Rapid diagnosis of tuberculous meningitis by a dot immunobinding assay To detect mycobacterial antigen in cerebrospinal fluid specimens

Detection and characterization of purified antigenic proteins from culture filtrate of Mycobacterium bovis strain AN5

BACKGROUND AND OBJECTIVES

Bovine tuberculosis diagnosis is usually performed by various tests with specific limitations. Mycobacterium bovis culture filtrate contains antigenic proteins that could be used to improve the sensitivity of bovine tuberculosis diagnosis. The objective of this study was to identify and purify antigenic proteins from culture filtrates of M. bovis strain AN5 for use in immunological assays.

MATERIALS AND METHODS

Secreted proteins were purified from the heat-treated culture filtrate of M. bovis strain AN5. Proteins were precipitated with ammonium sulfate, fractionated by Sephadex G50 chromatography. The protein concentrations and the approximate molecular weight were determined by lowry method and 12% sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), respectively. Immunological methods, including dot-blotting and western blotting, assessed the quality of the isolated proteins.

RESULTS

The quantity of antigenic proteins in the culture medium was measured at far more than 15% of the amount of proteins secreted into medium. Three main chromatographic fractions obtained and showed concentrations of proteins ranging from 14 to 60 μg/ μl with molecular weights in the 10 to 180 kDa range. The purified antigens showed positive reactions to the infected cattle serum throughout dot-blotting. Western blotting revealed a total of 15 to 70 kDa molecular weight proteins.

CONCLUSION

Immunoblotting analysis made it possible to detect and recognize novel antigens that are useful for bovine tuberculosis diagnosis improvement. This is significant since non-specific reactions were not observed when we utilized serum of cattle experimentally infected with M. bovis as a polyclonal antibody.

Dot-immunobinding assay (Dot-Iba)

Dot-immunobinding assay (Dot-Iba) is a simple and highly reproducible immunodiagnostic method. Antibody or antigen is dotted directly onto nitrocellulose membrane (NCM) discs. The diagnostic material to be checked can be incubated on this disc. Presence of antigen-antibody complex in NCM discs can be directly demonstrated with enzyme-conjugated antiglobulins and substrate. Development of a purple-pink colored, insoluble substrate product in the nitrocellulose membrane will be considered a positive result in the assay. This assay allows the processing of multiple specimens at a time and the entire operational procedures required only 4-6 h. Dot-IBA is rapid and the technical steps involved in the assay are much simpler than the other immunoassays such as enzyme-linked immunosorbent assay in detecting circulating antigen and antibody in clinical samples. The Dot-Iba showed an overall sensitivity of 60 % for tuberculous meningitis diagnosis and no false positive results were encountered. Hence this assay is highly specific for the diagnosis of paucibacillary diseases like extrapulmonary tuberculosis. Dot-Iba is best suited to laboratories in developing world where there are constraints in laboratory resources.

Aptameric system for the highly selective and ultrasensitive detection of protein in human serum based on non-stripping gold nanoparticles

A novel approach is proposed in this study for the development of an aptameric assay system for protein based on non-stripping gold nanoparticles (NPs)-triggered chemiluminescence (CL) upon target binding. The strategy chiefly depends on the formation of a sandwich-type immunocomplex among the capture antibody immobilized on the polystyrene microwells, target protein and aptamer-functionalized gold NPs. Introduction of target protein into the assay system leads to the attachment of gold NPs onto the surface of the microwells and thus the assembled gold NPs could trigger the reaction between luminol and AgNO(3) with a CL emission. Further signal amplification was achieved by a simple gold metal catalytic deposition onto the gold NPs. Such an amplified CL transduction allowed for the detection of model target IgE down to the 50 fM, which is better than most existing aptameric methods for IgE detection. This new protocol also provided a good capability in discriminating IgE from nontarget proteins such as IgG, IgA, IgM and interferon. The practical application of the proposed gold NPs-based immunoassay was successfully carried out for the determination of IgE in 35 human serum samples. Overall, the proposed assay system exhibits excellent analytical characteristics (e.g., a detection limit on the attomolar scale and a linear dynamic range of 4 orders of magnitude), and it is also straightforward to adapt this strategy to detect a spectrum of other proteins by using different aptamers. This new CL strategy might create a novel technology for developing simple biosensors in the sensitive and selective detection of target protein in a variety of clinical, environmental and biodefense applications.

