Rapid and Specific Diagnosis of Tuberculous Pleuritis With Immunohistochemistry by Detecting Mycobacterium Tuberculosis Complex Specific Antigen MPT64 in Patients From a HIV Endemic Area

Principles of Analytic Validation of Immunohistochemical Assays: Guideline Update

CONTEXT.—

In 2014, the College of American Pathologists developed an evidence-based guideline to address analytic validation of immunohistochemical assays. Fourteen recommendations were offered. Per the National Academy of Medicine standards for developing trustworthy guidelines, guidelines should be updated when new evidence suggests modifications.

OBJECTIVE.—

To assess evidence published since the release of the original guideline and develop updated evidence-based recommendations.

DESIGN.—

The College of American Pathologists convened an expert panel to perform a systematic review of the literature and update the original guideline recommendations using the Grading of Recommendations Assessment, Development and Evaluation approach.

RESULTS.—

Two strong recommendations, 1 conditional recommendation, and 12 good practice statements are offered in this updated guideline. They address analytic validation or verification of predictive and nonpredictive assays, and recommended revalidation procedures following changes in assay conditions.

CONCLUSIONS.—

While many of the original guideline statements remain similar, new recommendations address analytic validation of assays with distinct scoring systems, such as programmed death receptor-1 and analytic verification of US Food and Drug Administration approved/cleared assays; more specific guidance is offered for validating immunohistochemistry performed on cytology specimens.

Diagnosing adult and pediatric extrapulmonary tuberculosis by MPT64 antigen detection with immunohistochemistry and immunocytochemistry using reproduced polyclonal antibodies

Diagnosing extrapulmonary tuberculosis (EPTB) is challenging. Immunohistochemistry or immunocytochemistry has been used to diagnose tuberculosis (TB) by detection of MPT64 antigen from various extrapulmonary specimens and has shown good diagnostic performance in our previous studies. The test can distinguish between disease caused by Mycobacterium tuberculosis (Mtb) complex and nontuberculous mycobacteria and can be applied on formalin-fixed paraffin-embedded tissue. As the antibodies previously used were in limited supply, a new batch of polyclonal antibodies was developed for scale-up and evaluated for the first time in this study. Our aim was to assess the diagnostic accuracy of the MPT64 test with reproduced antibodies in the high burden settings of Pakistan and India. Patients were enrolled prospectively. Samples from suspected sites of infection were collected and subjected to histopathologic and/or cytologic evaluation, routine TB diagnostics, GeneXpert MTB/RIF (Xpert), and the MPT64 antigen detection test. Patients were followed until the end of treatment. Based on a composite reference standard (CRS), 556 patients were categorized as TB cases and 175 as non-TB cases. The MPT64 test performed well on biopsies with a sensitivity and specificity of 94% and 75%, respectively, against a CRS. For cytology samples, the sensitivity was low (36%), whereas the specificity was 81%. Overall, the MPT64 test showed higher sensitivity (73%) than Xpert (38%) and Mtb culture (33%). The test performed equally well in adults and children. We found an additive diagnostic value of the MPT64 test in conjunction with histology and molecular tests, increasing the yield for EPTB. In conclusion, immunochemical staining with MPT64 antibodies improves the diagnosis of EPTB in high burden settings and could be a valuable addition to routine diagnostics.

Diagnosis of Paediatric Extrapulmonary Tuberculosis by the MPT64 Antigen at a Tertiary Care Hospital

Background Tuberculosis (TB) remains a global health concern, with India bearing a substantial burden. Paediatric TB, especially extrapulmonary TB (EPTB), presents unique diagnostic challenges due to its paucibacillary nature and the difficulty in obtaining suitable samples in children. Accurate and timely diagnosis is crucial to initiate appropriate treatment and mitigate disease spread. The MPT64 antigen test has shown promise in diagnosing TB, but its performance in paediatric EPTB remains underexplored. This study aimed to evaluate the diagnostic utility of the MPT64 antigen test in paediatric EPTB cases at a tertiary care hospital in India. Methods We conducted a prospective cross-sectional study at the Indira Gandhi Institute of Medical Sciences (IGIMS), a tertiary care hospital in India. A total of 250 paediatric participants, aged 0-18 years, with clinical suspicion of extrapulmonary tuberculosis (EPTB) were included. Diagnostic samples (e.g., tissue biopsies, pus, cerebrospinal fluid (CSF), and lymph node aspirates) were obtained, and tests including microscopy for acid-fast bacilli (AFB), mycobacterial cultures, GeneXpert MTB/RIF assay, and the TB Antigen MPT64 Rapid ICT Kit were performed. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy of the MPT64 antigen test were calculated using culture and GeneXpert as reference standards. Results Among the 250 participants, 34 (13.6%) were confirmed to have EPTB. The MPT64 antigen test demonstrated a sensitivity of 70.6% and specificity of 92.1% in detecting EPTB cases. Mycobacterial cultures had the highest sensitivity (91.2%) and specificity (97.7%). GeneXpert showed a sensitivity of 70.6% and specificity of 93.9%. Overall diagnostic accuracy ranged from 88.7% for acid-fast bacteria (AFB) staining to 96.9% for mycobacterial cultures. The MPT64 antigen test had an area under the curve (AUC) of 0.814, indicating a good diagnostic accuracy. Conclusion The MPT64 antigen test demonstrates promising sensitivity and specificity for diagnosing paediatric EPTB, making it a valuable diagnostic tool, especially in resource-limited settings. However, mycobacterial cultures maintain the highest accuracy. Combining the MPT64 antigen test with other methods may enhance diagnostic capabilities.

