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

Pathophysiology of antigen 85 in patients with active tuberculosis: antigen 85 circulates as complexes with fibronectin and immunoglobulin G

Antigen 85 (Ag85) complex proteins are major secretory products of Mycobacterium tuberculosis and induce strong cellular and humoral immune responses in infected experimental animals and human beings. We have previously shown that nanogram doses of these 30- to 32-kDa fibronectin-binding proteins inhibit local expression of delayed hypersensitivity by a T-cell fibronectin-dependent mechanism. Circulating levels of Ag85 might be expected to be elevated in patients with active tuberculosis and possibly to play a role in systemic anergy in these patients. To test this hypothesis, Ag85 was measured in serum and urine by a monoclonal antibody-based dot immunobinding assay in 56 patients and controls with known skin test reactivity. Median serum Ag85 levels were 50- to 150-fold higher in patients with active tuberculosis than in patients with active M. avium-intracellulare disease or other nontuberculous pulmonary disease or in healthy controls (P < 0.001). The median and range of serum Ag85 in patients with active tuberculosis was not significantly different between skin test-positive and -negative subjects. Patients with active M. avium disease could be distinguished from those with disease due to M. tuberculosis by monoclonal anti-Ag85 antibodies of appropriate specificities. No increases in urinary Ag85 were detected in any patient, regardless of the Ag85 level in serum. Chromatographic analysis and immunoprecipitation studies of serum revealed that Ag85 existed in the serum of these patients complexed to either fibronectin or immunoglobulin G (IgG). Uncomplexed circulating Ag85 was demonstrable in serum from fewer than 20% of patients with active tuberculosis. In patients with active tuberculosis, Ag85 is therefore likely to circulate primarily as complexes with plasma fibronectin and IgG rather than in unbound form. The existence of Ag85 complexes with plasma proteins would account for its lack of urinary clearance.

T-cell determinants and antibody binding sites on the major mycobacterial secretory protein MPB59 of Mycobacterium bovis

Among the first proteins encountered by the host immune system upon infection or vaccination with mycobacteria are those secreted by the bacillus during growth. The antigen 85 complex of Mycobacterium bovis bacillus Calmette-Gúerin (BCG) is composed of three closely related members. The mature 85B protein of M. bovis (MPB59) has a high degree of amino acid identity with the M. bovis 85A protein (76%) and the Mycobacterium tuberculosis 85B (99%) and 85A (76%) proteins. We have examined the regions of MPB59 which stimulate human T- and B-cell responses by use of a set of 28 synthetic peptides, 20 amino acids (aa) in length and overlapping by 10 aa. Initial proliferative assays with recombinant MPB59 demonstrated that peripheral blood mononuclear cells from 95% of BCG vaccinees and 52% of tuberculosis patients responded to the whole mature protein. Peripheral blood mononuclear cells from MPB59 responders, but not nonresponders, were stimulated by peptides in a dose-dependent fashion. Five peptides were reactive in more than half of the MPB59 responders. The T-cell-reactive regions were essentially identical in the M. bovis and M. tuberculosis 85B proteins. Subjects with a variety of HLA-DR phenotypes responded to a number of these peptides. The dominant T-cell-reactive regions were distinct from the peptides recognized by sera from tuberculosis patients (aa 71 to 100) and the murine monoclonal antibody HYT27 (aa 61 to 90). The region reactive with antibodies overlapped part of the MPB59 sequence recently shown to participate in the binding of MPB59 to fibronectin.

