Beston Hamasur

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.

Mycobacterium tuberculosis arabinomannan–protein conjugates protect against tuberculosis

Lipoarabinomannan (LAM) is a major structural surface component of mycobacteria. Arabinomannan (AM) oligosaccharides derived from LAM of Mycobacterium tuberculosis H37Rv were isolated and covalently conjugated to tetanus toxoid (TT) or to short-term culture filtrate proteins (antigen 85B (Ag85B) or a 75kDa protein) from M. tuberculosis strain Harlingen. The different AM oligosaccharide (AMOs)-protein conjugate vaccine candidates proved to be highly immunogenic, inducing boosterable IgG responses against the AMOs portion of the conjugates in rabbits and guinea-pigs. Proliferation of T-cells from C57BL/6 mice immunized with the conjugates was seen upon in vitro stimulation with PPD. In C57BL/6 mice subcutaneous immunization with the AMOs-antigen 85B conjugate in alum provided significant protection compared to sham (alum only) immunized mice (P < 0.021) as estimated by long term survival against intravenous challenge with 10(5) M. tuberculosis H37Rv. Subcutaneous immunization followed by nasal boost with an AMOs-TT conjugate in Eurocine L3 adjuvant provided high (P < 0.025) protection as determined by long term survival after intranasal challenge with 10(5) virulent M. tuberculosis strain Harlingen. This level of protection was comparable to that obtained with the conventional live attenuated BCG vaccine. In guinea-pigs, immunization with AMOs-Ag85B in Eurocine L3 adjuvant followed by aerogenic challenge with M. tuberculosis H37Rv resulted in increased survival and reduced pathology in lungs and spleens relative to non-immunized animals.

Diagnostic evaluation of urinary lipoarabinomannan at an Ethiopian tuberculosis centre.

Direct capture enzyme-linked immunosorbent assay (ELISA) for lipoarabinomannan (LAM) was performed on urine samples from 200 tuberculosis (TB) patients and 800 non-TB patients routinely diagnosed among consecutive suspects in an Ethiopian TB centre. 50 healthy Ethiopians, 50 healthy individuals and 100 non-TB patients from Norway served as controls. Of the TB patients, 139 (69.5%) were positive for acid-fast bacilli (AFB). In the remaining cases the diagnosis was based on suggestive clinical findings. All Ethiopian non-TB patients were AFB negative and showed no clinical evidence of TB. In the Ethiopian groups, 148 (74%) of the TB patients, 105 (13.1%) of the non-TB patients and 5 (10%) of the healthy controls were positive by the LAM-ELISA. 113 (81.3%) of AFB positives and 35 (57.4%) of AFB-negative TB patients had positive LAM-ELISA. In the Norwegian groups all were LAM negative. The sensitivity and specificity of the LAM-ELISA for TB patients versus Ethiopian non-TB patients were 74% and 86.9%, respectively; the positive and negative predictive values were 58.5% and 93.0%. This study suggests that detection of LAM in the urine of TB patients may improve case finding and that diagnostic tests based on this principle may serve as valuable supplemental tools in TB control.Direct capture enzyme-linked immunosorbent assay (ELISA) for lipoarabinomannan (LAM) was performed on urine samples from 200 tuberculosis (TB) patients and 800 non-TB patients routinely diagnosed among consecutive suspects in an Ethiopian TB centre. 50 healthy Ethiopians, 50 healthy individuals and 100 non-TB patients from Norway served as controls. Of the TB patients, 139 (69.5%) were positive for acid-fast bacilli (AFB). In the remaining cases the diagnosis was based on suggestive clinical findings. All Ethiopian non-TB patients were AFB negative and showed no clinical evidence of TB. In the Ethiopian groups, 148 (74%) of the TB patients, 105 (13.1%) of the non-TB patients and 5 (10%) of the healthy controls were positive by the LAM-ELISA. 113 (81.3%) of AFB positives and 35 (57.4%) of AFB-negative TB patients had positive LAM-ELISA. In the Norwegian groups all were LAM negative. The sensitivity and specificity of the LAM-ELISA for TB patients versus Ethiopian non-TB patients were 74% and 86.9%, respectively; the positive and negative predictive values were 58.5% and 93.0%. This study suggests that detection of LAM in the urine of TB patients may improve case finding and that diagnostic tests based on this principle may serve as valuable supplemental tools in TB control.

