Production of monoclonal antibodies to lipoarabinomannan-B and use in the detection of mycobacterial antigens in sputum

Development and preliminary evaluation toward a new tuberculosis treatment monitoring tool: the PATHFAST TB LAM Ag assay

The PATHFAST TB LAM Ag assay is based on a chemiluminescent enzyme immunoassay to quantify lipoarabinomannan (LAM) in sputum within 1 h, and was developed as an alternative to conventional culture methods for monitoring tuberculosis (TB) treatment. This study aimed to evaluate the analytical performance and initial clinical feasibility of using five Mycobacterium tuberculosis variants, 178 non-tuberculous mycobacteria (NTM), 34 upper respiratory and oral cavity microorganisms, 100 sputum specimens from untreated patients, and potential interfering substances, including 27 drugs. The results reveled a single-site repeatability coefficient of variation (CV) of 5.2%-7.0%, and a multi-site reproducibility CV of 7.1%-8.4%. The limit of blank, limit of detection, and limit of quantification were 3.03 pg/mL, 6.67 pg/mL, and 7.44 pg/mL, respectively. Linearity was observed over the analytical measurement range (10.0 pg/mL-50,000 pg/mL), and no hook effect was observed. The assay tended to cross-react with slow-growing NTMs, but not with common upper respiratory and oral cavity microorganisms, except Nocardia asteroides, Nocardia farcinica, and Tsukamurella paurometabola. No interference was observed in the presence of mucin, blood, or major anti-TB, anti-HIV, and anti-pneumonia drugs. Regarding clinical performance, the assay had a sensitivity of 88.8% (95% CI: 80.0%-94.0%) and specificity of 100.0% (95% CI: 83.9%-100.0%) using mycobacterial culture as the reference standard, and a correlation (Spearman's r = -0.770) was observed between LAM concentration and time to detection of culture. These findings show, for the first time, that the PATHFAST TB LAM Ag assay has potential value for monitoring TB treatment.

Collected Thoughts on Mycobacterial Lipoarabinomannan, a Cell Envelope Lipoglycan

The presence of lipoarabinomannan (LAM) in the Mycobacterium tuberculosis (Mtb) cell envelope was first reported close to 100 years ago. Since then, numerous studies have been dedicated to the isolation, purification, structural definition, and elucidation of the biological properties of Mtb LAM. In this review, we present a brief historical perspective on the discovery of Mtb LAM and the herculean efforts devoted to structurally characterizing the molecule because of its unique structural and biological features. The significance of LAM remains high to this date, mainly due to its distinct immunological properties in conjunction with its role as a biomarker for diagnostic tests due to its identification in urine, and thus can serve as a point-of-care diagnostic test for tuberculosis (TB). In recent decades, LAM has been thoroughly studied and massive amounts of information on this intriguing molecule are now available. In this review, we give the readers a historical perspective and an update on the current knowledge of LAM with information on the inherent carbohydrate composition, which is unique due to the often puzzling sugar residues that are specifically found on LAM. We then guide the readers through the complex and myriad immunological outcomes, which are strictly dependent on LAM's chemical structure. Furthermore, we present issues that remain unresolved and represent the immediate future of LAM research. Addressing the chemistry, functions, and roles of LAM will lead to innovative ways to manipulate the processes that involve this controversial and fascinating biomolecule.

Sensitive electrochemiluminescence (ECL) immunoassays for detecting lipoarabinomannan (LAM) and ESAT-6 in urine and serum from tuberculosis patients

BACKGROUND

Tuberculosis (TB) infection was responsible for an estimated 1.3 million deaths in 2017. Better diagnostic tools are urgently needed. We sought to determine whether accurate TB antigen detection in blood or urine has the potential to meet the WHO target product profiles for detection of active TB.

MATERIALS AND METHODS

We developed Electrochemiluminescence (ECL) immunoassays for Lipoarabinomannan (LAM) and ESAT-6 detection with detection limits in the pg/ml range and used them to compare the concentrations of the two antigens in the urine and serum of 81 HIV-negative and -positive individuals with presumptive TB enrolled across diverse geographic sites.