Evaluation of Immunohistochemistry Technique for Diagnosis of Extrapulmonary Tuberculosis in Biopsy Tissue Specimen as Compared to Composite Diagnostic Criteria

Introduction

Diagnosis of extrapulmonary tuberculosis (EPTB) has been challenging owing to its paucibacillary nature and diverse clinical manifestations. Immunohistochemistry (IHC) on biopsy specimens has presented a new perspective toward improving tuberculosis diagnosis. MPT64 is a unique antigen that has shown high sensitivity and specificity compared to other conventional techniques in its ability to diagnose tuberculosis as well as differentiate it from nontubercular mycobacteria. In this study, we aimed to analyze the utility of anti-MPT64 in the diagnosis of EPTB.

Methods

In this cross-sectional study, conducted over a period of 1 year, 52 nonrepetitive samples from 52 participants with a presumptive diagnosis of EPTB were collected and processed. The specimens were subjected to Ziehl-Neelsen staining, GeneXpert, tissue culture by mycobacterium growth indicator tube, H and E staining, and IHC with anti-MPT64. The sensitivity and specificity of anti-MPT64 was computed against a composite diagnostic criterion.

Results

Fifty-two consecutive participants satisfying the study criteria were recruited. The mean age of the study population was 37.35 ± 18.71 years. Lymph node specimen accounted for majority of the specimen processed (n = 20, 38.5%). The sensitivity of anti-MPT64 in the diagnosis of EPTB was 68.29%, specificity was 90.90%, positive predictive value was 96.55%, and negative predictive value was 43.47%, when composite criteria were considered standard for diagnosis.

Conclusion

Immunohistochemical staining by anti-MPT64 is useful in establishing microbiological diagnosis of EPTB on biopsy specimens.

Improving diagnosis of tuberculous lymphadenitis by combination of cytomorphology and MPT64 immunostaining on cell blocks from the fine needle aspirates

BACKGROUND

Extra pulmonary tuberculosis (EPTB) constitutes 18% of all tuberculosis (TB) cases and tuberculous lymphadenitis (TBL) constitutes 20-40% of EPTB. Diagnosis of TBL is challenging because of the paucibacillary nature of the disease.

OBJECTIVE

To investigate the diagnostic potential of a new antigen detection test based on the detection of M. tuberculosis complex specific antigen MPT64 from fine needle aspirate (FNA) cytology smears and biopsies obtained from patients with clinically suspected TBL using immunohistochemistry (IHC).

MATERIALS AND METHODS

This study was conducted at Khyber Teaching Hospital and Rehman Medical Institute, Peshawar, Pakistan, from January 2018 to April 2019. Samples, including FNA (n = 100) and biopsies (n = 8), were collected from 100 patients with presumptive TBL. Direct smears and cell blocks were prepared from the FNA samples. All samples were subjected to hematoxylin-eosin (H&E) staining, Ziehl-Neelsen (ZN) staining, and immunostaining with polyclonal anti-MPT64 antibody. The culture was performed only for biopsy specimens. All patients were followed until the completion of anti-TB treatment. The response to treatment was included in the composite reference standard (CRS) and used as the gold standard to validate the diagnostic tests.

RESULTS

The sensitivity, specificity, positive and negative predictive values for ZN staining were 4.4%,100%,100%,56%, for culture were 66%,100%,100%,50%, for cytomorphology were 100%,90.91%,90%,100%, and for immunostaining with anti-MPT64 were all 100%,respectively. The morphology and performance of immunohistochemistry were better with cell blocks than with smears.

