Subcellular distribution of monoclonal antibody defined epitopes on immunodominant Mycobacterium tuberculosis proteins in the 30-kDa region: identification and localization of 29/33-kDa doublet proteins on mycobacterial cell wall

Mechanical Forces between Mycobacterial Antigen 85 Complex and Fibronectin

Adhesion to extracellular matrix proteins is an important first step in host invasion, employed by many bacterial pathogens. In mycobacteria, the secreted Ag85 complex proteins, involved in the synthesis of the cell envelope, are known to bind to fibronectin (Fn) through molecular forces that are currently unknown. In this study, single-molecule force spectroscopy is used to study the strength, kinetics and thermodynamics of the Ag85-Fn interaction, focusing on the multidrug-resistant Mycobacterium abscessus species. Single Ag85 proteins bind Fn with a strength of ~75 pN under moderate tensile loading, which compares well with the forces reported for other Fn-binding proteins. The binding specificity is demonstrated by using free Ag85 and Fn peptides with active binding sequences. The Ag85-Fn rupture force increases with mechanical stress (i.e., loading rate) according to the Friddle–Noy–de Yoreo theory. From this model, we extract thermodynamic parameters that are in good agreement with previous affinity determinations by surface plasmon resonance. Strong bonds (up to ~500 pN) are observed under high tensile loading, which may favor strong mycobacterial attachment in the lung where cells are exposed to high shear stress or during hematogenous spread which leads to a disseminated infection. Our results provide new insight into the pleiotropic functions of an important mycobacterial virulence factor that acts as a stress-sensitive adhesin.

Processing of Mycobacterium tuberculosis antigen 85B involves intraphagosomal formation of peptide-major histocompatibility complex II complexes and is inhibited by live bacilli that decrease phagosome maturation

Mycobacterium tuberculosis (MTB) inhibits phagosomal maturation to promote its survival inside macrophages. Control of MTB infection requires CD4 T cell responses and major histocompatibility complex (MHC) class II (MHC-II) processing of MTB antigens (Ags). To investigate phagosomal processing of MTB Ags, phagosomes containing heat-killed (HK) or live MTB were purified from interferon-gamma (IFN-gamma)-activated macrophages by differential centrifugation and Percoll density gradient subcellular fractionation. Flow organellometry and Western blot analysis showed that MTB phagosomes acquired lysosome-associated membrane protein-1 (LAMP-1), MHC-II, and H2-DM. T hybridoma cells were used to detect MTB Ag 85B(241-256)-I-A(b) complexes in isolated phagosomes and other subcellular fractions. These complexes appeared initially (within 20 min) in phagosomes and subsequently (>20 min) on the plasma membrane, but never within late endocytic compartments. Macrophages processed HK MTB more rapidly and efficiently than live MTB; phagosomes containing live MTB expressed fewer Ag 85B(241-256)-I-A(b) complexes than phagosomes containing HK MTB. This is the first study of bacterial Ag processing to directly show that peptide-MHC-II complexes are formed within phagosomes and not after export of bacterial Ags from phagosomes to endocytic Ag processing compartments. Live MTB can alter phagosome maturation and decrease MHC-II Ag processing, providing a mechanism for MTB to evade immune surveillance and enhance its survival within the host.

Identification of mycobacterial surface proteins released into subcellular compartments of infected macrophages

Considerable effort has focused on the identification of proteins secreted from Mycobacterium spp. that contribute to the development of protective immunity. Little is known, however, about the release of mycobacterial proteins from the bacterial phagosome and the potential role of these molecules in chronically infected macrophages. In the present study, the release of mycobacterial surface proteins from the bacterial phagosome into subcellular compartments of infected macrophages was analyzed. Mycobacterium bovis BCG was surface labeled with fluorescein-tagged succinimidyl ester, an amine-reactive probe. The fluorescein tag was then used as a marker for the release of bacterial proteins in infected macrophages. Fractionation studies revealed bacterial proteins within subcellular compartments distinct from mycobacteria and mycobacterial phagosomes. To identify these proteins, subcellular fractions free of bacteria were probed with mycobacterium-specific antibodies. The fibronectin attachment protein and proteins of the antigen 85-kDa complex were identified among the mycobacterial proteins released from the bacterial phagosome.

