Chemical composition of antigen 60 from Mycobacterium bovis BCG

Proteomic Analysis of Antigen 60 Complex of M. bovis Bacillus Calmette-Guérin Reveals Presence of Extracellular Vesicle Proteins and Predicted Functional Interactions

Tuberculosis (TB) is ranked among the top 10 causes of death worldwide. New biomarker-based serodiagnostics and vaccines are unmet needs stalling disease control. Antigen 60 (A60) is a thermostable mycobacterial complex typically purified from Bacillus Calmette-Guérin (BCG) vaccine. A60 was historically evaluated for TB serodiagnostic and vaccine potential with variable findings. Despite containing immunogenic proteins, A60 has yet to be proteomically characterized. Here, commercial A60 was (1) trypsin-digested in-solution, analyzed by LC-MS/MS, searched against M. tuberculosis H37Rv and M. bovis BCG Uniprot databases; (2) analyzed using STRING to predict protein-protein interactions; and (3) probed with anti-TB monoclonal antibodies and patient immunoglobulin G (IgG) on Western blot to evaluate antigenicity. We detected 778 proteins in two A60 samples (440 proteins shared), including DnaK, LprG, LpqH, and GroEL1/2, reportedly present in mycobacterial extracellular vesicles (EV). Of these, 107 were also reported in EVs of M. tuberculosis, and 27 key proteins had significant protein-protein interaction, with clustering for chaperonins, ribosomal proteins, and proteins for ligand transport (LpqH and LprG). On Western blot, 7/8 TB and 1/8 non-TB sera samples had reactivity against 37-50 kDa proteins, while LpqH, GroEL2, and PstS1 were strongly detected. In conclusion, A60 comprises numerous proteins, including EV proteins, with predicted biological interactions, which may have implications on biomarker and vaccine development.

A novel monoclonal antibody against A60 antigen of Mycobacterium bovis Bacillus Calmette-Guerin

Mycobacterium contains several immunologically active substances, which play a principal role in mycobacterial diseases. The majority of the highly antigenic proteins present in mycobacterial homogenates are components of the A60 complex. In this study, A60 antigen was prepared from cytoplasm of Mycobacterium bovis Bacillus Calmette-Guerin (BCG). Cytoplasm was fractionated by passage through the column of sepharose 6B and ConA-sepharose 4B. After purification of spleen cells of the immunized mice, the cells were fused with SP2/0 myeloma cells. Four clone cell lines producing antibody against A60 antigens were established and each clone was tested for immunoreactivity against purified A60 by ELISA and immunoblotting. The clone designated DEB7 reacted strongly with A60. Immunoblotting using MAb DEB7 showed that this MAb binds to a single protein of A60 subunit with a molecular weight of 65 kDa. This subunit of A60 M. bovis recognized by DEB7 MAb could be used to increase the sensitivity and specificity of immunoassay or other potential roles in mycobacterium infection.

Immunological relatedness of the protective mechanisms against tuberculosis and cancer

BACKGROUND

Bacille Calmette-Guérin (BCG), an attenuated strain of tuberculous bacillus, is the source of vaccines providing unclear and variable protection against tuberculosis (TB) and cancer. Thermostable macromolecular antigens (TMAs) are major mycobacterial complexes immunodominant in disease. A60 (TMA complex of BCG) protects mice against TB development, via T lymphocyte (TL)-mediated macrophage (Mphi) activation, halting intracellular mycobacterial replication. In most A60-primed mice, cytolytic TLs and Mphi infiltrate cancer tissue, resulting in 80-100% rejection. Adoptive TL transfer is indispensable for Mphi-dependent tumour cell inactivation via oxygen and nitrogen radicals. Neoplasm development induces immune anergy with depletion ofA60-specific TL and activated Mphi. A60 protects mice against TB and cancer by inducing the synthesis of three lymphokines: interleukin 2 (IL-2), interferon gamma (IFN-gamma) and tumour necrosis factor alpha (TNF-alpha). Tumour cells prevent A60-dependent synthesis of these lymphokines in vivo and in vitro.

