Clinical value of the measurement of Mycobacterium tuberculosis specific antibody in pulmonary tuberculosis

Male Sex Bias in Immune Biomarkers for Tuberculosis

Males have a bias toward developing sputum smear-positive pulmonary tuberculosis, whereas other forms of the disease have an equal sex ratio. Immune responses are known to be affected by estrogen and testosterone. Biomarkers may therefore be affected by these hormones, especially between 16 and 45 years of age when the differences are most marked. Using large data sets, we examined whether the male bias was significant in terms of diagnosis or predictive ability for the development of disease in those exposed to tuberculosis. Despite the large numbers, the need to specify homogeneous population groups for analysis affected the statistical power to discount a useful biomarker. In general, males showed higher interferon-gamma responses to TB antigens ESAT-6 and CFP-10, whilst females had stronger tuberculin responses in those with sputum smear- and culture-positive tuberculosis, but smaller responses in those who were screened for tuberculosis and who did not develop disease. Importantly, in contacts of sputum smear-positive pulmonary tuberculosis, more males who did not develop tuberculosis had tuberculin skin tests in the range between 10 and 14 mm, suggesting that sex-specific cut-offs might be better than general cut-off values for determining who should receive preventive treatment. Immunocytochemistry of the tuberculin responses correlated with cell numbers only in females. Total and anti-lipoarabinomannan IgM antibody levels were lower in males, whereas total and anti-BCG IgE antibody levels were higher. Evaluation of biomarkers should take account of the spectrum of tuberculosis and male sex bias for sputum smear-positive pulmonary tuberculosis. These findings improve our understanding of how immune responses contribute to the pathogenesis of infectious tuberculosis as well as suggesting clinical applications of the differences between the sexes.

Immune responses to Mycobacterium tuberculosis membrane-associated antigens including alpha crystallin can potentially discriminate between latent infection and active tuberculosis disease

Changes in expression of membrane antigens may accompany the transition of Mycobacterium tuberculosis (Mtb) from ‘dormant’ to ‘active’ states. We have determined whether antibody and T cell responses to Mtb membrane (MtM)-associated antigens, especially the latency-induced protein alpha crystallin (Acr), can discriminate between latent tuberculosis infection (LTBI) and active TB (ATB) disease. Study subjects comprised a previously described cohort of healthcare workers (HCWs, n = 43) and smear-positive ATB patients (n = 10). HCWs were further categorized as occupational contacts (OC, n = 30), household contacts of TB (HC, n = 8) and cured TB (CTB, n = 5). Levels (ΔOD) of serum antibody isotypes (IgG, IgA and IgM) were determined by ELISA and blood T cell proliferative responses were determined by flow cytometry using Ki67 protein as marker for DNA synthesis. Antibodies to MtM and Acr were predominantly IgG and their levels in HCWs and ATB did not differ significantly. However, HCWs showed a significantly higher level of anti-MtM IgM and a significantly lower level of anti-Acr IgA antibodies than the ATB patients. Also, a larger proportion of HCWs showed a high (>1) ΔOD_Acr/ΔOD_MtM ratio for IgG. HCWs also showed a higher, though not significantly different from ATB, avidity of anti-MtM (IgG) antibodies. A higher proportion of HCWs (35% of OC, 62.5% of HC and 20% of CTB), compared with ATB (10%) showed a positive T cell response to Acr along with significant difference (P <0.05) between HC and ATB. A significant correlation (r = 0.60, P <0.0001) was noted between T cell responses of HCWs towards Acr and MtM (reported earlier by us) and both responses tended to decline with rising exposure to the infection. Even so, positive responses to Acr (38.5%) were significantly lower than to MtM (92%). Neither antibody nor T cell responses to either antigen appeared affected by BCG vaccination or reactivity to tuberculin. Results of the study suggest that the levels of IgM antibodies to MtM, IgA antibodies to Acr and proliferative T cell responses to both the antigens can potentially discriminate between LTBI and active TB disease. They also underscore the necessity of SOPs for antibody assays.

Polymorphism of MPT64 and PstS1 in Mycobacterium tuberculosis is not likely to affect relative immune reaction in human

BACKGROUND

MPT64 and PstS1 are the earliest known immune-dominant antigens of Mycobacterium tuberculosis and have been commonly used as candidates in the diagnosis of tuberculosis.

METHODS

We constructed recombinant plasmids pET-32a-Rv0934 and pET-32a-Rv1980c to express both wild and mutant forms of MPT64 and PstS1 and purified them. From November 9 to December 9, 2016, and November 9 to December 10, 2017, 96 patients with tuberculosis, 53 patients without tuberculosis, and 96 healthy volunteers were enrolled in this study. We used the purified proteins as antigens to perform T-spot and enzyme-linked immunosorbent assay (ELISA) for samples obtained from healthy volunteers and tuberculosis patients.

RESULTS

Regarding T-spot, the area under the curve (AUC) values for MPT64-wild protein (MPT64-H37Rv) and MPT64-mutant protein (MPT64-FJ05395) were 0.723 and 0.750, respectively. The AUC values for PstS1-H37Rv, PstS1-FJ05132, and PstS1-JL06035 were 0.817, 0.796, and 0.745, respectively. With regard to ELISA, the AUC values for MPT64-H37Rv and MPT64-FJ05395 were 0.525 and 0.528, respectively, while those for PstS1-H37Rv, PstS1-FJ05132, PstS1-JL06035 were 0.588, 0.509, and 0.560, respectively. There was no difference between wild and mutant proteins when we used them as antigens to perform T-spot and ELISA assays.

CONCLUSION

MPT64 and PstS1 are likely candidate diagnostic antigens for M tuberculosis T-spot test, at least in combination with other proteins. Polymorphisms of MPT64 and PstS1 had little effect on cell-mediated and humoral immunity in the host.

Serological Markers of Pulmonary Tuberculosis and of Response to Anti-Tuberculosis Treatment in a Patient Population in Guinea

The aim of the study was to evaluate serological correlates of active tuberculosis and of response to antituberculosis treatment in a cohort of HIV-negative patients with pulmonary tuberculosis studied at diagnosis and during treatment at the Service de Pneumo-Phtisiologie, Centre Hospitalier-Universitaire Ignace Deen, Conakry, Republic of Guinea. Two similar cohorts of HIV-negative healthy households of patients and healthy community controls were included in the study. Plasma samples were obtained from 168 untreated tuberculosis patients, 167 healthy household controls, and 168 healthy community controls. Serial plasma samples were also obtained from the tuberculosis patients at 2 and 8 months after initiation of chemotherapy. IgG antibody levels were measured by an enzyme-linked immunosorbent assay (ELISA) using ten purified M. tuberculosis antigens. ELISA results were analysed by comparing geometric means of data. Of the ten antigens tested, five (14kDa Ag, 19kDa Ag, AlaDH, MS, and MPT83) elicited similar antibody responses in untreated TB patients and controls. In contrast, levels of three antibodies (ESAT-6, LAM, and 38kDa Ag) were higher in untreated TB patients than in household or community controls (p < 0.0001). Levels were higher in untreated patients than in community controls also for the anti-Rv2626c antibody (p = 0.0001) and, at a lower significance level, for the anti-FdxA antibody (p < 0.025). Antibody levels against ESAT-6 and Rv2626c decreased during therapy, while antibody levels to the 38 kDa antigen and LAM increased during therapy; FdxA antibody levels did not vary with treatment. Neither severity of presentation nor chest X-ray patterns affected levels of these antibodies before treatment. In contrast, after the 8-month therapeutic course, patients who presented with moderate/severe disease had higher levels of anti-ESAT-6, anti-FdxA, and anti-38kDa antibodies than those of patients with mild disease onset. Patients with bilateral lung lesions had significantly higher anti-38kDa and anti-LAM levels, both at diagnosis and after 8-month treatment, than patients with lesions involving only one lung. Antibodies to alanine dehydrogenase and malate synthetase measured at initiation of treatment were higher in tuberculosis patients who subsequently failed therapy than in those who were cured. The main conclusions of the study are: a) plasma levels of antibodies to a number of M. tuberculosis represent serological correlates of active disease; b) these correlates are affected in an antigen-specific fashion by anti-tuberculosis treatment; c) particular serological markers may be predictive of treatment outcome.

Performance of a lateral flow immunochromatography test for the rapid diagnosis of active tuberculosis in a large multicentre study in areas with different clinical settings and tuberculosis exposure levels

BACKGROUND

Tuberculosis (TB) continues to cause an outsized burden of morbidity and mortality worldwide, still missing efficient and largely accessible diagnostic tools determining an appropriate control of the disease. Serological tests have the potentially to impact TB diagnosis, in particular in extreme clinical settings.

