Proteomic approach for characterization of immunodominant membrane-associated 30- to 36-kiloDalton fraction antigens of Leishmania infantum promastigotes, reacting with sera from Mediterranean visceral leishmaniasis patients

Proteomics and Leishmaniasis: Potential Clinical Applications

Leishmaniases are diseases caused by protozoan parasites of the genus Leishmania. They are endemic in 98 countries, affect around 12 million people worldwide and may present several distinct clinical forms. Unfortunately, there are only a few drugs available for treatment of leishmaniasis, which are toxic and not always effective. Different parasite species and different clinical forms require optimization of the treatment or more specific therapies, which are not available. The emergence of resistance is also a matter of concern. Besides, diagnosis can sometimes be complicated due to atypical manifestations and associations with other pathologies. In this review, proteomic data are presented and discussed in terms of their application in important issues in leishmaniasis such as parasite resistance to chemotherapy, diagnosis of active disease in patients and dogs, markers for different clinical forms, identification of virulence factors, and their potential use in vaccination. It is shown that proteomics has contributed to the discovery of potential biomarkers for prognosis, diagnosis, therapeutics, monitoring of disease progression, treatment follow-up and identification of vaccine candidates for specific diseases. However, the authors believe its capabilities have not yet been fully explored for routine clinical analysis for several reasons, which will be presented in this review.

Understanding Leishmania parasites through proteomics and implications for the clinic

INTRODUCTION

Leishmania spp. are causative agents of leishmaniasis, a broad-spectrum neglected vector-borne disease. Genomic and transcriptional studies are not capable of solving intricate biological mysteries, leading to the emergence of proteomics, which can provide insights into the field of parasite biology and its interactions with the host. Areas covered: The combination of genomics and informatics with high throughput proteomics may improve our understanding of parasite biology and pathogenesis. This review analyses the roles of diverse proteomic technologies that facilitate our understanding of global protein profiles and definition of parasite development, survival, virulence and drug resistance mechanisms for disease intervention. Additionally, recent innovations in proteomics have provided insights concerning the drawbacks associated with conventional chemotherapeutic approaches and Leishmania biology, host-parasite interactions and the development of new therapeutic approaches. Expert commentary: With progressive breakthroughs in the foreseeable future, proteome profiles could provide target molecules for vaccine development and therapeutic intervention. Furthermore, proteomics, in combination with genomics and informatics, could facilitate the elimination of several diseases. Taken together, this review provides an outlook on developments in Leishmania proteomics and their clinical implications.

Using proteomics as a powerful tool to develop a vaccine against Mediterranean visceral leishmaniasis

Visceral leishmaniasis (VL) is a tropical infectious disease, which is called Mediterranean visceral leishmaniasis (MVL) in the Mediterranean area. In spite of many attempts, no effective commercial vaccine exists for MVL. To find new targets for developing antileishmanial vaccines, knowing parasite antigens that provoke the immune system are on demand. Nowadays, proteomics methods are defined as approaches for analysis of protein profiling of different cells. Within this framework, detection of new antigens is becoming more facilitated. In this review, we aimed to introduce possible targets using proteomics so; they could be used as candidates for developing vaccines against MVL. It can shed new light in the near future on the development of promising vaccines for MVL.

Liposomal Elongation Factor-1α Triggers Effector CD4 and CD8 T Cells for Induction of Long-Lasting Protective Immunity against Visceral Leishmaniasis

