Gene design, optimization of protein expression and preliminary evaluation of a new chimeric protein for the serological diagnosis of both human and canine visceral leishmaniasis

Construction and mouse antibody response evaluation of juvenile stage-specific chimeric protein from Fasciola gigantica

Fasciolosis, caused by the liver fluke Fasciola gigantica, is a major parasitic disease that affects livestock and therefore causes significant economic losses in tropical countries. Although anthelminthic drugs can kill the parasite, drug-resistant liver fluke populations are increasing. In this study, a recombinant F. gigantica chimeric protein (rFgCHI) consisting of cathepsin L1H (FgCL1H), cathepsin B3 (FgCB3), and Saposin-like protein 1 (FgSAP1) was designed and expressed in Escherichia coli (BL21). The molecular weight of rFgCHI was 61 kDa. To study the antibody response, male BALB/c mice were immunized via the subcutaneous injection of rFgCHI combined with Quil A. Immunization with rFgCHI showed the induction of IgG1 and IgG2a with a higher IgG1 isotype level, indicating the potential of mixed Th1/Th2 immune responses, with Th2 predominating. However, the results showed high levels of IgG against the single proteins, except for rFgSAP1. Through Western blotting, mouse anti-rFgCHI polyclonal antibodies could be detected to the native proteins obtained from the parasite at all stages. Immunolocalization also revealed that the anti-rFgCHI antibodies could detect targeted antigens in the cecal epithelium of the parasite. These results demonstrated that rFgCHI is immunogenic to the mouse immune system and may potentially be a protein candidate for the development of a fasciolosis vaccine.

Serodiagnosis of paucibacillary and multibacillary leprosy using a recombinant chimeric protein composed of specific B-cell epitopes derived from Mycobacterium leprae proteins

Leprosy diagnosis is difficult due to the clinical similarity with other infectious diseases, and laboratory tests presents problems related to sensitivity and/or specificity. In this study, we used bioinformatics to assess Mycobacterium leprae proteins and formulated a chimeric protein that was tested as a diagnostic marker for the disease. The amino acid sequences from ML0008, ML0126, ML0308, ML1057, ML2028, ML2038, ML2498 proteins were evaluated, and the B-cell epitopes QASVAYPATSYADFRAHNHWWNGP, SLQRSISPNSYNTARVDP and QLLGQTADVAGAAKSGPVQPMGDRGSVSPVGQ were considered M. leprae-specific and used to construct the gene encoding the recombinant antigen. The gene was constructed, the recombinant protein was expressed, purified and tested in ELISA using 252 sera, which contained samples from multibacillary (MB) or paucibacillary (PB) leprosy patients, from their household contacts and healthy individuals, as well as from patients with Chagas disease, visceral and tegumentary leishmaniases (VL/TL), malaria, tuberculosis, and HIV. Sensitivity (Se) and specificity (Sp) for MB and PB samples compared to sera from both healthy subjects and individuals with cross-reactive diseases were 100%. The Se value for MB and PB samples compared to sera from household contacts was 100%, but Sp was 64%. In conclusion, data suggest that this protein could be considered in future studies for leprosy diagnosis.

Diagnostic Potential for the Detection of Canine Visceral Leishmaniasis of an ELISA Assay Based on the Q5 Recombinant Protein: A Large-Scale and Comparative Evaluation Using Canine Sera with a Positive Diagnosis from the Dual-Path-Platform (DPP) Test