METHODS

The diagnostic performances of the TB-XT HEMA EXPRESS (HEMA-EXPRESS) immunochromatographic rapid test for active TB diagnosis, based on use of multiple Mycobacterium tuberculosis (MTB) specific antigens, have been evaluated in a large study multicentre TB case-finding study, in populations with different exposure level to TB. A total of 1,386 subjects were enrolled in the six participating centres in Peru: 290 active-TB and 1,096 unaffected subjects.

RESULTS

The TB prevalence (overall 20.5%) varied between 4.0% and 41.1% in the different study groups. Overall, the HEMA-EXPRESS test had 30.6% sensitivity (range 3.9-77.9%) and 84.6% specificity (range 51.6-97.3%). A significant inverse correlation between test accuracy (overall 73.5%, range 40.4-96.4%) and TB prevalence in the various study populations was observed (Pearson's r=-0.7985; P=0.05).

CONCLUSIONS

HEMA-EXPRESS, is rapid and relatively inexpensive test suitable for routine use in TB diagnosis. In low TB prevalence conditions, test performance appears in line with WHO Target Product Profile for TB diagnostics. Performances appear suboptimal in high TB prevalence settings. Appropriate set-up in operative clinical settings has to be considered for novel serological tests for TB diagnosis, particularly for formats suitable for point-of-care use.

Estimation of cerebrospinal fluid cortisol level in tuberculous meningitis

BACKGROUND

Central nervous system (CNS) involvement in tuberculosis is around 5-10%. Of the various manifestations of CNS tuberculosis, meningitis is the most common (70-80%). Delay in diagnosis and treatment results in significant morbidity and mortality.

OBJECTIVE

To study the cerebrospinal fluid (CSF) cortisol levels in tubercular meningitis and compare the levels with controls.

METHODS

Cross-sectional, prospective, observational, hospital-based study done in 20 patients of tubercular meningitis, 20 patients of aseptic meningitis (AM) and 25 control subjects without any preexisting neurological disorders who have undergone lumbar puncture for spinal anesthesia.

RESULTS

Cortisol was detected in all 40 CSF samples of patients (100%). Mean CSF cortisol level was 8.82, 3.47 and 1.05 in tubercular meningitis, AM and controls, respectively. Mean CSF cortisol level in tubercular meningitis was significantly higher as compared to AM and controls (P < 0.0001).

CONCLUSION

Cortisol level estimation in CSF is one of the rapid, relatively inexpensive diagnostic markers in early identification of tubercular meningitis along with CSF findings of elevated proteins, hypoglycorrhachia and lymphocytic pleocytosis. This aids in earlier institution of appropriate treatment and thereby decreasing morbidity and mortality. This is the first study on the estimation of CSF cortisol level in tuberculous meningitis.

Evaluation of antigen-specific immunoglobulin g responses in pulmonary tuberculosis patients and contacts

This study aimed to evaluate the serodiagnostic potential of immunoglobulin G (IgG) responses to Mycobacterium tuberculosis antigens in pulmonary tuberculosis (TB) patients, recent TB contacts with latent TB infection (LTBI), and healthy subjects. Infections were assessed using tuberculin skin tests, QuantiFERON-TB Gold In-Tube tests, drug susceptibility testing, and molecular genotyping of clinical isolates. Serum IgG responses to selective M. tuberculosis antigens, including the 38-kDa and 16-kDa antigens, lipoarabinomannan (LAM), and recombinant early secreted antigen target 6 kDa (ESAT-6) and culture filtrate protein 10 kDa (CFP-10), were determined. We found that the serum IgG responses to all antigens might differentiate between active TB and LTBI, with LAM having the highest diagnostic value (area under the curve [AUC] of 0.7756, P < 0.001). Recurrent TB cases showed significantly higher IgG responses to 38 kDa, CFP-10 (P < 0.01), and LAM (P < 0.05) than new cases, and male patients had higher levels of antigen-specific IgG than females (P < 0.05). Conversely, drug resistance and patient body mass index did not affect IgG responses (P > 0.05). LAM-specific IgG responses differentiated between acid-fast bacillus (AFB) smear-positive and -negative patients (P < 0.01), whereas antigen-specific IgG responses did not vary with the M. tuberculosis genotype (P > 0.05). Significantly higher IgG responses to 38 kDa and 16 kDa were observed in AFB smear-negative patients than in controls. These results suggest that assessment of serum IgG responses to selective purified M. tuberculosis antigens may help improve the diagnosis of active TB, particularly for sputum smear-negative patients or recurrent cases, and these may also help to differentiate between active TB and LTBI.

Mycobacterium tuberculosis adhesins: potential biomarkers as anti-tuberculosis therapeutic and diagnostic targets

Adhesion to host cells is a precursor to host colonization and evasion of the host immune response. Conversely, it triggers the induction of the immune response, a process vital to the host’s defence against infection. Adhesins are microbial cell surface molecules or structures that mediate the attachment of the microbe to host cells and thus the host–pathogen interaction. They also play a crucial role in bacterial aggregation and biofilm formation. In this review, we discuss the role of adhesins in the pathogenesis of the aetiological agent of tuberculosis, Mycobacterium tuberculosis. We also provide insight into the structure and characteristics of some of the characterized and putative M. tuberculosis adhesins. Finally, we examine the potential of adhesins as targets for the development of tuberculosis control strategies.

Epitope-specific antibody levels in tuberculosis: biomarkers of protection, disease, and response to treatment

Monoclonal antibodies restricted to Mycobacterium tuberculosis can measure epitope-specific antibody levels in a competition assay. Immunodominant epitopes were defined from clinical samples and related to the clinical spectrum of disease. Antibody to the immunodominant epitopes was associated with HLA-DR15. Occupational exposure showed a different response and was consistent with recognition of dormancy-related proteins and protection despite exposure to tuberculosis (TB). Studies in leprosy revealed the importance of immune deviation and the relationships between T and B cell epitopes. During treatment, antibody levels increased, epitope spreading occurred, but the affinity constants remained the same after further antigen exposure, suggesting constraints on the process of epitope selection. Epitope-specific antibody levels have a potential role as biomarkers for new vaccines which might prevent the progression of latent to active TB and as tools to measure treatment effects on subpopulations of tubercle bacilli.

Function and Potentials of M. tuberculosis Epitopes

Study of the function of epitopes of Mycobacterium tuberculosis antigens contributed significantly toward better understanding of the immunopathogenesis and to efforts for improving infection and disease control. Characterization of genetically permissively presented immunodominant epitopes has implications for the evolution of the host–parasite relationship, development of immunodiagnostic tests, and subunit prophylactic vaccines. Knowledge of the determinants of cross-sensitization, relevant to other pathogenic or environmental mycobacteria and to host constituents has advanced. Epitope-defined IFNγ assay kits became established for the specific detection of infection with tubercle bacilli both in humans and cattle. The CD4 T-cell epitope repertoire was found to be more narrow in patients with active disease than in latently infected subjects. However, differential diagnosis of active TB could not be made reliably merely on the basis of epitope recognition. The mechanisms by which HLA polymorphism can influence the development of multibacillary tuberculosis (TB) need further analysis of epitopes, recognized by Th2 helper cells for B-cell responses. Future vaccine development would benefit from better definition of protective epitopes and from improved construction and formulation of subunits with enhanced immunogenicity. Epitope-defined serology, due to its operational advantages is suitable for active case finding in selected high disease incidence populations, aiming for an early detection of infectious cases and hence for reducing the transmission of infection. The existing knowledge of HLA class I binding epitopes could be the basis for the construction of T-cell receptor-like ligands for immunotherapeutic application. Continued analysis of the functions of mycobacterial epitopes, recognized by T cells and antibodies, remains a fertile avenue in TB research.