Despite advances, identification and formulation of safe and effective vaccine for long-lasting protection against leishmaniasis is still inadequate. In this study, we have identified a novel antigen, leishmanial elongation factor-1α (EF1-α), as an immunodominant component of solubilized leishmanial membrane antigens that reacts with visceral leishmaniasis (VL) sera and induces cellular proliferative and cytokine response in PBMCs of cured VL subjects. Leishmanial EF1-α is a 50 kDa antigen that plays a crucial role in pathogen survival by regulating oxidative burst in the host phagocytes. Previously, immunodominant truncated forms of EF1-α from different species of Leishmania have been reported. Formulation of the L. donovani 36 kDa truncated as well as the cloned recombinant EF1-α in cationic liposomes induce strong resistance to parasitic burden in liver and spleen of BALB/c mice through induction of DTH and a IL-10 and TGF-β suppressed mixed Th1/Th2 cytokine responses. Multiparametric analysis of splenocytes for generation of antigen-specific IFN-γ, IL2, and TNF-α producing lymphocytes indicate that cationic liposome facilitates expansion of both CD4⁺ as well as CD8⁺ memory and effector T cells. Liposomal EF1-α is a novel and potent vaccine formulation against VL that imparts long-term protective responses. Moreover, the flexibility of this formulation opens up the scope to combine additional adjuvants and epitope selected antigens for use in other disease forms also.

Immunoprophylactic Potential of a Cocktail of Three Low Molecular Weight Antigens of Leishmania donovani along with Various Adjuvants Against Experimental Visceral leishmaniasis

BACKGROUND

Currently, there is no vaccine available for any form of leishmaniasis for human use, including visceral leishmaniasis (VL). The treatment relies on drugs associated with severe toxic side effects and increased parasite drug resistance. At present, there is a strong need to develop and implement a successful vaccine against this disease. Therefore, we evaluated immunoprophylactic potential of a cocktail of low molecular weight antigens along with various adjuvants.

METHODS

The three antigens (2015, Department of Zoology, Panjab University, Chandigarh), 31kDa, 36 kDa and 51 kDa of L. donovani were used in this study. Inbred BALB/c mice were immunized with 10 μg of cocktail antigens i.e. 31+36+51kDa alone and along with different adjuvants (ALD, saponin, and liposome). Mice were boosted twice at an interval of 2 wk and after last dose; mice were given challenge infection with 107 promastigotes. Mice have sacrificed15 d post immunization and on 30, 60, 90 post-challenge days for evaluation of different parameters.

RESULTS

Immunized animals showed reduced parasite load, increased DTH responses and elevated levels of IgG2a antibody. The levels of Th1 cytokines were higher as compared to Th2 cytokines in immunized animals.

CONCLUSION

Best results were obtained with cocktail of 31+36+51+liposome and this combination conferred maximum protection.

Evaluation of Leishmania (Leishmania) infantum excreted-secreted antigens for detection of canine leishmaniasis

The efficacy of tests with L. (L.) infantum excreted-secreted antigens (ESA) to detect canine leishmaniasis (CanL) was evaluated using immunoblotting (ESA-blot), ELISA (ESA-ELISA) and ELISA with alkaline extract from promastigotes (PAE). Of one hundred fifty-five domestic dogs tested, 100 were suspected of CanL, 23 had other diseases and 32 were healthy. Sera from the dogs suspected of CanL were tested by immunohistochemistry (IHC), and 54% were confirmed to be infected by L. (L.) infantum (38 symptomatic and 16 asymptomatic). Of these, 100% were positive by ESA-blot, ESA-ELISA and PAE-ELISA. In the ESA-blot their sera recognized polypeptides in the 26.5-31.5kDa region. Of the 46% of dogs with negative IHC, 44-53% tested positive in all three tests irrespective of clinical status. The twenty-three dogs with other diseases were negative by ESA-blot, but sera from 9% and 26% of them reacted with ESA-ELISA and PAE-ELISA, respectively. The 32 healthy dogs were negative in all the tests. ESA-blot showed good correlation with IHC in the detection of CanL and a high specificity index.

