Active tuberculosis patients have high levels of IgA anti-alpha-crystallin and isocitrate lyase proteins

SETTING

Mexico City, Mexico.

OBJECTIVE

To identify proteins synthetised by Mycobacterium tuberculosis in hypoxic culture, which resemble more closely a granuloma environment than aerobic culture, and to determine if they are recognised by antibodies from patients with active pulmonary tuberculosis (PTB).

DESIGN

Soluble extracts from M. tuberculosis H37Rv cultured under aerobic or hypoxic conditions were analysed using two-dimensional polyacrylamide gel electrophoresis, and proteins over-expressed under hypoxia were identified by mass spectrometry. The presence of immunoglobulin (Ig) G, IgA and IgM antibodies against these proteins was determined in the serum of 42 patients with active PTB and 42 healthy controls.

RESULTS

We selected three M. tuberculosis H37Rv proteins (alpha-crystallin protein [Acr, Rv2031c], universal stress protein Rv2623 and isocitrate lyase [ICL, RV0467]) that were over-expressed under hypoxia. Titres of anti-Acr and anti-ICL IgA antibodies were higher in patients than in healthy controls, with an area under the receiver operating characteristic curve of 0.71 for anti-ICL IgA antibodies.

CONCLUSION

ICL could be used in combination with other M. tuberculosis antigens to improve the sensitivity and specificity of current serological TB diagnostic methods.

A novel antigen-carrier system: the Mycobacterium tuberculosis Acr protein carried by raw starch microparticles

Microparticles have been used as promising carriers for in vivo vaccine delivery. However, the processes for immobilizing peptides or proteins on microparticles usually require the use of undesirable compounds and complex protocols. In this work, we propose a new immobilization and delivery system with raw starch microparticles and a starch binding domain (SBD) tag fusion protein. The heat shock protein alpha crystallin from Mycobacterium tuberculosis was used as model. The immunogenicity of the system was investigated in BALB/c mice inoculated with purified Acr-SBDtag protein (pAcr-SBDtag) and starch immobilized Acr-SBDtag protein (μAcr-SBDtag) by oral and intranasal routes. We demonstrated mucosal immunization with the μAcr-SBDtag protein induced systemic antibodies that were predominantly immunoglobulin G2a (IgG2a). An analysis of the cytokines from spleen cells and lung homogenates revealed that loaded microparticles induced the secretion of interferon-γ (INF-γ), suggesting an adjuvant effect from the immobilization. The immune responses induced by immobilized protein were primarily affected by the route of administration. These results demonstrate that the system exhibits the necessary characteristics to improve antigen release and presentation to antigen presenting cells (APCs) in the mucosae. Because no extra adjuvants were used, we posit that the system may be suitable for delivery and presentation to the field of subunit vaccine development.

Optimizing antigen cocktails for detection of Mycobacterium bovis in herds with different prevalences of bovine tuberculosis: ESAT6-CFP10 mixture shows optimal sensitivity and specificity

Bovine tuberculosis is a major problem in many countries; hence, new and better diagnostic tools are urgently needed. In this work, we have tested ESAT6, CFP10, PE13, PE5, MPB70, TB10.4, and TB27.4 for their potentials as diagnostic markers in field animals from Northern Ireland, Mexico, and Argentina, regions with low, medium, and high prevalences of bovine tuberculosis, respectively. At all three sites, ESAT6 and CFP10 were superior diagnostic antigens, while their combination performed even better at the two sites where the combination was tested, providing the best coverage for the detection of diseased populations. The high sensitivity in the skin test reactor groups, combined with the high specificity in the tuberculosis-free groups, indicated that a diagnosis could correctly be made for 85% of the infected animals, based on their responses to these two antigens. Furthermore, TB10.4, PE13, and PE5 have the potential to supplement ESAT6 and CFP10 in a future five-component diagnostic cocktail.

