Immunologic evaluation and validation of methods using synthetic peptides derived from Mycobacterium tuberculosis for the diagnosis of tuberculosis infection

Comparative Evaluation of Specific Antibody against Mycobacterium tuberculosis ESAT-6 Recombinant Antigen in Healthy Subject with Positive and Negative Skin Test

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (M. tuberculosis). The laboratory diagnosis of the disease includes various bacteriologic and immunologic methods. Despite the effectiveness of many of these methods in diagnosing active TB, their high cost and time-consuming nature have led researchers to adopt more accurate and rapid screening methods based on specific antigens for M. tuberculosis. The present study aimed to measure specific antibody serum levels against the early secretory antigenic target 6 kDa (ESAT-6) recombinant protein in healthy people and compare it to TB patients. The target population included 27 TB patients and 87 healthy individuals with no clinical TB symptoms. The healthy population was divided into two groups, including positive purified protein derivative (PPD) and negative PPD (35 and 52 people, respectively), using the Tuberculin skin test. The specific antibody level against the ESAT-6 recombinant antigen and the PPD protein was measured using an indirect Enzyme-Linked Immunosorbent Assay (ELISA) test. The results of the study showed that the majority of the healthy population with no symptoms of clinical TB and having negative skin test results did not have antibodies against the recombinant ESAT-6 (98%) and PPD (96%) antigens. On the other hand, there was a high level of the specific antibody of the ESAT-6 recombinant and PPD antigens in TB patients (77%). It is notable that in people with positive skin test results, the level of the antibody against the ESAT-6 recombinant antigen and PPD antigen was 94%. The results demonstrated that the ELISA method based on the measurement of antibodies against the ESAT-6 recombinant antigen can be a proper diagnostic method for rapid and accurate screening of healthy from infected people.

Diagnostic Potential of the Serological Response to Synthetic Peptides from Mycobacterium tuberculosis Antigens for Discrimination Between Active and Latent Tuberculosis Infections

Diagnosis and treatment of active tuberculosis (ATB) as well as latent tuberculosis infection (LTBI) are required for effective tuberculosis (TB) control, especially in TB endemic area. The usefulness of conventional tests to distinguish between ATB and LTBI has remained challenging. The present study was aimed to demonstrate the usefulness of the serological response to synthetic peptides from Mycobacterium tuberculosis (Mtb) antigens for discrimination between ATB and LTBI in Warao Amerindians. Serum IgG antibody levels were measured by the indirect ELISA assay using 22 designed and synthesized peptides derived from immunogenic Mtb ESAT-6 and Ag85A proteins. A total of 211 adult Warao Amerindians were included; cases with active TB (ATB, n = 75), latent TB infection (LTBI, n = 85) and non-infected (NI, n = 51). The approach’s diagnostic information was compared using receiver operating characteristic (ROC) curves. For ATB diagnostic performance between ATB and NI; ESAT-6; P-12037 had 100% of sensitivity (AUC = 0.812; 0.733 to 0.891 95% CI); and Ag85A; P-10997 had 100% of specificity (AUC = 0.691; 0.597 to 0.785 95% CI); and ATB and LTBI; Ag85A; P-29878 had 100% of sensitivity (AUC = 0.741; 0.666–0.817 95% CI), and P-29879 had 99% of specificity (AUC = 0.679; 0.593–0.765 95% CI). While that ESAT-6 P-12037 also allowed differentiation between LTBI and NI or healthy ones. It had 98.8% of sensitivity and 98.0% of specificity (AUC = 0.640; 0.545–0.735 95% CI). The potential of combination-antigen immunoassays with peptides could discriminate between Warao Amerindians with ATB, LTBI and NI. Further validation of this approach could lead to developing a complementary tool for rapid diagnosis of TB infections.

ESAT-6 and Ag85A Synthetic Peptides as Candidates for an Immunodiagnostic Test in Children with a Clinical Suspicion of Tuberculosis

Background

Tuberculosis (TB) is being underdetected in children as most are smear-negative. This work was aimed at evaluating ESAT-6 and Ag85A synthetic peptides' serodiagnostic potential for diagnosing children having a clinical suspicion of TB.