Identification of Immunoreactive Leishmania infantum Protein Antigens to Asymptomatic Dog Sera through Combined Immunoproteomics and Bioinformatics Analysis

Leishmania infantum is the etiologic agent of zoonotic visceral leishmaniasis (VL) in countries in the Mediterranean basin, where dogs are the domestic reservoirs and represent important elements in the transmission of the disease. Since the major focal areas of human VL exhibit a high prevalence of seropositive dogs, the control of canine VL could reduce the infection rate in humans. Efforts toward this have focused on the improvement of diagnostic tools, as well as on vaccine development. The identification of parasite antigens including suitable major histocompatibility complex (MHC) class I- and/or II-restricted epitopes is very important since disease protection is characterized by strong and long-lasting CD8⁺ T and CD4⁺ Th1 cell-dominated immunity. In the present study, total protein extract from late-log phase L. infantum promastigotes was analyzed by two-dimensional western blots and probed with sera from asymptomatic and symptomatic dogs. A total of 42 protein spots were found to differentially react with IgG from asymptomatic dogs, while 17 of these identified by Coommasie stain were extracted and analyzed. Of these, 21 proteins were identified by mass spectrometry; they were mainly involved in metabolism and stress responses. An in silico analysis predicted that the chaperonin HSP60, dihydrolipoamide dehydrogenase, enolase, cyclophilin 2, cyclophilin 40, and one hypothetical protein contain promiscuous MHCI and/or MHCII epitopes. Our results suggest that the combination of immunoproteomics and bioinformatics analyses is a promising method for the identification of novel candidate antigens for vaccine development or with potential use in the development of sensitive diagnostic tests.

Comparison of Proteome Profiling of Two Sensitive and Resistant Field Iranian Isolates of Leishmania major to Glucantime® by 2- Dimensional Electrophoresis

BACKGROUND

In this study, two-dimensional gel electrophoresis (2-DE) method was applied to determine and compare the protein spots expressed in the two field isolates of Leishmania major and recovered from the patients who were clinically sensitive and resistant to Glucantime® treatment.

METHODS

Leishmania parasites were isolated from the cutaneous lesions of two CL infected patients in Shiraz, south of Iran. The species of the two isolates were identified as L. major using Nested-PCR. Sensitivity (Sh-214S) and resistance (Sh-120R) of the two isolates to meglumine antimonite were checked by the standard in vitro assays. Both sensitive and resistant L. major isolates were harvested in RPMI 1640 medium. Protein extractions were performed using TCA/Acetone method and the protein spots were determined by a two-dimensional gel electrophoresis (2-DE). The gels were stained with silver nitrate and analyzed by Image Master 2D Melanie-6 software.

RESULTS

About 2967 protein spots were detected. Overall, 89 protein spots represented considerable changes of expression in the resistant isolate of L. major compared to the sensitive isolate. Of these, 60 and 29 protein spots were up-and down regulated, respectively. In addition, 11 protein spots present in the resistant isolate were noticed to be absent in the sensitive isolate.

CONCLUSION

A number of proteins showed significant changes of expression in the drug-resistant L. major; moreover, the roles of these proteins probably enhanced the parasite resistance to the drug and increased parasite survival in the cells.

Comparative Proteomic Profiling of Leishmania tropica: Investigation of a Case Infected with Simultaneous Cutaneous and Viscerotropic Leishmaniasis by 2-Dimentional Electrophoresis and Mass Spectrometry

BACKGROUND

Viscerotropic leishmaniasis caused by Leishmania tropica poses a significant problem in the diagnosis and treatment management. Since differential gene expression is more important in outcome of the infection, we employed proteomic approach to identify potential proteins involved in visceralization of L. tropica.

METHODS

The proteomes profiling of L. tropica isolated from cutaneous and visceral tissues of one host were compared by 2-DE/MS proteomics study. Moreover, the transcript level of some identified proteins was confirmed using real-time RT-PCR.