A marked difference in pathogenesis and immune response induced by different Mycobacterium tuberculosis genotypes

In the last decade, an unprecedented genetic diversity has been disclosed among Mycobacterium tuberculosis strains found worldwide. However, well-conserved genotypes seem to prevail in areas with high incidence of tuberculosis. As this may be related to selective advantages, such as advanced mechanisms to circumvent [M. bovis Bacille Calmette-Guerin (BCG)-induced] host defence mechanisms, we investigated the influence of strain diversity on the course of experimental disease. Twelve M. tuberculosis strains, representing four major genotype families found worldwide today, and the laboratory strain H37Rv were each used to infect BALB/c mice by direct intratracheal injection. Compared with H37Rv, infections with Beijng strains were characterized by extensive pneumonia, early but ephemeral tumour necrosis factor-alpha (TNF-alpha) and inducible isoform of nitric oxide synthetase (iNOS) expression, and significantly higher earlier mortality. Conversely, Canetti strains induced limited pneumonia, sustained TNF-alpha and iNOS expression in lungs, and almost 100% survival. Strains of the Somali and the Haarlem genotype families displayed less homogeneous, intermediate rates of survival. Previous BCG vaccination protected less effectively against infection with Beijing strains than against the H37Rv strain. In conclusion, genetically different M. tuberculosis strains evoked markedly different immunopathological events. Bacteria with the Beijing genotype, highly prevalent in Asia and the former USSR, elicited a non-protective immune response in mice and were the most virulent. Future immunological research, particularly on candidate vaccines, should include a broad spectrum of M. tuberculosis genotypes rather than a few laboratory strains.

Characterization of the Mycobacterium tuberculosis region containing the mpt83 and mpt70 genes

Like the products of the genes mpt83 and mpt70, the putative protein encoded by the gene located between these genes was undetectable in Mycobacterium tuberculosis with an antiserum raised against the recombinant protein. The protein showed 100% homology with M. tuberculosis Rv2874 and similarities with CcdA and DipZ proteins involved in cytochrome-c biogenesis in bacteria. Expression analysis by RT-PCR and transcriptional fusions of Rv2874 and their neighbor genes Rv2871, Rv2872, mpt83 and mpt70 with lacZ suggest that these genes are part of an operon and their transcription is driven by promoter regions located 5' upstream of mpt83 and of Rv2874 genes.

Molecular analysis ofMycobacterium tuberculosis phosphate specific transport system in Mycobacterium smegmatis. Characterization of recombinant 38 kDa (PstS-1)

The functionality of the putative Mycobacterium tuberculosis phosphate transport operon was studied by operon- lacZ promoterless fusions in Mycobacterium smegmatis. The expression of the operon genes was evaluated in transformed M. smegmatis growing in medium with low and high phosphate concentration. Although the gene fusions expressed beta-galactosidase in medium with phosphate, a higher activity was detected in bacteria growing in medium with low phosphate. In contrast, alkaline phosphatase activity from M. smegmatis was detected only in bacteria growing in medium with low phosphate. The expression of the operon genes was driven by a promoter located 5' upstream from the start codon of the pstB gene. A second putative internal promoter 5' upstream of the pstS-1 gene was also detected. Furthermore, comparative analysis between the native and recombinant PstS-1 proteins showed that they were very similar. Like the native protein, the recombinant protein was also secreted to the culture medium as a glycosylated band. The results show that M. smegmatis recognized phosphate regulatory signals of the M. tuberculosis phosphate transport operon genes, and open the possibility to study gene phosphate regulation in mycobacteria.

Binding and activation of human plasminogen by Mycobacterium tuberculosis

The first evidence of the interaction of Mycobacterium tuberculosis with the plasminogen system is herein reported. By FACScan analysis and affinity blotting, lysine-dependent binding of plasminogen to M. tuberculosis was demonstrated. The binding molecules were 30-, 60-, and 66-kDa proteins present in cell wall and soluble protein extracts. The activation of plasminogen, which occurred only in presence of fibrin and was not inhibited by the host serpin, alpha(2)-antiplasmin, was also demonstrated.

Co-stimulatory signals increase the reactivity of gammadelta T cells towards mycobacterial antigens

Although it has been shown that gammadelta T lymphocytes are able to react with different cell-associated or soluble antigens, the immune repertoire of these cells appears to be skewed to the recognition of mycobacterial antigens. We have studied the number and reactivity of gammadelta T cells towards several mycobacterial antigens in patients with tuberculosis and leprosy, as well as their healthy contacts and control individuals. We found an increased number of Vdelta2+ cells in healthy contacts (PPD+ and lepromin+) and tuberculoid leprosy patients. The gammadelta T cells from lepromatous leprosy showed a decreased response to all antigens tested, but some of these patients exhibited a significant response to the 30-kD glycoprotein of Mycobacterium tuberculosis. Interestingly, the reactivity of gammadelta T cells against mycobacterial antigens was significantly increased by costimulatory signals generated through CD7, LFA-1, CD50 and CD69 in all groups. However, signalling through CD69 did not enhance the responsiveness of gammadelta lymphocytes from lepromatous patients. On the other hand, the in vitro blockade of IL-10 with a specific antibody enhanced the cell proliferation of gammadelta lymphocytes from lepromatous leprosy patients, whereas exogenous IL-10 had an opposite effect in most individuals studied. These results suggest the potential role of different cell membrane receptors in the regulation of gammadelta T cell proliferation induced by mycobacteria, as well as the possible involvement of IL-10 in this phenomenon.