CONCLUSION

These data provide some clues to immune surveillance and tumour escape mechanisms, as well as to the antituberculous and antineoplastic BCG action.

Surfactant protein A (SP-A) mediates attachment of Mycobacterium tuberculosis to murine alveolar macrophages

Attachment of Mycobacterium tuberculosis organisms to alveolar macrophages (AMs) is an essential early event in primary pulmonary tuberculosis. Surfactant protein A (SP-A) is a nonimmune opsonin present in the alveolar spaces that binds carbohydrate residues such as mannose. It was hypothesized that SP-A attaches to M. tuberculosis and serves as a ligand between M. tuberculosis and AMs. [125I]SP-A was found to bind to M. tuberculosis in a time- and [Ca2+]-dependent manner with a Kd of 1.9 x 10(-9) M and an apparent number of 6.3 x 10(2) SP-A binding sites/organism. Further, deglycosylated SP-A had minimal binding to M. tuberculosis, indicating that sugar moieties are important in this interaction. SP-A specifically binds to a 60-kD cell-wall protein from M. tuberculosis. SP-A-mediated attachment of 51Cr-labeled M. tuberculosis organisms to AMs is dependent on time, SP-A concentration, and Ca2+. M. tuberculosis attachment to murine AMs in the absence of SP-A was 12.8 +/- 0.9%; however, in the presence of 5 microg/ml SP-A the attachment increased to 38.6 +/- 2.9% (P < 0.001). SP-A-mediated attachment was significantly decreased from 38.6 +/- 2.9% to 18.7 +/- 3.3% (P < 0.05) in the presence of antihuman SP-A antibodies. When the attachment assay was repeated in the presence of alpha-methylene-D-mannosepyranosidase (mannosyl-BSA) and type V collagen, SP-A-mediated attachment decreased from 38.6 +/- 2.9% to 16.6 +/- 1.5% (P < 0.001) and 19.1 +/- 1.4% (P < 0.05), respectively. Further, deglycosylated SP-A had only a minimal effect on M. tuberculosis attachment to AMs. These data indicate that SP-A can mediate M. tuberculosis attachment to AMs, and suggest possible underlying mechanisms for this.

In vitro analysis of cancer prevention by a mycobacterial antigen complex and of cancer-promoted inhibition of immune reactions

The antigen complex A60 of Mycobacterium bovis bacillus Calmette-Guérin protected mice against experimental tuberculous infection, and prevented cancer development after challenge with EMT 6 cells. Although humoral and cellular immune reactions elicited by A60 in vivo remained unaffected in cases of tumor rejection, they were suppressed in the case of neoplastic growth. In the present work, these in vivo observations were analyzed by in vitro techniques. Activated macrophages played a major role, and cytolytic T lymphocytes a minor role, in A60-promoted cancer cell cytolysis leading to tumor rejection. In vitro, EMT 6 cells weakly inhibited the proliferation of A60-specific B lymphocytes and strongly inhibited the functions of activated macrophages. However, the collapse of both humoral and cellular immune reactions during the course of cancer development was also accompanied by an inhibitory action of EMT 6 cells on the multiplication and functions of A60-specific T lymphocytes. Tumor-dependent repression of macrophage activation was therefore due to both a direct action of tumor cells on macrophages and an indirect one via inhibition of macrophage-activating T cell functions. On the other hand, tumor-induced collapse of the anti-A60 Ig synthesis was mainly due to inhibition of B-cell-activating T cells, with a weaker direct effect of tumor cells on B lymphocytes. Consequently, A60 and tumor cells exert opposite effects on the immune system at several levels.