RESULTS

Of the 700 protein spots that were detected reproducibly on each gel, 135 were found to be differentially expressed (P≤ 0.05). Most of responsive proteins in visceral isolate changed in less abundant compared to cutaneous isolate. Among differentially expressed proteins, 56 proteins were confidently identified and classified according to the biological process. The largest groups consist of proteins involved in carbohydrate metabolism and protein synthesis. Most of the identified proteins, which implicated in energy metabolism, cell signaling and virulence were down-regulated, whereas some proteins that have a role in protein folding, antioxidant defense and proteolysis were up-regulated in visceral form. Moreover, the transcript level of some identified proteins such as co-chaperon was confirmed using real-time RT-PCR.

CONCLUSION

L. tropica probably uses different mechanisms for survival and multiplication in viscera to establish viscerotropic leishmaniasis. The current study provides some clues into the mechanisms underlying the dissemination of L. tropica .

Rapid detection of human and canine visceral leishmaniasis: assessment of a latex agglutination test based on the A2 antigen from amastigote forms of Leishmania infantum

The diagnosis of visceral leishmaniasis (VL) in humans and animal reservoir hosts is difficult, particularly in rural areas where the disease is endemic and laboratory facilities are limited. This study aimed to develop a latex agglutination test (LAT) for the rapid detection of anti-Leishmania antibodies against the A2 antigen derived from the amastigote form as well as those against crude antigens derived from the promastigote form of an Iranian strain of Leishmania (Leishmania) infantum. The A2 antigen (42-100 kDa) was prepared from the amastigote form of L. infantum, purified with electroelution and compared with the crude antigen from the promastigote form of L. infantum. Both antigens showed appropriate intensity reactions, were selected using dot blotting of positive and negative pooled sera and used to sensitize 0.9-μm latex beads. The tests were carried out on sera from 43 symptomatic, human patients with VL confirmed by parasitological examination and direct agglutination test (DAT), 30 healthy controls and 32 patients with other infections but without VL. Canine sera were collected from 63 domestic dogs with VL confirmed using parasitological examinations and DAT and 31 healthy dogs from areas non-endemic for VL. Compared with the controls, human sera from DAT-confirmed patients yielded a sensitivity of 88.4% (95% CI, 82.1-94.5%) and specificity of 93.5% (95% CI, 87.0-99.7%) on A2-LAT (amastigote) when 1:3200 was used as the cut-off titre. A good degree of agreement was found between A2-LAT and DAT (0.914). LAT required 3-5 min to complete, versus the 12-18 h needed for DAT. Compared with the controls, A2-LAT of canine sera from DAT-confirmed cases yielded a sensitivity of 95.2% (95% CI, 95.0-95.4%) and specificity of 100% (95% CI 100%) when 1:320 was used as the cut-off titre. A good degree of agreement was found between A2-LAT and DAT (0.968). Similarly, the sensitivity and specificity of Pro.-LAT (promastigote) was calculated to be 88.4% and 91.9%, respectively for human sera and 96.8% and 90.3%, respectively for canine sera. No statistically significant differences were observed between A2-LAT and Pro.-LAT for the detection of human and canine L. infantum infections. In conclusion, A2-LAT and Pro.-LAT could be used in parallel to screen for L. infantum infections in humans and dogs in areas endemic for VL in Iran.

Identification of total and differentially expressed excreted-secreted proteins from Trypanosoma congolense strains exhibiting different virulence and pathogenicity

Animal trypanosomosis is a major constraint to livestock productivity in the tropics and has a significant impact on the life of millions of people globally (mainly in Africa, South America and south-east Asia). In Africa, the disease in livestock is caused mainly by Trypanosoma congolense, Trypanosoma vivax, Trypanosoma evansi and Trypanosoma brucei brucei. The extracellular position of trypanosomes in the bloodstream of their host requires consideration of both the parasite and its naturally excreted-secreted factors (secretome) in the course of pathophysiological processes. We therefore developed and standardised a method to produce purified proteomes and secretomes of African trypanosomes. In this study, two strains of T. congolense exhibiting opposite properties of both virulence and pathogenicity were further investigated through their secretome expression and its involvement in host-parasite interactions. We used a combined proteomic approach (one-dimensional SDS-PAGE and two-dimensional differential in-gel electrophoresis coupled to mass spectrometry) to characterise the whole and differentially expressed protein contents of secretomes. The molecular identification of differentially expressed trypanosome molecules and their correlation with either the virulence process or pathogenicity are discussed with regard to their potential as new diagnostic or therapeutic tools against animal trypanosomosis.