Dot-immunobinding assay

Dot-immunobinding assay (Dot-Iba) is a simple and highly reproducible immunodiagnostic method. Antibody or antigen is dotted directly onto nitrocellulose membrane (NCM) discs. The diagnostic material to be checked can be incubated on this disc. Presence of antigen-antibody complex in NCM discs can be directly demonstrated with enzyme-conjugated antiglobulins and substrate. Development of a purple-pink colored, insoluble substrate product in the NCM will be considered a positive result in the assay. This assay allows the processing of multiple specimens at a time and the entire operational procedures require only 4-6 h. Dot-Iba is rapid, and the technical steps involved in the assay are much simpler than in the other immunoassays such as enzyme-linked immunosorbant assay in detecting circulating antigen and antibody in clinical samples. The Dot-Iba showed an overall sensitivity of 60% for tuberculous meningitis diagnosis and no false positive results were encountered. Hence, this assay is highly specific for the diagnosis of paucibacillary diseases such as extrapulmonary tuberculosis. Dot-Iba is best suited to laboratories in developing world where there are constraints in laboratory resources.

Central nervous system tuberculosis: pathogenesis and clinical aspects

Tuberculosis of the central nervous system (CNS) is a highly devastating form of tuberculosis, which, even in the setting of appropriate antitubercular therapy, leads to unacceptable levels of morbidity and mortality. Despite the development of promising molecular diagnostic techniques, diagnosis of CNS tuberculosis relies largely on microbiological methods that are insensitive, and as such, CNS tuberculosis remains a formidable diagnostic challenge. Insights into the basic neuropathogenesis of Mycobacterium tuberculosis and the development of an appropriate animal model are desperately needed. The optimal regimen and length of treatment are largely unknown, and with the rising incidence of multidrug-resistant strains of M. tuberculosis, the development of well-tolerated and effective antibiotics remains a continued need. While the most widely used vaccine in the world largely targets this manifestation of tuberculosis, the BCG vaccine has not fulfilled the promise of eliminating CNS tuberculosis. We put forth this review to highlight the current understanding of the neuropathogenesis of M. tuberculosis, to discuss certain epidemiological, clinical, diagnostic, and therapeutic aspects of CNS tuberculosis, and also to underscore the many unmet needs in this important field.

Rapid and simple detection of a mycobacterium circulating antigen in serum of pulmonary tuberculosis patients by using a monoclonal antibody and Fast-Dot-ELISA

OBJECTIVES

Several immunoassays have been established for detection of Mycobacterium tuberculosis (MTB) antigens in serum, sputum and cerebrospinal fluid of tuberculous patients using polyclonal or monoclonal antibodies raised against different mycobacterium antigens. Some of these assays display both high sensitivity and specificity for the detection of these antigens. However, these assays require special and highly expensive equipment and the procedures require long periods for their completion. Thus, the rationale of this study was to establish and evaluate Fast-Dot-Enzyme-Linked Immunosorbent Assay (FD-ELISA) as a fast, cheap and field applicable assay for detection of mycobacterium antigen in serum of patients with pulmonary TB.

DESIGNS AND METHODS

This study included three groups: group I: 175 tuberculous patients with pulmonary TB proves with sputum Ziehl-Neelsen (ZN) for acid-fast bacilli and sputum culture (all cases were culture positive for MTB); Group II: 65 patients with diseases other than pulmonary TB as bronchial carcinoma (17 patients), bronchial asthma (29 patients) and chronic obstructive pulmonary disease (19 patients); group III: 50 healthy individuals. Groups II and III served as negative control groups. The target mycobacterium antigen was identified in both crude mycobacterium antigens extract and serum of patients with pulmonary TB, using western blotting technique and anti-TB monoclonal antibody (TB20-mAb) and then it was estimated in the serum samples of all studied groups as an index of tuberculosis, using a newly developed FD-ELISA.