CONCLUSION

MPT64 antigen detection test performed better than ZN and cytomorphology in diagnosing TBL. This test applied to cell blocks from FNA is robust, simple, and relatively rapid, and improves the diagnosis of TBL.

Improved diagnosis of extrapulmonary tuberculosis in adults with and without HIV in Mbeya, Tanzania using the MPT64 antigen detection test

Extrapulmonary tuberculosis (EPTB) in People Living with HIV (PLWHIV) is a diagnostic challenge. Our immunochemistry based MPT64 antigen detection test has shown improved sensitivity compared to current laboratory tests in the resource limited diagnostic setting. The aim of this study was to validate the implementability and diagnostic performance of the test in PLWHIV and HIV negative adults in a HIV endemic Tanzanian setting. Adult (>18 y) presumptive EPTB patients were prospectively enrolled at Mbeya Zonal Referral Hospital and followed to the end of treatment or until an alternative diagnosis was reached. Suspected sites of infection were sampled and were subject to routine diagnostics, GeneXpert MTB/RIF assay and the MPT64 test. The performance of the diagnostics tests was assessed using a composite reference standard that included clinical suspicion, mycobacterial culture, response to anti-tuberculosis (TB) therapy, cytological and radiological findings. Patients (N = 168) were categorized as 21 confirmed TB, 23 probable TB and 44 possible TB cases, 69 patients were categorized as non-TB cases and 11 were uncategorized. In the TB group, the three most common infections were adenitis (41%), peritonitis (19%) and pleuritis (14%). The TB and non-TB groups did not differ in HIV seropositivity (46% vs 42%) Among HIV negative and PLWHIV, the MPT64 test had a sensitivity of (91% vs 78%), specificity (75% vs 86%), positive predictive value (80% vs 88%), negative predictive value (89% vs 74%), and accuracy (84% vs 81%), respectively. Performance was not significantly reduced in PLWHIV, and sensitivity was higher than in the currently used tests, including the GeneXpert MTB/RIF assay. The MPT64 test improved the diagnosis of EPTB, irrespective of HIV status. The test performed better than currently used diagnostic test. The test was implementable in a tertiary level hospital with basic pathology services in a HIV endemic Tanzanian setting.

Immunochemistry-Based Diagnosis of Extrapulmonary Tuberculosis: A Strategy for Large-Scale Production of MPT64-Antibodies for Use in the MPT64 Antigen Detection Test

Tuberculosis (TB) is a global health problem. The immunohistochemistry (IHC)-based MPT64 antigen detection test has shown promising results for diagnosing extrapulmonary TB in previous studies. However, the anti-MPT64 antibody currently used in the test is in limited supply, and reproduction of a functional antibody is a prerequisite for further large-scale use. Various antigen-adjuvant combinations and immunisation protocols were tested in mice and rabbits to generate monoclonal and polyclonal antibodies. Antibodies were screened in IHC, and the final new antibody was validated on clinical human specimens. We were not able to generate monoclonal antibodies that were functional in IHC, but we obtained multiple functional polyclonal antibodies through careful selection of antigen-adjuvant and comprehensive screening in IHC of both pre-immune sera and antisera. To overcome the limitation of batch-to-batch variability with polyclonal antibodies, the best performing individual polyclonal antibodies were pooled to one final large-volume new anti-MPT64 antibody. The sensitivity of the new antibody was in the same range as the reference antibody, while the specificity was somewhat reduced. Our results suggest that it possible to reproduce a large-volume functional polyclonal antibody with stable performance, thereby securing stable supplies and reproducibility of the MPT64 test, albeit further validation remains to be done.

Mycobacterial antigens in pleural fluid mononuclear cells to diagnose pleural tuberculosis in HIV co-infected patients

Background

Extra pulmonary manifestation of tuberculosis (TB) accounts for approximately one-half of TB cases in HIV-infected individuals with pleural TB as the second most common location. Even though mycobacteria are cleared, mycobacterial antigens may persist in infected tissues, causing sustained inflammation and chronicity of the disease. The aim of this study was to explore various mycobacterial antigens in pleural effusions, the impact of HIV infection and CD4+ T-cell depletion on the presence of antigens, and the diagnostic potential of antigens for improved and rapid diagnosis of pleural TB.

Methods

Pleural fluid specimens were collected from patients presenting with clinically suspected pleural TB, and processed routinely for culture, cytology, and adenosine deaminase activity analysis. HIV status and CD4+ T-cell counts were recorded. Pleural fluid mononuclear cells (PFMC) were isolated, and cell smears were stained with acid-fast staining and immunocytochemistry for various mycobacterial antigens. Real-time and nested-PCR were performed. Patients were categorized as pleural TB or non-TB cases using a composite reference standard. Performance of the mycobacterial antigens as diagnostic test was assessed.

