Evaluation of an ELISA for canine leishmaniasis immunodiagnostic using recombinant proteins

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.

Impedimetric immunosensor for rapid and simultaneous detection of chagas and visceral leishmaniasis for point of care diagnosis

In this work, a dual detection system based on an impedimetric immunosensor was developed for the first time for the simultaneous detection of anti-Trypanosoma cruzi and anti-Leishmania infantum antibodies in human and dog serum samples. The IBMP 8.1 and rLci1A/rLci2B recombinant antigens were immobilized over the surface of dual screen-printed carbon electrodes (W1 and W2) modified with poly (4-hydroxyphenylacetic acid). Under optimized conditions, the immunosensor recognized specific interactions for anti-T. cruzi antibodies up to a dilution of 1:10,240 and for anti-L. infantum up to 1:5120 in canine serum samples. Relative standard deviation (RSD) values of 2.8% for W1 and 3.6% for W2 were obtained for T. cruzi (W1) and L. infantum antigen (W2) samples in three different electrodes for 3 days (n = 9). The immunosensor was stored at 4 °C for 8 weeks, with activity retention of 70.2% in W1 and 78.2% in W2. The results using the recombinant proteins revealed that all antigens discriminated between negative and positive samples (p < 0.0001) in both dog and human groups, as well as no cross-reactivity could be detected among sera with other infections. With this approach, immunosensor-based diagnostic tests achieved 100% accuracy, suggesting that the antigens are eligible to enter Phase-II studies.

Recent advances and new strategies in Leishmaniasis diagnosis

Leishmaniasis is a set of complex and multifaceted syndromes, with different clinical manifestations, caused by different species of the genus Leishmania spp. that can be characterized by at least four syndromes: visceral leishmaniasis (VL, also known as kala-azar), post-kala-azar dermal leishmaniasis (PKDL), cutaneous leishmaniasis (CL), and mucocutaneous leishmaniasis (MCL). Among the most serious clinical forms, VL stands out, which causes the death of around 59,000 people annually. Fast and accurate diagnosis in VL is essential to reduce the disease's morbidity and mortality. There are a large number of diagnostic tests for leishmaniasis, however they do cross-react with other protozoa and their sensitivity changes according to the clinical form of the disease. Thus, it is essential and necessary to provide a diagnosis that is sufficiently sensitive to detect asymptomatic infected individuals and specific to discriminate individuals with other infectious and parasitic diseases, thus enabling more accurate diagnostic tools than those currently used. In this context, the aim of this review is to summarize the conventional diagnostic tools and point out the new advances and strategies on visceral and cutaneous leishmaniasis diagnosis.

Multiplex flow cytometry serology to diagnosis of canine visceral leishmaniasis

An accurate diagnosis of visceral leishmaniasis is an essential tool for control of the disease. While serologic methods are very useful, these conventional methodologies still present limitations in terms of sensitivity and specificity. The use of flow cytometry is a worldwide trend in the development of high-performance diagnostic methods. Herein, we describe a new flow cytometry serology test, characterized by the employment of the Cytometric Bead Array microspheres A4 and E4 coated with the recombinant antigens rLci1A and rLci2B respectively, to improve the serodiagnosis of canine visceral leishmaniasis. The tests were conducted in a wide variety of sera groups (n = 140), where the diagnostics development would be optimized accounting not just the ability to identify infected dogs with different clinical status, but also to exclude cross-reaction and differentiate vaccinated dogs from dogs infected. Serological testing of the antigenic system A4-rLci1A showed a sensitivity of 90.0% and specificity of 75%, while the E4-rLci2B testing demonstrated a sensitivity of 95.0% and specificity of 82.5%. The use of a multiplex assay of A4-rLci1A and E4-rLci2B, resulted in a diagnostic improvement, with a sensitivity of 95.0% and specificity of 91.2%. Our results show that this novel flow cytometry serology test is a viable tool for sensitive and specific serodiagnosis. Notably, the combination of distinct antigenic systems allows us to test for antibodies to multiple recombinant antigens from a single serum sample. This benefit emphasizes the importance of this methodology as an alternative in the serological diagnosis.