The capsule of Mycobacterium tuberculosis and its implications for pathogenicity

Mycobacterium tuberculosis, one of the most prevalent causes of death worldwide, is a facultative intracellular parasite that invades and persists within the macrophages. Within host cells, the bacterium is surrounded by a capsule which is electron-transparent in EM sections, outside the bacterial wall and plasma membrane. Although conventional processing of samples for microscopy studies failed to demonstrate this structure around in vitro-grown bacilli, the application of new microscopy techniques to mycobacteria allows the visualization of a thick capsule in specimen from axenic cultures of mycobacteria. Gentle mechanical treatment and detergent extraction remove the outermost components of this capsule which consist primarily of polysaccharide and protein, with small amounts of lipid. Being at the interface between the bacterium and host cells, the capsule and its constituents would be expected to be involved in bacterial pathogenicity and past work supports this concept. Recent studies have identified several capsular substances potentially involved in the key steps of pathogenicity. In this respect, some of the capsular glycans have been shown to mediate the adhesion to and the penetration of bacilli into the host's cells; of related interest, secreted and/or surface-exposed enzymes and transporters probably involved in intracellular multiplication have been characterized in short-term culture filtrates of M. tuberculosis. In addition, the presence of inducible proteases and lipases has been shown. The capsule would also represent a passive barrier by impeding the diffusion of macromolecules towards the inner parts of the envelope; furthermore, secreted enzymes potentially involved in the detoxification of reactive oxygen intermediates have been identified, notably catalase/peroxidase and superoxide dismutase, which may participate to the active resistance of the bacterium to the host's microbicidal mechanisms. Finally, toxic lipids and contact-dependent lytic substances, as well as constituents that inhibit both macrophage-priming and lymphoproliferation, have been found in the capsule, thereby explaining part of the immunopathology of tuberculosis.

Activation of Human CD8+ αβ TCR+ Cells by Mycobacterium tuberculosis Via an Alternate Class I MHC Antigen-Processing Pathway

Human immune responses to M. tuberculosis are characterized by activation of multiple T cell subsets including CD4+, CD8+, and γδ T cells, and the role of CD8+ αβ TCR+ T cells in this response is poorly understood. Stimulation of T cells from healthy tuberculin skin test-positive persons with live M. tuberculosis-H37Ra or soluble M. tuberculosis Ags readily up-regulated IL-2Rα (CD25) expression on CD8+ T cells. Purified resting and activated CD8+ T cells produced IFN-γ and proliferated to both M. tuberculosis bacilli and soluble mycobacterial Ags with monocytes as APC. Precursor frequency of mycobacterial Ag-specific CD8+ T cells by IFN-γ enzyme-linked immunospot was 5–10-fold lower than the precursor frequency of CD4+ T cells, and IFN-γ secretion by CD8+ T cells was 50–100-fold lower. CD8+ T cells secreted ∼10-fold less IFN-γ per cell than CD4+ T cells in response to mycobacterial Ags. CD8+ T cell responses to M. tuberculosis bacilli were blocked by anti-MHC class I antibody and required Ag processing. Processing of M. tuberculosis bacilli by monocytes for presentation to MHC class I-restricted CD8+ T cells was insensitive to brefeldin A treatment, which blocks the conventional MHC class I Ag-processing pathway. These results represent the first demonstration that human cells can process pathogen Ags via an alternate Ag-processing pathway for MHC class I and suggest a mechanism for participation of IFN-γ-secreting CD8+ T cells in the human immune responses to M. tuberculosis.

The envelope layers of mycobacteria with reference to their pathogenicity

The review discusses current knowledge of the biosynthesis, composition and arrangement of the mycobacterial envelope, describes the biological activities of the constituents and considers how these activities may be relevant to the pathology of mycobacterial disease. The envelope possesses three structural components: plasma membrane, wall and capsule. Although the major biomolecules occurring in each of these parts are known, the distribution of numerous minor substances is poorly understood; an attempt has been made to assign them to particular positions on rational grounds. The plasma membrane appears to be a typical bacterial membrane but, though vital to the mycobacterium, probably plays little part in pathological processes. The wall partly resembles a Gram-positive wall, but is unusual in having a layer of lipid (mycolate esters) which is probably arranged to form a permeability barrier to polar molecules. The capsule, whose chemical composition has only recently been recognized, consists of polysaccharide and protein with traces of lipid; the arrangement of these components is imperfectly understood. Constituents of all parts of the envelope have biological activities which may be relevant. The likely importance of these activities in the overall effect of the envelope is considered.

