A Leishmania infantum hypothetical protein evaluated as a recombinant protein and specific B-cell epitope for the serodiagnosis and prognosis of visceral leishmaniasis

A systematic review of peptide-based serological tests for the diagnosis of leishmaniasis

Serological methods should meet the needs of leishmaniasis diagnosis due to their high sensitivity and specificity, economical and adaptable rapid diagnostic test format, and ease of use. Currently, the performances of serological diagnostic tests, despite improvements with recombinant proteins, vary greatly depending on the clinical form of leishmaniasis and the endemic area. Peptide-based serological tests are promising as they could compensate for antigenic variability and improve performance, independently of Leishmania species and subspecies circulating in the endemic areas. The objective of this systematic review was to inventory all studies published from 2002 to 2022 that evaluate synthetic peptides for serological diagnosis of human leishmaniases and also to highlight the performance (e.g., sensitivity and specificity) of each peptide reported in these studies. All clinical forms of leishmaniasis, visceral and tegumentary, and all Leishmania species responsible for these diseases were considered. Following PRISMA statement recommendations, 1,405 studies were identified but only 22 articles met the selection criteria and were included in this systematic review. These original research articles described 77 different peptides, of which several have promising performance for visceral or tegumentary leishmaniasis diagnosis. This review highlights the importance of and growing interest in synthetic peptides used for serological diagnosis of leishmaniases, and their performances compared to some widely used tests with recombinant proteins.

A Promising Tool in Serological Diagnosis: Current Research Progress of Antigenic Epitopes in Infectious Diseases

Infectious diseases, caused by various pathogens in the clinic, threaten the safety of human life, are harmful to physical and mental health, and also increase economic burdens on society. Infections are a complex mechanism of interaction between pathogenic microorganisms and their host. Identification of the causative agent of the infection is vital for the diagnosis and treatment of diseases. Etiological laboratory diagnostic tests are therefore essential to identify pathogens. However, due to its rapidity and automation, the serological diagnostic test is among the methods of great significance for the diagnosis of infections with the basis of detecting antigens or antibodies in body fluids clinically. Epitopes, as a special chemical group that determines the specificity of antigens and the basic unit of inducing immune responses, play an important role in the study of immune responses. Identifying the epitopes of a pathogen may contribute to the development of a vaccine to prevent disease, the diagnosis of the corresponding disease, and the determination of different stages of the disease. Moreover, both the preparation of neutralizing antibodies based on useful epitopes and the assembly of several associated epitopes can be used in the treatment of disease. Epitopes can be divided into B cell epitopes and T cell epitopes; B cell epitopes stimulate the body to produce antibodies and are therefore commonly used as targets for the design of serological diagnostic experiments. Meanwhile, epitopes can fall into two possible categories: linear and conformational. This article reviews the role of B cell epitopes in the clinical diagnosis of infectious diseases.

Evaluation from a B-cell epitope-based chimeric protein for the serodiagnosis of tegumentary and visceral leishmaniasis

The diagnosis of leishmaniasis presents problems due to the variable sensitivity and/or specificity of tests. In addition, high levels of anti-parasite antibodies can remain after treatment, making it difficult to conduct a prognostic follow-up of patients. In this context, it is necessary to identify new candidates to be examined for the sensitive and specific diagnosis of the disease. In the present study, four Leishmania proteins, previously shown as antigenic for tegumentary leishmaniasis (TL), were evaluated, and their linear specific B-cell epitopes were predicted and used to generate a new gene codifying chimeric protein called ChimB, which was cloned, and the recombinant version was expressed, purified, and evaluated in ELISA (Enzyme-Linked Immunosorbent Assay) to diagnose TL and visceral leishmaniasis (VL). A total of 220 human serum samples were used, and, when ChimB was used, results showed sensitivity, specificity, and positive and negative predictive values of 100% for the diagnosis of both diseases; however, when using peptides, the sensitivity values reached from 28.0% to 57.3% and specificity varied from 16.3% to 83.7%. A soluble Leishmania extract (SLA) showed sensitivity and specificity values of 30.7% and 45.9%, respectively. The area under the curve (AUC) value for ChimB was 1.0, while for synthetic peptides, this value reached between 0.502 and 0.635, whereas for SLA, the value was of 0.589. Serological assays using sera samples collected before and after treatment showed significant reductions in the anti-ChimB antibody levels after therapy, suggesting a prognostic role of this recombinant antigen. In conclusion, preliminary data suggest the use from ChimB as a potential candidate for the diagnosis and prognosis of leishmaniasis.