Evaluation of the polymerase chain reaction for the detection of Mycobacterium tuberculosis

The development of nucleic acid-based technologies has improved the sensitivity, specificity and speed of detection of Mycobacterium tuberculosis in clinical samples. Both commercially available and 'in-house' polymerase chain reaction (PCR) systems are in use, and a significant number of reports compare such systems with more traditional diagnostic tools for tuberculosis. Few studies, however, have focused on the reproducibility of the results when submitting a sample batch to PCR in different laboratories, especially in developing countries. Consequently, PCR results obtained from six laboratories in six different Latin American countries for samples reconstituted with defined amounts of M. tuberculosis cells were evaluated. Each laboratory used specific conditions of sample processing, nucleic acid amplification and amplicon detection. Analysis of results allowed large differences in sensitivity and specificity to be observed. We conclude that in its present setting, in-house PCR cannot be used as a single diagnostic tool for tuberculosis, and that special care needs to be taken upon interpretation of results by inclusion of a proper number of positive and negative controls.

A novel 27 kDa lipoprotein antigen from Mycobacterium bovis

A novel Mycobacterium bovis antigen was identified from an expression library using sera from naturally infected cattle. The Escherichia coli recombinant clone expressed a 27 kDa protein, named P27. A rabbit serum against the recombinant antigen recognized a protein of 27 kDa in cellular extracts from M. bovis and M. tuberculosis. No protein was recognized in the culture supernatant. Sequence analysis indicated that P27 has a molecular mass of 24 kDa, showing a characteristic signal sequence for lipoprotein modification (a signal peptidase type II site). The gene is identical to a gene identified in the M. tuberculosis genome sequencing project. Cellular fractionation experiments suggested that P27 is an integral membrane protein. The antigen was recognized by individual sera and peripheral blood mononuclear cells (PBMC) from diseased cattle. PCR experiments with specific primers directed to the P27 structural gene indicated that it is only present in the M. tuberculosis species complex. In conclusion, a novel immunogenic lipoprotein in M. bovis/M. tuberculosis has been identified. The results presented here and elsewhere suggest that mycobacterial lipoproteins should be considered in the design of new recombinant vaccines and diagnostic methods.

Human CD4-CD8- alpha beta + T-cell receptor T cells recognize different mycobacteria strains in the context of CD1b

Double-negative alpha beta+ T-cell receptor (TCR) human T cells have been reported to recognize antigen in the context of the HLA class I-like (Ib) CD1 complex. In particular, the CD1b molecule has been shown to act as the element of genetic restriction for antigens derived from Mycobacterium tuberculosis. The stenotopic nature of these major histocompatibility complex (MHC) class Ib molecules raised the question of whether the antigenic moiety recognized by CD4-CD8- alpha beta+ TCR T cells was shared by different mycobacteria. We demonstrate here that a CD4-CD8- alpha beta+ TCR T-cell line and three clones raised against M. tuberculosis proliferated following stimulation with soluble extracts from organisms of the M. tuberculosis complex, M. leprae and 10 out of 16 tested isolates of M. avium complex; however, four species of weakly or non-pathogenic mycobacteria were not stimulatory. Furthermore, the M. tuberculosis soluble extract (MTSE)-derived, recognized antigenic moiety proved to be proteinase K resistant and to have a molecular weight greater than 5000 MW, thus it differed from the reported antigenic moiety, recognized by CD4-CD8- gamma delta+ TCR cells. Our results suggest that a common antigenic moiety, presented by CD1b molecules to CD4-CD8- alpha beta+ TCR T cells, is shared by many mycobacterial species. Therefore they raise interest in the question of whether CD4-CD8- alpha beta+ TCR T cells, elicited by M. tuberculosis, may play a role in the natural history of other mycobacterial infections.