Methods

The study involved 438 children: 77 Creole nonindigenous (13 suspected of having TB and 64 healthy ones) and 361 Warao indigenous children (39 suspected of TB and 322 healthy children). The approach's diagnostic information was compared using operational characteristics and receiver-operating characteristic (ROC) curves.

Results

Ag85A P-29879 had 94.6% sensitivity (AUC = 0.741: 0.651 to 0.819 95% CI) in indigenous children. ESAT-6 P-12036 and P-12037 had 100% and 92.3% of sensitivity (AUC = 0.929: 0.929: 0.846 to 0.975 95% CI and 0.791: 63.9 to 98.7 95% CI, respectively) in Creole children. ESAT-6 peptides also allowed a differentiation between children with TB and healthy ones.

Conclusions

Further validation of this approach could lead to developing a complementary tool for rapid TB diagnosis in children.

Evaluation of multi-antigen serological screening for active tuberculosis among people living with HIV

Better triage tests for screening tuberculosis (TB) disease are needed for people living with HIV (PLHIV). We performed the first evaluation of a previously-validated 8-antigen serological panel to screen PLHIV for pulmonary TB in Kampala, Uganda. We selected a random 1:1 sample with and without TB (defined by sputum culture) from a cohort of PLHIV initiating antiretroviral therapy. We used a multiplex microbead immunoassay and an ensemble machine learning classifier to determine the area under the receiver operating characteristic curve (AUC) for Ag85A, Ag85B, Ag85C, Rv0934-P38, Rv3881, Rv3841-BfrB, Rv3873, and Rv2878c. We then assessed the performance with the addition of four TB-specific antigens ESAT-6, CFP-10, Rv1980-MPT64, and Rv2031-HSPX, and every antigen combination. Of 262 participants (median CD4 cell-count 152 cells/μL [IQR 65-279]), 138 (53%) had culture-confirmed TB. The 8-antigen panel had an AUC of 0.53 (95% CI 0.40-0.66), and the additional 4 antigens did not improve performance (AUC 0.51, 95% CI 0.39-0.64). When sensitivity was restricted to ≥90% for the 8- and 12-antigen panel, specificity was 2.2% (95% CI 0-17.7%) and 8.1% (95% CI 0-23.9%), respectively. A three-antigen combination (Rv0934-P38, Ag85A, and Rv2031-HSPX) outperformed both panels, with an AUC of 0.60 (95% CI 0.48-0.73), 90% sensitivity (95% CI 78.2-96.7%) and 29.7% specificity (95% CI 15.9-47%). The multi-antigen panels did not achieve the target accuracy for a TB triage test among PLHIV. We identified a new combination that improved performance for TB screening in an HIV-positive sample compared to an existing serological panel in Uganda, and suggests an approach to identify novel antigen combinations specifically for screening TB in PLHIV.

Utility of dominant epitopes derived from cell-wall protein LppZ for immunodiagnostic of pulmonary tuberculosis

Background

Serological antibodies tests for tuberculosis (TB) are widely used in developing countries. They appear to have some advantages- faster, simple and could be used for extrapulmonary TB. However, most of current commercial TB serological tests are failed to provide sufficient sensitivity and specificity. Improved serological biomarkers were essential. In this study, we present an approach using peptide array to discover new immunodiagnostic biomarkers based on immunodominant epitopes of TB antigens.

Results

The Probable conserved lipoprotein LppZ, which is difficult to express and purify in vivo was selected as the model antigen. We use two-step screening for dominant epitope selection. Based on peptide array data from 170 TB patients and 41 control samples, two dominant epitopes were identified to have diagnostic value for TB patients. Truncation assay was used to identify the core reactive sequence. Peptide- based ELISA was used to evaluate the diagnostic ability of pep-LppZ-1 and pep-LppZ-13. Pep-LppZ-1 has a sensitivity of 49.2% and a specificity of 83.3% in TB diagnose. Pep-LppZ-13 has a sensitivity of 43.3% and a specificity of 88.5% in TB diagnose.

