Diagnostic and prognostic potential of a competitive enzyme-linked immunosorbent assay for leishmaniasis in India

Quantification of Soluble or Insoluble Fractions of Leishmania Parasite Proteins in Microvolume Applications: A Simplification to Standard Lowry Assay

Protein quantification is often an essential step in any research field that involves proteins. Although the standard Lowry assay and its modifications are most abundantly used in protein quantification, the existing methods are rigid or often demonstrate nonlinearity between protein concentration and color intensity. A method for fast and accurate qualitative and/or quantitative determination of total soluble/insoluble proteins or micro-well plate immobilized proteins isolated from Leishmania parasites in microvolumes was described in the current study. Improvements in cost-effective techniques are necessary to increase the research outputs in resource-limited settings. This method is a modification to the established Lowry assay for protein quantification. Concentrations of unknown samples were calculated using a standard curve prepared using a standard series of bovine serum albumin (BSA). The optimized reagents were 2 N NaOH (sodium hydroxide), 2% Na₂CO₃ (sodium carbonate), 1% CuSO₄ (copper sulfate), 2% KNaC₄H₄O₆ (potassium sodium tartrate), and 2 N Folin and Ciocalteu's phenol. This modified protein assay was sensitive for quantifying Leishmania proteins in a total crude extract or in a soluble fraction within the approximate range of 10–500 μg/ml (1–50 μg/assay) and showed a linearity between color intensity and concentration of the protein. This is an easier, fast, and accurate method for quantifying proteins with microvolumes in a cost-effective manner for routine use in research laboratories in resource-limited settings.

A rapid diagnostic test for human Visceral Leishmaniasis using novel Leishmania antigens in a Laser Direct-Write Lateral Flow Device

Visceral Leishmaniasis (VL) causes high morbidity and mortality in low-to-middle-income countries worldwide. In this study, we used Laser Direct-Write (LDW) technology to develop a new Lateral Flow Device (LFD) with double-channel geometry on a low-cost paper platform as a rapid and accurate serodiagnostic assay for human VL. This Duplex VL-LFD was based on a laser-patterned microfluidic device using two recombinant Leishmania proteins, β-tubulin and LiHyp1, as novel diagnostic antigens. The VL-LFD assay was tested with blood/serum samples from patients diagnosed with VL, Tegumentary Leishmaniasis, Leishmaniasis of unknown identity, other parasitic diseases with similar clinical symptoms, i.e. Leprosy Disease and Chagas Disease, and blood from healthy donors, and compared in parallel with commercial rK39 IT-LEISH^® Kit. Clinical diagnosis and real-time Polymerase Chain Reaction assay were used as reference standards. VL-LFD Sensitivity (S ± 95% Confidence Intervals (CI)) of 90.9 (78.9-100) and Specificity (Sp ± 95% CI) of 98.7 (96.1-100) outperformed the IT-LEISH^® Kit [S = 77.3 (59.8-94.8), Sp = 94.7 (89.6-99.8)]. This is the first study reporting successful development of an LFD assay using the LDW technology and the VL-LFD warrants comparative testing in larger patient cohorts and in areas with endemic VL in order to improve diagnosis and disease management.

Systematic review on antigens for serodiagnosis of visceral leishmaniasis, with a focus on East Africa

Background

Accurate and accessible diagnosis is key for the control of visceral leishmaniasis (VL). Yet, current diagnostic tests for VL have severe limitations: they are invasive or not suitable as point of care (POC) test or their performance is suboptimal in East Africa. We analysed the antigens in the VL serodiagnostics development pipeline to identify shortcomings and to propose strategies in the development of an alternative POC test for VL in East Africa.

Objectives

The objective of this study was to identify and to analyse all antigens for VL serodiagnosis that have been published before 2018 in order to identify candidates and gaps in the pipeline for a new POC test in East Africa.

Methods

A systematic literature search was performed on PubMed for original research articles on Leishmania-specific antigens for antibody detection of VL in humans. From each article, the following information was extracted: the antigen name, test format and characteristics, its reported sensitivity and specificity and study cohort specifications.

Results

One hundred and seven articles containing information about 96 tests based on 89 different antigens were included in this study. Eighty six of these tests, comprising 80 antigens, were evaluated in phase I and II studies only. Only 20 antigens, all of which are native, contain a carbohydrate and/or lipid moiety. Twenty-four antigens, of which 7 are non-native, are composed of antigen mixtures. Nineteen tests, comprising 18 antigens, have been evaluated on East African specimens, of which only 2 (rK28 based immunochromatographic test and intact promastigote based indirect fluorescent antibody technique) consistently showed sensitivities above 94 and specificities above 97% in a phase III study and one in a phase II study (dot blot with SLA). Only rK28 is a non-native mixture of antigens which we consider suitable for further evaluation and implementation.