cDNA expression library screening and identification of two novel antigens: ubiquitin and receptor for activated C kinase (RACK) homologue, of the fish parasite Trypanosoma carassii

Trypanosoma carassii is a kinetoplastid parasite infecting cyprinid fish with a high prevalence in nature. Antibodies have been shown to play a protective role in the immune response against this parasite in common carp, Cyprinus carpio. To identify immunogenic and putative protective T. carassii antigens we constructed a lambdaTriplEx2 expression library of the parasite and screened this with pooled carp immune serum collected 6 weeks post-infection. Screening of the library not only revealed ribosomal proteins but identified ubiquitin and a homologue of the receptor for activated C kinase (RACK) as immunogenic proteins. Equivalents of all these proteins have been identified as immunogenic in expression library screenings of other Trypanosomatida, suggesting an evolutionary conservation of their immunogenicity. The possibility that ubiquitin and/or the homologue of RACK could represent protective antigens and be targets for the design of novel therapies is discussed.

Proteomic approaches for discovery of new targets for vaccine and therapeutics against visceral leishmaniasis

Visceral leishmaniasis (VL) is the most devastating type caused by Leishmania donovani, Leishmania infantum, and Leishmania chagasi. The therapeutic mainstay is still based on the antiquated pentavalent antimonial against which resistance is now increasing. Unfortunately, due to the digenetic life cycle of parasite, there is significant antigenic diversity. There is an urgent need to develop novel drug/vaccine targets against VL for which the primary goal should be to identify and characterize the structural and functional proteins. Proteomics, being widely employed in the study of Leishmania seems to be a suitable strategy as the availability of annotated sequenced genome of Leishmania major has opened the door for dissection of both protein expression/regulation and function. Advances in clinical proteomic technologies have enable to enhance our mechanistic understanding of virulence/pathogenicity/host-pathogen interactions, drug resistance thereby defining novel therapeutic/vaccine targets. Expression proteomics exploits the differential expression of leishmanial proteins as biomarkers for application towards early diagnosis. Further using immunoproteomics efforts were also focused on evaluating responses to define parasite T-cell epitopes as vaccine/diagnostic targets. This review has highlighted some of the relevant developments in the rapidly emerging field of leishmanial proteomics and focus on its future applications in drug and vaccine discovery against VL.

Establishing a liquid-phase IEF in combination with 2-DE for the analysis of Leishmania proteins

The recent completion of genome sequencing projects for Leishmania major and near completion for two other species, L. infantum and L. braziliensis, has provided the needed genomic information for investigating the proteomes of Leishmania parasites. However, the design of effective 2-DE-based proteome mapping for complex protozoan parasites like Leishmania has proven to be severely compromised due to extensive overcrowding of spots especially in the acidic regions, coupled to a relatively low representation of basic proteins. In the present study, we optimized a liquid-phase IEF in combination with 2-DE for L. amazonensis promastigote as a way of reducing protein complexity and enhancing representation for low-abundance proteins on gels. Of 20 pH-based fractions eluted from Rotofor cells, 5 representative fractions selected from acidic, basic or neutral regions of the proteome and with adequate protein concentration were further analyzed by 2-DE using medium-range IPG strips. On this basis, we were able to generate high-resolution 2-DE maps encompassing both the acidic and basic ends of the proteome with enhanced spot representation.