Tuberculosis antigen A60 serodiagnosis in tuberculous infection: application in extrapulmonary and smear-negative pulmonary tuberculosis

An ELISA diagnostic test for tuberculosis antigen A60 (TBA60) IgG/IgM was used in a tertiary referral hospital in Taiwan. From June 1992 to December 1993, serum samples obtained from 907 patients were analyzed for TBA60 IgG and IgM titres. The final diagnosis of these patients was confirmed by microbiological study and clinical follow up for 18-24 months. Among 147 patients with active pulmonary tuberculosis, IgG was positive in 112 (76.2%), IgM was positive in 14 (9.52%). Among 90 patients with active extrapulmonary tuberculosis, IgG was positive in 53 (58.9%), IgM was positive in 9 (10%). Among 153 patients with inactive tuberculosis, IgG was positive in 28 (18.3%), IgM was positive in 1 (1.6%). Among 517 patients with nontuberculous disease, IgG was positive in 50 (9.7%), IgM was positive in 3 (0.6%). In this study population with 26% (237/907) active tuberculous infection rate, the TBA60 ELISA IgG had a diagnostic sensitivity of 69.6% and a specificity of 92.1%. These results indicate a positive predictive value of 67.9% and a negative predictive value of 89.2%. The sensitivity of IgM was 10.5% and specificity, 99.4%. The serum IgG tire had good correlation with the extent of pulmonary TB had a higher percentage of IgG seropositivity (83.9%) than those with smear-negative pulmonary TB (70.6%) and extrapulmonary TB (58.9%). In 50 cases with active tuberculosis, follow-up examinations were carried out one month after treatment. In 18 cases with initially negative IgG and IgM titres, 13 showed elevation of serum IgG titres into positive level, one had positive seroconversion of IgM which was the only serological marker indicating active infection. Therefore, 77.8% (14/18) gained diagnostic benefit from follow-up serological examination. It was concluded that TBA60 IgG and IgM ELISA is a useful test when diagnosing tuberculosis. This test also assists in the clinical judgement of tuberculosis when used as an adjunct to symptoms and sputum smear, and for monitoring therapeutic response at the commencement of treatment.

Comparative cutaneous testing with purified protein derivative and the antigen complex A60 in vaccinated subjects and tuberculosis patients

Some 840 bacille Calmette-Guérin (BCG)-vaccinated healthy controls and tuberculosis patients from two Chinese hospitals were submitted to comparative skin tests with purified protein derivative of tuberculin (PPD; as reference) and with the antigen complex A60 from Mycobacterium bovis BCG. In a first trial, including 581 persons (185 healthy juveniles, 180 healthy adults and 216 tuberculosis patients), a limited dose of A60 (1 microgram) was used. Performance of the A60 test was similar to that of 5 I.U. PPD for controls (cut-off values = 5 mm induration diameter), but lower than that seen for tuberculosis patients (10 mm cut-off values). A second survey was conducted on 259 persons (109 recently revaccinated healthy persons, considered as tuberculin-negative in the first trial, and 150 tuberculosis patients), using a higher dose of A60 (2 micrograms) and the same dose of PPD (5 I.U.). Similar results were obtained with the two tests in all cases, thus supporting the possibility of PPD replacement by A60 in cutaneous testing. The pattern of induration diameter distribution in healthy subjects who took part in the first testing round (64% positively rate) was displaced to the inactivity side (with a peak at 5 to 9-mm diameter), in comparison with the second round (90% positivity rate and peak at 10-14 mm). This indicates a progressive fading of cellular immunity reactions after BCG vaccination. In tuberculosis patients, no correlation was found among the following three parameters: positivity at cutaneous testing (with PPD or A60), titer of anti-A60 mycobacterial immunoglobulins in blood (IgG titer higher than cut-off line) and presence of mycobacteria in sputum.

Composition and immunoreactivity of the A60 complex and other cell fractions from Mycobacterium bovis BCG