IgA response to ESAT-6/CFP-10 and Rv2031 antigens varies in patients with culture-confirmed pulmonary tuberculosis, healthy Mycobacterium tuberculosis-infected and non-infected individuals in a tuberculosis endemic setting, Ethiopia

Little attention has been given to the role of antibodies against Mycobacterium tuberculosis (Mtb) infection. We have compared the levels of IgA and IgG against ESAT-6/CFP-10 and Rv2031c antigens in sera of patients with culture-confirmed pulmonary tuberculosis (PTB), healthy Mtb-infected and non-infected individuals in endemic TB settings. Venous blood samples were collected from 166 study participants; sera were separated and assayed by an enzyme-linked immunosorbent assay (ELISA). QuantiFERON-TB Gold In-Tube (QFTGIT) assay was used for the screening of latent TB infection. The mean optical density (OD) values of IgA against ESAT-6/CFP-10 and Rv2031 were significantly higher in sera of patients with culture-confirmed PTB compared with healthy Mtb-infected and non-infected individuals (P < 0.001). The mean OD values of IgG against ESAT-6/CFP-10 and Rv2031 were also significantly higher in sera of patients with culture-confirmed PTB compared with healthy Mtb-infected and non-infected individuals (P < 0.05). The mean OD values of IgA against both antigens were also higher in sera of healthy Mtb-infected cases compared with non-infected individuals. There were positive correlations (P < 0.05) between the level of IFN-γ induced in QFTGIT assay and the OD values of serum IgA against both antigens in healthy Mtb-infected subjects. This study shows the potential of IgA response against ESAT-6/CFP-10 and Rv2031 antigens in discriminating clinical TB from healthy Mtb-infected and non-infected cases. Nevertheless, further well-designed cohort study is needed to fully realize the full potential of this diagnostic marker.

Mycobacterium tuberculosis PstS1 amplifies IFN-γ and induces IL-17/IL-22 responses by unrelated memory CD4+ T cells via dendritic cell activation

The immunological mechanisms that modulate protection during Mycobacterium tuberculosis (Mtb) infection or vaccination are not fully understood. Secretion of IFN-γ and, to a lesser extent, of IL-17 by CD4(+) T cells plays a major role both in protection and immunopathology. Few Mtb Ags interacting with DCs affect priming, activation, and regulation of Ag-unrelated CD4(+) T-cell responses. Here we demonstrate that PstS1, a 38 kDa-lipoprotein of Mtb, promotes Ag-independent activation of memory T lymphocytes specific for Ag85B or Ag85A, two immunodominant protective Ags of Mtb. PstS1 expands CD4(+) and CD8(+) memory T cells, amplifies secretion of IFN-γ and IL-22 and induces IL-17 production by effector memory cells in an Ag-unrelated manner in vitro and in vivo. These effects were mediated through the stimulation of DCs, particularly of the CD8α(-) subtype, which respond to PstS1 by undergoing phenotypic maturation and by secreting IL-6, IL-1β and, to a lower extent, IL-23. IL-6 secretion by PstS1-stimulated DCs was required for IFN-γ, and to a lesser extent for IL-22 responses by Ag85B-specific memory T cells. These results may open new perspectives for immunotherapeutic strategies to control Th1/Th17 immune responses in Mtb infections and in vaccinations against tuberculosis.

pstS1 polymorphisms of Mycobacterium tuberculosis strains may reflect ongoing immune evasion

The mycobacterial antigen PstS1 is a highly immunogenic and immunostimulatory component of the mycobacterial cell membrane and a good candidate for the diagnosis and vaccination against tuberculosis. Here we selected 180 clinical isolates of Mycobacterium tuberculosis complex (MTBC) in China and 11 different Bacille Calmette Guerin (BCG) strains, amplified the gene of the PstS1 antigen and compared the sequences with those of four other Mycobacterium bovis and BCG strains from the NCBI genome website. Some of the mutations, especially 2 frameshift mutations, occurred in the PstS1antigen, which may have resulted in the protein function alteration and ongoing immune evasion. A unique single nucleotide polymorphism of the M. bovis and BCG strains was found in this antigen and may be useful for differentiating M. bovis and BCG strains from M. tuberculosis strains.

Antigen 85A and mycobacterial DNA-binding protein 1 are targets of immunoglobulin G in individuals with past tuberculosis

Development of accurate methods for predicting progression of tuberculosis (TB) from the latent state is recognized as vitally important in controlling TB, because a majority of cases develop from latent infections. Past TB that has never been treated has a higher risk of progressing than does latent Mycobacterium tuberculosis infection in patients who have previously received treatment. Antibody responses against 23 kinds of M. tuberculosis proteins in individuals with past TB who had not been medicated were evaluated. These individuals had significantly higher concentrations of antibodies against Antigen 85A and mycobacterial DNA-binding protein 1 (MDP1) than did those with active TB and uninfected controls. In addition, immunohistochemistry revealed colocalization of tubercle bacilli, antigen 85 and MDP1 inside tuberculous granuloma lesions in an asymptomatic subject, showing that M. tuberculosis in lesions expresses both antigen 85 and MDP1. Our study suggests the potential usefulness of measuring antibody responses to antigen 85A and MDP1 for assessing the risk of TB progression.

Detection of Mycobacterium tuberculosis GlcB or HspX Antigens or devR DNA impacts the rapid diagnosis of tuberculous meningitis in children

Background

Tuberculous meningitis (TBM) is the most common form of neurotuberculosis and the fifth most common form of extrapulmonary TB. Early diagnosis and prompt treatment are the cornerstones of effective disease management. The accurate diagnosis of TBM poses a challenge due to an extensive differential diagnosis, low bacterial load and paucity of cerebrospinal fluid (CSF) especially in children.

Methodology/Principal Findings

We describe the utility of ELISA and qPCR for the detection of Mycobacterium tuberculosis (M. tb) proteins (GlcB, HspX, MPT51, Ag85B and PstS1) and DNA for the rapid diagnosis of TBM. CSF filtrates (n = 532) derived from children were classified as ‘Definite’ TBM (M. tb culture positive, n = 29), ‘Probable and Possible’ TBM (n = 165) and ‘Not-TBM’ including other cases of meningitis or neurological disorders (n = 338). ROC curves were generated from ELISA and qPCR data of ‘Definite’ TBM and Non-Tuberculous infectious meningitis (NTIM) samples and cut-off values were derived to provide ≥95% specificity. devR qPCR, GlcB, HspX and PstS1 ELISAs showed 100% (88;100) sensitivity and 96–97% specificity in ‘Definite’ TBM samples. The application of these cut-offs to ‘Probable and Possible’ TBM groups yielded excellent sensitivity (98%, 94;99) and specificity (98%, 96;99) for qPCR and for GlcB, HspX and MPT51 antigen ELISAs (sensitivity 92–95% and specificity 93–96%). A test combination of qPCR with GlcB and HspX ELISAs accurately detected all TBM samples at a specificity of ∼90%. Logistic regression analysis indicated that these tests significantly added value to the currently used algorithms for TBM diagnosis.

Conclusions

The detection of M. tb GlcB/HspX antigens/devR DNA in CSF is likely to improve the utility of existing algorithms for TBM diagnosis and also hasten the speed of diagnosis.

Immunodiagnosis of tuberculosis: a dynamic view of biomarker discovery

Infection with Mycobacterium tuberculosis causes a variety of clinical conditions ranging from life-long asymptomatic infection to overt disease with increasingly severe tissue damage and a heavy bacillary burden. Immune biomarkers should follow the evolution of infection and disease because the host immune response is at the core of protection against disease and tissue damage in M. tuberculosis infection. Moreover, levels of immune markers are often affected by the antigen load. We review how the clinical spectrum of M. tuberculosis infection correlates with the evolution of granulomatous lesions and how granuloma structural changes are reflected in the peripheral circulation. We also discuss how antigen-specific, peripheral immune responses change during infection and how these changes are associated with the physiology of the tubercle bacillus. We propose that a dynamic approach to immune biomarker research should overcome the challenges of identifying those asymptomatic and symptomatic stages of infection that require antituberculosis treatment. Implementation of such a view requires longitudinal studies and a systems immunology approach leading to multianalyte assays.

Serodiagnosis of tuberculosis: due to shift track

Development of novel diagnostics for tuberculosis has so far been governed by the clinical requirement of improving the detection of patients with paucibacillary forms of the disease. For this aim, serological assays have been evaluated using several antigens, but were found insufficiently sensitive, because antibody production associates with the bacterial load of the disease. Consequently, detection of antibodies against a relatively small number of selected well-defined antigens has a much higher sensitivity for sputum smear-positive pulmonary disease in adult HIV-negative patients. They are the most active in generating and spreading aerosols containing live tubercle bacilli, but their detection is often delayed, thus perpetuating the transmission of the infection and disease in the population. High volume throughput serological screening of clinical suspects with mild clinical symptoms may help to achieve diagnosis earlier, than currently used procedures. Such expanded testing could be done more efficiently in laboratories, than at 'points-of-care' and at a lower cost than other tests. The feasibility of this approach towards reducing the delayed diagnosis of the most infectious cases of pulmonary tuberculosis needs to be ascertained in prospective diagnostic trials, in populations at a high risk. Reducing the transmission of tuberculosis is of key importance for achieving its continued decline and therefore it is proposed, that the aims of serological screening should shift from clinical to public health priorities.