Conclusions

The development pipeline for an alternative serodiagnostic test for VL is almost empty. Most antigens are not sufficiently evaluated. Non-protein antigens and antigen mixtures are being neglected. We propose to expand the evaluation of existing antigen candidates and to investigate the diagnostic potential of defined non-native carbohydrate and lipid antigens for VL serodiagnosis in East Africa.

Visceral leishmaniasis is a potentially fatal disease that affects more than 20 000 people every year. Its diagnosis is difficult since the clinical symptoms are not specific and the existing diagnostic tests are not useful in limited resource countries or they a not accurate enough in East Africa. In this review we performed a systematic search of the published literature to analyse the potential candidate antigens in the pipeline for a new antibody detection test in East Africa. We found 96 tests based on 89 antigens. Eighty six of these tests were evaluated in a study design that is insufficient (phase I and II) to make conclusions on their performance in clinical practice. We found that the candidate antigens either lacked carbohydrate or lipid structures or are based on single antigens as opposed to mixtures or are extracted from the causative parasite itself, making them expensive and prone to variations. Considering that the most widely used diagnostic test does not detect all cases of visceral leishmaniasis in East Africa, we analysed how many of the candidate antigens were tested on East African specimens: We found that only 2 tests (rK28 based immunochromatographic test and the intact promastigote based indirect fluorescent antibody technique) that were tested in a phase III study and only one (dot blot with SLA) that was tested in a phase II study performed well according to our criteria. Due to the antigen characteristics we consider only the rK28 based test as suitable for further evaluation and implementation.

Systematic Review into Diagnostics for Post-Kala-Azar Dermal Leishmaniasis (PKDL)

Identification of post-kala-azar dermal leishmaniasis (PKDL) is important due to the long and toxic treatment and the fact that PKDL patients may serve as a reservoir for visceral leishmaniasis (VL). We summarized the published literature about the accuracy of diagnostic tests for PKDL. We searched Medline for eligible studies investigating the diagnostic accuracy of any test for PKDL. Study quality was assessed using QUADAS-2. Data were extracted from 21 articles including 43 separate studies. Twenty-seven studies evaluated serological tests (rK39 dipstick, ELISA, DAT, and leishmanin tests), six studies molecular tests, eight microscopy, and two cultures. Only a few of these studies reported a valid estimate of diagnostic accuracy, as most were case-control designs or used a reference standard with low sensitivity. The included studies were very heterogeneous, for example, due to a large variety of reference standards used. Hence, no summary estimates of sensitivity or specificity could be made. We recommend well-designed diagnostic accuracy trials that evaluate, side-by-side, all currently available diagnostics, including clinical symptoms, serological, antigen, molecular, and parasitological tests and possible use of statistical modelling to evaluate diagnostics when there is no suitable gold standard.

Leishmania cell surface prohibitin: role in host-parasite interaction

Proteins selectively upregulated in infective parasitic forms could be critical for disease pathogenesis. A mammalian prohibitin orthologue is upregulated in infective metacyclic promastigotes of Leishmania donovani, a parasite that causes visceral leishmaniasis. Leishmania donovani prohibitin shares 41% similarity with mammalian prohibitin and 95-100% within the genus. Prohibitin is concentrated at the surface of the flagellar and the aflagellar pole, the aflagellar pole being a region through which host-parasite interactions occur. Prohibitin is attached to the membrane through a GPI anchor. Overexpression of wild-type prohibitin increases protein surface density resulting in parasites with higher infectivity. However, parasites overexpressing a mutant prohibitin with an amino acid substitution at the GPI anchor site to prevent surface expression through GPI-link show lesser surface expression and lower infective abilities. Furthermore, the presence of anti-prohibitin antibodies during macrophage-Leishmania interaction in vitro reduces infection. The cognate binding partner for Leishmania prohibitin on the host cell appears to be macrophage surface HSP70, siRNA mediated downregulation of which abrogates the capability of the macrophage to bind to parasites. Leishmania prohibitin is able to generate a strong humoral response in visceral leishmaniasis patients. The above observations suggest that prohibitin plays an important role in events leading to Leishmania-host interaction.