Surface static cultures of Mycobacterium bovis BCG contained cells embedded in an extracellular matrix, whose mechanical removal yielded free cells that were pressure disrupted and fractionated into cytoplasm and walls. Cell envelopes were either mechanically disrupted or extracted with detergents. Intracellular and extracellular fractions were analysed for proteins, polysaccharides, and antigen 6O (A60), a major complex immunodominant in tuberculosis. A60 was present in extracellular matrix, cytoplasm and walls: it represented a substantial portion of the proteins and polysaccharides of these fractions. While the protein/polysaccharide ratio varied according to the origin of A60 preparations, the electrophoretic patterns of A60 proteins (which accounted for the immunogenicity of the complex) remained unchanged. Western blots pointed to the proteins present within the 29-45 kDa range as the A60 components endowed with the highest immunogenicity level. Since the most heavily stained protein bands in SDS-PAGE patterns were located outside the region best recognized by antisera, a striking discordance was found between concentration and immunogenicity patterns of A60 proteins. The electrophoretic patterns of A60- and non-A60-proteins from cytoplasm were also different. A60 complexes in dot blots and some electrophoresed A60 proteins reacted with monoclonal antibodies directed against lipoarabinomannan (LAM), a highly immunogenic polymer of cell envelope. This contaminating compound was removed from A60 with organic solvents and detergents. SDS-PAGE and Western blot patterns of proteins from delipidated A60 were similar to those of native A60 proteins.

Antibodies to antigen A60 in cerebrospinal fluid from patients with tuberculous meningitis

Cerebrospinal fluid (CSF) anti-mycobacterial antigen 60 (A60) IgM, IgG and IgA in patients affected by meningitis of different etiologies were assayed as a rapid diagnostic test in cases of tuberculous meningitis. A commercial EIA was used to test 127 CSF samples classified as follows: tuberculous meningitis (n = 27 CSF samples from 16 patients, 6 of them with AIDS), pyogenic meningitis (n = 13), non-tuberculous aseptic meningitis (n = 43) and 44 normal CSF samples (16 of them from HIV-positive patients, 8 of whom had extraneurological tuberculosis). Anti-A60 IgM was positive only in two cases (1 tuberculous meningitis and 1 self-resolving aseptic meningitis). Positive CSF anti-A60 IgG and IgA were observed in eight and nine out of 16 patients with tuberculous meningitis, but only in four and five out of 13 samples studied prior to or in the first ten days of treatment, respectively. Most of the patients with false-positive IgG and IgA (16%) had pyogenic meningitis, but without intrathecal synthesis of antibodies. In patients with aseptic meningitis, the finding of CSF anti-A60 IgG plus IgA, initially or during follow-up, can be used as a diagnostic criterion for tuberculous meningitis, with a specificity of 100%, a positive predictive value of 1, and a negative predictive value of 0.81. However, its sensitivity is only 50% in immunocompetent patients and 16% in patients with AIDS.

Immunological analysis of the components of the antigen complex A60 of Mycobacterium bovis BCG

The antigen complex of A60 of Mycobacterium bovis BCG was analyzed by different immunological techniques to assess its relevance to tuberculosis and the involvement of its components in the immune reactions elicited in humans by tuberculous infection. A60 is composed of about 30 components, of which 8 were identified by available monoclonal antibodies (lipoarabinomannan, a glycolipid, and proteins of 65, 40, 38, 35, 19, and 14 kDa). The majority (87.5%) of anti-mycobacterial antibodies in sera from tuberculosis patients was directed against A60. Western blot (immunoblot) analysis indicated that the majority of the highly antigenic proteins present in mycobacterial homogenates were components of the A60 complex. A small percentage (7.8%) of A60 epitopes proved to be species specific. Thus, A60 proteins of 66, 41, 38, 37, 35, 34, 32, and 22 kDa were found to contain B-cell epitopes specific for M. bovis and not shared by Mycobacterium leprae oR Mycobacterium avium.

Mycobacterial antigen complex A60-specific T-cell repertoire during the course of pulmonary tuberculosis

