for each of the virulent strains using a hamster (Mesocricetus auratus) model. Five of seven Brazilian isolates induced lethality in a hamster model, with inocula lower than 200 leptospires. Histopathological examination of infected animals showed typical lesions found in both natural and experimental leptospirosis. Results described here demonstrated the potential use of Brazilian isolates as highly virulent strains in challenge experiments using hamster as an appropriate animal model for leptospirosis. Furthermore these strains may be useful in heterologous challenge studies which aim to evaluate cross-protective responses induced by subunit vaccine candidates.
Leptospira; leptospirosis; lethal dose; isolation; animal model; virulence
Leptospirosis, a worldwide zoonosis, lacks an effective, safe, and cross-protective vaccine. LipL32, the most abundant, immunogenic, and conserved surface lipoprotein present in all pathogenic species of Leptospira, is a promising antigen candidate for a recombinant vaccine. However, several studies have reported a lack of protection when this protein is used as a subunit vaccine. In an attempt to enhance the immune response, we used LipL32 coupled to or coadministered with the B subunit of the Escherichia coli heat-labile enterotoxin (LTB) in a hamster model of leptospirosis. After homologous challenge with 5× the 50% lethal dose (LD50) of Leptospira interrogans, animals vaccinated with LipL32 coadministered with LTB and LTB::LipL32 had significantly higher survival rates (P < 0.05) than animals from the control group. This is the first report of a protective immune response afforded by a subunit vaccine using LipL32 and represents an important contribution toward the development of improved leptospirosis vaccines.
Leptospirosis is a widespread zoonotic disease worldwide. The lack of an adequate laboratory test is a major barrier for diagnosis, especially during the early stages of illness, when antibiotic therapy is most effective. Therefore, there is a critical need for an efficient diagnostic test for this life threatening disease.
In order to identify new targets that could be used as diagnostic makers for leptopirosis, we constructed a protein microarray chip comprising 61% of Leptospira interrogans proteome and investigated the IgG response from 274 individuals, including 80 acute-phase, 80 convalescent-phase patients and 114 healthy control subjects from regions with endemic, high endemic, and no endemic transmission of leptospirosis. A nitrocellulose line blot assay was performed to validate the accuracy of the protein microarray results.
We found 16 antigens that can discriminate between acute cases and healthy individuals from a region with high endemic transmission of leptospirosis, and 18 antigens that distinguish convalescent cases. Some of the antigens identified in this study, such as LipL32, the non-identical domains of the Lig proteins, GroEL, and Loa22 are already known to be recognized by sera from human patients, thus serving as proof-of-concept for the serodiagnostic antigen discovery approach. Several novel antigens were identified, including the hypothetical protein LIC10215 which showed good sensitivity and specificity rates for both acute- and convalescent-phase patients.
Our study is the first large-scale evaluation of immunodominant antigens associated with naturally acquired leptospiral infection, and novel as well as known serodiagnostic leptospiral antigens that are recognized by antibodies in the sera of leptospirosis cases were identified. The novel antigens identified here may have potential use in both the development of new tests and the improvement of currently available assays for diagnosing this neglected tropical disease. Further research is needed to assess the utility of these antigens in more deployable diagnostic platforms.
Leptospirosis is an infectious zoonotic disease that causes non-specific signs and symptoms in humans, which hampers the clinical diagnosis and treatment by physicians. Complications can occur if the proper treatment is not initiated early in the course of illness. Although the early diagnosis is critical for preventing unnecessary complications, currently available tests do not exhibit sufficient diagnostic sensitivity in the beginning of disease. We took advantage of high throughput techniques to perform an embracing study of the humoral immune response to the bacteria in order to identify antigens that could be used in a new test for the diagnosis of leptospirosis. A protein microarray chip containing 2,241 leptospiral proteins was constructed and probed with serum samples from patients and healthy individuals. We identified 24 proteins that are recognized by patients' sera but not by healthy individuals. These proteins are potential diagnostic markers, especially the ones identified for acute-phase patients, which can discriminate between a positive and a negative leptospirosis case within a few days after onset of symptoms. This work establishes the protein microarray approach for improving our understanding of the serological response to leptospirosis. Further research is needed to assess the performance of these antigens in the clinical setting.
Leptospira interrogans are bacterial pathogens of animal that cause zoonotic infections in human. Outer membrane proteins of leptospire are among the most effective antigens which can stimulate remarkable immune responses during the infection processes, and thus are currently considered leading candidate vaccine antigens. The objective of the present study is to predict and confirm major combined B and T cell epitopes of leptospiral outer membrane proteins OmpL1 and LipL41, as well as to evaluate their capacity in the induction of immune responses in BALB/c mice.