RESULTS

The target mycobacterium antigen was identified at 20 kDa molecular mass in crude mycobacterium antigens extract as well as in serum of patients with pulmonary TB. The developed FD-ELISA detected the mycobacterium antigen in the sera of 159 out of 175 pulmonary TB patients with a sensitivity of 90.8% and 93.0% positive predictive value (PPV). In addition, it identified 12 false weakly positive cases out of 115 samples of negative control groups (7 out of 65 non-TB patients and 5 out of 50 healthy individuals) with a specificity of 89.6% and 86.6% negative predictive value (NPV). Standardization of the FD-ELISA using a serial dilution of the purified mycobacterium antigen indicated that the assay was able to detect 1.8 microg/ml as a lowest detectable antigen concentration.

CONCLUSIONS

The newly developed FD-ELISA is a simple, rapid and highly sensitive assay for detection of mycobacterium antigen in patients with pulmonary TB. Moreover, all steps were performed at room temperature and without the need to use expensive equipment, and this may enhance the application of this assay in tuberculosis screening programs. Further study is needed for confirmation of FD-ELISA reproducibility in light infected pulmonary TB patients and in a large population.

Progress in serodiagnosis of Mycobacterium tuberculosis infection

One-third of the world population is estimated to have Mycobacterium tuberculosis infection. Accurate and timely identification of infected individuals is critical for treatment and control. The current diagnostic methods lack the desired sensitivity and specificity, require sophisticated equipment and skilled workforce or take weeks to yield results. Diagnosis of extrapulmonary TB, TB-HIV co-infection, childhood TB and sputum smear-negative pulmonary TB pose serious challenges. Interest in developing serodiagnostic methods is increasing because detection of antibody is rapid, simple and relatively inexpensive, and does not require a living cell for detection. Three types of tests, namely screening tests to overcome diagnostic delay, specific tests for diagnosis of extrapulmonary TB and other bacteriologically negative cases, and tests for vaccine-induced immunity need critical consideration. Several factors must be considered to develop serodiagnostic methods for TB. Antigen recognition by infected individuals is highly heterogeneous due to stage of disease, differences in HLA types, strain of the bacilli, health of the patient and bacillary load. With advances in molecular biological techniques, a number of novel antigens have been identified. Some of these antigens have proven valuable in detecting specific antibodies in some of the most challenging TB patients. The best example is a fusion protein containing several M. tuberculosis proteins (e.g. CFP-10, MTB8, MTB48, MTB81 and the 38-kDa protein) which showed encouraging results in detecting antibodies in sera of patients, including TB-HIV co-infection. This review presents progress made in the serodiagnosis of TB during the last decade.

[Innovative strategies to diagnose and monitor tuberculosis patients]

Mycobacterium tuberculosis is the single most deadly microorganism worldwide. A third of the world population is thought to have latent tuberculosis and approximately 2 million people die of the disease each year. Short and closely supervised treatment regimens are needed, but it is also essential to develop new strategies to ensure prompt diagnosis of the disease. In particular, cheap methods are needed to tackle tuberculosis from a population perspective. The present article reviews the advances in immunology and molecular strategies for epidemiological diagnosis and monitoring of tuberculosis patients.

Diagnosis of tuberculous meningitis: clinical and laboratory parameters

BACKGROUND

Confirming the clinical suspicion of tuberculous meningitis (TBM) has always been problematic. Whilst smear and culture positivity are diagnostic, these tests have low sensitivity. The polymerase chain reaction (PCR) assay has given variable results.

AIM

This study attempted to improve the diagnostic yield by: (a) increasing the cerebrospinal fluid (CSF) volumes; (b) testing the yield from three specimens of CSF assumed to represent lumbar, cervico-thoracic cord, and base of brain CSF samples; (c) undertaking PCR assays using multiple primer sets; and (d) using real-time PCR.