RESULTS

LAM and ESAT-6 overall sensitivities in urine were 93% and 65% respectively. LAM and ESAT-6 overall sensitivities in serum were 55% and 46% respectively. Overall specificity was ≥97% in all assays. Sensitivities were higher in HIV-positive compared to HIV-negative patients for both antigens and both sample types, with signals roughly 10-fold higher on average in urine than in serum. The two antigens showed similar concentration ranges within the same sample type and correlated.

CONCLUSIONS

LAM and ESAT-6 can be detected in the urine and serum of TB patients, regardless of the HIV status and further gains in clinical sensitivity may be achievable through assay and reagent optimization. Accuracy in urine was higher with current methods and has the potential to meet the WHO accuracy target if the findings can be transferred to a point-of-care TB test.

Lipoarabinomannan in sputum to detect bacterial load and treatment response in patients with pulmonary tuberculosis: Analytic validation and evaluation in two cohorts

BACKGROUND

Lipoarabinomannan (LAM) is a major antigen of Mycobacterium tuberculosis (MTB). In this report, we evaluated the ability of a novel immunoassay to measure concentrations of LAM in sputum as a biomarker of bacterial load prior to and during treatment in pulmonary tuberculosis (TB) patients.

METHODS AND FINDINGS

Phage display technology was used to isolate monoclonal antibodies binding to epitopes unique in LAM from MTB and slow-growing nontuberculous mycobacteria (NTM). Using these antibodies, a sandwich enzyme-linked immunosorbent assay (LAM-ELISA) was developed to quantitate LAM concentration. The LAM-ELISA had a lower limit of quantification of 15 pg/mL LAM, corresponding to 121 colony-forming units (CFUs)/mL of MTB strain H37Rv. It detected slow-growing NTMs but without cross-reacting to common oral bacteria. Two clinical studies were performed between the years 2013 and 2016 in Manila, Philippines, in patients without known human immunodeficiency virus (HIV) coinfection. In a case-control cohort diagnostic study, sputum specimens were collected from 308 patients (aged 17-69 years; 62% male) diagnosed as having pulmonary TB diseases or non-TB diseases, but who could expectorate sputum, and were then evaluated by smear microscopy, BACTEC MGIT 960 Mycobacterial Detection System (MGIT) and Lowenstein-Jensen (LJ) culture, and LAM-ELISA. Some sputum specimens were also examined by Xpert MTB/RIF. The LAM-ELISA detected all smear- and MTB-culture-positive samples (n = 70) and 50% (n = 29) of smear-negative but culture-positive samples (n = 58) (versus 79.3%; 46 positive cases by the Xpert MTB/RIF), but none from non-TB patients (n = 56). Among both LAM and MGIT MTB-culture-positive samples, log10-transformed LAM concentration and MGIT time to detection (TTD) showed a good inverse relationship (r = -0.803, p < 0.0001). In a prospective longitudinal cohort study, 40 drug-susceptible pulmonary TB patients (aged 18-69 years; 60% male) were enrolled during the first 56 days of the standard 4-drug therapy. Declines in sputum LAM concentrations correlated with increases of MGIT TTD in individual patients. There was a 1.29 log10 decrease of sputum LAM concentration, corresponding to an increase of 221 hours for MGIT TTD during the first 14 days of treatment, a treatment duration often used in early bactericidal activity (EBA) trials. Major limitations of this study include a relatively small number of patients, treatment duration up to only 56 days, lack of quantitative sputum culture CFU count data, and no examination of the correlation of sputum LAM to clinical cure.

CONCLUSIONS

These results indicate that the LAM-ELISA can determine LAM concentration in sputum, and sputum LAM measured by the assay may be used as a biomarker of bacterial load prior to and during TB treatment. Additional studies are needed to examine the predictive value of this novel biomarker on treatment outcomes.

A Novel Sensitive Immunoassay Targeting the 5-Methylthio-d-Xylofuranose-Lipoarabinomannan Epitope Meets the WHO's Performance Target for Tuberculosis Diagnosis

The only currently commercialized point-of-care assay for tuberculosis (TB) that measures lipoarabinomannan (LAM) in urine (Alere LF-LAM) has insufficient sensitivity. We evaluated the potential of 100 novel monoclonal antibody pairs targeting a variety of LAM epitopes on a sensitive electrochemiluminescence platform to improve the diagnostic accuracy.