Leishmania LiHyC protein is immunogenic and induces protection against visceral leishmaniasis

AIMS

Treatment against visceral leishmaniasis (VL) presents problems by toxicity of drugs, high cost and/or emergence of resistant strains. The diagnosis is hampered by variable sensitivity and/or specificity of tests. In this context, prophylactic vaccination could represent a control measure against disease. In this study, the protective efficacy from Leishmania LiHyC protein was evaluated in murine model against Leishmania infantum infection.

METHODS AND RESULTS

LiHyC was used as recombinant protein (rLiHyC) associated with saponin (rLiHyC/S) or Poloxamer 407-based polymeric micelles (rLiHyC/M) to immunize mice. Animals received also saline, saponin or empty micelles as controls. The immunogenicity was evaluated before and after challenge, and results showed that vaccination with rLiHyC/S or rLiHyC/M induced the production of high levels of IFN-γ, IL-12 and GM-CSF in cell culture supernatants, as well as higher IFN-γ expression evaluated by RT-qPCR and involvement from CD4⁺ and CD8⁺ T cell subtypes producing IFN-γ, TNF-α and IL-2. A positive lymphoproliferative response was also found in cell cultures from vaccinated animals, besides high levels of rLiHyC- and parasite-specific nitrite and IgG2a antibodies. Immunological assays correlated with significant reductions in the parasite load in spleens, livers, bone marrows and draining lymph nodes from vaccinated mice, when compared to values found in the controls. The micellar composition showed slightly better immunological and parasitological data, as compared to rLiHyC/S.

CONCLUSION

Results suggest that rLiHyC associated with adjuvants could be considered for future studies as a vaccine candidate against VL.

In Silico Design of Recombinant Chimera T Cell Peptide Epitope Vaccines for Visceral Leishmaniasis

Visceral leishmaniasis (VL) is a neglected tropical disease caused by protozoan parasites of the genus Leishmania. Systemic VL is fatal if untreated and there are no prophylactic human vaccines available. Several studies suggest that Th1 cell-mediated immunity plays a major role in protecting against VL. In this chapter we describe a method for designing recombinant chimera vaccines in silico based on the prediction of T cell epitopes within protein antigens identified as potential protective immunogens. Development of a recombinant chimera protein (RCP) vaccine using T cell epitope peptides identified from four Leishmania proteins is used as an exemplar of this method.

Antigens and their diagnostic performance for Canine Visceral Leishmaniasis: A critical review

Canine visceral leishmaniasis (CVL) is the most aggressive and lethal form of leishmaniasis manifesting in dogs and represents a major public health concern. Although there are sufficiently sensitive molecular tools for CVL diagnosis, they are not accessible at the main points of disease dissemination, in which context serodiagnosis has been used as an alternative tool on the epidemiological control. As an attempt to develop more accurate immunodiagnostic assays, many antigens have been tested over the years, on different platforms. This review aimed to access studies reporting new antigens that can be applied for CVL serodiagnosis. Articles published from January of 2016 to March of 2021 were retrieved from Google Scholar, Science Direct, and PubMed, using "Canine Visceral Leishmaniasis" and "Serodiagnosis" as keywords. In total, 1527 articles were identified, of which 42 were selected based on exclusion factors. Sensitivity, specificity, sample size, and sample quality data were extracted by manual curation and analyzed. Of the selected articles, 26 contemplated ELISA, which enabled a more thorough comparison and a critical review of these studies. Soluble Leishmania Antigens (SLA) and the A2 protein were used as controls in 53.8 and 46.15 % of these articles, respectively, and were evaluated separately; their frequent use was questioned. Subsequently, articles that evaluated other assay platforms, such as immunochromatography, immunosensors, and others, were also reported and evaluated. Finally, data relative to validation studies of commercial kits were briefly discussed. Our results show that there are several antigens with great potential for the development of accurate diagnostic tools, but further testing is required. The critical analysis also brings insights that can be useful for more assertive diagnostic development of more robust tools for CVL serodiagnosis.

Diagnostic application of sensitive and specific phage-exposed epitopes for visceral leishmaniasis and human immunodeficiency virus coinfection