Comparative analysis of subcellular distribution of protein antigens in Mycobacterium bovis bacillus Calmette-Guérin

The distribution of protein antigens in purified subcellular fractions of Mycobacterium bovis bacillus Calmette-Guérin (BCG) was comparatively analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting with specific monoclonal antibodies and polyclonal sera. The 19- and 38-kDa lipoproteins were mainly detected in the cell wall and cell membrane enriched fractions, and they were extracted from the former by Triton X-114 and Nonidet P-40. The 65-kDa heat-shock protein (hsp) was present in the cytoplasmic fraction and only trace amounts were found in the crude cell wall preparation. In contrast, the 14-kDa hsp was highly represented in the cell wall fraction, besides being present in cytoplasmic fraction. Both superoxide dismutase (SOD) and antigen 85 complex (Ag 85) were abundantly released in culture medium, and to a lower extent, they were present in the cell wall fraction; SOD was present in comparable amounts also in the cytoplasmic fraction, while Ag 85 was far less represented in the same. Sera from mice immunized with culture filtrate (CF) proteins of BCG recognized several antigens in CFs, which were not detectable in cell wall, cell membrane, and cytoplasmic fractions, indicating that CF proteins include secreted antigens which have not yet been identified.

Monoclonal antibodies to P24 and P61 immunodominant antigens from Nocardia brasiliensis

We prepared a Nocardia brasiliensis cell extract and purified two immunodominant antigens with molecular weights of 61,000 and 24,000. The isolated proteins were shown to be reasonably pure when analyzed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (8 to 18% polyacrylamide gradient) and stained with Coomassie blue and silver nitrate. By using an immunoelectrotransfer blot method (Western blotting), we demonstrated that these two purified proteins reacted strongly with serum from N. brasiliensis-infected mycetoma patients. To obtain anti-P61 and anti-P24 monoclonal antibodies (MAbs), we used an N. brasiliensis cell extract as the antigen for the first immunization; 2 weeks later female mice were reimmunized with a semipurified antigen containing the P24 or P61 fraction. A booster injection was given 3 days before the fusion was carried out. Two hybrids that reacted strongly with P24 were cloned by limiting dilution, the generated MAbs were analyzed for isotyping, and their specificity was tested in a Western blot assay with cell extracts from Nocardia asteroides and Mycobacterium tuberculosis cultures. Anti-P24 MAbs were shown to be specific for N. brasiliensis HUJEG-1 and did not cross-react with either the N. asteroides or M. tuberculosis strains used. However, additional studies with several N. asteroides and N. brasiliensis strains are needed to investigate whether there are cross-reactions between strains or species when these MAbs are used. The anti-P61 and anti-24 MAbs were used to locate the antigen in N. brasiliensis cells by immunofluorescence. The lack of reaction with intact cells suggests that the P24 and P61 antigens are not exposed in the complete bacterial cell surface or that the recognized epitopes are different. Only one anti-P61 MAb that reacted specifically with the N. brasiliensis cell extract was obtained.

Effect of intestinal resection on serum antibodies to the mycobacterial 45/48 kilodalton doublet antigen in Crohn's disease

Interest in the role of mycobacterial infection in Crohn's disease has been revived by the cultural detection of Mycobacterium paratuberculosis in patients with Crohn's disease. This hypothesis was examined serologically using assays with high specificity for Crohn's disease. The effect of intestinal resection on serum antibodies specific for Crohn's disease was investigated with an immunoblot assay and an enzyme linked immunosorbent assay using the 45/48 kilodalton doublet antigen of Mycobacterium tuberculosis. Antibodies were detected in 64.7% of patients with Crohn's disease (n = 17), 10% of patients with ulcerative colitis (n = 10), 5% of patients with carcinoma of the colon (n = 20), and none of 10 healthy subjects with the immunoblot assay. Statistical comparison of the Crohn's disease patients with each control group resulted in p = 0.0000236. Immunoglobulin G was essentially unchanged 75 days (mean) after surgery. After more than 180 days, however, the antibody response was reduced in all of five patients studied, and was no longer demonstrable in two of them (40%). Simultaneously, the Crohn's disease activity index (CDAI) decreased. Both the high specificity of this assay for Crohn's disease and the diminished antibody response after intestinal resection in parallel with decreased CDAI support a mycobacterial aetiology of Crohn's disease.