Dogs are considered the major domestic reservoir for human visceral leishmaniasis, a serious disease caused by the Leishmania infantum parasite. Diagnosis of canine visceral leishmaniasis (CVL) is critical for disease control, with several methods currently available. Among the serological tests, the DPP rapid test and the EIE-LVC, more commonly used in Brazil, are associated with variable sensitivity and specificity. Research with novel recombinant proteins such as the ELISA with the recombinant chimeric protein Q5 may therefore improve the CVL diagnosis. This study aimed to evaluate the true diagnostic potential of Q5 in an ELISA assay using a large number of CVL-suspected sera (406) with a previous positive diagnosis based on the rapid DPP test. Sera from the DPP-positive dogs, also assessed with the EIE-LVC test, were compared with sera from healthy dogs (n = 46) and used for ELISA tests using the recombinant Q5. The resulting data as well as the correlation with the clinical signs and the environmental characteristics of the animals were analyzed using Medal and GraphPad Prism 8.0. Overall, similar levels of lower sensitivity (67-68%) were seen for both the commercial EIE-LVC test and the Q5 ELISA when all assessed sera were considered, but a much greater sensitivity (92%) was seen for those samples from symptomatic dogs only. In contrast, many negative results were observed for the DPP-positive sera from asymptomatic dogs or those with no clinical information available. A selection of those sera were tested yet again in new ELISA assays using a second batch of the recombinant Q5, purified under milder denaturing conditions, as well as using another recombinant protein (Lci13). The results reveal a higher-than-expected incidence of likely false-positive results for DPP, reinforcing the need for other recombinant proteins, such as the chimeric Q5, to be investigated as possible alternatives to the currently used CVL diagnostic methods.

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.

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.

Sensitive and specific serodiagnosis of tegumentary leishmaniasis using a new chimeric protein based on specific B-cell epitopes of Leishmania antigenic proteins

Serological tests used for the diagnosis of tegumentary leishmaniasis (TL) presents problems, mainly related to their variable sensitivity and/or specificity, which can be caused by low levels of antileishmanial antibodies or by presence of cross-reactive diseases, respectively. In this context, the search for new antigenic candidates presenting higher sensitivity and specificity is urgently required. In the present study, the amino acid sequences of the LiHyT, LiHyD, LiHyV, and LiHyP proteins, which were previously showed to be antigenic in the visceral leishmaniasis (VL), were evaluated and eight B-cell epitopes were predicted and used for construction of gene codifying a chimeric protein called ChimLeish. The protein was expressed, purified and evaluated as a recombinant antigen in ELISA (Enzyme-Linked Immunosorbent Assay) for the diagnosis of TL. The own B cell epitopes used to construct the chimera were synthetized and also evaluated as antigens, as well as a soluble Leishmania braziliensis antigenic extract (SLA). Results showed that ChimLeish presented 100% sensitivity and specificity to diagnose TL, while synthetic peptides showed sensitivity varying from 9.1% to 90.9%, while specificity reached from 98.3% to 99.1%. SLA showed sensitivity and specificity of 18.2% and 98.3%, respectively. A preliminary prognostic evaluation showed that anti-ChimLeish IgG antibodies declined in significant levels, when serological reactivity was compared before and six months after treatment, suggesting also a possible prognostic role of this antigen for TL.

ChimLeish, a new recombinant chimeric protein evaluated as a diagnostic and prognostic marker for visceral leishmaniasis and human immunodeficiency virus coinfection

Visceral leishmaniasis (VL) is a neglected tropical disease of global importance caused by parasites of the genus Leishmania, and coinfection with human immunodeficiency virus (HIV) is common in countries where both diseases are endemic. In particular, widely used immunological tests for VL diagnosis have impaired sensitivity (Se) and specificity (Sp) in VL/HIV coinfected patients and there is also cross-reactivity with other endemic diseases, e.g., Chagas disease, malaria, and tuberculosis. To develop new antigens to improve the diagnosis of VL and VL/HIV coinfection, we predicted eight specific B-cell epitopes of four Leishmania infantum antigens and constructed a recombinant polypeptide chimera antigen called ChimLeish. A serological panel of 195 serum samples was used to compare the diagnostic capabilities of ChimLeish alongside the individual synthetic peptides. ChimLeish reacted with sera from all VL and VL/HIV coinfected patients [Se = 100%; Sp = 100%; area under the curve (AUC) = 1.0]. Peptides showed lower reactivities (Se = 76.8 to 99.2%; Sp = 67.1 to 95.7%; AUC between 0.87 and 0.98) as did a L. infantum antigenic preparation used as an antigen control (Se = 56.8%; Sp = 69.5%: AUC = 0.45). Notably, ChimLeish demonstrated a significant reduction (p < 0.05) of anti-ChimLeish antibodies after treatment and cure of a small number of patients. Although only a limited serological panel was tested, preliminary data suggest that ChimLeish should be evaluated in larger sample studies for the diagnosis of VL and VL/HIV coinfection.