Results

A total of 41 patients were enrolled, of which 32 were classified as pleural TB and 9 as non-TB. Thirteen patients had culture confirmed pleural TB, 26 (81%) were HIV-TB co-infected, and 64% had < 100 CD4+ T-cells/microL. Both secreted and cell-wall mycobacterial antigens were detected in PFMC. Lipoarabinomannan (LAM) was the most frequently detected antigen. There was no direct correlation between positive culture and antigens. Cases with low CD4+ T-cell counts had higher bacterial and antigen burden. By combining detection of secreted antigen or LAM, the sensitivity and specificity to diagnose pleural TB was 56 and 78%, respectively, as compared to 41 and 100% for culture, 53 and 89% for nested PCR, and 6 and 100% for real-time PCR.

Conclusion

Mycobacterial antigens were detectable in PFMC from tuberculous pleural effusions, even in cases where viable mycobacteria or bacterial DNA were not always detected. Thus, a combination of secreted antigen and LAM detection by immunocytochemistry may be a complement to acid-fast staining and contribute to rapid and accurate diagnosis of pleural TB.

Diagnosis of extrapulmonary tuberculosis using the MPT64 antigen detection test in a high-income low tuberculosis prevalence setting

BACKGROUND

Extrapulmonary tuberculosis (EPTB) poses diagnostic challenges due to the paucibacillary nature of the disease. The immunochemistry-based MPT64 antigen detection test (MPT64 test) has shown promising results for diagnosing EPTB in previous studies performed in low-resource settings, with higher sensitivity than microscopy and culture. The aim of this study was to investigate the performance of the MPT64 test in a routine clinical setting in a high-income low TB prevalence country.

METHODS

Extrapulmonary samples sent for TB diagnostics to microbiology and pathology laboratories at three regional tertiary care hospitals in Norway in a one-year period were included and subjected to the MPT64 test in parallel to the routine TB diagnostic tests.

RESULTS

Samples from 288 patients were included and categorised as confirmed TB cases (n = 26), clinically diagnosed TB cases (n = 5), non-TB cases (n = 243) and uncategorised (n = 14), using a composite reference standard (CRS). In formalin-fixed biopsies, the sensitivity (95% CI) of the MPT64 test, microscopy, PCR-based tests pooled, and culture was 37% (16-62), 20% (4-48), 37% (16-62) and 50% (23-77), respectively, against the CRS. The MPT64 test showed a good positive predictive value (88%) and an excellent specificity (99, 95% CI 92-100) in formalin-fixed biopsies. In fine-needle aspirates, pus and fluid samples, the test performance was lower.

CONCLUSIONS

The MPT64 test was implementable in pathology laboratories as part of routine diagnostics, and although the sensitivity of the MPT64 test was not better than culture in this setting, the test supplements other rapid diagnostic methods, including microscopy and PCR-based tests, and can contribute to strengthen the diagnosis of EPTB in formalin-fixed biopsies in the absence of culture confirmation.

Rapid and Specific Diagnosis of Extrapulmonary Tuberculosis by Immunostaining of Tissues and Aspirates With Anti-MPT64

BACKGROUND

Extrapulmonary tuberculosis (EPTB) constitutes about 15% to 20% of all cases of tuberculosis (TB). The confirmation of EPTB has always been a challenge to laboratory personnel. We aim to evaluate the diagnostic potential of immunostaining with anti-MPT64 in various EPTB specimens.

MATERIALS AND METHODS

We studied a total of 51 TB cases and 38 non-TB control specimens comprising of fine-needle aspirates and formalin-fixed biopsies. These were investigated using a combination of the Ziehl-Neelsen method, the Lowenstein-Jensen culture, immunostaining with anti-MPT64 and anti-BCG, and nested-polymerase chain reaction (PCR) for IS6110. Results of all the tests were compared using nested-PCR as the gold standard.

RESULTS

Diagnostic validation of immunostaining for anti-MPT64 was performed using nested-PCR as the gold standard. The overall sensitivity, specificity, and positive and negative predictive values for immunostaining with anti-MPT64 were 100%, 97%, 97%, and 100%, respectively.

CONCLUSIONS

Immunostaining using anti-MPT64 is a rapid and sensitive method for establishing an early and specific diagnosis of Mycobacterium tuberculosis infection. The technique is simple to be incorporated into routine pathology laboratories.