The Mycobacterium bovis antigen complex A60 is known to be immunodominant in tuberculosis and to have a protective effect against experimental infection in vitro and in vivo. To identify immunodominant and possibly protective antigens in pulmonary tuberculosis, the T-cell repertoire directed to nitrocellulose-bound fractions of A60 antigen was analyzed in active tuberculosis patients during the course of the infection and after recovery. The results show that patients infected with Mycobacterium tuberculosis acquired complete A60-T-cell reactivity only in the late phases of infection. At disease onset, patients with active tuberculosis were characterized by (i) T-cell unresponsiveness to most A60 fractions, (ii) high tumor necrosis factor alpha production, and (iii) low gamma interferon (IFN-gamma) release. Several weeks after chemotherapy, the unresponsive state disappeared and the following reverse situation was observed: (i) high blastogenic response to almost all A60 fractions, (ii) low tumor necrosis factor alpha release, and (iii) high IFN-gamma production. In addition, 60% of these patients significantly responded against seven A60 fractions (61 to 58, 56 to 53, 49 to 46, 46 to 44, 35 to 33, 33 to 30, and 30 to 28 kDa), indicating that they included immunodominant antigens. Furthermore, only the fractions within the molecular mass ranges of 56 to 44 and 35 to 28 kDa induced IFN-gamma synthesis. One year after complete recovery from infection, more than 60% of past-active tuberculosis subjects had memory T cells specific for the immunodominant fractions of 61 to 58, 56 to 53, 49 to 46, and 33 to 30 kDa. Since the same fractions induced the strongest IFN-gamma production, known to exhibit antimycobacterial effects, it is suggested that these may represent the inducers of a protective immune response.

Induction of cellular immune reactions by A36, an antigen complex of Mycobacterium paratuberculosis: comparison of A36 and johnin components

Paratuberculosis (Johne's disease) is a chronic enteritis syndrome of ruminants, which is due to infection by Mycobacterium paratuberculosis. Cutaneous testing with proteins extracted from a mycobacterial culture fluid (johnin-PPD) is currently used to evaluate the cellular immune status. We have compared the components of johnin-PPD with those of the A36 complex, a thermostable macromolecular antigen (TMA) present in the cytoplasm and associated with the cell wall of M. paratuberculosis. The presence in the johnin-PPD of fifteen A36 components has been shown by Western blotting. Moreover, monoclonal antibodies, which bind respectively to the 65-kDa M. leprae heat shock protein, the 28-kDa M. leprae superoxide dismutase, and M. tuberculosis lipoarabinomannan, recognized components of the johnin-PPD. The ability of A36 to trigger delayed hypersensitivity reactions in sensitized rabbits, and to induce the proliferation of T lymphocytes from the lymph nodes of A36-sensitized mice, matched that of johnin-PPD. The homology levels of T epitopes between A36 and the TMA complexes of M. phlei, M. bovis, M. tuberculosis and M. avium were estimated, in a lymphoproliferation assay, to be 51, 52, 59 and 94% respectively. A strong cross-reactivity of A36 with an M. leprae sonicate was also observed by cutaneous testing. The A36 components within the 45.2-26.8-kDa and the 21.6-19.8-kDa ranges were proved to induce the proliferation of T lymphocytes from sensitized mice. This work supports the possible use of the A36 complex, and of some of its components, for cutaneous tests and lymphocyte proliferation assays, in order to monitor cellular immunity in Johne's disease.

Serological response of tuberculosis patients to antigen 60 of BCG

Two ELISA tests (IgG and IgM) for the serodiagnosis of tuberculosis, both based on antigen 60 (A60) of M. bovis BCG, were applied to 1,644 controls and patients to analyse the immune response in different forms of this infectious disease. Out of 200 healthy individuals, 148 being tuberculin--positive BCG-vaccinated adults, only 10 contacts--nurses of the pneumology department and laboratory technicians of the mycobacterial laboratory--were found positive for anti-A60 IgG. One quarter of hospitalized patients affected by non-tuberculous pneumopathies (194 in total) were found weakly positive for anti-A60 IgG. We suppose that these positive cases have suffered from inapperant infections and are in a "persistent state". Out of 344 cases of primary pulmonary tuberculosis, 88% were positive for anti-A60 IgG and 75% for the corresponding IgM. Among 97 cases of primary extra-pulmonary tuberculosis, 94% were found IgG positive and 33% IgM positive. The difference between active and inactive post-primary (chronic) tuberculosis was striking: about 100% of both pulmonary and extra-pulmonary cases (367 altogether) had high titers of anti-A60 IgG but IgM positivity was observed in only 15% of the cases, whereas in inactive and quiescent noncavitary tuberculosis (442 cases), 57% of the patients were weakly positive for anti-A60 IgG and none were positive for IgM. Kinetics of synthesis of anti-A60 IgG and IgM were analysed in primary and post-primary (chronic) active tuberculosis. The IgM tracing immune response to A60 was shorter and lower during primary tuberculosis as compared to post-primary tuberculosis. Our findings point to the high prognostic value of the A60- ELISA test for tuberculosis. Anti-A60 IgM mark initial stages of the disease or reactivation processes whereas anti-A60 IgG last longer than IgM and provide an evaluation of the intensity of the infectious process. Repeated serological tests allow monitoring of the course of the infection and the efficacy of therapy. The test is negative in healthy BCG-vaccinated persons (tuberculin-positive) and healed tuberculous infection cases. The combined use of both IgG and IgM tests helps in the correct diagnosis of "false positive" cases.