Recombinant antigens used as diagnostic tools for lymphatic filariasis

Lymphatic filariasis (LF) is a parasitic disease caused by the worms Wuchereria bancrofti, Brugia malayi, or Brugia timori. It is a tropical and subtropical illness that affects approximately 67 million people worldwide and that still requires better diagnostic tools to prevent its spread and enhance the effectiveness of control procedures. Traditional parasitological tests and diagnostic methods based on whole protein extracts from different worms are known for problems related to sample time collection, sensitivity, and specificity. More recently, new diagnostic tools based on immunological methods using recombinant antigens have been developed. The current review describes the several recombinant antigens used as tools for lymphatic filariasis diagnosis in antigen and antibody capture assays, highlighting their advantages and limitations as well as the main commercial tests developed based on them. The literature chronology is from 1991 to 2021. First, it describes the historical background related to the identification of relevant antigens and the generation of the recombinant polypeptides used for the LF diagnosis, also detailing features specific to each antigen. The subsequent section then discusses the use of those proteins to develop antigen and antibody capture tests to detect LF. So far, studies focusing on antibody capture assays are based on 13 different antigens with at least six commercially available tests, with five proteins further used for the development of antigen capture tests. Five antigens explored in this paper belong to the SXP/RAL-2 family (BmSXP, Bm14, WbSXP-1, Wb14, WbL), and the others are BmShp-1, Bm33, BmR1, BmVAH, WbVAH, BmALT-1, BmALT-2, and Wb123. It is expected that advances in research with these antigens will allow further development of tests combining both sensitivity and specificity with low costs, assisting the Global Program to Eliminate Lymphatic Filariasis (GPELF).

Serodiagnosis of canine leishmaniasis using a novel recombinant chimeric protein constructed with distinct B-cell epitopes from antigenic Leishmania infantum proteins

Visceral leishmaniasis (VL) is an important public health problem in the world, and control measures are insufficient to avoid the spread of this neglected disease. Dogs are important domestic reservoirs of Leishmania parasites in countries where VL is a zoonosis, representing a major source of infection between sand fly vectors and humans. In this context, a precise diagnosis of canine leishmaniasis (CanL) could help to reduce the number of human cases. Distinct approaches for the diagnosis of CanL have used recombinant proteins in serological assays. However, variable results of the antigens have been found, mainly to diagnosis asymptomatic cases. The present study used bioinformatics to select specific B-cell epitopes of four Leishmania infantum proteins, which had previously been proven to be antigenic in VL, aiming to produce a novel chimeric protein and to evaluate it for the diagnosis of CanL. Seven B-cell epitopes were identified and used to construct the chimera, which was analyzed in a recombinant format through an ELISA assay against a canine serological panel. A soluble Leishmania antigenic extract (SLA) was used as an antigen control. Results showed 100 % sensitivity and specificity for chimera, while when using SLA the values were 26.0 % and 96.4 %, respectively. The performance of chimera was compared with a commercial kit using asymptomatic and symptomatic dog sera, and the data showed that no false-negative result was found when the recombinant protein was used. However, when using the commercial kit, 40.0 % and 16.0 % of the false-negative results were found, respectively. In conclusion, the recombinant chimera showed an antigenic potential to be evaluated in new studies against a larger serological panel for the diagnosis of CanL.