9-O-acetylated sialoglycoproteins are important immunomodulators in Indian visceral leishmaniasis

Overexpression of disease-associated 9-O-acetylated sialoglycoproteins (9-O-AcSGPs) on peripheral blood mononuclear cells (PBMC) of visceral leishmaniasis (VL) patients (PBMC(VL)) compared to their levels of expression in healthy individuals has been demonstrated using a lectin, achatinin-H, with specificity toward 9-O-acetylated sialic acid derivatives alpha2-6 linkage with subterminal N-acetylgalactosamine (9-O-AcSAalpha2-6GalNAc). The decreased presence of disease-associated 9-O-AcSGPs on different immune cells of parasitologically cured individuals after successful treatment relative to the levels in patients with active VL prior to treatment was demonstrated. However, their contributory role as immunomodulatory determinants on PBMC(VL) remained unexplored. Accordingly, 9-O-AcSGPs on PBMC(VL) were sensitized with achatinin-H, leading to their enhanced proliferation compared to that observed with different known mitogens or parasite antigen. This lymphoproliferative response was characterized by evaluation of the TH1/TH2 response by intracellular staining and enzyme-linked immunosorbent assay for secreted cytokines, and the results were corroborated by their genetic expression. Sensitized PBMC(VL) evidenced a mixed TH1/TH2 cellular response with a predominance of the TH1 response, indicating the ability of 9-O-AcSGPs to modulate the host cell toward a favorable response. Interestingly, the humoral and cellular responses showed a good correlation. Further, high levels of anti-9-O-AcSGP antibodies with an order of distribution of immunoglobulin M (IgM) > IgG1 = IgG3 > IgG4 > IgG2 > IgE could be explained by a mixed TH1/TH2 response. A good correlation of enhanced 9-O-AcSGPs with both the cell-mediated (r = 0.98) and humoral (r = 0.99) response was observed. In summary, it may be concluded that sensitization of 9-O-AcSGPs on PBMC(VL) may provide a basis for the modulation of the host's immune response by their controlled expression, leading to a beneficial immune response and influencing the disease pathology.

Development and evaluation of a competitive ELISA for estimation of rabies neutralizing antibodies after post-exposure rabies vaccination in humans

OBJECTIVES

Currently three tests are approved for the estimation of neutralizing antibodies after rabies vaccination: the mouse neutralization test (MNT), the rapid fluorescent focus inhibition test (RFFIT), and the fluorescent antibody virus neutralization (FAVN) test. Performance of these tests requires a lot of expertise and is generally carried out in reference laboratories and, hence, they are not available to many people. The aim of the present study was to develop and evaluate a competitive ELISA (C-ELISA) for estimation of neutralizing antibodies in order to make this testing more widely available.

METHODS

The C-ELISA was designed based on competition between a murine neutralizing monoclonal antibody (Mab) and the antibodies in serum of vaccinated people. The test was initially standardized using known negative and known positive serum samples for determining the optimal dilution of the Mab as well as the cut-off value (%) for ascertaining the level of inhibition. Nine hundred and ninety serum samples were tested from 250 people who had been administered purified chick embryo cell vaccine (PCECV). Serum samples were collected on days 0, 14, 30 and 90 post-vaccination, and were tested by C-ELISA.

RESULTS

All the serum samples that were positive by RFFIT were also positive by C-ELISA. The titers obtained with C-ELISA were marginally higher than the RFFIT titers, but a significant correlation was noted between the two tests (r=0.897). None of the negative controls were detected to be positive for rabies antibodies by either of these tests. Therefore the C-ELISA was found to be 100% specific and sensitive in comparison to RFFIT. Further, the initial rise and fall of antibody titers on different days post-vaccination was comparable for both tests.

CONCLUSIONS

The C-ELISA described herein can be used to quantify rabies neutralizing antibody levels after vaccination. This test is simple and can be conveniently used under field conditions for monitoring seroconversion after post-exposure rabies vaccination. Moreover it does not require handling of infectious virus by the end user.