A novel aptamer-based test for the rapid and accurate diagnosis of pleural tuberculosis

Pleural tuberculosis (pTB) is diagnosed by using a composite reference standard (CRS) since microbiological methods are grossly inadequate and an accurate diagnostic test remains an unmet need. The present study aimed to evaluate the utility of Mycobacterium tuberculosis (Mtb) antigen and DNA-based tests for pTB diagnosis. Patients were classified as 'Definite TB', 'Probable TB' and 'Non-TB' disease according to the CRS. We assessed the performance of in-house antigen detection assays, namely antibody-based Enzyme-Linked ImmunoSorbent Assay (ELISA) and aptamer-based Aptamer-Linked Immobilized Sorbent Assay (ALISA), targeting Mtb HspX protein and DNA-based tests namely, Xpert MTB/RIF and in-house devR-qPCR. ROC curves were generated for the combined group of 'Definite TB' and 'Probable TB' vs. 'Non-TB' disease group and cut-off values were derived to provide specificity of ≥98%. The sensitivity of ALISA was ∼93% vs. ∼24% of ELISA (p-value ≤0.0001). devR-qPCR exhibited a sensitivity of 50% vs. ∼22% of Xpert (p-value ≤0.01). This novel aptamer-based ALISA test surpasses the sensitivity criterion and matches the specificity requirement spelt out in the 'Target product profile' for extrapulmonary tuberculosis samples by Unitaid (Sensitivity ≥80%, Specificity 98%). The superior performance of the aptamer-based ALISA test indicates its translational potential to bridge the existing gap in pTB diagnosis.

MPT64 antigen detection test improves routine diagnosis of extrapulmonary tuberculosis in a low-resource setting: A study from the tertiary care hospital in Zanzibar

BACKGROUND

Extrapulmonary tuberculosis (EPTB) is a diagnostic challenge. An immunochemistry-based MPT64 antigen detection test (MPT64 test) has reported higher sensitivity in the diagnosis of EPTB compared with conventional methods. The objective of this study was to implement and evaluate the MPT64 test in routine diagnostics in a low-resource setting.

METHODS

Patients with presumptive EPTB were prospectively enrolled at Mnazi Mmoja Hospital, Zanzibar, and followed to the end of treatment. Specimens collected were subjected to routine diagnostics, GeneXpert® MTB/RIF assay and the MPT64 test. The performance of the MPT64 test was assessed using a composite reference standard, defining the patients as tuberculosis (TB) cases or non-TB cases.

RESULTS

Patients (n = 132) were classified as confirmed TB (n = 12), probable TB (n = 34), possible TB (n = 18), non-TB (n = 62) and uncategorized (n = 6) cases. Overall, in comparison to the composite reference standard for diagnosis, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy of the MPT64 test was 69%, 95%, 94%, 75% and 82%, respectively. The MPT64 test performance was best in TB lymphadenitis cases (n = 67, sensitivity 79%, specificity 97%) and in paediatric TB (n = 41, sensitivity 100%, specificity 96%).

CONCLUSIONS

We show that the MPT64 test can be implemented in routine diagnostics in a low-resource setting and improves the diagnosis of EPTB, especially in TB lymphadenitis and in children.

Lung Infections

A review of pulmonary infections of all types with diagnostic and morphological features.

HIV-1 and the Mycobacterium tuberculosis granuloma: A systematic review and meta-analysis

Infection with HIV-1 greatly increases the risk of active tuberculosis (TB). Although hypotheses suggest HIV-1 disrupts Mycobacterium tuberculosis (Mtb) granuloma function, few studies have examined this directly. The objective of this study was to determine what evidence exists about the effect HIV-1 co-infection has upon Mtb granulomas. A systematic search of PubMed, Web of Science, and Medline up to 20 March 2015 was conducted, to identify studies comparing Mtb-infected tissue from HIV-1 infected and uninfected persons, or HIV-1 infected persons with stratified peripheral CD4 T cell (pCD4) counts. We summarized findings that focused on how HIV-1 changes granuloma formation, bacterial presence, cellular composition, and cytokine production. Nineteen studies with a combined sample size of 899 persons were included. Although studies frequently were limited by variable or inadequately described definitions of outcomes and analytical methods, HIV-1 was found to be associated with increased bacillary load within Mtb-infected tissue. Reductions in pCD4 counts within co-infected persons associated with both poorer granuloma formation and higher bacterial load. The high degree of heterogeneity among studies combined with experimental limitations made it difficult to conclusively support previously published and prevalent hypotheses about HIV-1/Mtb co-infection granulomas. To elucidate the validity of these hypotheses we have described areas that can be improved in future studies in order to clarify the influence HIV-1 co-infection has upon the Mtb granuloma.