Circulating antibodies to lipoarabinomannan in relation to sputum microscopy, clinical features and urinary anti-lipoarabinomannan detection in pulmonary tuberculosis

An enzyme-linked immunosorbent assay (ELISA)-based investigation of anti-lipoarabinomannan (LAM) antibody levels in the sera of patients with acid-fast bacilli (AFB)-positive pulmonary tuberculosis (PTB), AFB-negative PTB and non-TB respiratory tract symptoms was conducted. The anti-LAM results were further evaluated using urine LAM detection and a clinical diagnostic score (DS) system as references. Using sputum AFB as a reference, positive anti-LAM was found in 66.9% of 139 AFB-positive PTB, 34.4% of 61 AFB-negative PTB and 23.5% of 800 non-TB patients and in 8% of 50 healthy individuals. The positive and negative predictive values were 48.7% and 87.4%, respectively. Using the DS as a reference, the sensitivity and specificity were 50.5% and 78.3%, respectively, whereas 45.8% of urine LAM positives and 77.9% of urine LAM negatives were correctly identified by the anti-LAM ELISA. In TB endemic areas a negative anti-LAM could be of practical value, particularly when other indicators of PTB are negative. Using any of these methods as a reference, a positive anti-LAM would mislead in about one-quarter of cases. Had all the 3 methods been combined and at least 2 positive tests sufficed, 90.6% of AFB-positive PTB, 52.5% of AFB-negative PTB and 94.9% of non-TB patients would have been correctly diagnosed. Apart from the possible impact of HIV, the low accuracy of the current assay could be due to intravascular formation of LAM-anti-LAM complexes, latent TB or environmental mycobacterial infections.

Clinical and Radiological Features in Relation to Urinary Excretion of Lipoarabinomannan in Ethiopian Tuberculosis Patients

We have previously reported on the diagnostic potential of urinary lipoarabinomannan (LAM) detection in active tuberculosis (TB). In this study, we identified clinical and radiological parameters that were significantly associated with urine LAM positivity in a clinical sample of 931 patients attending a TB control center in Addis Ababa, Ethiopa. These parameters were attributed weights and used in a diagnostic score (DS) system. Using urinary LAM as a reference, this DS system showed a sensitivity of 65.4% and a specificity of 82.9%. The positive and negative predictive values were 56.8% and 87.4%, respectively. HIV or other coinfections or deficiencies may have blurred the clinical manifestations of pulmonary TB (PTB) and thereby contributed to the relatively high number of false-positive DS results obtained. Although additional markers may be required to improve the sensitivity of the DS system, the relatively high specificity of this simple approach may be of some practical use in the field. Thus, in PTB-suspected, DS-negative cases, the likelihood of ongoing PTB is < 20%.

Synthesis and immunologic characterisation of Mycobacterium tuberculosis lipoarabinomannan specific oligosaccharide-protein conjugates.

Lipoarabinomannan (LAM) is a major structural surface component of all mycobacteria, and has been reported to have a wide range of biological effects. Immunogenic LAM specific oligosaccharide protein conjugates were synthesized and immunologically characterized. Oligosaccharides were derived from LAM purified from Mycobacterium tuberculosis H37 Rv and covalently conjugated to tetanus toxoid and cross reactive mutant (CRM197) diphtheria toxoid. Both types of LAM oligosaccharide protein conjugates proved to be highly immunogenic, inducing a boosterable T helper cell dependent IgG response. These conjugates are currently evaluated as components in a subcellular experimental TB vaccine.

Mycobacterial glycoconjugates as vaccine candidates against tuberculosis

There is an urgent need for an efficient vaccine against tuberculosis. Here, we explore the potential role of carbohydrate antigens as part of a new tuberculosis vaccine. Emphasis is placed on carbohydrate-protein conjugate vaccines, using the arabinomannan portion of lipoarabinomannan, a major structural surface component of Mycobacterium tuberculosis covalently conjugated to (mycobacterial) protein antigens. Such conjugate vaccines show good protective efficacy in mice and guinea pigs in terms of prolonged survival and reduced pathology. Special attention is paid to the immunology underlying their protective capacity. Conjugate vaccines induce both cellular and humoral responses and, although antibody responses have been thought to be the main protective component, cellular responses - possibly through the CD1 pathway - are also likely to be involved.