Development of a semi-automated colorimetric assay for screening anti-leishmanial agents

MTS or {3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl}-2H-tetrazolium, inner salt) is converted into soluble formazan by mitochondrial dehydrogenase of viable cells, thus serving as an indicator of cell viability. Accordingly, a MTS-based assay was developed to evaluate anti-leishmanial activity in Leishmania promastigotes from strains responsible for visceral, cutaneous or mucocutaneous leishmaniasis. The assay was initially optimized for the appropriate wavelength (490 nm), culture medium (M-199), incubation time (3 h) and temperature (37 degrees C). Increasing absorbance with increasing cell density confirmed linearity of the assay that was maintained up to 2.5 x 10(6) cells/200 microl. The growth kinetics of six L. donovani strains and six non-L. donovani strains consistently indicated higher absorbances in the L. donovani strains highlighting the importance of strain-specific customization of the MTS assay. The IC(50) values (i.e., the concentration at which 50% of growth was inhibited) of amphotericin B, miltefosine and pentamidine isethionate obtained by the MTS assay corroborated with previously published data. Taken together, the MTS assay thus permits a simple, reproducible and reliable semi-automated method for evaluating cell viability, effective for drug-screening and growth kinetic studies.

Application of an improved method for the recombinant k 39 enzyme-linked immunosorbent assay to detect visceral leishmaniasis disease and infection in Bangladesh

Several serology-based immunoassays are used to diagnose visceral leishmaniasis (VL), a chronic protozoan parasitic disease caused by the Leishmania donovani complex. These tests are primarily designed to diagnose the most severe clinical form of VL, known as kala-azar. However, leishmanial infection is frequently asymptomatic and may manifest only as a positive serologic response or positive leishmanin skin test. We modified a previously described enzyme-linked immunosorbent assay (ELISA) that detects patient antibodies reactive with the recombinant Leishmania protein K39 (rK39) to confirm suspected kala-azar and to detect asymptomatic infection in a community study in Bangladesh. With the inclusion of a standard curve on each ELISA plate, the rK39 ELISA was more repeatable (kappa coefficient of agreement=0.970) and more reliable compared to the original method (kappa=0.587, P<0.001). The cutoff point for a positive antibody response was chosen based on the 99th percentile of the ELISA distribution for the negative-control sera. However, we found that sera from all patients with active kala-azar yielded values more than twice the magnitude of this cutoff. Using receiver-operator characteristic curves, we determined a second cutoff value predictive of kala-azar. Using these criteria, the sensitivity and specificity of the modified ELISA for kala-azar were 97.0% and 98.9%, respectively, for sera from our study population. We hypothesize that individuals with antibody levels greater than the 99th percentile of the negative controls but less than the cutoff point for kala-azar have asymptomatic leishmanial infections.

The flow-cytometry-based evaluation of cellular immunity in cases of cutaneous leishmaniasis and healthy controls from the endemic area in southern Israel

Only limited data are available on the early immunological events associated with human cutaneous leishmaniasis (CL). In this study, peripheral-blood mononuclear cells were obtained from 66 individuals (34 patients with cutaneous lesions and 32 apparently healthy controls) who had each spent no more than 3 months in the endemic region of Qetzioth, in southern Israel. These cells' responses to Leishmania major antigen were then explored, by the flow-cytometry-based evaluation of blast transformation (BT). The lymphocytes from 17 (50%) of the patients but only one (3%) of the controls displayed BT. When, in an ELISA, most (52) of the subjects were checked for anti-L. major antibodies, none of the 22 controls investigated but 19 (63%) of the 30 patients were found seropositive. Although 14 (47%) of the 30 patients who were checked for antibodies were BT-positive, the seropositive patients were not significantly more or less likely to be BT-positive than the seronegative patients (P<0.919). These data indicate that, in CL, the hosts' cellular and humoral responses develop independently within the first 3 months post-infection, but further investigation is required to confirm this hypothesis.

Post-kala-azar dermal leishmaniasis

Post-kala-azar dermal leishmaniasis (PKDL) is a complication of visceral leishmaniasis (VL); it is characterised by a macular, maculopapular, and nodular rash in a patient who has recovered from VL and who is otherwise well. The rash usually starts around the mouth from where it spreads to other parts of the body depending on severity. It is mainly seen in Sudan and India where it follows treated VL in 50% and 5-10% of cases, respectively. Thus, it is largely restricted to areas where Leishmania donovani is the causative parasite. The interval at which PKDL follows VL is 0-6 months in Sudan and 2-3 years in India. PKDL probably has an important role in interepidemic periods of VL, acting as a reservoir for parasites. There is increasing evidence that the pathogenesis is largely immunologically mediated; high concentrations of interleukin 10 in the peripheral blood of VL patients predict the development of PKDL. During VL, interferon gamma is not produced by peripheral blood mononuclear cells (PBMC). After treatment of VL, PBMC start producing interferon gamma, which coincides with the appearance of PKDL lesions due to interferon-gamma-producing cells causing skin inflammation as a reaction to persisting parasites in the skin. Diagnosis is mainly clinical, but parasites can be seen by microscopy in smears with limited sensitivity. PCR and monoclonal antibodies may detect parasites in more than 80% of cases. Serological tests and the leishmanin skin test are of limited value. Treatment is always needed in Indian PKDL; in Sudan most cases will self cure but severe and chronic cases are treated. Sodium stibogluconate is given at 20 mg/kg for 2 months in Sudan and for 4 months in India. Liposomal amphotericine B seems effective; newer compounds such as miltefosine that can be administered orally or topically are of major potential interest. Although research has brought many new insights in pathogenesis and management of PKDL, several issues in particular in relation to control remain unsolved and deserve urgent attention.