Composition and immunological properties of the protein fraction of A36, a major antigen complex of Mycobacterium paratuberculosis

TMA (thermostable macromolecular antigens) are major mycobacterial complexes present in all mycobacteria. We have purified A36, the TMA complex of M. paratuberculosis, the etiological agent of paratuberculosis (Johne's disease), and shown by the immune electron microscopy approach its presentation at the cell surface. The immunodominance of the A36 complex in Johne's disease was suggested by comparative ELISA analysis of infected bovine sera, using either A36 or M. paratuberculosis total soluble sonicate as antigens. The cross-reactivity of TMA complexes from different mycobacteria was evaluated by immunoenzymometric measurements. Percentage of shared epitopes was high for the couple M. paratuberculosis-M. avium, and somewhat lower for the couple M. paratuberculosis.-M. bovis. Immunological kinship between M. paratuberculosis and M. leprae was suggested by the finding that out of eleven anti-M. leprae monoclonals, four cross-reacted with A36 proteins. The specificity missing at the level of the whole A36 complex was sought at the level of its protein components. Comparative immunoblot analysis of electrophoresed A36 proteins indicated three of them to contain epitopes not shared by M. bovis proteins, and one of them to contain epitopes specific with respect to M. avium, M. bovis and M. phlei. The latter component, a 34-kDa protein, could be an ideal reagent for a serological test for Johne's disease, being immunodominant in infected cattle and endowed with species-specific epitopes.

Immunization of mice with the antigen A60 of Mycobacterium bovis BCG

Antigen 60 (A60) is a thermostable component of the cytoplasm of Mycobacterium tuberculosis and BCG which can be fractionated into at least 15 protein bands when analysed by Western blot. Normal B6D2 mice were immunized subcutaneously with 20 micrograms of the A60 protein suspended in Freund's incomplete adjuvant (FIA) or in saline. Three weeks later the mice received a second dose of vaccine followed 2 weeks later by an aerogenic challenge with approximately 10(3) CFU of M. tuberculosis Erdman. The mice receiving the adjuvanted A60 showed a significant reduction (P less than 0.05) in the number of viable organisms recovered from the lungs and the spleen 3 weeks after challenge. However, this response was less than that seen in BCG vaccinated controls.

Composition and immunogenicity of the polysaccharide components of the thermostable macromolecular antigen group of mycobacterial antigens

The thermostable macromolecular antigen (TMA) group includes major components of the mycobacterial cell envelope and cytoplasm, which elicit humoral and cellular immune reactions, and seems to play important roles in infectious diseases. The best known member of this group, antigen A60 of Mycobacterium bovis BCG, was previously shown to contain three moieties of polysaccharides, free lipids, and polypeptides. In this work, the TMA polysaccharides of three pathogenic mycobacteria (M. avium, M. bovis and M. paratuberculosis) have been analyzed by coupled gas chromatography-mass spectrometry. In all cases the cores of the TMA complexes were represented by branched glucans of high molecular mass (about 10(6) daltons), for which structural models have been proposed. The immunogenicity of the polysaccharide components from the three TMA was verified with several immunological procedures (immunodiffusion and immunoelectrophoresis of the antigen, and immunoblotting of the corresponding electrofocused immunoglobulins). All tests tallied in showing a negligible immunogenicity of the glucans examined (inability to produce, upon injection, the synthesis of specific immunoglobulins), thus pointing to the protein moiety of TMA as the one responsible for the high immunoreactivity of the complexes.