Antigenic and structural similarities between Mycobacterium tuberculosis 50- to 55-kilodalton and Mycobacterium bovis BCG 45- to 47-kilodalton antigens

The relationship between Mycobacterium tuberculosis 50- to 55-kDa protein and Mycobacterium bovis BCG 45- to 47-kDa antigen was examined by using immunological and biochemical criteria. Reciprocal cross-reactivity with a rabbit polyclonal antiserum against the M. bovis BCG protein and with a monoclonal antibody raised against the M. tuberculosis antigen was observed. The epitope recognized by this antibody was apparently present only in proteins of M. tuberculosis and M. bovis BCG among the 11 mycobacterial species tested. The amino-terminal sequences and total amino acid contents of these proteins showed strong similarities. Both antigens are glycoproteins as assessed by binding of concanavalin A, labeling of carbohydrate moieties with biotin-hydrazide, and digestion of carbohydrates with jack bean alpha-D-mannosidase, which produced a reduction of the molecular weights of the proteins and totally eliminated concanavalin A binding. Both M. tuberculosis and M. bovis BCG proteins are secreted, since they were found mainly in the culture medium. Analysis of M. tuberculosis 50- to 55-kDa antigen by two-dimensional gel electrophoresis showed at least seven different components, as previously described for the M. bovis BCG antigen. Solid-phase immunoassays showed that the purified M. tuberculosis 50- to 55-kDa protein was recognized by serum specimens from 70% of individuals with pulmonary tuberculosis from a total of 77 Mexican patients examined.

Raised agalactosyl IgG and antimycobacterial humoral immunity in Takayasu's arteritis

OBJECTIVE

Takayasu's arteritis is an inflammatory occlusive disease of the aorta and its main branches of unknown etiology. Some suggested causes include inapparent infection with Mycobacterium tuberculosis, or autoimmunity evoked by this organism. We have therefore sought links with mycobacterial disease.

METHODS

We assayed the % agalactosyl IgG, antibody to a tuberculosis-specific 38 kDa protein, and antibody to the mycobacterial 65 kDa heat shock protein (HSP), in patients with active or inactive Takayasu's arteritis, in whom the diagnosis of tuberculosis was excluded. The results were compared with findings in tuberculosis (positive controls), normal donors and patients with Wegener's granulomatosis.

RESULTS

The % agalactosyl IgG in patients with active arteritis was in the range previously seen only in rheumatoid arthritis, Crohn's disease, and the mycobacterioses. Similarly, significantly raised antibody to the purified 38-kDa protein of M. tuberculosis, and to the 65-kDa HSP of M. leprae, was found in 78% of patients with Takayasu's arteritis, and the levels were higher in those with active disease.

CONCLUSION

These results suggest that Takayasu's arteritis particularly clearly illustrates the occasional relationship between mycobacteria and diseases of superficially autoimmune pathogenesis.

[Takayasu's arteritis. A seroimmunological test of its relationship to mycobacterial infection]

Takayasu's arteritis is an inflammatory arteritis of unknown origin. It affects the aorta, its main branches and at times the pulmonary artery. Takayasu's arteritis is a worldwide disease, however, there is predilection to affect young women of mongoloid ancestry, therefore most cases do occur in the Far East and Latin America. For more than 50 years a relationship with mycobacterial infection has been sought without definite proof. In this investigation we found a circulating IgG antibody in the sera of Takayasu's arteritis patients, which recognizes a 38 kD glycoprotein of M. tuberculosis. This glycoprotein is an specific antigen in the human immune response against mycobacterial infection.

Phosphate starvation enhances expression of the immunodominant 38-kilodalton protein antigen of Mycobacterium tuberculosis: demonstration by immunogold electron microscopy

In this work, we grew Mycobacterium tuberculosis in an enriched Proskauer-Beck-Youmans culture medium in the presence and in the absence of phosphate salts. Immunoblot analysis of sonic extracts showed overexpression of the 38-kDa protein antigen by bacilli grown in the medium without phosphate. These observations were confirmed by immunogold electron microscopy, which showed that the number of gold particles was significantly higher in bacilli grown in medium without phosphate than in bacilli grown in medium with phosphate. The 38-kDa protein was located mainly in the wall and on the cell surface.