The only currently commercialized point-of-care assay for tuberculosis (TB) that measures lipoarabinomannan (LAM) in urine (Alere LF-LAM) has insufficient sensitivity. We evaluated the potential of 100 novel monoclonal antibody pairs targeting a variety of LAM epitopes on a sensitive electrochemiluminescence platform to improve the diagnostic accuracy. In the screening, many antibody pairs showed high reactivity to purified LAM but performed poorly at detecting urinary LAM in clinical samples, suggesting differences in antigen structure and immunoreactivity of the different LAM sources. The 12 best antibody pairs from the screening were tested in a retrospective case-control study with urine samples from 75 adults with presumptive TB. The best antibody pair reached femtomolar analytical sensitivity for LAM detection and an overall clinical sensitivity of 93% (confidence interval [CI], 80% to 97%) and specificity of 97% (CI, 85% to 100%). Importantly, in HIV-negative subjects positive for TB by sputum smear microscopy, the test achieved a sensitivity of 80% (CI, 55% to 93%). This compares to an overall sensitivity of 33% (CI, 20% to 48%) of the Alere LF-LAM and a sensitivity of 13% (CI, 4% to 38%) in HIV-negative subjects in the same sample set. The capture antibody targets a unique 5-methylthio-d-xylofuranose (MTX)-dependent epitope in LAM that is specific to the Mycobacterium tuberculosis complex and shows no cross-reactivity with fast-growing mycobacteria or other bacteria. The present study provides evidence that improved assay methods and reagents lead to increased diagnostic accuracy. The results of this work have informed the development of a sensitive and specific novel LAM point-of-care assay with the aim to meet the WHO's performance target for TB diagnosis.

Capillary electrophoresis as a method to determine underivatized urinary lipoarabinomannans, a biomarker of active tuberculosis caused by Mycobacterium tuberculosis

Tuberculosis is a devastating contagious disease caused by Mycobacterium tuberculosis. This is the first report describing the development of novel capillary electrophoresis methods to detect lipoarabinomannans shed into the blood circulation by replicating bacteria. The novelty of the methods is the detection without derivatization. The lipoarabinomannan is detected owing to the ionization of the diverse functional groups of the structure, such as the multibranched mannan domain or the phosphatidyl group. Four alkaline solutions were used; normal polarity in three of them and reversed polarity in one. Urinary lipoarabinomannans by saccharide domains were identified with direct absorbance detection. The accuracy and the analytical sensitivity were then validated with cello-, manno- and xylooligosaccharides. Lipoarabinomannan detection was feasible within 20 min (RSD 2.1%). This method worked at the dynamic range of 0.1-10 μg/mL. With reversed polarity, indirect absorbance detection, and pH 9.0 electrolyte were used, the analytes migrated already within 5 min (RSD 0.01%). Inorganic nonabsorbing ions were used for this method optimization. This improvement resulted in the detection limit of 1 pg/mL in water and in the linear dynamic range of 1 pg/mL to 10 ng/mL. In conclusion, the described method has great potential as a point-of-care assay for clinical use.

Utility of a lateral flow assay for culture confirmation of Mycobacterium tuberculosis complex

BACKGROUND

Therapy for the clinical management of patients with Mycobacterium tuberculosis complex (MTBC) and non tuberculous mycobacteria (NTM) is different. Prompt detection and discrimination is necessary for administration of suitable therapy.

METHODS

The aim of the study was to evaluate the performance of a Immunochromatographic Test (ICT) in rapid differentiation of MTBC from NTM grown in Lowenstein-Jensen medium and MGIT broth in comparison to molecular methods.

RESULTS

Of the 106 isolates in this study, 96 and 95 were identified as MTBC by 16S rRNA PCR and MPT64 respectively. The sensitivity and specificity of MPT64 was found to be 99% and 100% respectively.

CONCLUSION

The Lateral Flow Assay Test is a useful and specific tool in rapid differentiation of M. tuberculosis complex from culture. Therefore proper identification avoids unnecessary ATT to patients infected with NTM.