In this study, four epitopes from OmpL1 and four from LipL41 conserved regions were evaluated for their potential utilization in leptospire vaccines. Firstly, combined B and T cell epitopes were predicted by softwares and expressed using a phage display system. OmpL1 residues 87-98 and 173-191 (OmpL187-98 and OmpL1173-191) and LipL4130-48, LipL41233-256 of LipL41 were identified as immunodominant B cell epitopes by Western blot. Epitopes OmpL1173-191, OmpL1297-320 of OmpL1 and LipL41233-256, LipL41263-282 of LipL41 were identified as immunodominant CD4+ T cell epitopes through proliferation analysis of splenocytes from recombinant OmpL1 (rOmpL1) or recombinant LipL41 (rLipL41)-immunized BALB/c (H-2d) mice. These epitopes induced responses of CD4+ T cells and Th1 (T helper cells) type cytokine responses during the infection.
This work identified combined T and B cell immunodominant epitopes in outer membrane proteins OmpL1 and LipL41 of Leptospira interrogans. OmpL1173-191 of OmpL1 and LipL41233-256 of LipL41 could be useful in a vaccine against Leptospira. The findings could also contribute to the development of effective cross-protective vaccine strategies for leptospirosis.
The leptospiral immunoglobulin-like (Lig) proteins LigA and LigB possess immunoglobulin-like domains with 90-amino-acid repeats and are adhesion molecules involved in pathogenicity. They are conserved in pathogenic Leptospira spp. and thus are of interest for use as serodiagnostic antigens and in recombinant vaccine formulations. The N-terminal amino acid sequences of the LigA and LigB proteins are identical, but the C-terminal sequences vary. In this study, we evaluated the protective potential of five truncated forms of LigA and LigB proteins from Leptospira interrogans serovar Canicola as DNA vaccines using the pTARGET mammalian expression vector. Hamsters immunized with the DNA vaccines were subjected to a heterologous challenge with L. interrogans serovar Copenhageni strain Spool via the intraperitoneal route. Immunization with a DNA vaccine encoding LigBrep resulted in the survival of 5/8 (62.5%) hamsters against lethal infection (P < 0.05). None of the control hamsters or animals immunized with the other vaccine preparations survived. The vaccine induced an IgG antibody response and, additionally, conferred sterilizing immunity in 80% of the surviving animals. Our results indicate that the LigBrep DNA vaccine is a promising candidate for inclusion in a protective leptospiral vaccine.
Subunit vaccines are a potential intervention strategy against leptospirosis, which is a major public health problem in developing countries and a veterinary disease in livestock and companion animals worldwide. Leptospiral immunoglobulin-like (Lig) proteins are a family of surface-exposed determinants that have Ig-like repeat domains found in virulence factors such as intimin and invasin. We expressed fragments of the repeat domain regions of LigA and LigB from Leptospira interrogans serovar Copenhageni. Immunization of Golden Syrian hamsters with Lig fragments in Freund’s adjuvant induced robust antibody responses against recombinant protein and native protein, as detected by ELISA and immunoblot, respectively. A single fragment, LigANI, which corresponds to the six carboxy-terminal Ig-like repeat domains of the LigA molecule, conferred immunoprotection against mortality (67-100%, P <0.05) in hamsters which received a lethal inoculum of L. interrogans serovar Copenhageni. However, immunization with this fragment did not confer sterilizing immunity. These findings indicate that the carboxy-terminal portion of LigA is an immunoprotective domain and may serve as a vaccine candidate for human and veterinary leptospirosis.
Leptospirosis; subunit vaccine; Leptospiral immunoglobulin-like protein; recombinant protein; immunity; antibodies; hamsters
Leptospirosis is one of the zoonotic diseases in animals and humans throughout the world. LipL21 is one of the important surface-exposed lipoproteins in leptospires and the most effective cross protective immunogenic antigen. It is widely considered as a diagnostic marker for leptospirosis. In this study, we evaluated the serodiagnostic potential of LipL21 protein of Leptospira interrogans serovar Pomona. We have successfully amplified, cloned, and expressed LipL21 in E. coli and evaluated its specificity by immunoblotting. Purified recombinant LipL21 (rLipL21) was inoculated into rabbits for the production of polyclonal antibody. Characterization of the purified IgG antibody against rLipL21 was performed by cross reactivity assay. Only sera from leptospirosis patients and rabbit hyperimmune sera recognized rLipL21 while the nonleptospirosis control sera showed no reaction in immunoblotting. We confirmed that anti-rLipL21-IgG antibody cross reacted with and detected only pathogenic leptospiral species and it did not react with nonpathogenic leptospires and other bacterial species. Results observed showed that anti-rLipL21-IgG antibody has high specificity and sensitivity to leptospires. The findings indicated that the antibody could be used in a diagnostic assay for detection of leptospires or their proteins in the early phase of infection.