Borrelia burgdorferi BmpA-BBK32 and BmpA-BBA64: New Recombinant Chimeric Proteins with Potential Diagnostic Value

Currently, the diagnosis of Lyme disease is based mostly on two-tiered serologic testing. In the new generation of immunoenzymatic assays, antigens comprise whole-cell lysates of members of the Borrelia burgdorferi sensu lato (s.l.) species complex, with the addition of selected recombinant proteins. Due to the high diversity of members of the B. burgdorferi s.l. genospecies and the low degree of conservation among the amino acid sequences of their proteins, serodiagnostic methods currently in use are not sufficient for the correct diagnosis of borreliosis. Two divalent chimeric proteins (BmpA-BBK32 and BmpA-BBA64) were expressed in Escherichia coli. Following purification by one-step metal-affinity chromatography, preparations were obtained containing milligram levels of chimeric protein exhibiting electrophoretic purity in excess of 98%. Reactivity of the new chimeric proteins with specific human IgG antibodies was preliminarily determined by Western blot. For this purpose, 20 negative sera and 20 positive sera was used. The new chimeric proteins were highly reactive with IgG antibodies contained in the serum of patients suffering from borreliosis. Moreover, no immunoreactivity of chimeric proteins was observed with antibodies in the sera of healthy people. These promising results suggest that new chimeric proteins have the potential to discriminate between positive and negative sera.

A critical review of the applicability of serological screening for Leishmaniasis in blood banks in Brazil

Leishmaniasis is a group of diseases caused by several species of protozoa. It is a major public health concern in its visceral form, accounting annually for 59,000 deaths, and an estimated 12 million infected patients per year. The importance of VL resides not only in its high incidence and wide distribution but also in the possibility of the disease progressing to the severe and lethal forms, especially in children and immunosuppressed individuals, when associated with malnutrition and concomitant infections. This study is a bibliographical review, aiming to understand the sensitivity and specificity parameters of the tests used to detect Leishmaniasis, as well as to understand if there is any relevance in proposing a serological screening for Leishmaniasis in blood banks. In general, we observed that there are currently several types of tests for detecting Leishmaniasis: parasitological, serological and molecular. In such tests, many serological methods and kits are available for the detection of asymptomatic visceral leishmaniasis, but there is variability in sensitivity and specificity among the methods. The gold standard for the diagnosis of visceral leishmaniasis is the parasitological method, through the aspiration of bone marrow, with higher sensitivity by splenic puncture. Due to the relevance of the disease and the available data from research centers, there is evidence to propose a transfusion serological screening for visceral Leishmaniasis, pointing to the need for further studies.

Identification of immunodominant proteins of Leishmania infantum by immunoproteomics to evaluate a recombinant multi-epitope designed antigen for serodiagnosis of human visceral leishmaniasis

Visceral leishmaniasis (VL) is a protozoan disease caused by Leishmania infantum in the Mediterranean region including Iran. In 95% of cases, the disease can be fatal if not rapidly diagnosed and left untreated. We aimed to identify immunoreactive proteins of L. infantum (Iranian strain), and to design and evaluate a recombinant multi-epitope antigen for serodiagnosis of human VL. To detect the immunoreactive proteins of L. infantum promastigotes, 2DE immunoblotting technique was performed using different pooled sera of VL patients. The candidate immunoreactive proteins were identified using MALDI-TOF/TOF mass spectrophotometry. Among 125 immunoreactive spots detected in 2-DE gels, glucose-regulated protein 78 (GRP78), ubiquitin-conjugating enzyme E2, calreticulin, mitochondrial heat shock 70-related protein 1 (mtHSP70), heat shock protein 70-related protein, i/6 autoantigen-like protein, ATPase beta subunit, and proteasome alpha subunit 5 were identified. The potent epitopes from candidate immunodominant proteins including GRP78, mtHSP70 and ubiquitin-conjugating enzyme E2 were then selected to design a recombinant antigenic protein (GRP-UBI-HSP). The recombinant antigen was evaluated by ELISA and compared to direct agglutination test for detection of anti L. infantum human antibodies. We screened 34 sera of VL patients from endemic areas and 107 sera of individuals without L. infantum infection from non-endemic area of VL. The recombinant protein-based ELISA provided a sensitivity of 70.6% and a specificity of 84.1%. These results showed that GRP78, ubiquitin-conjugating enzyme E2, and mtHSP70 proteins are potential immunodominant targets of the host immune system in response to the parasite and they can be considered as potential candidate markers for diagnosis purposes.