METHOD

Patients suspected of having cranial or spinal meningeal tuberculosis were entered into the study. Three aliquots of CSF were subjected to smear, culture, and conventional and real-time PCR. Three sets of primers - IS6110, MPB64, and PT8/9 - were used. Patients were retrospectively classified into four categories: 'definite TB' (culture positive), 'probable TB' (clinical and other tests suggestive of TB), 'not TB', and 'uncertain diagnosis'.

RESULTS

A total of 68 patients were studied. There were 20 patients classified as definite TB, 24 probable TB, 17 not TB, and seven uncertain diagnosis. Forty-eight of 57 (84.2%) patients tested were HIV seropositive. The IS6110 PCR was positive in 27 patients which included 18/20 culture positive cases, six in the probable TB group, and three in the not TB group. The MPB64 and PT8/9 primers did not increase the yield. Real-time PCR was positive in seven additional patients. Combining the definite and probable TB, the sensitivity of all PCR assays was 70.5% (31/44) and specificity 87.5% (21/24).

CONCLUSION

Targeting multiple sites of the TB genome using conventional PCR did not increase the number of positive cases. Real-time PCR was more sensitive. However, all the current techniques are still too insensitive to confidently exclude the diagnosis on laboratory grounds.

Application of a circulating antigen detection immunoassay for laboratory diagnosis of extra-pulmonary and pulmonary tuberculosis

BACKGROUND

Diagnosis of extra-pulmonary tuberculosis is often difficult to establish using standard methods. Recently, a 55-kDa mycobacterial antigen was identified in sera of individuals with pulmonary TB using a simple and rapid dot-ELISA based on monoclonal antibody (TB-55 mAb). Here, we have evaluated the application of the dot-ELISA for the detection of target antigen in sera of individuals with extra-pulmonary TB.

METHODS

The Western blot and indirect immunoperoxidase staining was used to identify the target TB antigen using the TB-55 mAb. The dot-ELISA was used to detect the target antigen in serum samples.

RESULTS

The target antigen was identified at 55-kDa molecular weight in serum, ascitic fluid and CSF samples from individuals with extra-pulmonary TB. The purified antigen from these samples showed similar biochemical properties to the previously described antigen. The target antigen was localized in areas without caseous necrosis in lymph tissues. The dot-ELISA detected the target antigen in 90% sera of individuals with extra-pulmonary TB and in 87% sera of individuals with pulmonary TB with a specificity of 97% among control individuals.

CONCLUSION

The detection of the 55-kDa antigen using dot-ELISA can be routinely employed to support clinical diagnosis of extra-pulmonary TB and pulmonary TB.

Status of immunodiagnosis and immunocontraceptive vaccines in India

The article focuses on the Indian initiative of making kits for diagnosis of various infectious and non-infectious diseases as well as reproductive hormones and hormones in various other endocrine disorders. Indigenous diagnostic kits for the detection of various infections such as filariasis, typhoid, amebiasis, Japanese encephalitis, hepatitis, HIV, dengue, leishmaniasis, malaria, rabies, toxoplasmosis, rotavirus, and group A streptococci have been developed. Agreements to transfer the know-how of some of these leads to industries have been signed. The know-how of enzyme-linked immunosorbent assay (ELISA) for detection of hepatitis C has been successfully transferred to industry and is being commercially produced. For detection of HIV-1 and HIV-2, indigenous diagnostic kits based on three different formats, namely ELISA, Western blot and rapid test have been developed and are being commercially produced by Indian industries. The factors influencing the successful transfer of laboratory-scale diagnostic assays from academia to industry and their commercial exploitation have been discussed. Indian scientists have made seminal contributions in exploring the possibility to develop an effective and safe contraceptive vaccine to control the increasing human population of India. Achieving contraception by means of vaccine is a novel approach, which entails generation of a specific antibody response against antigens critically involved in the process of mammalian reproduction. In India, three major programs on contraceptive vaccines based on the beta-subunit of human chorionic gonadotrophin ((beta)hCG) for women, ovine follicle stimulating hormone (oFSH) for men, and riboflavin carrier protein for both males and females have been initiated. The work at the National Institute of Immunology, New Delhi on contraceptive vaccine for women, based on (beta)hCG, has demonstrated, for the first time, that it is feasible to regulate fertility by such an approach. Basic research being carried out to achieve immunocontraception by interfering at sperm-oocyte interaction level has been briefly discussed. These developments are still at the research stage. In addition to advances in the area of contraceptive vaccines, a non-steroidal contraceptive oral pill has been developed by Central Drug Research Institute, Lucknow, commercially produced by two Indian pharmaceutical companies and has been incorporated in the National Family Welfare Program. Another interesting approach for fertility regulation in male has been developed in India, which involves vas occlusion with styrene maleic anhydride (SMA) and is currently undergoing clinical trials in human subjects.