Immune parameters differentiating active from latent tuberculosis infection in humans

Tuberculosis remains a highly prevalent infectious disease worldwide. Identification of the immune parameters that differentiate active disease from latent infection will facilitate the development of efficient control measures as well as new diagnostic modalities for tuberculosis. Here, we investigated the cytokine production profiles of monocytes and CD4(+) T lymphocytes upon encountering mycobacterial antigens. In addition, cytokines and lipid mediators with immune-modulating activities were examined in plasma samples ex vivo. Comparison of these parameters in active tuberculosis patients and healthy subjects with latent infection revealed that, active tuberculosis was associated with diminished Th1-type cytokine secretion from CD4(+) T cells and less augmented inflammatory cytokine secretion from monocytes induced by IFN-γ than that in latent tuberculosis infection. In addition, a higher plasma concentration of lipoxin A4 and lower ratio of prostaglandin E2 to lipoxin A4 were observed in active cases than in latent infections. These findings have implications for preparing new therapeutic strategies and for differential diagnosis of the two types of tuberculosis infection.

Diagnostic accuracy of a urine lipoarabinomannan test for tuberculosis in hospitalized patients in a High HIV prevalence setting

BACKGROUND

Effective tuberculosis (TB) control in HIV-prevalent settings is hindered by absence of accurate, rapid TB diagnostic tests. We evaluated the accuracy of a urine lipoarabinomannan (LAM) test for TB diagnosis in South Africa.

METHODS

Hospitalized adults with signs and/or symptoms of active TB were enrolled. Sputum smear microscopy and mycobacterial culture, mycobacterial blood culture, and HIV testing were performed. A spot urine specimen was tested for LAM.

RESULTS

Four hundred ninety nine participants were enrolled; 422 (84.6%) were HIV infected. In microbiologically confirmed TB patients, the LAM test was positive in 114 of 193 [sensitivity 59%, (95% confidence interval: 52 to 66)], including 112 of 167 [67% (59 to 74)] who were HIV infected. Among individuals classified as "not TB", the LAM test was negative in 117 of 122 [specificity 96% (91 to 99)], including 83 of 88 [94% (87 to 98)] who were HIV infected. In confirmed TB patients, the LAM test was more sensitive than sputum smear microscopy (42%, 82 of 193, P < 0.001) and detected 56% (62 of 111) of those who were sputum smear negative. HIV infection [adjusted odds ratio (AOR 13.4)], mycobacteremia (AOR 3.21), and positive sputum smear (AOR 2.42) were risk factors for a positive LAM test.

CONCLUSIONS

The urine LAM test detected a subset of HIV-infected patients with severe TB in whom sputum smear microscopy had suboptimal sensitivity. The combination of urine LAM testing and sputum smear microscopy is attractive for use in settings with high HIV burden.

Rapid detection of Mycobacterium tuberculosis in sputum by Patho-TB kit in comparison with direct microscopy and culture

The usefulness of a new rapid diagnostic test (Patho-TB) using antibodies specific to mycobacterial antigens was evaluated for the rapid discrimination between pulmonary tuberculosis (TB) and non-TB pulmonary diseases on sputa. One hundred sputa collected from 79 active TB patients and from 21 patients with non-TB pulmonary diseases (asthma and chronic obstructive pulmonary disease) were enrolled into the study and tested for the presence of Mycobacterium tuberculosis by Ziehl-Neelsen smear, Patho-TB kit, and Löwenstein-Jensen culture. The sensitivity, specificity, positive predictive value, and negative predictive value of the Patho-TB test were 95%, 100%, 100%, and 84%, respectively. Patho-TB test is simple, quick, and easy to perform. Its sensitivity, specificity, and positive predictive value are satisfactory. Therefore, it could be used as a screening test in poorly equipped laboratories of TB endemic areas.

Low sensitivity of a urine LAM-ELISA in the diagnosis of pulmonary tuberculosis

Background

The development and evaluation of rapid and accurate new diagnostic tools is essential to improve tuberculosis (TB) control in developing countries. In a previous study, the first release of a urine LAM-ELISA by Chemogen (Portland, USA) has been evaluated with a promising sensitivity and specificity for the diagnosis of pulmonary TB. In the present study, the now commercially available assay has been clinically assessed regarding its diagnostic value alone and in combination with clinical co-factors.