Novel regulatory functions for Toll-like receptor-activated B cells during intracellular bacterial infection

Infections by intracellular bacterial pathogens remain a major cause of human diseases worldwide. Despite intensive efforts, the development of effective vaccines or immunotherapies against these diseases has largely remained unsuccessful, asking for the exploration of new aspects of the host response to these pathogens. Genetic studies have demonstrated beyond doubt that cell-mediated mechanisms of host defense involving innate immunity and T cells are of crucial importance for the control of these diseases. By contrast, the role of B cells during intracellular bacterial infection has so far received little attention besides their role as antibody-producing cells. However, the general knowledge of B-cell immunology and in particular of their antibody-independent functions has greatly increased during the last years. Recently, it was found in a model of Salmonella typhimurium infection that Toll-like receptor triggering on B cells resulted through interleukin-10 secretion in a marked suppression of innate defense mechanisms ultimately leading to uncontrolled growth of the bacteria and earlier death from the disease during both primary and secondary infections. This article reviews the protective and deleterious roles of B cells during intracellular bacterial infections and discusses how manipulating their antibody-independent functions may be a powerful means to therapeutically improve host resistance against these diseases.

Definition of novel cell envelope associated proteins in Triton X-114 extracts of Mycobacterium tuberculosis H37Rv

Background

Membrane- and membrane-associated proteins are important for the pathogenicity of bacteria. We have analysed the content of these proteins in virulent Mycobacterium tuberculosis H37Rv using Triton X-114 detergent-phase separation for extraction of lipophilic proteins, followed by their identification with high resolution mass spectrometry.

Results

In total, 1417 different proteins were identified. In silico analysis of the identified proteins revealed that 248 proteins had at least one predicted trans-membrane region. Also, 64 of the identified proteins were predicted lipoproteins, and 54 proteins were predicted as outer membrane proteins. Three-hundred-and-ninety-five of the observed proteins, including 91 integral membrane proteins were described for the first time. Comparison of abundance levels of the identified proteins was performed using the exponentially modified protein abundance index (emPAI) which takes into account the number of the observable peptides to the number of experimentally observed peptide ions for a given protein. The outcome showed that among the membrane-and membrane-associated proteins several proteins are present with high relative abundance. Further, a close examination of the lipoprotein LpqG (Rv3623) which is only detected in the membrane fractions of M. tuberculosis but not in M. bovis, revealed that the homologous gene in M. bovis lack the signal peptide and lipobox motif, suggesting impaired export to the membrane.

Conclusions

Altogether, we have identified a substantial proportion of membrane- and membrane-associated proteins of M. tuberculosis H37Rv, compared the relative abundance of the identified proteins and also revealed subtle differences between the different members of the M. tuberculosis complex.

Performance of purified antigens for serodiagnosis of pulmonary tuberculosis: a meta-analysis

Serological antibody detection tests for tuberculosis may offer the potential to improve diagnosis. Recent meta-analyses have shown that commercially available tests have variable accuracies and a limited clinical role. We reviewed the immunodiagnostic potential of antigens evaluated in research laboratories (in-house) for the serodiagnosis of pulmonary tuberculosis and conducted a meta-analysis to evaluate the performance of comparable antigens. Selection criteria included the participation of at least 25 pulmonary tuberculosis patients and the use of purified antigens. Studies evaluating 38 kDa, MPT51, malate synthase, culture filtrate protein 10, TbF6, antigen 85B, alpha-crystallin, 2,3-diacyltrehalose, 2,3,6-triacyltrehalose, 2,3,6,6'-tetraacyltrehalose 2'-sulfate, cord factor, and TbF6 plus DPEP (multiple antigen) were included in the meta-analysis. The results demonstrated that (i) in sputum smear-positive patients, sensitivities significantly >or=50% were provided for recombinant malate synthase (73%; 95% confidence interval [CI], 58 to 85) and TbF6 plus DPEP (75%; 95% CI, 50 to 91); (ii) protein antigens achieved high specificities; (iii) among the lipid antigens, cord factor had the best overall performance (sensitivity, 69% [95% CI, 28 to 94]; specificity, 91% [95% CI, 78 to 97]); (iv) compared with the sensitivities achieved with single antigens (median sensitivity, 53%; range, 2% to 100%), multiple antigens yielded higher sensitivities (median sensitivity, 76%; range, 16% to 96%); (v) in human immunodeficiency virus (HIV)-infected patients who are sputum smear positive, antibodies to several single and multiple antigens were detected; and (vi) data on seroreactivity to antigens in sputum smear-negative or pediatric patients were insufficient. Potential candidate antigens for an antibody detection test for pulmonary tuberculosis in HIV-infected and -uninfected patients have been identified, although no antigen achieves sufficient sensitivity to replace sputum smear microscopy. Combinations of select antigens provide higher sensitivities than single antigens. The use of a case-control design with healthy controls for the majority of studies was a limitation of the review. Efforts are needed to improve the methodological quality of tuberculosis diagnostic studies.

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.

Carotid atherosclerosis is not related to past tuberculosis in hypercholesterolemic patients

BACKGROUND

Tuberculosis is a chronic recurrent infection and inflammation is part of the disease which may remain undiagnosed for months. Furthermore immunization with recombinant heat shock protein-65-rich mycobacterium tuberculosis increased atherogenesis in hypercholesterolemic animal models.

OBJECTIVE

To investigate the potential interrelationships between past tuberculosis with carotid and femoral atherosclerosis in hypercholesterolemic patients.

DESIGN AND SETTING

Case control study in a university hospital.

PATIENTS

Two groups of hypercholesterolemic patient group (n=147) studied in a cardiovascular prevention unit during the same quarter, age (+/-1 year) and sex-matched. The first group presented a history of tuberculosis in the past and the second group never.

METHODS

Atherosclerosis was assessed by carotid and femoral external echography. Measurements of maximum plaque diameter were done in longitudinal planes, and the extent of atherosclerosis was graded according to the most severe visible changes on the scanned arteries.

RESULTS

The frequency and the distribution of atherosclerosis was similar in the two groups, whatever the arterial site explored, carotid or femoral. None of the clinical and biological studied variables were different between the two groups of patients.

CONCLUSION

Past tuberculosis is not associated with increased frequency of atherosclerotic lesions in hypercholesterolemic patients.

Tuberculosis in elephants: antibody responses to defined antigens of Mycobacterium tuberculosis, potential for early diagnosis, and monitoring of treatment

Tuberculosis (TB) in elephants is a re-emerging zoonotic disease caused primarily by Mycobacterium tuberculosis. Current diagnosis relies on trunk wash culture, the only officially recognized test, which has serious limitations. Innovative and efficient diagnostic methods are urgently needed. Rapid identification of infected animals is a crucial prerequisite for more effective control of TB, as early diagnosis allows timely initiation of chemotherapy. Serology has diagnostic potential, although key antigens have not been identified and optimal immunoassay formats are not established. To characterize the humoral responses in elephant TB, we tested 143 serum samples collected from 15 elephants over time. These included 48 samples from five culture-confirmed TB cases, of which four were in Asian elephants infected with M. tuberculosis and one was in an African elephant with Mycobacterium bovis. Multiantigen print immunoassay (MAPIA) employing a panel of 12 defined antigens was used to identify serologic correlates of active disease. ESAT-6 was the immunodominant antigen recognized in elephant TB. Serum immunoglobulin G antibodies to ESAT-6 and other proteins were detected up to 3.5 years prior to culture of M. tuberculosis from trunk washes. Antibody levels to certain antigens gradually decreased in response to antitubercular therapy, suggesting the possibility of treatment monitoring. In addition to MAPIA, serum samples were evaluated with a recently developed rapid test (RT) based on lateral flow technology (ElephantTB STAT-PAK). Similarly to MAPIA, infected elephants were identified using the RT up to 4 years prior to positive culture. These findings demonstrate the potential for TB surveillance and treatment monitoring using the RT and MAPIA, respectively.