High antibody levels to the mycobacterial fibronectin-binding antigen of 30-31 kD in tuberculosis and lepromatous leprosy

Immunoblot assays showed that mycobacterial fibronectin-binding antigens are important targets of the humoral immune response in tuberculosis and leprosy. Using culture filtrate antigens of Mycobacterium tuberculosis, strong reactivity with the fibronectin-binding of 30-31 kD (Fn 30-31) was demonstrated in 55.9% of tuberculosis sera and in 56.5% of lepromatous leprosy sera. Sera from patients with tuberculoid leprosy and control sera gave very weak binding. Reactivity of tuberculosis and lepromatous leprosy sera with the fibronectin-binding antigen of 58-60 kD (Fn 58-60) was less conspicuous. The ability to react with fibronectin of the antigens of 58-60 and 30-31 kD was demonstrated by parallel labelling with a fibronectin-biotin conjugate. Fn 30-31 was purified to homogeneity by a two-step procedure and used for ELISA. Positive titres were found in 63% out of 65 tuberculosis sera and in 60.5% out of 43 lepromatous leprosy sera. Antibody titres in lepromatous leprosy sera were higher than in tuberculosis sera. Our observations indicate indirectly that M. leprae possess a highly immunogenic molecule homologous to M. tuberculosis Fn 30-31, which elicits a high antibody response in lepromatous leprosy but not in tuberculoid leprosy. In this investigation, direct evidence for the presence of this antigen in M. leprae was obtained by immunochemistry of lepromatous leprosy lesions with a monospecific antibody raised against M. tuberculosis Fn 30-31.

The antigenic structure of Mycobacterium tuberculosis examined by immunoblot and ELISA. Influence of the age of the culture and of the obtaining method on the composition of the antigenic extracts

In this study we have examined by immunoblot (IB) and enzyme-linked immunosorbent assay (ELISA) the humoral immune response in pulmonary tuberculosis. As a previous step, in an attempt to obtain the optimal antigen preparation for these studies, the influence of the culture age and of the obtention method on the composition of the extracts was analyzed. The highest number of antigenic bands was found in culture filtrates of 6 and 8 weeks; at these times two thick bands of 65 and 63 kilodaltons (kDa) were identified. These bands were absent from younger and older cultures. When analyzing the source of antigens, we found that culture filtrates contained more antigenic bands than sonic extracts. In view of these findings, culture filtrates of 6 weeks of age were used as test antigens. With 19 tuberculous sera a total of 16 antigenic bands were observed by IB. The response was very heterogeneous with respect to the intensity of the detected reactions and the number of reacting bands. The most frequently recognized bands were those of 31, 32, 38, 58 and 94 kDa. By ELISA with 49 tuberculous sera and with 48 control sera, a specificity of 0.98 and a sensitivity of 0.70 were obtained.

Identification, isolation and partial characterization of Mycobacterium tuberculosis glycoprotein antigens

In Mycobacterium tuberculosis culture filtrates, three concanavalin A (ConA)-binding bands of 55, 50 and 38 kilodaltons (kD) were identified by labelling blotted proteins with a ConA-peroxidase conjugate. Binding was inhibited by the competitor sugar alpha-methyl mannoside and by reduction with sodium m-periodate. Bands of 55, 50 and 38 kD stained with Coomasie blue were sensitive to digestion with proteases, thus indicating that they are proteins. Glycoproteins were isolated by lectin affinity chromatography or by elution from nitrocellulose membranes. On the isolated form, the 55-50 kD doublet glycoprotein was 65.4% protein and 34.6% sugar. The purified 38 kD molecule was 74.3% protein and 25.7% carbohydrate. By immunoblot, antibodies against mycobacterial glycoproteins were demonstrated in immunized rabbits and in patients with pulmonary tuberculosis, but not in healthy individuals. Treatment with sodium m-periodate abolished binding of rabbit antibodies to the 38 kD glycoprotein. Reactivity of the 55-50 kD doublet glycoprotein was not altered by reduction. By immunoblot with monoclonal antibodies TB71 and TB72, a carbohydrate-dependent and a carbohydrate-independent epitope could be identified on the 38 kD glycoprotein.

A 38-kD Mycobacterium tuberculosis antigen associated with infection. Its isolation and serologic evaluation

To identify antigens that could be specifically associated with tuberculosis infection, the antibody response to Mycobacterium tuberculosis antigens of patients with pulmonary tuberculosis and of healthy individuals were compared by immunoblot. In healthy individuals, serum antibodies were found in the majority of cases. Bands of 60 and 32-31 kilodaltons (kD) were the antigens more frequently recognized by antibodies of normal sera (55.8 and 64.7%, respectively). In patients with pulmonary tuberculosis, the number and intensity of the developed antigen bands were much higher than in normal individuals. Antigens reacting preferentially with tuberculosis sera were also identified. Furthermore, a unique disease-associated protein antigen of 38 kD was found to react with 57% of patients' sera but with none of the controls. This antigen was isolated by elution from nitrocellulose membranes and tested as an ELISA reagent in the serodiagnosis of pulmonary tuberculosis. A specificity of 0.96 and sensitivity of 0.68 were obtained.