Methods

The test was applied to two urine samples from 291 consecutively enrolled Tanzanian patients with suspected pulmonary tuberculosis. The participants were subsequently assigned to classification groups according to microbiological, clinical and radiological findings at recruitment and during a maximum follow up period of 56 days.

Results

Only 35 out of 69 pulmonary TB cases -confirmed by smear microscopy and/or solid culture and/or liquid culture- showed at least one positive LAM-ELISA result (sensitivity 50.7%). The sensitivity was noticeably higher in females (66.7%) and in HIV positive participants (62.0%). The specificity amounted to 87.8% and was determined in participants with negative results in all microbiological tests and with sustained recovery under antibiotic treatment at day 56. Correlation with urinalysis revealed that proteinuria was significantly and positively associated with LAM-positivity (P = 0.026).

Conclusion

This commercially available generation of LAM-ELISA does not appear to be useful as an independent diagnostic test for pulmonary tuberculosis. The question whether the assay is suitable as a supplemental device in the diagnosis of HIV-associated TB, requires further investigations.

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.

Facing the crisis: improving the diagnosis of tuberculosis in the HIV era

Although the human immunodeficiency virus (HIV) infection pandemic has had a catastrophic impact on tuberculosis (TB) control efforts, especially in sub-Saharan Africa, most of the fundamental concepts reflected in the directly observed treatment, short course (DOTS) strategy still hold true in the HIV era. What has changed, and dramatically, is the importance of speedy and accurate TB diagnosis and the difficulty of achieving this. The disproportionate amount of smear-negative disease in sub-Saharan Africa, which shoulders two-thirds of the global burden of HIV infection and acquired immunodeficiency syndrome, has greatly complicated TB case detection and disease control. Now, 15 years after TB rates began to soar in countries where HIV infection is prevalent, we have learned that the conventional approach -- passively waiting for patients with advanced symptomatic disease to make their way to microscopy centers for diagnosis -- has disastrous consequences. Without better diagnostic tools for TB and effective strategies for their implementation, transmission will not be interrupted, mortality will not be checked, and TB will not be controlled in areas where HIV infection is prevalent. Fortunately, a number of technical opportunities exist for the creation of improved diagnostic tests. Developing and exploiting such tests to support TB control in HIV-infected populations is an urgent priority. A substantial public sector effort is under way to work in partnership with the biotechnology industry to accelerate progress toward that goal. In this article, we will define the need for better TB tests and describe technologies being developed to meet that need.

Current issues on molecular and immunological diagnosis of tuberculosis

Laboratory diagnosis of tuberculosis (TB) traditionally relies on smear microscopy and culture of Mycobacterium tuberculosis from clinical samples. With recent advances in technology, there have been numerous efforts to develop new diagnostic tests for TB that overcome the low sensitivity and specificity and long turnover time associated with current diagnostic tests. Molecular biological tests based on nucleic acid amplification have brought an unprecedented opportunity for the rapid and specific detection of M. tuberculosis from clinical specimens. With automated sequencing analysis, species identification of mycobacteria is now easier and more accurate than with conventional methods, and rapid detection of mutations in the genes associated with resistance to TB drugs provides early information on the potential drug resistance for each clinical isolate or for clinical samples. In addition, immunological tests for the detection of M. tuberculosis antigens and antibodies to the antigens have been explored to identify individuals at risk of developing TB or with latent TB infection (LTBI). The recent introduction of commercial IFN-gamma assay kits for the detection of LTBI provides a new approach for TB control even in areas with a high incidence of TB. However, these molecular and immunological tools still require further evaluation using large scale cohort studies before implementation in TB control programs.

Rapid diagnosis of tuberculosis by detection of mycobacterial lipoarabinomannan in urine

There is an urgent need for improved tools for laboratory diagnosis of active tuberculosis (TB). Here, we describe two methods, a catch-up ELISA and a dipstick test based on the detection in urine of lipoarabinomannan (LAM). LAM is a major and specific glycolipid component of the outer mycobacterial cell wall. Preliminary experiments showed that LAM is excreted in the urine of mice injected intraperitoneally with a crude cell wall preparation of Mycobacterium tuberculosis. Both methods were highly sensitive, detecting LAM at concentrations of 1 ng/ml and 5 pg/ml, respectively. Of 15 patients with active TB, all showed intermediate to high levels of LAM in their urine (absorbance values from 0.3 to 1.2, mean 0.74). Only one sample showed an absorbance value below the chosen cut off value of 0.4. All but one of the urine samples from 26 healthy nursing workers exhibited OD value below 0.4 cut off. These methods may prove valuable for rapid and simple diagnosis of TB in particular in developing countries lacking biosafety level 3 (BSL3) facilities.