Principles of analytic validation of immunohistochemical assays: Guideline from the College of American Pathologists Pathology and Laboratory Quality Center

CONTEXT

Laboratories must validate all assays before they can be used to test patient specimens, but currently there are no evidence-based guidelines regarding validation of immunohistochemical assays.

OBJECTIVE

To develop recommendations for initial analytic validation and revalidation of immunohistochemical assays.

DESIGN

The College of American Pathologists Pathology and Laboratory Quality Center convened a panel of pathologists and histotechnologists with expertise in immunohistochemistry to develop validation recommendations. A systematic evidence review was conducted to address key questions. Electronic searches identified 1463 publications, of which 126 met inclusion criteria and were extracted. Individual publications were graded for quality, and the key question findings for strength of evidence. Recommendations were derived from strength of evidence, open comment feedback, and expert panel consensus.

RESULTS

Fourteen guideline statements were established to help pathology laboratories comply with validation and revalidation requirements for immunohistochemical assays.

CONCLUSIONS

Laboratories must document successful analytic validation of all immunohistochemical tests before applying to patient specimens. The parameters for cases included in validation sets, including number, expression levels, fixative and processing methods, should take into account intended use and should be sufficient to ensure that the test accurately measures the analyte of interest in specimens tested in that laboratory. Recommendations are also provided for confirming assay performance when there are changes in test methods, reagents, or equipment.

Differential in vivo expression of mycobacterial antigens in Mycobacterium tuberculosis infected lungs and lymph node tissues

Background

The clinical course of tuberculosis (TB) infection, bacterial load and the morphology of lesions vary between pulmonary and extrapulmonary TB. Antigens expressed in abundance during infection could represent relevant antigens in the development of diagnostic tools, but little is known about the in vivo expression of various M. tuberculosis antigens in different clinical manifestations. The aim of this study was to study the differences in the presence of major secreted as well as somatic mycobacterial antigens in host tissues during advanced rapidly progressing and fatal pulmonary disease with mainly pneumonic infiltrates and high bacterial load, and to compare this to the presence of the same antigens in TB lymphadenitis cases, which is mainly chronic and self-limiting disease with organised granulomas and lower bacterial load.

Methods

Human pulmonary (n = 3) and lymph node (n = 17) TB biopsies, and non-TB controls (n = 12) were studied. Ziehl-Neelsen stain, nested PCR 1S6110 and immunohistochemistry were performed. Major secreted (MPT32, MPT44, MPT46, MPT51, MPT53, MPT59, MPT63, and MPT64) and somatic mycobacterial antigens (Mce1A, Hsp65, and MPT57) were detected by using rabbit polyclonal antibodies.

Results

Plenty of bacilli were detectable with Ziehl-Neelsen stain in the lung biopsies while no bacilli were detected in the lymph node biopsies. All the cases were shown to be positive by PCR. Both secretory and somatic antigens were expressed in abundance in pulmonary infiltrates, while primarily somatic antigens were detected in the lymphadenitis cases. Of the secreted antigens, only MPT64 was consistently detected in both cases, indicating a preferential accumulation of this antigen within the inflammatory cells, even if the cells of the granuloma can efficiently restrict bacterial growth and clear away the secreted antigens.

Conclusions

This study shows that major secreted mycobacterial antigens were found in high amounts in advanced pulmonary lesions without proper granuloma formation, while their level of staining was very low, or absent, in the lymph node TB lesions with organised granulomas and very low bacillary load, with one exception of MPT64, suggesting its role in the persistence of chronic infection. These findings have implication for development of new diagnostic tools.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-535) contains supplementary material, which is available to authorized users.

Tuberculosis diagnosis using immunodominant, secreted antigens of Mycobacterium tuberculosis

Tuberculosis (TB) remains a major public health concern in most low-income countries. Hence, rapid and sensitive TB diagnostics play an important role in detecting and preventing the disease. In addition to established diagnostic methods, several new approaches have been reported. Some techniques are simple but time-consuming, while others require complex instrumentation. One prominent and readily available approach is to detect proteins that Mycobacterium tuberculosis secretes, such as Mpt64, the 6-kDa early secreted antigenic target (Esat6), the 10-kDa culture filtrate protein (Cfp10), and the antigen 85 (Ag85) complex. Although their functions are not fully understood, a growing body of molecular evidence implicates them in M. tuberculosis virulence. Currently these biomarkers are either being used or investigated for use in skin patch tests, biosensor analyses, and immunochromatographic, immunohistochemical, polymerase chain reaction-based, and enzyme-linked immunosorbent assays. This review provides a comprehensive discussion of the roles these immunodominant antigens play in M. tuberculosis pathogenesis and compares diagnostic methods based on the detection of these proteins with more established tests for TB.