Toward developing an effective vaccine capable of conferring heterologous protection, the putative lipoprotein LemA, which presents an M3 epitope similar to that of Listeria, was evaluated as a vaccine candidate in the hamster model of leptospirosis. LemA is conserved (>70% pairwise identity) among the pathogenic Leptospira spp., indicating its potential in stimulating a cross-protective immune response. Using different vaccination strategies, including prime-boost, DNA vaccine, and a subunit preparation, recombinant LemA conferred different levels of protection in hamsters. Significant protection against mortality was observed for the prime-boost and the DNA vaccine strategies, which showed 87.5% (P < 0.01) and 62.5% (P < 0.05) efficacy, respectively. Although the subunit vaccine preparation protected 50.0% of immunized hamsters, the level of protection was not significant. None of the hamsters in the control groups survived challenge with a virulent strain of Leptospira interrogans serogroup Icterohaemorrhagiae. Characterization of the immune response found that the strongest antibody response was stimulated by the subunit vaccine preparation, followed by the prime-boost strategy. The DNA vaccine failed to elicit an antibody response in immunized hamsters.
Leptospira interrogans is a spirochaete responsible for leptospirosis in mammals. The molecular mechanisms of the Leptospira virulence remain mostly unknown. Recently, it has been demonstrated that L. interrogans ClpB (ClpBLi) is essential for bacterial survival under stressful conditions and also during infection. The aim of this study was to provide further insight into the role of ClpB in L. interrogans and answer the question whether ClpBLi as a potential virulence factor may be a target of the humoral immune response during leptospiral infections in mammals.
ClpBLi consists of 860 amino acid residues with a predicted molecular mass of 96.3 kDa and shows multi-domain organization similar to that of the well-characterized ClpB from Escherichia coli. The amino acid sequence identity between ClpBLi and E. coli ClpB is 52 %. The coding sequence of the clpBLi gene was cloned and expressed in E. coli BL21(DE3) strain. Immunoreactivity of the recombinant ClpBLi protein was assessed with the sera collected from Leptospira-infected animals and uninfected healthy controls. Western blotting and ELISA analysis demonstrated that ClpBLi activates the host immune system, as evidenced by an increased level of antibodies against ClpBLi in the sera from infected animals, as compared to the control group. Additionally, ClpBLi was found in kidney tissues of Leptospira-infected hamsters.
ClpBLi is both synthesized and immunogenic during the infectious process, further supporting its involvement in the pathogenicity of Leptospira. In addition, the immunological properties of ClpBLi point to its potential value as a diagnostic antigen for the detection of leptospirosis.
ClpB; Leptospira interrogans; Leptospirosis; Molecular chaperone; Pathogen
We report in this work that Leptospira strains, virulent L. interrogans serovar Copenhageni, attenuated L. interrogans serovar Copenhageni and saprophytic L. biflexa serovar Patoc are capable of binding fibrinogen (Fg). The interaction of leptospires with Fg inhibits thrombin- induced fibrin clot formation that may affect the haemostatic equilibrium. Additionally, we show that plasminogen (PLG)/plasmin (PLA) generation on the surface of Leptospira causes degradation of human Fg. The data suggest that PLA-coated leptospires were capable to employ their proteolytic activity to decrease one substrate of the coagulation cascade. We also present six leptospiral adhesins and PLG- interacting proteins, rLIC12238, Lsa33, Lsa30, OmpL1, rLIC11360 and rLIC11975, as novel Fg-binding proteins. The recombinant proteins interact with Fg in a dose-dependent and saturable fashion when increasing protein concentration was set to react to a fix human Fg concentration. The calculated dissociation equilibrium constants (KD) of these reactions ranged from 733.3±276.8 to 128±89.9 nM for rLIC12238 and Lsa33, respectively. The interaction of recombinant proteins with human Fg resulted in inhibition of fibrin clot by thrombin-catalyzed reaction, suggesting that these versatile proteins could mediate Fg interaction in Leptospira. Our data reveal for the first time the inhibition of fibrin clot by Leptospira spp. and presents adhesins that could mediate these interactions. Decreasing fibrin clot would cause an imbalance of the coagulation cascade that may facilitate bleeding and help bacteria dissemination
Leptospirosis is probably the most widespread zoonosis in the world. Caused by spirochaetes of the genus Leptospira, it has greater incidence in tropical and subtropical regions. The disease has become prevalent in cities with sanitation problems and a large population of urban rodent reservoirs, which contaminate the environment through their urine. Understanding the mechanisms involved in pathogenesis of leptospirosis should contribute to new strategies that would help fight the disease. We show in this work that Leptospira strains, virulent, attenuated or saprophytic are capable of binding fibrinogen (Fg). The interaction of leptospires with Fg inhibits the formation of fibrin clot that may result of an imbalance in the haemostatic equilibrium. In addition, we show that plasminogen (PLG)/plasmin (PLA) generation on the surface of leptospires can lead to Fg degradation, showing evidence of possible route of fibrinolysis in leptospirosis. We also present six leptospiral proteins, as novel Fg-binding proteins, capable of inhibiting fibrin clot formation by thrombin-catalyzed reaction, suggesting that in Leptospira these multifunctional proteins could mediate Fg interaction. Our data suggest possible mechanisms that leptospires could employ to affect the coagulation cascade and fibrinolytic system that might lead to bacteria spreading.