Towards new tuberculosis vaccine

According to WHO, about one third of the world’s population is infected with bacteria of the Mycobacterium tuberculosis complex. Currently there is globally 9.15 million recorded cases of overt tuberculosis (TB) annually and due to lack of adequate diagnostics presumably a large but unknown number of non-recorded cases. TB is estimated to cause 1.65 million deaths per annum which accounts for one-fifth of all deaths by infectious diseases of adults in low-income countries. During recent years a rapid spread of multi-drug resistant bacteria causing about 0.5 million TB cases per year has worsened the problem. The live attenuated Bacillus Calmette-Guérin (BCG) vaccine which is the only currently available TB vaccine does not confer any significant protection against the most common and contagious form of TB – adult pulmonary TB.

Mycobacterium tuberculosis lipoarabinomannan enhances LPS-induced TNF-α production and inhibits NO secretion by engaging scavenger receptors

Lipoarabinomannan capped with terminal oligomannosides (ManLAM) is a component of mycobacteria cell wall enabling Mycobacterium tuberculosis to infect macrophages. We found that short treatment (3.5h) of macrophage-like J774 cells and thioglycollate-elicited peritoneal murine macrophages with ManLAM and its deacylated form enhanced LPS-stimulated release of tumor necrosis factor-α (TNF-α). In contrast, prolong incubation of J774 cells with ManLAM (16h) led to inhibition of LPS-stimulated TNF-α production. LPS-triggered secretion of nitric oxide (NO) was suppressed by ManLAM and its deacylated form. Effects of ManLAM and its deacylated derivative were mimicked by dextran sulfate, a general ligand of scavenger receptors. The enhancement of LPS-induced TNF-α production by dextran sulfate was partially reversed by an antibody neutralizing scavenger receptor SR-PSOX/CXCL16 while the stimulatory activity of deacylated ManLAM was reversed by an antibody neutralizing class B scavenger receptor CD36. Our data suggest that CD36 mediates the activity of ManLAM and its deacylated form leading to TNF-α release in LPS-stimulated J774 cells and peritoneal murine macrophages, while NO production is modulated by unknown scavenger receptors.

Divergent Effects of Mycobacterial Cell Wall Glycolipids on Maturation and Function of Human Monocyte-Derived Dendritic Cells

Background Mycobacterium tuberculosis (Mtb) is able to evade the immune defenses and may persist for years, decades and even lifelong in the infected host. Mtb cell wall components may contribute to such persistence by modulating several pivotal types of immune cells. Dendritic cells (DCs) are the most potent antigen-presenting cells and hence play a crucial role in the initial immune response to infections by connecting the innate with the adaptive immune system. Principal Findings We investigated the effects of two of the major mycobacterial cell wall-associated types of glycolipids, mannose-capped lipoarabinomannan (ManLAM) and phosphatidylinositol mannosides (PIMs) purified from the Mtb strains H37Rv and Mycobacterium bovis, on the maturation and cytokine profiles of immature human monocyte-derived DCs. ManLAM from Mtb H37Rv stimulated the release of pro-inflammatory cytokines TNF, IL-12, and IL-6 and expression of co-stimulatory (CD80, CD86) and antigen-presenting molecules (MHC class II). ManLAM from M. bovis also induced TNF, IL-12 and IL-6 but at significantly lower levels. Importantly, while ManLAM was found to augment LPS-induced DC maturation and pro-inflammatory cytokine production, addition of PIMs from both Mtb H37Rv and M. bovis strongly reduced this stimulatory effect. Conclusions These results indicate that the mycobacterial cell wall contains macromolecules of glycolipid nature which are able to induce strong and divergent effects on human DCs; i.e while ManLAM is immune-stimulatory, PIMs act as powerful inhibitors of DC cytokine responses. Thus PIMs may be important Mtb-associated virulence factors contributing to the pathogenesis of tuberculosis disease. These findings may also aid in the understanding of some earlier conflicting reports on the immunomodulatory effects exerted by different ManLAM preparations.