A cocktail of affinity-purified antibodies reactive with diagnostically useful mycobacterial antigens ES-31, ES-43, and EST-6 for detecting the presence of Mycobacterium tuberculosis

A cocktail of affinity-purified antibodies against diagnostically useful Mycobacterium tuberculosis H37Ra excretory-secretory protein antigens ES-31, ES-43, and EST-6 was explored for detection of circulating free and immune-complexed (IC) antigen in sera of patients with confirmed tuberculosis (TB) by sandwich enzyme-linked immunosorbent assay and compared with monospecific anti-ES-31 antibody. Out of 68 smear-positive TB cases studied, using cocktail antibody, a sensitivity of 97% (66/68) for immune-complexed cocktail antigen and 91% (62/68) for free cocktail-antigen detection was observed, compared to 91% (62/68) for immune-complexed ES-31 and 79% (54/68) for free ES-31 antigen when anti-ES-31 antibody was used alone. Thus, combinatorial use of antibodies showed improved sensitivity and was thus observed to be better than single antibody. The specificity was observed to be 99% for immune-complexed antigen using cocktail antibody. Furthermore, analysis of different groups of TB sera showed that circulating immune-complexed antigen is a sensitive marker than free antigen.

Recognition of stage-specific mycobacterial antigens differentiates between acute and latent infections with Mycobacterium tuberculosis

Mycobacterium tuberculosis is estimated to infect 80 to 100 million people annually, the majority of whom do not develop clinical tuberculosis (TB) but instead maintain the infection in a latent state. These individuals generally become positive in response to a tuberculin skin test and may develop clinical TB at a later date, particularly if their immune systems are compromised. Latently infected individuals are interesting for two reasons. First, they are an important reservoir of M. tuberculosis, which needs to be considered for TB control. Second, if detected prior to recrudescence of the disease, they represent a human population that is making a protective immune response to M. tuberculosis, which is very important for defining correlates of protective immunity. In this study, we show that while responsiveness to early secretory antigenic target 6 is a good marker for M. tuberculosis infection, a strong response to the 16-kDa Rv2031c antigen (HspX or alpha-crystallin) is largely restricted to latently infected individuals, offering the possibility of differential immunodiagnosis of, or therapeutic vaccination against, TB.

Immunogenicity of the Mycobacterium tuberculosis PPE55 (Rv3347c) protein during incipient and clinical tuberculosis

Clinical tuberculosis (TB), whether noncavitary or cavitary, is the late stage of a chronic disease process, since Mycobacterium tuberculosis is a slowly growing organism. Our studies have shown that the profiles of antigenic proteins expressed by the in vivo bacteria that elicit antibodies differ in cavitary and noncavitary TB. To gain insight into antigenic proteins expressed during incipient, subclinical TB, an expression library of M. tuberculosis genomic DNA was screened with sera obtained during subclinical TB from guinea pigs infected with aerosols of M. tuberculosis H37Rv. One of the proteins recognized by antibodies elicited during subclinical TB infection of guinea pigs is the 309-kDa PPE55 (Rv3347c) protein. Genomic hybridization studies suggest that the PPE55 gene is specific to the M. tuberculosis complex and is present in a majority of clinical isolates tested. Antibodies to the C-terminal, approximately 100-kDa fragment of PPE55 (PPE-C) were detectable in sera from 29/30 (97%) human immunodeficiency virus-negative/TB-positive (HIV(-) TB(+)) patients and 17/24 (71%) HIV(+) TB(+) patients tested but not in sera from purified-protein derivative-positive healthy controls, suggesting that the in vivo expression of PPE55 protein correlates with active M. tuberculosis infection. Anti-PPE-C antibodies were also detected in retrospective sera obtained months prior to manifestation of clinical TB from 17/21 (81%) HIV(+) TB(+) individuals tested, providing evidence that the protein is expressed during incipient, subclinical TB in HIV-infected humans. Thus, PPE55 is a highly immunogenic protein that may be useful for differentiating between latent TB and incipient, subclinical TB.

Role of IgA in the defense against respiratory infections IgA deficient mice exhibited increased susceptibility to intranasal infection with Mycobacterium bovis BCG

IgA is the predominant Ig isotype in mucosal tissue and is believed to be involved in defense against viral and bacterial infections at these sites. Here, we examined the role of IgA in the protection against intranasal (i.n.) infection with Mycobacterium bovis Bacillus Calmette-Guerin (BCG). IgA deficient (IgA-/-) mice and wild type non-targeted littermate (IgA+/+) mice were immunized by i.n. route with the mycobacterium surface antigen PstS-1 formulated with cholera toxin (CT). Our data showed that IgA-/- mice were more susceptible to BCG infection compared to IgA+/+ mice, as revealed by the higher bacterial loads in the lungs and bronchoalveolar lavage (BAL). Analysis of the Ig levels and the antibody responses to PstS-1 showed that IgA-/- mice had no detectable IgA either in the saliva or in the BAL. However, these mice displayed higher levels of total and specific IgM than IgA+/+ mice in both mucosal fluids. More importantly, analysis of the cytokine responses revealed a reduction in the IFN-gamma and TNF-alpha production in the lungs of IgA-/- compared to IgA+/+ mice. Altogether, our results suggest that IgA may play a role in protection against mycobacterial infections in the respiratory tract by blocking the pathogen entrance and/or by modulating the pro-inflammatory responses.

Epitope-specific antibody levels demonstrate recognition of new epitopes and changes in titer but not affinity during treatment of tuberculosis

Antibody levels rise during treatment of tuberculosis. This study examined when this rise occurred, whether there was recognition of new antigen binding sites (epitopes) on the same or different antigens, and how long specific antibody persisted. Forty patients with smear-positive pulmonary tuberculosis provided serum before and during treatment. Antibody levels were measured using a monoclonal antibody competition assay to epitopes restricted to the Mycobacterium tuberculosis complex and an enzyme-linked immunosorbent assay for lipoarabinomannan. Significant increases in antibody levels were apparent after 7 days of treatment. Five samples (12.5%) had positive titers to all epitopes at the start of treatment, and this increased to 23 (58%) during treatment. Antibody to epitopes with the poorest sensitivity (the TB23 epitope of the 19-kDa antigen and the TB78 epitope of hsp65) showed the greatest increases after treatment. Antibody to these two epitopes was also absent in some patients with relapsed tuberculosis until after treatment. Antibody titers showed a biphasic response, with a fall at 2 to 3 months of treatment. Sera from two patients showed changes in the affinity of epitope-specific antibody during treatment, whereas the majority did not. Those infected with isoniazid-resistant strains of M. tuberculosis showed a late rise in antibody. Antibody to the TB68 epitope of the 16-kDa alpha-crystallin homolog was short-lived, but it recurred with bacteriological relapse during treatment. Positive antibody titers persisted for at least 3 to 18 months after treatment. Diagnostic tests for tuberculosis should be evaluated using only pretreatment sera. Delayed antigenic recognition could be due to active suppression and/or failure to engage internal antigens of M. tuberculosis.

Humoral response to low molecular weight antigens of Mycobacterium tuberculosis by tuberculosis patients and contacts

Much effort has been devoted to the identification of immunologically important antigens of Mycobacterium tuberculosis and to the combination of target antigens to which antibodies from serum of tuberculous patients could react specifically. We searched for IgG antibodies specific for antigens of 45 to 6 kDa obtained after sonication of the well-characterized wild M. tuberculosis strain in order to detect differences in the antibody response to low molecular weight antigens from M. tuberculosis between patients with pulmonary tuberculosis and contacts. Specific IgG antibodies for these antigens were detected by Western blot analysis of 153 serum samples collected from 51 patients with confirmed pulmonary tuberculosis. Three samples were collected from each patient: before therapy, and after 2 and 6 months of treatment. We also analyzed 25 samples obtained from contacts, as well as 30 samples from healthy individuals with known tuberculin status, 50 samples from patients with other lung diseases and 200 samples from healthy blood donors. The positive predictive value for associated IgG reactivity against the 6-kDa and 16-kDa antigens, 6 and 38 kDa, and 16 and 38 kDa was 100% since simultaneous reactivity for these antigens was absent in healthy individuals and individuals with other lung diseases. This association was observed in 67% of the patients, but in only 8% of the contacts. The humoral response against antigens of 16 and 6 kDa seems to be important for the detection of latent tuberculosis since the associated reactivity to these antigens is mainly present in individuals with active disease.