Characterization of a 10- to 14-kilodalton protease-sensitive Mycobacterium tuberculosis H37Ra antigen that stimulates human gamma delta T cells

gamma delta T-cell receptor-bearing T cells (gamma delta T cells) are readily activated by intracellular bacterial pathogens such as Mycobacterium tuberculosis. The bacterial antigens responsible for gamma delta T-cell activation remain poorly characterized. We have found that heat treatment of live M. tuberculosis bacilli released into the supernatant an antigen which stimulated human gamma delta T cells. gamma delta T-cell activation was measured by determining the increase in percentage of gamma delta T cells by flow cytometry in peripheral blood mononuclear cells stimulated with antigen and by proliferation of gamma delta T-cell lines with monocytes as antigen-presenting cells. Supernatant from heat-treated M. tuberculosis was fractionated by fast-performance liquid chromatography (FPLC) on a Superose 12 column. Maximal gamma delta T-cell activation was measured for a fraction of 10 to 14 kDa. Separation of the supernatant by preparative isoelectric focusing demonstrated peak activity at a pI of < 4.0. On two-dimensional gel electrophoresis, the 10- to 14-kDa FPLC fraction contained at least seven distinct molecules, of which two had a pI of < 4.5. Protease treatment reduced the bioactivity of the 10- to 14-kDa FPLC fraction for both resting and activated gamma delta T cells. Murine antibodies raised to the 10- to 14-kDa fraction reacted by enzyme-linked immunosorbent assay with antigens of 10 to 14 kDa in lysate of M. tuberculosis. In addition, gamma delta T cells proliferated in response to an antigen of 10 to 14 kDa present in M. tuberculosis lysate. gamma delta T-cell-stimulating antigen was not found in culture filtrate of M. tuberculosis but was associated with the bacterial pellet and lysate of M. tuberculosis. These results provide a preliminary characterization of a 10- to 14-kDa, cell-associated, heat-stable, low-pI protein antigen of M. tuberculosis which is a major stimulus for human gamma delta T cells.

Isolation of a 32 kDa Mycobacterium tuberculosis protein by lectin affinity chromatography

A 32 kDa antigen from delipidated M. tuberculosis H37Rv culture filtrate protein extract (CFPE) was purified by affinity chromatography on immobilized Lens culinaris lectin and electroelution. This antigen represents 0.4% of the total CFPE carbohydrate content and possesses galactose, xylose, mannose and GlcNAc (5:2:3:1 mol. ratio). A monoclonal antibody against the purified antigen reacted with the 32 kDa as well as a 30 kDa antigen in H37Rv CFPE, thus suggesting that both antigens represent closely related allelomorphic forms of the same antigen.

The mycobacterial secreted antigen 85 complex possesses epitopes that are differentially expressed in human leprosy lesions and Mycobacterium leprae-infected armadillo tissues

The granulomatous skin lesions in leprosy are thought to be initiated by the immune response to certain antigens of the causative agent, Mycobacterium leprae. The antigen 85 complex is one of the major targets in the immune response to M. leprae infection. In the present study, a panel of previously characterized monoclonal antibodies (MAbs) (3A8, Rb2, A4g4, A2h11, Pe12, and A3c12) reacting with different epitopes of the 85 complex proteins of Mycobacterium tuberculosis and M. leprae was employed in a comparative immunohistological analysis to demonstrate the in situ expression of 85 complex antigenic epitopes in leprosy lesions across the clinical spectrum and in M. leprae-infected armadillo liver tissues. These MAbs showed a heterogeneous staining pattern in a given leprosy lesion. In highly bacilliferous borderline and lepromatous leprosy lesions, MAbs Rb2, A4g4, A2h11, and Pe12 stained clear rod-shaped M. leprae bacilli within macrophages, and the degree of staining correlated with the bacillary index of the lesion. On the other hand, MAbs 3A8 and A3c12 staining was mostly seen as a diffuse staining pattern within interstitial spaces and on the membranes of the infiltrated cells but not the bacilli. In paucibacillary borderline and tuberculoid leprosy lesions, only 3A8, Rb2, and A3c12 showed distinct staining in association with infiltrates in the granuloma. None of these MAbs showed any detectable reaction with control nonleprosy skin lesions, while MAb A3c12 positively stained the granulomas of both leprosy and control specimens. In situ reactivity of these MAbs with M. leprae-infected armadillo liver tissues also showed a heterogeneous staining pattern. Interestingly, a clear difference in expression of these epitopes was observed between armadillo tissues and human leprosy lesions. By immunogold ultracytochemistry, we further showed the differential localization of these MAb-reactive epitopes on the cell surface, in the cytosol, and at the vicinity of M. leprae within Kupffer cells of armadillo liver tissues. Our results indicate that these antigenic epitopes of the antigen 85 complex are differentially expressed in leprosy lesions and infected armadillo tissues and that they could be target determinants in the immunopathological responses during M. leprae infection.