Conclusions

Our result demonstrated that peptide array screening would be an advantage strategy of screening TB diagnostic peptides.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0243-2) contains supplementary material, which is available to authorized users.

Fast and efficient detection of tuberculosis antigens using liposome encapsulated secretory proteins of Mycobacterium tuberculosis

PURPOSE

A rapid and efficient diagnostic test was developed for the detection of Mycobacterium tuberculosis antigens in serum samples of active tuberculosis (TB) and extrapulmonary TB patients via a liposomal agglutination-based method.

METHODS

A rapid card test has been developed to facilitate the recognition of high-affinity binding rabbit raised purified culture filtrate protein antibodies coupled on the surface of activated liposomal preparation. In the presence of TB antigens, the polyclonal antibodies bound to the liposomal particles demonstrate a visible agglutination reaction.

RESULTS

The developed assay was simple, rapid, reliable, sensitive, and specific as a diagnostic test for the detection of antigens in serum samples of clinically confirmed cases of TB within 4-5 minutes' duration. The test was evaluated at different hospitals, medical colleges, and pathology centers, and involved 1483 participants. This investigation was conducted to detect the presence of these antigens during the period of active growth of the microorganism in serum samples for pulmonary TB and processed tissue biopsy for other extrapulmonary TB. Results obtained using this test were compared with acid-fast bacilli smear and culture results.

CONCLUSION

Our study demonstrated that the newly developed liposome tuberculosis antigen card test detected antigens in our study population with approximately 97.48% sensitivity and 95.79% specificity. This is the first study to report the liposomal encapsulation of culture filtrate proteins from M. tuberculosis for diagnostic application.

Diagnostic utility of 99mTc-EDDA-tricine-HYNIC-Tyr3-octreotate SPECT for differentiation of active from inactive pulmonary tuberculosis

OBJECTIVE

The current study was performed to evaluate the impact of Tc-EDDA-tricine-HYNIC-Tyr-octreotate in the differentiation of active from inactive pulmonary tuberculosis lesions.

PATIENTS AND METHODS

Ten consecutive patients (six male and four female, age range 24-83 years) with proven pulmonary tuberculosis (with a positive smear or culture) were enrolled in the study. At 120 min after injection of 740 MBq of Tc-EDDA-tricine-HYNIC-Tyr-octreotate, planar and single-photon emission computed tomography (SPECT) images of the thorax were taken. A semiquantitative evaluation of lesion and nonlesion areas was performed. The scan was repeated following the same protocol after standard treatment for tuberculosis after a negative sputum culture.

RESULTS

Semiquantitative evaluation of the lesions showed a statistically significant higher uptake before treatment in both planar and SPECT images (P=0.005 and 0.007, respectively). Lesion-to-nonlesion ratios were also higher in the pretreatment sets on both planar and SPECT images (1.4±0.2 vs. 1.19±0.15, P=0.001, for planar images and 2.32±0.55 vs. 1.32±0.32, P=0.0001, for SPECT images).

CONCLUSION

Tc-EDDA-tricine-HYNIC-Tyr-octreotate scintigraphy may help to differentiate between active and inactive pulmonary tuberculosis. SPECT imaging and semiquantitative evaluation are indispensable for increasing the diagnostic yield of this method. Larger studies are needed to corroborate our results.

Immunoreactivity of synthetic peptides derived from proteins of Cryptococcus gattii

AIM

To determine the immunoreactivity of synthetic Cryptococcus-derived peptides.

MATERIALS & METHODS

A total of 63 B-cell epitopes from previously identified Cryptococcus gattii immunoreactive proteins were synthesized and evaluated as antigens in ELISAs. The peptides were first evaluated for their ability to react against sera from immunocompetent subjects carrying cryptococcal meningitis. Peptides that yielded high sensitivity and specificity in the first test were then retested with sera from individuals with other fungal pathologies for cross-reactivity determination.

RESULTS

Six of 63 synthetic peptides were recognized by antibodies in immunoassays, with a specificity of 100%, sensitivity of 78% and low cross-reactivity.

CONCLUSION

We successfully determined the immunoreactivity of selected synthetic peptides of C. gattii derived proteins.