Approach to the Diagnosis and Management of Tuberculous Meningitis

Meningitis caused by Mycobacterium tuberculosis remains an important cause of morbidity and mortality worldwide, and presents specific challenges in terms of diagnosis and management. The nonspecific clinical presentation of tuberculous meningitis has led researchers to develop newer biochemical and molecular methods of making the diagnosis. Several of these methods have excellent sensitivity and specificity, although are not yet available for clinical use. Successful therapy for tuberculous meningitis requires a combination of antimicrobial agents, with vigilance towards the possibility of disease caused by resistant organisms. Adjunctive corticosteroids also have a role in treating this potentially devastating infection. With proper therapy, morbidity and mortality can be minimized in patients with tuberculous meningitis.

Immunocytochemical method for early laboratory diagnosis of tuberculous meningitis

A simple immunocytochemical method was standardized for the direct demonstration of mycobacterial antigen in cerebrospinal fluid (CSF) specimens of patients with tuberculous meningitis (TBM). CSF-cytospin smears were prepared from 22 patients with a clinical diagnosis of TBM and also from an equal number of patients with nontuberculous neurological diseases (disease control). Immunocytological demonstration of mycobacterial antigens in the cytoplasm of monocytoid cells was attempted, by using rabbit immunoglobulin G to Mycobacterium tuberculosis as the primary antibody. Of the 22 CSF-cytospin smears from TBM patients, 16 showed positive immunostaining, while all of the CSF-cytospin smears from the disease control showed negative immunostaining for mycobacterial antigen. The technical aspects of this immunocytological method for the demonstration of mycobacterial antigens are simple, rapid, and reproducible, as well as specific, and therefore can be applied for the early diagnosis of TBM, particularly in patients in whom bacteriological methods did not demonstrate the presence of M. tuberculosis in the CSF.

A comparative evaluation of dot immunobinding assay (Dot-Iba) and polymerase chain reaction (PCR) for the laboratory diagnosis of tuberculous meningitis

The results of a Dot immunobinding assay (Dot Iba) for the detection of mycobacterial antigen in the cerebrospinal fluid (CSF) of 45 patients with tuberculous meningitis (TBM) were compared with the results of a polymerase chain reaction (PCR) for the detection of Mycobacterium tuberculosis. In eight patients with culture proven TBM, Dot-Iba gave positive results, while PCR yielded positive results only in six patients. The overall sensitivities of Dot-Iba and PCR in 37 patients with culture negative (probable) TBM were 75.67% and 40.5% respectively. Dot-Iba, in contrast to PCR is a rapid and relatively easier method. More importantly, Dot-Iba is suitable for the routine application for the laboratory diagnosis of TBM and therefore best suited to laboratories in the developing world.

Clinical applications of new cerebrospinal fluid analytic techniques for the diagnosis and treatment of central nervous system infections

Advances in molecular biology and immunology provide new, highly sensitive and specific techniques that can be applied to analysis of cerebrospinal fluid to enhance the diagnosis and treatment of central nervous system (CNS) infections. In addition to improved accuracy and speed of diagnosis, these modalities may offer improved means of monitoring treatment efficacy, establishing prognosis, detecting organism resistance, and tracking epidemic sources. This brief review discusses a number of recent papers applying these methods, in order to illustrate their value and significance for clinical neurologic practice. Some of these applications are commonly available, whereas others are likely to enter the physician's armamentarium in the near future. As they do, they can be expected to improve the treatment of CNS infections.