Leishmania infantum LeIF protein is an ATP-dependent RNA helicase and an eIF4A-like factor that inhibits translation in yeast

LeIF, a Leishmania protein similar to the eukaryotic initiation factor eIF4A, which is a prototype of the DEAD box protein family, was originally described as a Th1-type natural adjuvant and as an antigen that induces an IL12-mediated Th1 response in the peripheral blood mononuclear cells of leishmaniasis patients. This study aims to characterize this protein by comparative biochemical and genetic analysis with eIF4A in order to assess its potential as a target for drug development. We show that a His-tagged, recombinant, LeIF protein of Leishmania infantum, which was purified from Escherichia coli, is both an RNA-dependent ATPase and an ATP-dependent RNA helicase in vitro, as described previously for other members of the DEAD box helicase protein family. In vivo experiments show that the LeIF gene cannot complement the deletion of the essential TIF1 and TIF2 genes in the yeast Saccharomyces cerevisiae that encode eIF4A. In contrast, expression of LeIF inhibits yeast growth when endogenous eIF4A is expressed off only one of its two encoding genes. Furthermore, in vitro binding assays show that LeIF interacts with yeast eIF4G. These results show an unproductive interaction of LeIF with translation initiation factors in yeast. Furthermore, the 25 amino terminal residues were shown to enhance the ability of LeIF to interfere with the translation machinery in yeast.

Proteomic analysis of antigens fromLeishmania infantum promastigotes

Leishmaniasis is a zoonotic disease caused by the species of the genus Leishmania, flagellated protozoa that multiply inside mammalian macrophages and are transmitted by the bite of the sandfly. The disease is widespread and due to the lack of fully effective treatment and vaccination the search for new drugs and immune targets is needed. Proteomics seems to be a suitable strategy because the annotated sequenced genome of L. major is available. Here, we present a high-resolution proteome for L. infantum promastigotes comprising of around 700 spots. Western blot with rabbit hyperimmune serum raised against L. infantum promastiogote extracts and further analysis by MALDI-TOF and MALDI-TOF/TOF MS allowed the identification of various relevant functional antigenic proteins. Major antigenic proteins were identified as propionil carboxilasa, ATPase beta subunit, transketolase, proteasome subunit, succinyl-diaminopimelate desuccinylase, a probable tubulin alpha chain, the full-size heat shock protein 70, and several proteins of unknown function. In addition, one enzyme from the ergosterol biosynthesis pathway (adrenodoxin reductase) and the structural paraflagellar rod protein 3 (PAR3) were found among non-antigenic proteins. This study corroborates the usefulness of proteomics in identifying new proteins with crucial biological functions in Leishmania parasites.

Kinetics and diagnostic and prognostic potential of quantitative Western blot analysis and antigen-specific enzyme-linked immunosorbent assay in experimental canine leishmaniasis

Quantitative computerized Western blot analysis of antibody responses during experimental canine Leishmania infantum infection distinguished between immunodominant and nonimmunodominant protein bands. Six infected beagles, positive by both PCR and parasite culture, were monitored over 75 weeks postinfection and during a 12-week allopurinol treatment course. All dogs were symptomatic at the time of treatment. Of 12 antigenic bands examined, the immunodominant bands (12, 14, 24, 29, 48, and 68 kDa) showed significantly increased intensities (P<0.01) and higher frequencies of recognition than the nonimmunodominant bands at all time points. Detection of the former bands at 6 weeks postinfection preceded seroconversion by enzyme-linked immunosorbent assay (ELISA) both on crude Leishmania antigen or the recombinant proteins rK39 and HSP70. Reactivity with the 14-, 48-, and 68-kDa bands signified early infection, whereas increased reactivity with the 14-, 24-, and 29-kDa bands was associated with posttreatment parasite persistence and potential unfavorable prognosis. Total lane intensity (TLI) emerged as a sensitive marker for early infection and increased as early as 4 weeks postinfection. TLI had a significantly higher (P<0.01) relative increase rate than crude Leishmania antigen or HSP70 or rK39 ELISA at all time points. These immunodominant antigens and TLI, as determined by quantitative Western blotting, will be valuable for early detection and treatment evaluation of canine leishmaniasis.