Induction of in vivo functional Db-restricted cytolytic T cell activity against a putative phosphate transport receptor of Mycobacterium tuberculosis

Using plasmid vaccination with DNA encoding the putative phosphate transport receptor PstS-3 from Mycobacterium tuberculosis and 36 overlapping 20-mer peptides spanning the entire PstS-3 sequence, we determined the immunodominant Th1-type CD4(+) T cell epitopes in C57BL/10 mice, as measured by spleen cell IL-2 and IFN-gamma production. Furthermore, a potent IFN-gamma-inducing, D(b)-restricted CD8(+) epitope was identified using MHC class I mutant B6.C-H-2(bm13) mice and intracellular IFN-gamma and whole blood CD8(+) T cell tetramer staining. Using adoptive transfer of CFSE-labeled, peptide-pulsed syngeneic spleen cells from naive animals into DNA vaccinated or M. tuberculosis-infected recipients, we demonstrated a functional in vivo CTL activity against this D(b)-restricted PstS-3 epitope. IFN-gamma ELISPOT responses to this epitope were also detected in tuberculosis-infected mice. The CD4(+) and CD8(+) T cell epitopes defined for PstS-3 were completely specific and not recognized in mice vaccinated with either PstS-1 or PstS-2 DNA. The H-2 haplotype exerted a strong influence on immune reactivity to the PstS-3 Ag, and mice of the H-2(b, p, and f) haplotype produced significant Ab and Th1-type cytokine levels, whereas mice of H-2(d, k, r, s, and q) haplotype were completely unreactive. Low responsiveness against PstS-3 in MHC class II mutant B6.C-H-2(bm12) mice could be overcome by DNA vaccination. IFN-gamma-producing CD8(+) T cells could also be detected against the D(b)-restricted epitope in H-2(p) haplotype mice. These results highlight the potential of DNA vaccination for the induction and characterization of CD4(+) and particularly CD8(+) T cell responses against mycobacterial Ags.

Effect of growth state on transcription levels of genes encoding major secreted antigens of Mycobacterium tuberculosis in the mouse lung

Arrest of the multiplication of Mycobacterium tuberculosis caused by expression of adaptive immunity in mouse lung was accompanied by a 10- to 20-fold decrease in levels of mRNAs encoding the secreted Ag85 complex and 38-kDa lipoprotein. esat-6 mRNA levels were high throughout infection. The data imply that multiplying and nonreplicating tubercle bacilli have different antigen compositions.

Isotype-specific anti-38 and 27 kDa (mpt 51) response in pulmonary tuberculosis with human immunodeficiency virus coinfection

There is a need for rapid diagnostic methods to identify tuberculosis among human immunodeficiency virus-positive cases (HIV-TB). This study evaluated the serodiagnostic potential of the native 38 kDa and recombinant 27 kDa (mpt 51) antigens of Mycobacterium tuberculosis purified in the laboratory, when applied to HIV-TB patients. The antibody response was studied using enzyme-linked immunosorbent assays (ELISA). In the HIV-TB group, anti-38 kDa antibody of the immunoglobulin G (IgG), IgA and IgM isotypes was found in 38%, 43% and 7%, of patients, respectively. Antibodies to the 27 kDa antigen occurred in 50%, 31%, and 1%, for IgG, IgA and IgM, respectively. The sensitivity increased upon combination of the results of IgG and IgA isotypes for each of the antigens, without compromising specificity. When the results were analysed based on the smear positivity, 71-78% and 54-69% were positive among smear-positive and smear-negative HIV-TB cases, respectively. A higher sensitivity (71% and 69%) was obtained using the 27 kDa antigen. The use of both antigens offered a sensitivity of 82% in smear-positive and 69% in smear-negative cases. There was no difference in antibody response among the HIV-TB cases, related to CD4 counts. Thus, the combination of the 38 and 27 kDa (mpt 51) antigens proved to be of diagnostic utility in HIV-TB, irrespective of the severity of immunosuppression, in smear-positive and smear-negative TB.

Evaluation of a rapid immunochromatographic test for the serologic diagnosis of tuberculosis in Italy

OBJECTIVE

To determine specificity, sensitivity and predictive values of a rapid immunochromatographic assay (ICT tuberculosis) for the diagnosis of tuberculosis (TB) in an Italian clinical setting, and to identify tentative new guidance for the interpretation of test results.

METHODS

The ICT tuberculosis test is an immunochromatographic test based on the detection of IgG antibodies directed against five highly purified antigens secreted by Mycobacterium tuberculosis during active growth. Sera from 60 patients with active pulmonary (48 sputum smear-positive and six sputum smear-negative cases) and extrapulmonary (six cases) TB were obtained. Personal, anamnestic and clinical data were investigated and recorded for each patient. The control groups comprised 156 subjects: 40 healthy individuals, half of them Mycobacterium bovis BCG-vaccinated, and 116 patients with mycobacterial diseases other than TB (five cases), with nonmycobacterial lung diseases (30 cases), with nonmycobacterial nonlung diseases (30 cases), with nonmycobacterial diseases and rheumatoid factors positivity (30 cases), and with asymptomatic HIV infection (21 cases). For 21 individuals the test was simultaneously performed with both serum and whole blood sample. Each positive result of the ICT test was reported with regard to the number (1-4), position (A, B, C, D) and color intensity (+ to ++++) of the evidenced lines in order to assess the quality of the antibody response.

RESULTS

The overall sensitivity and specificity were 56.7% and 90.4%, respectively. The sensitivity for pulmonary TB patients was 61.1% (66.7% for smear-positive and 16.7% for smear-negative cases) and 16.7% for extrapulmonary TB patients. The difference between ICT results in pulmonary TB patients and control subjects was statistically significant (P < 0.0001). The analysis of the positive ICT tests revealed that samples with strong color intensity (>/=++) and specific antibodies bound to antigens immobilized on line D were significantly more frequent in TB patients than in controls (P = 0.001 and P= 0.027, respectively). ICT test results with the presence of at least three visible lines were more often observed in the TB patients than in controls, although not reaching statistical significance (P = 0.052). No difference was observed between the results of the ICT test performed both on serum and whole blood sample.

CONCLUSIONS

The ICT tuberculosis test was confirmed to be rapid and easy to perform without requiring special equipment, both on serum and whole blood sample. Our data, in accordance with those obtained in a previous study conducted in extra-European countries, confirmed higher sensitivities for the smear-positive TB patients than for the smear-negative TB patients, and for pulmonary TB patients than for the extrapulmonary TB patients. Data obtained on the quality of antibody response in the ICT positive samples, might be used to improve the performance of the test.

Changes in avidity and level of immunoglobulin G antibodies to Mycobacterium tuberculosis in sera of patients undergoing treatment for pulmonary tuberculosis

Much is known about specific antibodies and their titers in patients with tuberculosis. However, little is known about the avidity of these antibodies or whether changes in avidity occur during the progression of the disease or during treatment. The aims of this study were to determine the avidity of antibodies to Mycobacterium tuberculosis in patients with pulmonary tuberculosis, to explore the value of avidity determination for the diagnosis of tuberculosis, and to study changes in levels of antibodies and their avidity during treatment. Antibody avidity was measured by an enzyme-linked immunosorbent assay with thiocyanate elution. Avidity indices and serum levels of immunoglobulin G to M. tuberculosis were determined for 22 patients with pulmonary tuberculosis before and during treatment and for 24 patients with other pulmonary diseases. Antibody levels and avidity were both significantly higher in untreated tuberculosis patients than in the controls. Avidity determination had more diagnostic potential than determination of the antibody levels. Tuberculosis patients with a long duration of symptoms had higher antibody avidity than those with a recent onset of symptoms, indicating affinity maturation of specific antibodies during active disease. In the early phase of treatment, a decrease in antibody avidity was observed for 73% of all tuberculosis patients, accompanied by an initial increase in antibody levels in 36% of these patients. These phenomena could be explained by an intense stimulation of the humoral response by antigens released from killed bacteria, reflecting early bactericidal activity of antituberculous drugs leading to the production of low-affinity antibodies against these released antigens.

Serologic diagnosis of tuberculosis using a simple commercial multiantigen assay

SETTING

Seven primary health clinics and a pulmonary disease specialty clinic in Rio de Janeiro City, Brazil.

OBJECTIVE

To evaluate a commercial immunochromatographic test kit (ICT Tuberculosis; AMRAD-ICT; Sidney, Australia) employing five recombinant Mycobacterium tuberculosis proteins for the detection of pulmonary tuberculosis (TB).

DESIGN

Serology test results were compared with duplicate sputum microscopy and culture in 277 patients with symptomatic pulmonary disease (243 with pulmonary TB and 34 with nontuberculous disease). An additional 110 healthy control subjects were also tested.

RESULTS

The serology test was simple and rapid to perform and detected 64.2% of smear-positive and 46.3% of smear-negative TB patients overall. HIV co-infection was present in 15.3% of TB patients, and serology was much less sensitive (overall 27.6%) in this small group, as was microscopy (13.8%). Specificity of the serology test was 100% in healthy control subjects and 85.2% in the small number of control patients with pulmonary disease, including those with prior TB. Combined with microscopy, serology detected 72.8% of TB patients.