Development of antigen detection assay for diagnosis of tuberculosis using sputum samples

The rising incidence of tuberculosis worldwide means an increasing burden on diagnostic facilities, so tests simpler than Ziehl-Neelsen staining are needed. Such tests should be objective, reproducible, and have at least as good a detection limit as 10(4) bacteria/ml. A capture enzyme-linked immunosorbent assay (ELISA) was developed for detection of lipoarabinomannan (LAM) in human sputum samples. As a capture antibody, we used a murine monoclonal antibody against LAM, with rabbit antiserum against Mycobacterium tuberculosis as a source of detector antibodies. The sensitivity of the capture ELISA was evaluated by using purified LAM and M. tuberculosis whole cells. We were able to detect 1 ng of purified LAM/ml and 10(4) M. tuberculosis whole cells/ml. LAM could also be detected in culture filtrate of a 3-week-old culture of M. tuberculosis. The culture filtrate contained approximately 100 microgram of LAM/ml. The detection limit in sputum pretreated with N-acetyl-L-cysteine and proteinase K was 10(4) M. tuberculosis whole cells per ml. Thirty-one (91%) of 34 sputum samples from 18 Vietnamese patients with tuberculosis (32 smear positive and 2 smear negative) were positive in the LAM detection assay. In contrast, none of the 25 sputum samples from 21 nontuberculous patients was positive. This specific and sensitive assay for the detection of LAM in sputum is potentially useful for the diagnosis of tuberculosis.

Monoclonal antibodies to surface antigens of Mycobacterium tuberculosis and their use in a modified enzyme-linked immunosorbent spot assay for detection of mycobacteria

Three monoclonal antibodies (MAbs) were generated from splenocytes of a BALB/c mouse immunized with heat-killed Mycobacterium tuberculosis. All three MAbs bound to surface epitopes of M. tuberculosis as shown by whole-cell enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence, and immunoelectron microscopy. One immunoglobulin M (IgM) MAb bound to lipoarabinomannan, the second IgM MAb bound to mycolyl-arabinogalactan-peptidoglycan complex, and the third MAb, an IgG3, bound to a surface epitope of an uncertain nature. The MAbs demonstrated different cross-reactivity patterns with other mycobacteria. Two of the MAbs were used to develop a modified ELISA spot assay for the detection of mycobacteria.

Production of monoclonal antibody to a phenolic glycolipid of Mycobacterium tuberculosis and its use in detection of the antigen in clinical isolates

A monoclonal antibody (MAbIII604) specific to phenolic glycolipid Tb (PGL-Tb), a Mycobacterium tuberculosis-specific antigen, was produced and used in the detection of the antigen. MAbIII604 reacted with the PGL-Tb antigen but not with other phenolic glycolipids from Mycobacterium leprae, M. bovis, and M. kansasii, thus indicating the specificity of the monoclonal antibody to PGL-Tb. A dot enzyme-linked immunosorbent assay with MAbIII604 was employed to detect the PGL-Tb antigen in lipids purified from M. tuberculosis clinical isolates. Of 50 isolates, 32 (64.0%) showed clear evidence of the PGL-Tb antigen by the dot enzyme-linked immunosorbent assay, but there were marked variations in the intensities and sizes of spots. This suggests differences in PGL-Tb antigen production among M. tuberculosis strains even when they are grown in the same culture media and conditions. This was most evident from the fact that in only eight (16.0%) of the isolates examined was the PGL-Tb antigen detectable by thin-layer chromatography, which is much less sensitive for the detection of glycolipid antigens. This study shows that monoclonal antibodies specific to PGL-Tb are useful in detecting the antigen in lipid extracts and that there is a marked variation in the PGL-Tb production among M. tuberculosis clinical isolates.