Prime-boost vaccination with rBCG/rAd35 enhances CD8⁺ cytolytic T-cell responses in lesions from Mycobacterium tuberculosis-infected primates

To prevent the global spread of tuberculosis (TB) infection, a novel vaccine that triggers potent and long-lived immunity is urgently required. A plasmid-based vaccine has been developed to enhance activation of major histocompatibility complex (MHC) class I-restricted CD8⁺ cytolytic T cells using a recombinant Bacille Calmette-Guérin (rBCG) expressing a pore-forming toxin and the Mycobacterium tuberculosis (Mtb) antigens Ag85A, 85B and TB10.4 followed by a booster with a nonreplicating adenovirus 35 (rAd35) vaccine vector encoding the same Mtb antigens. Here, the capacity of the rBCG/rAd35 vaccine to induce protective and biologically relevant CD8⁺ T-cell responses in a nonhuman primate model of TB was investigated. After prime/boost immunizations and challenge with virulent Mtb in rhesus macaques, quantification of immune responses at the single-cell level in cryopreserved tissue specimen from infected organs was performed using in situ computerized image analysis as a technological platform. Significantly elevated levels of CD3⁺ and CD8⁺ T cells as well as cells expressing interleukin (IL)-7, perforin and granulysin were found in TB lung lesions and spleen from rBCG/rAd35-vaccinated animals compared with BCG/rAd35-vaccinated or unvaccinated animals. The local increase in CD8⁺ cytolytic T cells correlated with reduced expression of the Mtb antigen MPT64 and also with prolonged survival after the challenge. Our observations suggest that a protective immune response in rBCG/rAd35-vaccinated nonhuman primates was associated with enhanced MHC class I antigen presentation and activation of CD8⁺ effector T-cell responses at the local site of infection in Mtb-challenged animals.

A systematic review of the epidemiology, immunopathogenesis, diagnosis, and treatment of pleural TB in HIV-infected patients

BACKGROUND

High HIV burden countries have experienced a high burden of pleural TB in HIV-infected patients.

OBJECTIVE

To review the epidemiology, immunopathogenesis, diagnosis, and treatment of pleural TB in HIV-infected patients.

METHODS

A literature search from 1950 to June 2011 in MEDLINE was conducted.

RESULTS

Two-hundred and ninety-nine studies were identified, of which 30 met the inclusion criteria. The immunopathogenesis as denoted by cells and cytokine profiles is distinctly different between HIV and HIV-uninfected pleural TB disease. Adenosine deaminase and interferon gamma are good markers of pleural TB disease even in HIV-infected patients. HIV-uninfected TB suspects with pleural effusions commonly have a low yield of TB organisms however the evidence suggests that in dually infected patients smear and cultures have a higher yield. The Gene Xpert MTB/RIF assay has significant potential to improve the diagnosis of pleural TB in HIV-positive patients.

CONCLUSIONS

Pleural TB in HIV-infected patients has a different immunopathogenesis than HIV-uninfected pleural TB and these findings in part support the differences noted in this systematic review. Research should focus on developing an interferon gamma-based point of care diagnostic test and expansion of the role of Gene Xpert in the diagnosis of pleural TB.

Selection and application of peptide mimotopes of MPT64 protein in Mycobacterium tuberculosis

Antibody responses can be useful markers of tuberculosis (TB) infection, especially in the screening of extra-pulmonary TB. MPT64 is an important antigen in Mycobacterium tuberculosis (MTB) infection and is used in serological diagnosis. However, large variability in the diagnostic accuracy of MPT64 as a serological tool has limited its application. Phage-displayed random peptide libraries have emerged as a powerful technique to select peptides (epitopes) or mimotopes that may serve as surrogate diagnostic markers in serological tests. In the present study, this method was employed to identify mimotopes of the MPT64 protein of MTB by screening a linear heptapeptide library with rabbit antibodies raised against MPT64 protein. Two antigenic mimotopes (M2 and M6) resembling B-cell epitopes of MPT64 were identified that bound the affinity purified anti-MPT64 polyclonal antibodies and competed with MPT64 for antibody binding. From the results of sequence alignment and a structure modelling figure of MPT64, the sequence of the 2nd to 5th amino acids (DSML) of M2 was totally consistent with the sequence of the 224th to 227th amino acids of MPT64 and the peptide is located on the surface of the space structure of MPT64, suggesting that it might be a linear epitope of MPT64. The recognition of both phage-displayed and synthetic peptides of M2 by the anti-MPT64 polyclonal antibodies also supported this. Although no recurring sequence and no analogue to MPT64 of M6 were found for sequence alignment, the recognition of both phage-displayed and synthetic peptides of M6 by the anti-MPT64 polyclonal antibodies indicated that it might be a mimotope of a conformational epitope of MPT64. According to the results of the reactivity of human sera with synthetic M2 and M6 peptides and MPT64, M2 showed a significantly higher AUC and sensitivity than M6 and MPT64, especially for the sera from sputum-negative TB patients, suggesting that the M2 mimotope may be useful in serological diagnostic testing for TB.