CONCLUSION

Depending on the population studied, multiantigen serologic tests for TB may be as sensitive as microscopy, but detect a different and overlapping subset of patients. The use of multiple antigens in this kit increased test sensitivity without significant loss of specificity. Bacille Calmette-Guérin vaccination and tuberculin sensitivity did not affect serology results. Estimating specificity in clinical use will require testing a much larger cohort of symptomatic patients with nontuberculous disease. The TB diagnostic performance of this group of antigens in HIV co-infected individuals was poor.

A novel ultrasound-enhanced latex agglutination test for the detection of antibodies against Mycobacterium tuberculosis in serum

A novel ultrasound-enhanced latex agglutination test is described for the detection of serum antibodies against Mycobacterium tuberculosis. The use of ultrasound to detect the low level of antibodies in serum enhances the sensitivity of the test. The technique is based on the fact that suspended latex particles become concentrated in an ultrasonic standing wave field, thereby increasing the rate of particle-particle collisions compared to the standard agglutination test procedure. Reactions were performed on piezo-ceramic wafers, which were connected to an oscillator at a frequency of 100 kHz. This method improved sensitivity significantly so that even 20 times diluted serum samples exhibited agglutination, which was clearly visible to the naked eye.

Purification and characterization of three immunodominant proteins (38, 30, and 16 kDa) of Mycobacterium tuberculosis

Specific mycobacterial antigens are an important prerequisite in the serodiagnosis of tuberculosis. Many studies have reported the use of both native and recombinant proteins. Even though recombinant proteins can form standardized reagents with unlimited supply, their diagnostic test characteristics were not satisfactory in some cases. In this study we have purified the 38-, 30- (antigen 85B), and 16-kDa native antigens of Mycobacterium tuberculosis by procedures with limited number of steps. Starting with the secreted antigens of M. tuberculosis H37Rv, the 38-kDa form was purified by preparative isoelectric focusing, followed by preparative electrophoresis. Separation of antigen 85 components was achieved by anion-exchange chromatography, followed by hydrophobic interaction chromatography. Gel-permeation chromatography was employed for the isolation of the 16-kDa form, from the cytosol fraction of M. tuberculosis H37Rv. By using a minimal number of steps, considerable yields of these proteins were obtained without loss of immunological activity. The native proteins purified were characterized by analytical two-dimensional electrophoresis, HPLC, and circular dichroism studies. Conformation of the native 38-kDa form purified in our laboratory was different from that of the recombinant 38-kDa form from the WHO Bank. The identities of these native antigens were established by immunoblotting with known monoclonal antibodies from the WHO Bank.

Specific and early detection of IgG, IgA and IgM antibodies to Mycobacterium tuberculosis 38kDa antigen in pulmonary tuberculosis

The objective was to apply the purified 38kDa protein antigen of Mycobacterium tuberculosis in ELISA to estimate the IgG, IgA and IgM antibody levels in sera and circulating immune complexes of tuberculosis patients. Sera from smear and culture positive tuberculosis patients were positive for anti 38kDa IgG, IgA and IgM antibodies, with a sensitivity of 61%, 30% and 10%, respectively, and with a specificity of 100% for IgG. The sensitivity of the test improved to a level of 68% for IgG+IgA and of 71.4% for IgG+IgA+IgM without significantly compromising the specificity (IgG of 100%, IgG+IgA of 96%, IgG+IgA+IgM of 90%). Among the smear, culture-negative but X-ray-positive cases, 60% were serum positive for IgG antibody, while in smear-negative but culture-positive cases, 54% were positive for IgG antibody. Measurement of 38kDa antibodies showed a greater than 95% sensitivity in smear and culture-positive, and smear-negative and culture-positive patients, through a combination of assays for serum IgG and circulating immune complex antibodies, while the specificity was 100%.

Homogeneity of antibody responses in tuberculosis patients

The goals of the present study were twofold: (i) to compare the repertoires of antigens in culture filtrates of in vitro-grown Mycobacterium tuberculosis that are recognized by antibodies from noncavitary and cavitary tuberculosis (TB) patients and (ii) to determine the extent of variation that exists between the antigen profiles recognized by individual TB patients. Lipoarabinomannan-free culture filtrate proteins of M. tuberculosis were fractionated by one-dimensional (1-D) and 2-D polyacrylamide gel electrophoresis, and the Western blots were probed with sera from non-human immunodeficiency virus (non-HIV)-infected cavitary and noncavitary TB patients and from HIV-infected, noncavitary TB patients. In contrast to earlier studies based on recombinant antigens of M. tuberculosis which suggested that antibody responses in TB patients were heterogeneous (K. Lyashchenko et al., 1998, Infect. Immun. 66:3936-3940, 1998), our studies with native culture filtrate proteins show that the antibody responses in TB patients show significant homogeneity in being directed against a well-defined subset of antigens. Thus, there is a well-defined subset of culture filtrate antigens that elicits antibodies during noncavitary and cavitary disease. In addition, another set of antigens is recognized primarily by cavitary TB patients. The mapping with individual patient sera presented here suggests that serodiagnostic tests based on the subset of antigens recognized during both noncavitary and cavitary TB will enhance the sensitivity of antibody detection in TB patients, especially in difficult-to-diagnose, smear-negative, noncavitary TB patients.

Accuracy and utility of commercially available amplification and serologic tests for the diagnosis of minimal pulmonary tuberculosis

Diagnosis of patients with minimal active tuberculosis (TB) is difficult, as there is no single test with high sensitivity and specificity. The yield and clinical utility of a combination of diagnostic tests were prospectively studied among 500 consecutive patients referred for sputum induction for diagnosis of possible active TB. Patients underwent sputum induction, chest X-ray, tuberculin testing, and had blood drawn for serologic testing (Detect-TB test; Biochem ImmunoSystems). Sputum was examined with fluorescent microscopy and PCR (Amplicor MTB-Roche) and cultured for mycobacteria using liquid (BACTEC) and solid media. For the diagnosis of the 60 cases of active TB, sensitivity and specificity, respectively, of the following diagnostic tests were mycobacterial culture, 73% and 100%; PCR, 42% and 100%; chest X-ray, 67-77% and 66-76%; tuberculin testing, 94% and 20%; and serology, 33% and 87%. After consideration of PCR and radiographic and clinical characteristics, a positive serologic test was independantly associated with diagnosis of active disease (adjusted odds of disease if positive, 2.6; 95% confidence limits, 1.1,6.1). No currently available test has sensitivity and specificity high enough for the accurate diagnosis of minimal pulmonary TB. Utilization of a combination of tests, together with consideration of key clinical characteristics, could improve diagnostic accuracy.

Induction of antibody and T-cell responses by immunization with ISCOMS containing the 38-kilodalton protein of Mycobacterium tuberculosis

In this study, we investigated the influence of different amounts of N-(palmitoyloxy) succinimide (PA-NHS): attachment of lipid tails to the protein and Quil A on the immunogenicity of the 38-kDa mycobacterial protein incorporated into immunostimulating complexes (ISCOMS; 38-kDa ISCOMS). The addition of higher amounts of Quil A during the ISCOMS preparation increased the amount of protein incorporated into ISCOMS, whereas the use of higher amounts of PA did not influence this parameter. Low antibody responses were observed after primary immunization with all 38-kDa ISCOMS preparations which, however, strongly increased after booster injections. IgG2a is the major subclass IgG induced by these ISCOMS preparations. There were only slight differences between the various ISCOMS formulations in their capacity to induce cytotoxic T-lymphocytes (CTLs). Spleen cells primed with ISCOMS prepared with the highest amount of Quil A produced high levels of IFN-gamma after stimulation with T helper cell type one (Th1) peptide of the 38-kDa protein (aa 70-84), 38-kDa protein or purified protein derivate (PPD). Spleen cells primed with ISCOMS prepared with the lowest amount of Quil A only substantial IFN-gamma levels were detected after stimulation with 38-kDa protein. IL-4 secretion was very low or not detectable with all ISCOM preparations. These results therefore demonstrated that all 38 kDa-ISCOMS preparations were: (1) immunogenic by inducing antibodies, Th1 and CTL responses; (2) that the way in which the ISCOMS were prepared, e.g. the amount of Quil A used, modulates the epitope specificity of the Th1 response.