Identification of a novel 27-kDa protein from Mycobacterium tuberculosis culture fluid by a monoclonal antibody specific for the Mycobacterium tuberculosis complex

Mycobacterium tuberculosis antigens inducing species-specific immune responses are likely to be particularly important for serodiagnosis or for skin testing of tuberculosis. In the present study, we describe the characterization of two novel monoclonal antibodies (MoAbs) A3h4 (IgG2a) and B5g1 (IgM) that are directed to M. tuberculosis 27-kDa and 25-kDa proteins respectively. Specificity analysis by immunoblotting using 20 different species of mycobacterial sonicates revealed that MoAb A3h4 was specific for M. tuberculosis complex alone while MoAb B5g1 showed a limited cross-reactivity. Direct comparison with previously characterized MoAbs revealed that these MoAbs A3h4 and B5g1 defined new antigenic determinants of M. tuberculosis. By using M. tuberculosis complex-specific MoAb A3h4 we have identified a distinct 27-kDa protein in the M. tuberculosis H37Rv culture fluid. Since this MoAb did not bind to the previously characterized MPT44, MPT59, MPT45, MPT51 and MPT64 proteins as well as the 23-kDa superoxide dismutase (SOD) protein of M. tuberculosis, we conclude that MoAb A3h4 recognizes a novel protein in the M. tuberculosis H37Rv culture fluid. Studies of the subcellular distribution of these MoAb-reactive proteins indicate that the MoAb A3h4-reactive 27-kDa protein is present not only in the culture fluid but also in the cytosol and the cell wall of M. tuberculosis. By contrast, B5g1-reactive protein is mainly a cytosolic protein. When these MoAbs were tested in a previously established ELISA with intact mycobacteria derived from early cultures, only MoAb A3h4 showed the positive reactivity to mycobacteria belonging to the M. tuberculosis complex. In addition, during the present comparative studies of MoAbs we have also found that the previously described MoAb F116-5, which is known to recognize the mycobacterial 23-kDa SOD protein [17], cross-reacted with the MPT44, MPT59, MPT45 and MPT51 secreted proteins but not with MPT64 and MPB70. These findings indicate that the family of four secreted proteins of M. tuberculosis share a common epitope with M. tuberculosis SOD protein.

Antibodies to mycobacterial 65-kDa heat shock protein and other immunodominant antigens in patients with psoriasis

An association of microbial agents and autoimmunity has been suggested for the pathogenesis of psoriasis. Mycobacteria are common environmental microbes and their antigens, especially the highly conserved mycobacterial 65-kDa heat shock protein (hps65), have been implicated in the pathogenesis of autoimmune arthritis and other idiopathic diseases. In this context, we investigated a possible mycobacterium-induced humoral immune response in psoriasis. Sera from 17 patients with chronic plaque-type psoriasis were studied by immunoblotting using the whole sonicate of Mycobacterium tuberculosis and purified recombinant mycobacterial hsp65. Immunoblot analysis demonstrated that 58% of the psoriasis patients compared to patients with acne and DLE, and normal controls showed strong antibody activity to 65-kDa and 48/45 doublet antigens from M. tuberculosis sonicate, whereas 47% of the patients showed antibody activity to mycobacterial hsp65. Only 10-20% of the patients had an antibody response to 16-kDa and 80-kDa antigens. Similar antibody activity to 65 kDa and 48/45 kDa was also found consistently with eight different sonicated mycobacterial species by immunoblotting, indicating that these seroreactive antigens are crossreactive and are present in common environmental mycobacteria. Antibody activities to both mycobacterial 65-kDa and hsp65 showed a positive correlation (r = 0.76) with the psoriasis disease activity, whereas antibodies to 48/45-kDa doublet antigens showed a weak correlation (r = 0.54). By enzyme-linked immunosorbent assay (ELISA), 47% of the psoriasis patients showed significantly elevated antibody titers to hsp65 (p < 0.003) as compared to control groups, and the antibody response by ELISA also showed a significant positive correlation (r = 0.76) with disease activity. Anti-mycobacterial antibody activity may be related to severity of disease and may be useful in monitoring disease activity in psoriasis.