T-cell-epitope mapping of the major secreted mycobacterial antigen Ag85A in tuberculosis and leprosy

Lymphoproliferation and gamma interferon (IFN-gamma) secretion in response to 28 overlapping 20-mer synthetic peptides covering the complete sequence of the mature (295-amino-acid) 85A component of the major secreted, fibronectin-binding antigen 85 complex from Mycobacterium tuberculosis and Mycobacterium bovis BCG (MTAg85A) was examined by using peripheral blood mononuclear cell (PBMC) cultures from healthy tuberculin- and lepromin-positive volunteers and from patients with tuberculosis and leprosy. Peptide recognition was largely promiscuous, with a variety of human leukocyte antigen haplotypes reacting to the same peptides. PBMC from all tuberculin-positive subjects reacted to Ag85, and the majority proliferated in response to peptide 6 (amino acids 51 to 70), peptides 13, 14, and 15 (amino acids 121 to 160), or peptides 20 and 21 (amino acids 191 to 220). PBMC from tuberculosis patients demonstrated a variable reactivity to Ag85 and its peptides, and the strongest proliferation was observed against peptide 7 (amino acids 61 to 80). MTAg85A peptides were also recognized by PBMC from healthy lepromin-positive volunteers and paucibacillary leprosy patients (again in a promiscuous manner), but despite a 90% homology between the 85A proteins of M. leprae and M. tuberculosis, the peptides recognized were different. PBMC from lepromin-positive healthy contacts reacted against peptide 2 (amino acids 11 to 30), peptide 5 (amino acids 41 to 60), and peptides 25 and 26 (amino acids 241 to 270). PBMC from paucibacillary patients reacted preferentially against peptide 1 (amino acids 1 to 20) and peptide 5. Multibacillary patients were not reactive to Ag85 or the MT85A peptides. IFN-gamma production was generally detected simultaneously with positive lymphoproliferative responses, although peptide 1 mostly stimulated proliferation and peptides 27 and 28 mostly elicited an IFN-gamma response. In conclusion, regions 41 to 80 and 241 to 295 demonstrated powerful and promiscuous T-cell-stimulatory properties, resulting in proliferative responses and IFN-gamma secretion, respectively, in the majority of reactive subjects tested in this study. These results could be of value in the development of a subunit vaccine for tuberculosis and leprosy.

Immunity to mycobacteria

Recent progress in the field of immunity to mycobacteria has centered on T cell subset responses and the cytokines these cells secrete. In addition, there has been steady progress in identifying and characterizing several classes of major mycobacterial proteins; included amongst these are the secreted/export proteins of Mycobacterium tuberculosis, which several laboratories now believe may represent the key protective immunity-inducing antigens of the bacillus.

T-cell stimulation with purified mycobacterial antigens in patients and healthy subjects infected with Mycobacterium leprae: secreted antigen 85 is another immunodominant antigen

Peripheral blood leucocytes from 9 paucibacillary and 12 multibacillary leprosy patients, from 18 healthy controls and from 34 healthy leprosy contacts were stimulated with three mycobacterial heat shock proteins with respective molecular weights of 70, 65 and 18 kDa and with the secreted 30-32 kDa protein, also called antigen 85. Antigen 85 was found to be the most powerful T-cell antigen (as measured by lymphoproliferation and IFN-gamma secretion), eliciting a positive response in all (100%) paucibacillary patients and in all lepromin-positive controls and contacts. The three heat shock proteins (hsp) were less active T-cell stimuli. Reactivity to the 70 kDa hsp was found in only 44% of the paucibacillary patients, in 80% of the lepromin-positive controls and in 60% of the lepromin-positive leprosy contacts. The 65 kDa hsp stimulated T cells in 89% of the paucibacillary patients and in 80% of the lepromin-positive controls and contacts. Responsiveness to the 18 kDa hsp, finally, was clearly more frequent in tuberculoid leprosy patients (78%) than in lepromin-positive controls (40%) or lepromin-positive leprosy contacts (4%). T-cell reactivity of 8 lepromin-negative controls, of 9 lepromin-negative contacts and of 12 multibacillary leprosy patients was low to all the antigens tested. Although proliferative and IFN-gamma responses were generally closely related, some subjects demonstrated a dissociation of these two immune parameters. Our data confirm previous findings on the powerful T-cell stimulatory properties of antigen 85 during M. leprae infection and suggest that this antigen is indeed a potentially protective T-cell immunogen.

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.

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.

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.