The diagnosis of visceral leishmaniasis (VL) has improved with the search of novel antigens; however, their performance is limited when samples from VL/human immunodeficiency virus (HIV)-coinfected patients are tested. In this context, studies conducted to identify more suitable antigens to detect both VL and VL/HIC coinfection cases should be performed. In the current study, phage display was performed using serum samples from healthy subjects and VL, HIV-infected and VL/HIV-coinfected patients; aiming to identify novel phage-exposed epitopes to be evaluated with this diagnostic purpose. Nine non-repetitive and valid sequences were identified, synthetized and tested as peptides in enzyme-linked immunosorbent assay experiments. Results showed that three (Pep2, Pep3 and Pep4) peptides showed excellent performance to diagnose VL and VL/HIV coinfection, with 100% sensitivity and specificity values. The other peptides showed sensitivity varying from 50.9 to 80.0%, as well as specificity ranging from 60.0 to 95.6%. Pep2, Pep3 and Pep4 also showed a potential prognostic effect, since specific serological reactivity was significantly decreased after patient treatment. Bioinformatics assays indicated that Leishmania trypanothione reductase protein was predicted to contain these three conformational epitopes. In conclusion, data suggest that Pep2, Pep3 and Pep4 could be tested for the diagnosis of VL and VL/HIV coinfection.

Molecular Tracking of the Leishmania Parasite

With the Visceral Leishmaniasis/Kala-azar Elimination Program in South Asia in its consolidation phase, the focus is mainly on case detection, vector control, and identifying potential sources of infection. Accordingly, emphasis is presently on curbing transmission, which is potentially achievable by identification and elimination of potential reservoirs. The strongest contenders for being the disease reservoir are cases of Post Kala-azar Dermal Leishmaniasis (PKDL) which occurs in a minor proportion of individuals apparently cured of Visceral Leishmaniasis (VL). The demonstration of parasites in tissue aspirates despite being a risky and invasive process is the gold standard for diagnosis of VL, but is now being replaced by serological tests e.g., rK39 strip test and direct agglutination test. However, these antibody based tests are limited in their ability to diagnose relapses, detect cases of PKDL, and monitor effectiveness of treatment. Accordingly, detection of antigen or nucleic acids by polymerase chain reaction has been successfully applied for monitoring of parasite kinetics. This review article provides updated information on recent developments regarding the available antibody or antigen/nucleic acid based biomarkers for longitudinal monitoring of patients with VL or PKDL and emphasizes the need for availability of studies pertaining to quantification of treatment response or relapse.

High Performance of ELISA test using recombinant rLiNTPDase2 from Leishmania infantum: a Phase II diagnosis of Canine Visceral Leishmaniasis

Canine visceral leishmaniasis (CVL) has been the theme of several studies given the importance of dog as natural reservoir of the pathogen Leishmania infantum in endemic regions and its role on dissemination of CVL and human visceral Lesihmaniasis (VL). The current immunodiagnosis of CVL has limitations concerning accuracy, specificity and sensitivity. Therefore, improvements are required. rLiNTPDase2 has been previously highlighted as a new recombinant antigen from L. infantum to the CVL diagnosis by ELISA assay (rLiNTPDase2-ELISA). In this study, we aimed to evaluate rLiNTPDase2-ELISA in a Phase II study with 651 dog sera samples, also comparing it with methodologies previously established and used in epidemiology surveillance in Brazil, an endemic country of CVL and VL. The rLiNTPDase2-ELISA using standard control sera showed high capability to distinguish between positive and negative sera, sensitivity of 92.6% and specificity of 88.5%. The test was reproductive and the kappa statistics judgement "substantial agreement". rLiNTPDase2-ELISA does not show cross-reactivity with ehrlichiosis-reagent sera. However, we verified 15.3% of cross-reactivity with Chagas disease-reagent sera. The performance of rLiNTPDase2-ELISA was evaluated using sera samples from vaccinated dogs (Leish-Tec®). The results showed high agreement with parasitological and PCR results (sensitivity of 100.0% and specificity of 91.7%). Furthermore, we compared the performance of rLiNTPDase2-ELISA in CVL-reagent sera samples from endemic areas, which were previously diagnosed using other tests for CVL: immunofluorescent (IFI-LVC-Bio-Manguinhos), IFI-LVC-Bio-Manguinhos coupled to ELISA (EIE-LVC-Bio-Manguinhos) and the Rapid Dual Path Platform® (TR-DPP®-Bio-Manguinhos) coupled to EIE-LVC-Bio-Manguinhos. rLiNTPDase2-ELISA showed high level of concordance with IFI-LVC-Bio-Manguinhos (88.6%) and with IFI-LVC-Bio-Manguinhos coupled to EIE-LVC-Bio-Manguinhos (82.9%) but not with TR-DPP® -Bio-Manguinhos coupled to EIE-LVC-Bio-Manguinhos (33.3%), which casts doubts on the effectiveness of this latest test. In addition, the rLiNTPDase2 antigen adsorbed in 96-well plate was stable enough to be used at least for three months. Taken together, our data confirmed, by Phase II study using hundreds samples, the good potential of rLiNTPDase2-ELISA to be used in the field as a new diagnostic assay for CVL.