Heterogeneity of monoclonal antibody-reactive epitopes on mycobacterial 30-kilodalton-region proteins and the secreted antigen 85 complex and demonstration of antigen 85B on the Mycobacterium leprae cell wall surface

Proteins of the antigen 85 complex in the 30-kDa region secreted by live mycobacteria are important in the immune response against mycobacterial infections and may play an important biological role in the host-parasite interaction. In the present study, we have characterized epitopes of the 30-kDa-region proteins and the antigen 85 complex by using a panel of 13 monoclonal antibodies (MAbs) reacting with these antigens, 6 of which have not been described before. By using five previously characterized related secreted proteins of Mycobacterium tuberculosis, MPT44 (85A), MPT59 (85B), MPT45 (85C), MPT51 (27 kDa), and MPT64 (26 kDa), we have identified at least 10 different MAb-reactive epitopes on the proteins of the antigen 85 complex. A heterogeneous distribution of epitopes was observed within the components of the antigen 85 complex. Two distinct epitopes specific for antigen 85B and two other epitopes restricted to the 85A and 85B components were recognized. Two of them were shared with a previously unidentified 27-kDa protein present in M. tuberculosis culture fluid from which all MPT proteins were derived. The rest of the MAb-reactive epitopes were found to be present mostly in antigens 85A and 85B and to a lesser extent in antigen 85C. None of these MAbs recognized component 85C alone nor did they bind to the related MPT51 and MPT64 proteins. Interestingly, most of the MAbs reacted with purified native proteins of the antigen 85 complex but not to them in their denatured forms. In contrast, reactivity of the MAbs with the cytosol fraction of M. tuberculosis in immunoblotting revealed that they bound to a closely related cytosolic 30-kDa protein(s) even when they were denatured. Heterogeneity of these MAb-reactive epitopes of the antigen 85 complex was further evident as they were found to be distributed in various patterns among 19 different mycobacterial species. By using fusion proteins of the Mycobacterium leprae 30/31-kDa antigen 85 complex, we have localized at least six different epitopes within amino acid residues 55 to 266 of the M. leprae antigen 85 complex. Finally, by immunohistochemical analysis, we have demonstrated the in situ expression of one of the novel MAb-reactive epitopes specific for antigen 85B on the cell wall surface of M. leprae within macrophages in lepromatous leprosy lesions and thus provide direct evidence for the presence of the B component of the antigen 85 complex on the surface of intact M. leprae.

The antigen 85 complex: a major secretion product of Mycobacterium tuberculosis

The large number of different proteins synthesized by the mycobacterial cell are currently classified and studied in terms of groups of proteins with certain common properties such as physical and chemical characteristics, function, and localization in the mycobacterial cell. Proteins that are actively secreted during culture on synthetic media represent a particular group of great current interest. At least eight proteins secreted by Mycobacterium tuberculosis have been isolated and characterized to various extents. The genes coding for five proteins secreted from M. tuberculosis and/or Mycobacterium bovis BCG have been cloned and sequenced. All of them contain typical signal sequences. The proteins of the antigen 85 complex, which form the main subject of this review, are often the most common proteins in M. tuberculosis culture fluid. The constituents denoted 85A, 85B, and 85C are encoded by three genes located at different sites in the mycobacterial genome and show extensive cross-reactivity as well as homology at amino acid and gene levels. The proteins differ slightly in molecular mass in the 30- to 31-kDa region, and all of them are fibronectin-binding proteins, but the significance of the latter observation and the role of these proteins in mycobacterial physiology and interaction with the infected host remain to be elucidated. The antigen 85 complex proteins are strongly immunogenic in natural and experimental mycobacterial infections in terms of both induction of antibody synthesis and T-cell-mediated reactions. The well-recognized difference in the efficacy of live and dead mycobacterial vaccines should be considered in relation to the group of secreted antigens. After inoculation, live bacteria in vaccines such as BCG multiply in the host, probably releasing several constituents belonging to the class of secreted proteins and hence resulting in more efficient stimulation of the immune system. Secreted mycobacterial antigens are expected to be of particular significance in induction of various immune responses that are responsible for development of protective immunity in some individuals and for clinical symptoms and complications of the ensuing disease in others.