Clinical usefulness of serological measurements obtained by antigen 60 in mycobacterial infections: development of a new concept

The humoral immune response occurring during mycobacterial infections was analysed with an ELISA test based on antigen 60. With tuberculosis, IgM antibodies indicate a primo-infection or a process of reactivation while IgG determinations allow an evaluation of the intensity of the infectious process. The test is also applicable to extrapulmonary tuberculosis, provided its sensitivity be adapted to these particular cases. This is particularly clear for tuberculous meningitis. The test is not species-specific and allows the detection of antibodies in atypical mycobacterioses and in leprosy patients. The final differentiation must be done by clinical examinations and cultures. In leprosy patients, IgM antibodies are detected nearly as frequently as IgG antibodies. In HIV-seropositive patients, the A60 seropositivity is correlated with a reactivation of former tuberculous infections and with primary tuberculous infections. At the AIDS stage, the A-60 seropositivity is due to atypical mycobacteria, with a better IgM than IgG response. Healthy people are negative in serology: the positive cases observed are due to inapparent infections gained by contact with an infectious focus. The seropositive cases observed in non-tuberculous hospitalized patients are restricted to some disease types, essentially lung infections (cystic fibrosis, cancer pneumopathies, sarcoidosis). Some patients have low levels of antibodies. This anergy may be traced to the formation of immune complexes or else to a weak avidity of the specific antibodies produced. This test should not be considered to be a diagnostic tool by itself. It should be used in conjunction with other diagnostic means that, together, allow the determination of a diagnosis.

Mycobacterial proliferation in macrophages is prevented by incubation with lymphocytes activated in vitro with a mycobacterial antigen complex

Antigen A60 from Mycobacterium bovis bacillus Calmette Guérin was shown to trigger both humoral and cellular immune reactions. We explored the ability of A60 to block intracellular proliferation of phagocytosed mycobacteria with a model system involving peritoneal murine macrophages infected with Mycobacterium avium. Mixed lymphocytes from lymph nodes of mice inoculated with A60 hindered intracellular proliferation of this mycobacterium, owing to A60-specific cells, proliferation of which was induced in vitro in an antigen concentration-dependent manner. The lymphokines released by A60-stimulated T lymphocytes in vitro were identified as interleukin 2 (IL2) and interferon-gamma (IFN-gamma): their production showed a clear A60 dose dependence. When supernatants of such induced lymphocyte cultures were incubated with anti-IFN-gamma antibodies, macrophage activation was prevented, whereas anti-IL 2 immunoglobulin had little effect. Treatment of infected macrophages with recombinant IFN-gamma reduced intracellular proliferation of mycobacteria, while exogenous IL 2 and tumor necrosis factor were ineffective. Therefore, A60 elicits in vitro proliferation of T lymphocytes responding specifically to this antigen with production of IFN-gamma, which in turn activates macrophages and prevents multiplication of phagocytosed mycobacteria.

Public health application of a serological test for tuberculosis: study of the incidence of inapparent infections among the employees of an Alsatian supermarket

A serodiagnostic test based on antigen 60 has been used to analyse the presence of IgG antibodies specific for mycobacteria, in the serum of the employees of a food supermarket. More than fourteen percent of the employees were seropositive, compared to 1.5% in a health adult population. The seropositives were restricted to those employees who were in direct contact with the customers.