High accuracy of an ELISA test based in a flagella antigen of Leishmania in serodiagnosis of canine visceral leishmaniasis with potential to improve the control measures in Brazil - A Phase II study

BACKGROUND

Canine Visceral leishmaniasis (CVL) is a serious public health problem, thus for its control, the Ministry of Health in Brazil recommends the rapid diagnosis and euthanasia of seropositive dogs in endemic areas. Therefore, our group had previously selected six recombinant proteins (rLci1, rLci2, rLci4, rLci5, rLci8, and rLci12) due to their high potential for CVL diagnostic testing. The present study aims to produce an immunodiagnostic test using the aforementioned antigens, to improve the performance of the diagnosis of CVL recommended by Brazilian Ministry of Health.

METHODOLOGY/PRINCIPAL FINDINGS

To evaluate the recombinant proteins in the serological assays, positive and negative samples were selected based on parasitological test (culture) and molecular test (qPCR) of splenic aspirate. Initially, we selected 135 dog serum samples, 73 positives (symptomatic and asymptomatic) and 62 negatives to screen recombinant proteins on ELISA platform. Then, for rLci5 ELISA validation, 361 serum samples collected in a cross-sectional study were selected, being 183 positives (symptomatic and asymptomatic) and 178 negatives. In the screening of the recombinant proteins, rLci5 was the only protein to present a performance statistically higher than the performance presented by EIE-LVC test, presenting 96% (IC 95%; 85-99%) vs. 83% (IC 95%; 69-92%) of sensitivity for symptomatic dogs, 71% (IC 95%; 49-97%) vs. 54% (IC 95%; 33-74%) for asymptomatic dogs and 94% (IC 95%; 83-99%) vs, 88% (IC 95%; 76-95% of specificity. Thus, the rLci5 protein was selected to compose a final ELISA test. Validation of rLci5 ELISA showed 87% (IC 81-91%) of sensitivity, 94% (IC 95%; 90-97%) of specificity and 90% accuracy. Testing the EIE-LVC with the same validation panel, we observed a lower performance when compared to ELISA rLci5 (sensitivity of 67% (IC 95%; 59-74%), specificity of 87% (IC 95%; 81-92%), and accuracy of 77%). Finally, the performance of current CVL diagnostic protocol recommended by Brazilian Ministry of Health, using DPP-LVC as screening test and EIE-LVC as confirmatory test, was compared with a modified protocol, replacing EIE-LVC by rLci5 ELISA. The current protocol presented a sensitivity of 59% (IC 95%; 52-66%), specificity of 98% (IC 95%; 95-99%) and accuracy of 80% (IC 95%; 76-84%), while the modified protocol presented a sensitivity of 71% (IC 95%; 63-77%), specificity of 99% (IC 95%; 97-100%) and accuracy of 86% (IC 95%; 83-89%).

CONCLUSION

Thus, we concluded that rLci5 ELISA is a promising test to replace EIE-LVC test and increase the diagnostic performance of CVL in Brazil.

Diagnostic application of recombinant Leishmania proteins and evaluation of their in vitro immunogenicity after stimulation of immune cells collected from tegumentary leishmaniasis patients and healthy individuals

The present study evaluated the cytokine profile in PBMC supernatants and the humoral response in mucosal leishmaniasis (ML) patients and in healthy subjects living in an endemic area. Four proteins, which had previously proven to be antigenic in the human disease, were tested: LiHyM, enolase, eukaryotic initiation factor 5a, and Beta-tubulin. Results showed that all of the proteins stimulated human cells with higher IFN-γ and lower IL-4 and IL-10 levels. The analysis of antibody isotypes correlated with cell response, since the IgG2 production was higher than IgG1 in both groups. By contrast, a Th2 response was found when an antigenic Leishmania extract was used. Serological analyses revealed high sensitivity and specificity values for the serodiagnosis of the disease, when compared to the data obtained using the antigenic preparation. In conclusion, this study presents new candidates to be evaluated as biomarkers in tegumentary leishmaniasis.