Identification and characterization of epitopes shared between the mycobacterial 65-kilodalton heat shock protein and the actively secreted antigen 85 complex: their in situ expression on the cell wall surface of Mycobacterium leprae

Both mycobacterial hsp65 and the actively secreted antigen 85 complex of 30-kDa region proteins are considered to be major immune targets in mycobacterial diseases. In this study, by using a novel series of monoclonal antibodies (MAbs) directed to these antigens, we identified and partially characterized three unique epitopes (Rb2, Pe12, and A2h11) that are shared between mycobacterial hsp65 and the individual components of the antigen 85 complex. Dot blot assays with native purified proteins revealed that all three MAbs are strongly bound to hsp65 and antigens 85A (MPT44) and 85B (MPT59), while a weak reaction or no reaction was found with antigen 85C (MPT45). Immunoblotting showed that MAb Rb2 reacted strongly with both hsp65 and the antigen 85 complex proteins, whereas MAbs Pe12 and A2h11 reacted strongly with the former but weakly with the latter. Moreover, these MAbs did not react with other closely related MPT51 and MPT64 secreted proteins. Further characterization of these epitopes was performed by using recombinant fusion and truncated proteins of Mycobacterium bovis BCG hsp65 (MbaA) and the M. leprae 30- and 31-kDa antigen 85 complex fusion proteins. In hsp65, Rb2-Pe12- and A2h11-reactive epitopes were found to reside in the C-terminal region of amino acid residues 479 to 540 and 303 to 424, respectively. In the M. leprae 30- and 31-kDa antigen 85 complex, all three epitopes were located in an N-terminal region of amino acid residues 55 to 266, one of the known fibronectin-binding sites of the M. leprae antigen 85 complex. Comparison of these MAb-reactive amino acid sequence regions between mycobacterial hsp65 and the components of the antigen 85 complex revealed that these regions show certain amino acid sequence identities. Furthermore, by immunoperoxidase and immunogold ultracytochemistry, we demonstrated that Rb2-, Pe12-, and A2h11-reactive epitopes are expressed both on the cell wall surface and in the cytosol of M. leprae bacilli within the lesions of lepromatous leprosy patients and in M. leprae-infected armadillo liver tissue.

Mycobacterium leprae produces extracellular homologs of the antigen 85 complex

The antigen 85 complex is a set of at least three closely related secreted proteins (85A, 85B, and 85C) of 30 to 32 kDa produced by Mycobacterium tuberculosis and other mycobacteria. Their prominence in Mycobacterium leprae, the one obligate intracellular pathogen of the genus, had been assumed on the basis of immunological evidence and proof of the existence of the gene encoding the 85B protein of the complex. We have now observed the production of this family of proteins by M. leprae through analysis of various fractions by Western blotting (immunoblotting) with monospecific rabbit antisera raised against the individual Mycobacterium bovis BCG 85A, 85B, and 85C proteins. A predominant cross-reactive band with an apparent molecular mass of 30 kDa was detected in extracts of nondisrupted whole M. leprae and in soluble fractions prepared from the tissues of M. leprae-infected armadillos. Further studies of the subcellular distribution of this protein within the bacterium confirmed that it is secreted by the organism, an observation that explains past difficulties in detecting the antigen 85 complex in M. leprae. Confirmation that the M. leprae product is a member of the antigen 85 complex was obtained by comparison of peptide fingerprints with those from the BCG product. The pattern of reactivity of the M. leprae antigen 85 complex with anti-M. bovis BCG 85B serum, as well as two-dimensional electrophoresis, established that the 85B component was the predominant member of the complex in M. leprae. The fibronectin-binding capacity of the M. leprae and BCG 85 complexes was reinvestigated by new approaches and is questioned. Nevertheless, the results obtained with the native proteins reinforce previous reports, derived primarily from the use of homologous proteins, that the antigen 85 complex is one of the dominant protein immunogens of the leprosy bacillus.