Leptospirosis is a potentially fatal zoonosis transmitted by reservoir host animals that harbor leptospires in their renal tubules and shed the bacteria in their urine. Leptospira interrogans serovar Copenhageni transmitted from Rattus norvegicus to humans is the most prevalent cause of urban leptospirosis. We examined L. interrogans LigA, domains 7 to 13 (LigA7-13), as an oral vaccine delivered by Escherichia coli as a lipidated, membrane-associated protein. The efficacy of the vaccine was evaluated in a susceptible hamster model in terms of the humoral immune response and survival from leptospiral challenge. Four weeks of oral administration of live E. coli expressing LigA7-13 improved survival from intraperitoneal (i.p.) and intradermal (i.d.) challenge by L. interrogans serovar Copenhageni strain Fiocruz L1-130 in Golden Syrian hamsters. Immunization with E. coli expressing LigA7-13 resulted in a systemic antibody response, and a significant LigA7-13 IgG level after the first 2 weeks of immunization was completely predictive of survival 28 days after challenge. As in previous LigA vaccine studies, all immunized hamsters that survived infection had renal leptospiral colonization and histopathological changes. In summary, an oral LigA-based vaccine improved survival from leptospiral challenge by either the i.p. or i.d. route.
NETosis is a process by which neutrophils extrude their DNA together with bactericidal proteins that trap and/or kill pathogens. In the present study, we evaluated the ability of Leptospira spp. to induce NETosis using human ex vivo and murine in vivo models. Microscopy and fluorometric studies showed that incubation of human neutrophils with Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130 (LIC) resulted in the release of DNA extracellular traps (NETs). The bacteria number, pathogenicity and viability were relevant factors for induction of NETs, but bacteria motility was not. Entrapment of LIC in the NETs resulted in LIC death; however, pathogenic but not saprophytic Leptospira sp. exerted nuclease activity and degraded DNA. Mice infected with LIC showed circulating NETs after 2 days post-infection (dpi). Depletion of neutrophils with mAb1A8 significantly reduced the amount of intravascular NETs in LIC-infected mice, increasing bacteremia at 3 dpi. Although there was a low bacterial burden, scarce neutrophils and an absence of inflammation in the early stages of infection in the kidney and liver, at the beginning of the leptospiruric phase, the bacterial burden was significantly higher in kidneys of neutrophil-depleted-mice compared to non-depleted and infected mice. Surprisingly, interstitial nephritis was of similar intensity in both groups of infected mice. Taken together, these data suggest that LIC triggers NETs, and that the intravascular formation of these DNA traps appears to be critical not only to prevent early leptospiral dissemination but also to preclude further bacterial burden.
Neutrophils extracellular traps (NETs) are a relatively novel pathogen-killing mechanism for extracellular microbes independent of phagocytic uptake and degranulation. Although it was originally proposed that NETs are formed exclusively in tissues at sites of infection, NETs have also been found within blood vessels where they ensnare microbes in circulation during sepsis. Leptospirosis is a global zoonosis that has become prevalent in slum areas, where its diagnosis and treatment may be overlooked. Here, for the first time, we characterized NETs formation as a result of Leptospira spp. stimulus. We also showed that mice lacking neutrophils exhibit early reduced levels of circulating NETs, but higher bacteremia, a fact that was later associated with higher bacterial burden in kidney. The present results demonstrate that Leptospira spp. can trigger NET formation and that this innate immune mechanism can play a role in the pathogenesis of leptospirosis.