Serodiagnostic potential of culture filtrate antigens of Mycobacterium tuberculosis

Our studies of the humoral responses of tuberculosis (TB) patients have defined the repertoire of culture filtrate antigens of Mycobacterium tuberculosis that are recognized by antibodies from cavitary and noncavitary TB patients and demonstrated that the profile of antigens recognized changes with disease progression (K. Samanich et al., J. Infect. Dis. 178:1534-1538, 1998). We have identified several antigens with strong serodiagnostic potential. In the present study we have evaluated the reactivity of cohorts of human immunodeficiency virus (HIV)-negative, smear-positive; HIV-negative, smear-negative; and HIV-infected TB patients, with three of the candidate antigens, an 88-kDa protein, antigen (Ag) 85C, and MPT32, and compared the reactivity of the same patient cohort with the 38-kDa antigen and Ag 85A. We have also compared the reactivity of native Ag 85C and MPT32 with their recombinant counterparts. The evaluation of the reactivity was done by a modified enzyme-linked immunosorbent assay described earlier (S. Laal et al., Clin. Diag. Lab. Immunol. 4:49-56, 1997), in which all sera are preadsorbed against Escherichia coli lysates to reduce the levels of cross-reactive antibodies. Our results demonstrate that (i) antigens identified on the basis of their reactivity with TB patients' sera provide high sensitivities for serodiagnosis, (ii) recombinant Ag 85C and MPT32, expressed in E. coli, show reduced reactivity with human TB sera, and (iii) of the panel of antigens tested, the 88-kDa protein is the most promising candidate for serodiagnosis of TB in HIV-infected individuals. Moreover, these results reaffirm that both the extent of the disease and the bacterial load may play a role in determining the antigen profile recognized by antibodies.

Mass spectrometric identification of mtb81, a novel serological marker for tuberculosis

We have used serological proteome analysis in conjunction with tandem mass spectrometry to identify and sequence a novel protein, Mtb81, which may be useful for the diagnosis of tuberculosis (TB), especially for patients coinfected with human immunodeficiency virus (HIV). Recombinant Mtb81 was tested by an enzyme-linked immunosorbent assay to detect antibodies in 25 of 27 TB patients (92%) seropositive for HIV as well as in 38 of 67 individuals (57%) who were TB positive alone. No reactivity was observed in 11 of 11 individuals (100%) who were HIV seropositive alone. In addition, neither sera from purified protein derivative (PPD)-negative (0 of 29) nor sera from healthy (0 of 45) blood donors tested positive with Mtb81. Only 2 of 57 of PPD-positive individuals tested positive with Mtb81. Sera from individuals with smear-positive TB and seropositive for HIV but who had tested negative for TB in the 38-kDa antigen immunodiagnostic assay were also tested for reactivity against Mtb81, as were sera from individuals with lung cancer and pneumonia. Mtb81 reacted with 26 of 37 HIV(+) TB(+) sera (70%) in this group, compared to 2 of 37 (5%) that reacted with the 38-kDa antigen. Together, these results demonstrate that Mtb81 may be a promising complementary antigen for the serodiagnosis of TB.

RECENT ADVANCES IN TUBERCULOSIS DIAGNOSTIC TECHNIQUES

Tuberculosis is re-emerging as an important cause of morbidity and mortality in man. This article outlines current strategies available for the diagnosis of tuberculosis, and its applicability. Fluorescent staming, modified culture methods, antigen detection, ELISA based assays against various antigen preparation and recent advances in molecular techniques have been outlined. Present strategies being developed at Armed Forces Medical College for the early diagnosis, speciation, antibiotic sensitivity testing and epidemiologic testing have also been alluded to.

ADA1/ADAp ratio in pleural tuberculosis: an excellent diagnostic parameter in pleural fluid

We analysed the efficacy of pleural adenosine deaminase (ADAp) and the ADA1/ADAp ratio in the diagnosis of pleural tuberculosis in 103 pleural effusions, 27 of which were tuberculosis (TB) and 76 other diagnoses (non-TB). Smears, cultures and pleural biopsies were carried out in all cases, and were used for final diagnosis. The diagnostic yield of the parameters under study were as follows: smears/cultures of mycobacteria in fluid 11.1%/33.3%; biopsy 33.3%/51.8% and tuberculosis granulomas 85.1%. The levels of ADAp and ADA1/ADAp ratio in TB and non-TB groups showed very significant differences (P < 0.00001); in the TB group: ADAp 54.7 +/- 23.5 IU and ADA1/ADAp 0.27 +/- 0.08; in the non-TB group: ADAp 18.3 +/- 43.2 IU and ADA1/ADAp 0.64 +/- 0.14. The assay established ADA levels in pleural fluid > or = 40 IU and an ADA1/ADAp ratio < or = 0.42 as cut-off levels to identify individuals in the TB group, with a sensitivity of 88.8%/100%, a specificity of 92%/98.6%, a positive predictive value (PPV) of 80%/96.4%, a negative predictive value (NPV) of 95.8%/100% and an accuracy of 91.2%/99.02%. The ADAp levels in 27 patients with TB, showed close correlation with the number of monocyte macrophages (P = 0.001), but not with the number of lymphocytes (P = n.s.). The ADA1/ADAp ratio overcomes the limitations of ADAp (false positives and negatives), and is the most useful parameter for diagnosis on account of a high diagnostic yield, low cost and speed of the assay for identifying a pleural tuberculosis diagnosis, when compared with traditional methods.

Immunogenicity and Protective Efficacy of Tuberculosis DNA Vaccines Encoding Putative Phosphate Transport Receptors

Using culture filtrate Ag-specific mAbs generated from mycobacteria-infected H-2b haplotype mice, we have previously identified three genes in the Mycobacterium tuberculosis genome, encoding proteins homologous to the periplasmic ATP-binding cassette phosphate-binding receptor PstS of the phosphate-specific transport system of E. coli. To define the potential vaccinal properties of these phosphate-binding proteins, female C57BL/6 mice were injected i.m. with plasmid DNA encoding PstS-1, PstS-2, or PstS-3 proteins from M. tuberculosis and immunogenicity and protective efficacy against i.v. challenge with M. tuberculosis H37Rv was analyzed. Significant levels of highly Ag-specific Abs and Th1-type cytokines IL-2 and IFN-γ could be detected following vaccination with each of the three genes. However, only mice vaccinated with PstS-3 DNA demonstrated significant and sustained reduction in bacterial CFU numbers in spleen and lungs for 3 mo after M. tuberculosis challenge, as compared with CFU counts in mice vaccinated with control DNA. Vaccination with PstS-2 DNA induced a modest reduction in CFU counts in spleen only, whereas vaccination with PstS-1 DNA was completely ineffective in reducing bacterial multiplication. In conclusion, our results indicate that DNA vaccination is a powerful and easy method for comparative screening of potentially protective Ags from M. tuberculosis and that the PstS-3 protein is a promising new subunit vaccine candidate.

Definition of Mycobacterium tuberculosis culture filtrate proteins by two-dimensional polyacrylamide gel electrophoresis, N-terminal amino acid sequencing, and electrospray mass spectrometry

A number of the culture filtrate proteins secreted by Mycobacterium tuberculosis are known to contribute to the immunology of tuberculosis and to possess enzymatic activities associated with pathogenicity. However, a complete analysis of the protein composition of this fraction has been lacking. By using two-dimensional polyacrylamide gel electrophoresis, detailed maps of the culture filtrate proteins of M. tuberculosis H37Rv were generated. In total, 205 protein spots were observed. The coupling of this electrophoretic technique with Western blot analysis allowed the identification and mapping of 32 proteins. Further molecular characterization of abundant proteins within this fraction was achieved by N-terminal amino acid sequencing and liquid chromatography-mass spectrometry. Eighteen proteins were subjected to N-group analysis; of these, only 10 could be sequenced by Edman degradation. Among the most interesting were a novel 52-kDa protein demonstrating significant homology to an alpha-hydroxysteroid dehydrogenase of Eubacterium sp. strain VPI 12708, a 25-kDa protein corresponding to open reading frame 28 of the M. tuberculosis cosmid MTCY1A11, and a 31-kDa protein exhibiting an amino acid sequence identical to that of antigen 85A and 85B. This latter product migrated with an isoelectric point between those of antigen 85A and 85C but did not react with the antibody specific for this complex, suggesting that there is a fourth member of the antigen 85 complex. Novel N-terminal amino acid sequences were obtained for three additional culture filtrate proteins; however, these did not yield significant homology to known protein sequences. A protein cluster of 85 to 88 kDa, recognized by the monoclonal antibodies IT-57 and IT-42 and known to react with sera from a large proportion of tuberculosis patients, was refractory to N-group analysis. Nevertheless, mass spectrometry of peptides obtained from one member of this complex identified it as the M. tuberculosis KatG catalase/peroxidase. Thus, the detailed mapping of M. tuberculosis proteins, combined with state-of-the-art analytical techniques such as mass spectrometry, provides a basis for further analysis and rapid identification of biologically relevant molecules.