Development of an assay for quantification of linkage-specific O-acetylated sialoglycans on erythrocytes; its application in Indian visceral leishmaniasis

We have developed a noninvasive approach for the quantification of linkage-specific 9-O-acetylated sialoglycans on mammalian erythrocytes using a lectin, Achatinin-H, whose lectinogenic epitope has previously been defined as 9-O-acetylated sialoglycoconjugates (9-O-AcSGs) alpha 2-->6 linked to subterminal GalNAc. Titration and checkerboard analysis were performed to optimize the assay using rabbit, rat and human erythrocytes that contain differing amounts of this glycotope. Assay specificity was established by decreased binding of erythrocytes to immobilised Achatinin-H when pre-incubated with excess lectin. The intra-assay coefficient of variation (CV) for rat and human erythrocytes was 8.6-9.2% and 11.1-13.0%, respectively. The inter-assay CV for rat and human erythrocytes was 9.9-10.1% and 15.2-16.6%, respectively. In previous studies, we have identified an enhanced presence of cell surface 9-O-AcSGs on the erythrocytes of patients with visceral leishmaniasis (VL) [Am. J. Trop. Med. Hyg. 58 (1998) 551]. Our assay when evaluated on erythrocytes from VL patients (n=30) showed a fourfold increase in lectin binding as compared to endemic controls. The mean +/- S.E.M. of the A(405) nm value was 1.14 +/- 0.04 vs. 0.23 +/- 0.03, respectively (p<0.0001). Following effective chemotherapy, a significant reduction of this glycotope on the erythrocytes of VL patients indicates that this assay has both a diagnostic and prognostic potential. Taken together, we conclude that this antigen-based assay is a specific and reproducible method for monitoring the disease status of VL patients and could be used in retrospective and prospective trials.

Optimisation of an ELISA for the serodiagnosis of visceral leishmaniasis using in vitro derived promastigote antigens

An antibody detection ELISA was developed for diagnosis of visceral leishmaniasis. Antigens released by Leishmania donovani promastigotes into a protein-free medium were used. SDS-PAGE analysis has indicated that Ld-ESM contain several protein antigens. Titration and chequer-board analyses were performed to optimise the assay protocol. Optimal results were obtained when antigen (50 microg/ml) was coated with PBS-methyl glyoxal buffer, and wells blocked with 0.5% casein. A serum dilution of 1:500 in antigen-coated wells, blocked with 0.5% casein, generated lowest absorbance with Ref-ve sera and higher absorbance with Ref+ve sera. All steps of the ELISA were performed at room temperature. The S/N ratio, the differential absorbance between the negative sample vs. the test or Ref+ve sample, was used to quantify the specific antigen and antibody reactions. An anti-human monoclonal antibody conjugated with HRP (MAb-conjugate) outperformed a commercially available anti-human polyclonal antibody conjugate (PAb-conjugate). The MAb-conjugate gave minimal background reactions with endemic sera. Optimised final assay steps mentioned below were used to evaluate sera samples from field trials. ELISA wells were coated with 50 microg/ml Ld-ESM mixed in PBS-methyl glyoxal overnight, and after removing the antigen, blocked with 0.5% casein for 1 h at RT. Patient sera along with control sera, diluted to 1:500 in PBS/T, were reacted for 1 h at RT. After washing the plate with PBS/T, wells were reacted with MAb-conjugate for 40 min at RT, and after washing, binding of antibodies was visualized by using TMB as a chromogen substrate. The relative specific binding was quantified by the S/N ratio. A batch of n=22 endemic sera from North Africa were evaluated and resulted with 100% specificity and sensitivity, 99.99% PPV and 95.45% NPV. The specificity and sensitivity of this assay will be further evaluated in planned retrospective and prospective multi-site trials.