Use of Recombinant Antigens for Sensitive Serodiagnosis of American Tegumentary Leishmaniasis Caused by Different Leishmania Species

American tegumentary leishmaniasis (ATL) (also known as cutaneous leishmaniasis [CL]) is caused by various species of protozoa of the genus Leishmania. The diagnosis is achieved on a clinical, epidemiological, and pathological basis, supported by positive parasitological exams and demonstration of leishmanin delayed-type hypersensitivity. Serological assays are not routinely used in the diagnosis because many are considered to have low sensitivity and the particular Leishmania species causing the disease can lead to variable performance. In the present study, we generated recombinant versions of two highly conserved Leishmania proteins, Leishmania (Viannia) braziliensis-derived Lb8E and Lb6H, and evaluated both in enzyme-linked immunosorbent assays (ELISA). Recombinant Lb6H (rLb6H) had better performance and reacted with 100.0% of the ATL and 89.4% of the VL samples. These reactions with rLb6H were highly specific (98.5%) when compared against those for samples from healthy control individuals. We then assessed rLb6H against sera from ATL patients infected with different species of Leishmania prevalent in Brazil [Leishmania (Leishmania) amazonensis, L. (Viannia) braziliensis, and L. (V.) guyanensis] and samples from patients with other infectious diseases. In analyses of 500 sera, ELISA using rLb6H detected all 219 ATL samples (sensitivity of 100.0%) with an overall specificity of 93.9% (considering healthy individuals and other infectious diseases patients). Only a minority of samples from Chagas disease patients possessed antibodies against rLb6H, and all of these responses were low (with a highest reactivity index of 2.2). Taken together, our data support further evaluation of rLb6H and the potential for its routine use in the serological diagnosis of ATL.

A proteomic road to acquire an accurate serological diagnosis for human tegumentary leishmaniasis

Diagnostic tools are important for clinical management and epidemiological evaluation of Tegumentary (TL) and Visceral (VL) Leishmaniasis. Serology is not frequently used for the diagnosis of the TL form because low antibody titers and cross-reaction with VL. Therefore, it is crucial to identify specific and immunogenic antigens from species associated with the TL form. Here we employed a proteomic approach coupled to an in silico analysis and identified the most abundant and immunogenic proteins from Leishmania amazonensis, Leishmania braziliensis and Leishmania infantum. Of 16 species specific proteins, nine were from the species causative of the TL form (L. amazonensis and L. braziliensis). In silico analysis revealed 18 B-cell epitopes with 0% similarity to Trypanosoma cruzi orthologs and, therefore, less likely to crossreact with sera of patients with Chagas disease. Two proteins reacted exclusively with serum from TL patients and presented several B-cell epitopes without similarity to T. cruzi orthologs: the hypothetical protein GI 134063939 and the metallo-peptidase Clan MA(E)-Family M3. The immunoassay revealed nine peptides with strong reactivity to sera from TL patients. These proteins and peptides may be good candidates to improve the specificity and sensibility of serological tests aiming to diagnose the TL of this neglected human disease.

BIOLOGICAL SIGNIFICANCE

As no gold-standard test for tegumentary leishmaniasis (TL) exists, a combination of different diagnostic techniques is often necessary to obtain precise results. Thus, the identification of species-specific, highly immunogenic and abundant proteins that stimulate the humoral immune response in the host should help in the development of serological tests for human TL. Herein we searched for these potential antigens in Leishmania species related to American Leishmaniasis (L. amazonensis, L. braziliensis and L. infantum). To this end, we employed an immunoproteomic approach using proteins from these Leishmania species and sera from TL and Visceral Leishmaniasis (VL) patients. Our study unveils specific proteins and peptides that may represent antigens that will help the efforts to improve the accuracy of serological tests to diagnose the TL form.