Antibodies against secreted and non-secreted antigens in mice after infection with live Mycobacterium tuberculosis

Mice from four different inbred strains were infected with live Mycobacterium tuberculosis and the immune response to M. tuberculosis was followed for 24 weeks, using Western blotting. Nearly all mice, irrespective of H-2 type, reacted with the 38-kDa protein band. Antibodies against this secreted 38-kDa protein were the first to appear, 4 weeks after infection. Thereafter the secreted 19-kDa protein and non-secreted antigens, such as the 65-kDa and 33-kDa proteins, were recognized. The immune response against the non-secreted antigens was influenced by the mouse strain. However, the 33-kDa protein band was recognized by all mouse strains after a second injection with live M. tuberculosis. The specificity of the antibodies was analysed in Western blot using sonicates of M. tuberculosis, M. kansasii, M. avium, M. terrae, M. gordonae and Escherichia coli. Antibodies against the 38-kDa and 33-kDa protein bands seemed to be specific for M. tuberculosis, while antibodies against the 19-kDa protein band showed limited cross-reactivity. Antibodies against the 65-kDa protein were strongly cross-reactive. These results suggest that the 38-kDa protein is secreted in vivo and, therefore, may be available to the humoral immune system at an early stage of infection. The non-secreted 33-kDa protein is only recognized by all mouse strains after prolonged contact with M. tuberculosis.

Association of the mycobacterial 30-kDa region proteins with the cutaneous infiltrates of leprosy lesions. Evidence for the involvement of the major mycobacterial secreted proteins in the local immune response of leprosy

The granulomatous skin lesions of human leprosy are known to be due to the cutaneous immune reaction to various mycobacterial antigens. In the present study, by immunohistochemical analysis using a previously characterized monoclonal antibody (MoAb) 3A8 we have demonstrated a selective expression of the 3A8 epitope of mycobacterial 30-kDa proteins, the major secreted proteins of mycobacteria, in various forms of leprosy lesions across the clinical spectrum. The localization of MoAb 3A8 staining is confined to the areas of cellular infiltrates of the lesions. In tuberculoid lesions the intense 3A8 staining was seen mostly in association with the membrane of the dermal cellular infiltrates whereas in highly bacilliferous lepromatous lesions the staining seems to be diffused with granular appearance but not in the form of bacteria. In patients with reversal reaction the staining was specifically extended to cells infiltrating the epidermis. MoAb 3A8 did not show any reactivity with inflammatory skin lesions of patients other than those with leprosy. Since the 3A8 epitope of 30-kDa proteins has been shown to be present in all cellular compartments of the mycobacteria and in the actively secreted BCG 85 antigen complex, MoAb 3A8 reactive protein(s) in leprosy lesions may be derived either from degraded somatic mycobacterial products or from antigens actively secreted by live bacilli. The latter could be true in the cases of untreated lepromatous lesions with high bacterial load since live M. leprae has also been considered to secrete corresponding 30-kDa proteins similar to other closely related mycobacteria. By double immunoenzyme staining we clearly demonstrate the expression of 3A8 epitope on CD68+ macrophages in the granulomas of tuberculoid leprosy, whereas in highly bacilliferous lepromatous lesions most of the double staining was seen in a diffuse pattern within the interstitial space of the cellular infiltrate as well as in the cytoplasm of CD68+ macrophages. In lesions from reversal reaction the 3A8 epitope is more strongly expressed on CDla+ dendritic Langerhans cells (LC) both in the epidermis and in the dermis as compared with other types of leprosy. This provides evidence for the involvement of LC in handling of mycobacterial antigenic epitopes in leprosy lesions. Further, immunoenzyme double staining revealed that the expression of this mycobacterial 3A8 epitope on antigen presenting cells such as CD68+ macrophages and CDla+ LC is present in juxtaposition with CD3+ T cells including the alpha beta and gamma delta receptor-bearing T cells in the granuloma.(ABSTRACT TRUNCATED AT 400 WORDS)