Assessment of the IgA immunoassay diagnostic potential of the Mycobacterium tuberculosis MT10.3-MPT64 fusion protein in tuberculous pleural fluid

Pleural tuberculosis (PL-TB) remains difficult to diagnose. An enzyme-linked immunosorbent assay (ELISA) was developed based on a construction containing the fusion of the Rv3019c (MT10.3) and Rv1980c (MPT64) gene sequences, and its performance was evaluated in an area where TB is endemic. A total of 92 pleural fluid (PF) samples at serial dilutions of 1:50 to 1:800 were included in the ELISA IgA MT10.3-MPT64 evaluation: 70 from TB patients and 22 from patients with other pleurisies. Confirmation of the expression and subsequent purification of the protein was made by SDS-PAGE and Western blot assays, resulting in a 36-kDa protein. ELISA IgA MT10.3-MPT64 showed sensitivities of 61.4%, 58.6%, 62.9%, 67.1%, and 70% at each PF dilution, respectively. The cumulative results of all dilutions increased sensitivity to 81.4% without jeopardizing specificity. Similar results were also obtained at the combined dilutions of 1:50, 1:200, and 1:800 or 1:50 plus 1:800 dilutions (80%). The overall sensitivity of the reference test, i.e., histopathological examination, was 74%. But, via the ELISA IgA MT10.3-MPT64 test, sensitivity was high for specimens with a negative culture (23/27; 85.2%) or nonspecific histopathology (17/18; 94.4%). Our findings demonstrated the promising use of this test as an adjunct in PL-TB diagnoses, particularly in cases with lower bacterial loads and false-negative results in the reference tests, since the new test includes such important features as quick and easy application, high sensitivity and, perhaps most importantly, affordability, which is so crucial for its widespread use in developing countries.

Biomarkers of disease activity, cure, and relapse in tuberculosis

The changing face of tuberculosis, with epidemics fueled by HIV and urbanization in much of the world and a relative increase in the importance of latent tuberculosis as a source of cases in the more economically developed countries, has led to a demand for more robust, clinically applicable diagnostic tools. As a result, research aiming to identify biomarkers of Mycobacterium tuberculosis infection and disease has flourished. This article discusses the most recent findings of that work.

Adenosine deaminase activity is a sensitive marker for the diagnosis of tuberculous pleuritis in patients with very low CD4 counts

BACKGROUND

Adenosine Deaminase Activity (ADA) is a commonly used marker for the diagnosis of tuberculous pleural effusion. There has been concern about its usefulness in immunocompromised patients, especially HIV positive patients with very low CD4 counts. The objective of this study was to evaluate the sensitivity of ADA in pleural fluid in patients with low CD4 counts.

MATERIALS AND METHODS

This was a retrospective case control study. Medical files of patients with tuberculous pleuritis and non-tuberculous pleuritis were reviewed. Clinical characteristics, CD4 cell counts in blood and biochemical markers in pleural fluid, including ADA were recorded.

RESULTS

One ninety seven tuberculous pleuritis and 40 non-tuberculous pleuritis patients were evaluated. Using the cut-off value of 30 U/L, the overall sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio of ADA was 94%, 95%, 19, and 0.06 respectively. The mean CD4 cell counts among TB pleuritis patients was 29 and 153 cells/microL in patients with CD4 <50 cells/microL and >50 cells/microL, (p<0.05) respectively. The corresponding mean ADA values for these patients were 76 U/L and 72 U/L respectively (p>0.5). There was no correlation between ADA values and CD4 cell counts (r = -0.120, p = 0.369).

CONCLUSION

ADA analysis is a sensitive marker of tuberculous pleuritis even in HIV patients with very low CD4 counts in a high TB endemic region. The ADA assay is inexpensive, rapid, and simple to perform and is of great value for the immediate diagnosis of tuberculous pleuritis while waiting for culture result and this has a positive impact on patient outcome.