Multi-antigen print immunoassay (MAPIA)-based evaluation of novel recombinant Leishmania infantum antigens for the serodiagnosis of canine visceral leishmaniasis

Background

Domestic dogs are the principal reservoir hosts of Leishmania infantum in regions where visceral leishmaniasis (VL) is endemic. Although serologic methods are frequently used for the screening of infected dogs, antibody-based tests require further assessment, due to lack of sensitivity and specificity. In this study, we employed a multi-antigen printing immunoassay (MAPIA) to compare the antibody responses to novel recombinant proteins of L. infantum with the potential for the detection of canine VL.

Findings

MAPIA strips were prepared employing 12 recombinant proteins. Antibody reactivity to these antigens was compared using a panel of sera collected from clinically asymptomatic (n = 16) and symptomatic (n = 41) culture-positive animals. Our findings showed that the canine immune response to antigen differs between dogs and depends on infection status. Using this screening assay, when five out of the 12 antigens were combined, an overall 81% detection rate of L. infantum-infected dogs was achieved.

Conclusions

We conclude that MAPIA is an effective screening tool to rapidly select multiple antigens of diagnostic utility to be used in a more sensitive point of care diagnostic test such as the Dual-Path Platform (DPP) multiplex test for the rapid detection of infected dogs.

A multicentric evaluation of the recombinant Leishmania infantum antigen-based immunochromatographic assay for the serodiagnosis of canine visceral leishmaniasis

Background

Visceral leishmaniasis (VL) is a serious public health challenge in Brazil and dogs are considered to be the main urban reservoir of the causative agent. The culling of animals to control VL in some countries makes the accurate diagnosis of canine VL (CVL) essential. Recombinant antigens rLci1A and rLci2B were selected from a cDNA library of Leishmania infantum amastigotes due to their strong potential as candidates in diagnostic testing for CVL. The present multicentric study aimed to evaluate the sensitivity of a prototype test using these antigens (DPP rLci1A/rLci2B) against 154 sera obtained from symptomatic dogs within three endemic areas of VL in Brazil. The specificity was evaluated using 40 serum samples from negative dogs and dogs infected with other pathogens. Sensitivity and specificity rates of DPP rLci1A/rLci2B prototype were compared to rates from other diagnostic tests currently in use by the Brazilian Ministry of Health, including DPP®LVC, EIE®LVC.

Findings

DPP rLci1A/rLci2B prototype offered similar performance to that offered by DPP®LVC rapid test, as follows: sensitivity of 87% (CI 81–91) and 88% (CI 82–93) and specificity of 100% (CI 91–100) and 97% (CI 87–100), respectively for DPP rLci1A/rLci2B and DPP®LVC. When results of these two tests were considered concomitantly, sensitivity increased to 93.5% (CI 89–96).

Conclusions

The recombinant antigens rLci1A and rLci2B represent promising candidates for use in a multi-antigen rapid test for CVL. The inclusion of novel antigens to the DPP rLci1A/rLci2B prototype model could offer additionally enhanced sensitivity to detect animals infected by L. infantum.

Towards a more precise serological diagnosis of human tegumentary leishmaniasis using Leishmania recombinant proteins

Background

Exposure to Leishmania induces a humoral immune response that can be used as a marker of parasite exposure.

Methodology/Principal Findings

Herein, ELISA was used to screen sera from patients with Tegumentary Leishmaniasis (TL) against different L. infantum-chagasi-derived recombinant proteins (rHSP70, rH2A, rH2B, rH3, rH4 and rKMP11). Among the recombinant proteins, rHSP70 and rH2A showed the best reactivity against human sera obtained from endemic areas of TL. Receiver-Operator Characteristics (ROC) curve analysis was used to identify the effectiveness of these proteins for serodiagnosis of TL. ROC curves confirmed the superior performance of rHSP70 and rH2A, in comparison to the other tested recombinant proteins. Additionally, we evaluated the specificity of the response to rHSP70 and rH2A by testing sera obtained from patients with Chagas' disease, Tuberculosis, Leprosy or Systemic Lupus Erythematosus. In this case, rHSP70 displayed an increased ability to discriminate diseases, in comparison to SLA.

Conclusion

Our results raise possibility of using rHSP70 for the serodiagnosis of TL