Intrathecal synthesis of anti-mycobacterial antibodies in patients with tuberculous meningitis. An immunoblotting study

Cerebrospinal fluid (CSF) and serum samples from eight patients with bacteriologically proven (6) or clinically suspected (2) tuberculous meningitis were tested for the presence of anti-mycobacterial IgG antibodies by an affinity-mediated immunoblot technique. This technique is based on agarose gel isoelectric focusing of paired CSF and serum samples diluted to the same IgG concentration, and transfer of the specific IgG antibodies onto mycobacterial antigen-loaded nitrocellulose sheets. An intrathecal synthesis of anti-mycobacterial oligoclonal IgG antibodies, often superimposed on diffuse polyclonal production was shown in all patients but not in patients with tension headache or other neurological disorders. Similar results were obtained when a purified mycobacterial antigen, A60, was used for coating the nitrocellulose sheets in place of a whole mycobacterial homogenate, indicating that A60 was a major immunogen. The number of anti-mycobacterial oligoclonal IgG bands increased with time, and persisted for years even in clinically cured patients. Some IgG bands had no detectable anti-mycobacterial activity, at least with the antigens preparations used in this study. The demonstration of such anti-mycobacterial IgG bands in the CSF could be a useful adjunct for the diagnosis of tuberculous meningitis, especially in the case of negative cultures.

Serological analysis of human tuberculosis by an ELISA with mycobacterial antigen 60

An ELISA method for detecting serum antibodies against A60, an antigen prepared from the cytoplasm of Mycobacterium bovis BCG, has been applied to 385 subjects, namely 197 controls (neonates, healthy adults, and tuberculin negative, nontuberculous patients), and 188 subjects at various stages of tuberculous infection and disease. Most IgM determinations gave negative results. While the neonates and normal adults had titers of IgG anti-A60 antibodies below the cut off value, wide variations in antibody titers were observed among the various types of subjects infected by M. tuberculosis. The results obtained with nontuberculous subjects were: 100% negative IgG in neonates and healthy adult individuals and 6.4% "false positive" cases among 124 non-tuberculous patients. The percentage of serologically positive cases of tuberculosis was: 5.9% in latent active primary forms, 42.8% in patent active primary forms, and 82.8% in active postprimary forms. Tuberculous infections had a positively rate of 14.7%, while inactive postprimary tuberculosis had a positivity rate of 50%. The results obtained with A60 can favourably be compared with other serum ELISA tests for tuberculous antibodies against purified or semipurified mycobacterial antigens. Anti-A60 ELISA IgG antibody test can be useful to monitor the kinetics of humoral immunological response during tuberculous infection, disease and chemotherapy. A positive IgG ELISA test may support the diagnosis of active tuberculous disease.

Delayed hypersensitivity reactions by the mycobacterial antigen A60 and cutaneous testing in tuberculosis

Antigen A60 has been purified from the cytoplasm of Mycobacterium bovis BCG, and its composition has been determined: it has proved to be able to elicit immune reactions of both humoral and cellular type. Inoculation of A60 into the footpad of mice previously sensitized with the same antigen, or with whole mycobacterial cells produced a footpad swelling showing a peak at 24 h. Similar delayed hypersensitivity reactions were induced in sensitized guinea-pigs by subcutaneous injection of an A60 dose of 0.01 micrograms (minimal revealing dose). A quantity thousandfold higher (15 micrograms A60) was unable to induce in unsensitized guinea pigs the mounting of a cellular immunisation against A60, as shown by negative cutaneous testings 1 month later. Our results show that A60 preparations satisfied the requirements of the European Pharmacopoeia Commission and met the WHO recommendations for new tuberculins. Handicaps of old tuberculin and PPD (heterogeneous mixtures titrated biologically and unstable in solution) can be overcome by A60 preparations (a single antigen spectrophoretically measurable and stable).

Purification of a major Mycobacterium bovis antigen for the diagnosis of bovine tuberculosis

A Mycobacterium bovis antigen has been purified from culture filtrate by chromatofocusing. This antigen is a major component of culture filtrate and cell extracts and shows a considerable degree of micro-heterogeneity in electric charge and molecular weight. Studies with monoclonal and polyclonal antibodies raised against the purified antigen show that some of its antigenic determinants also occur in higher molecular weight species in culture filtrate and particularly in whole cell preparations. Immunoblotting and ELISA studies, using sera from M.bovis-infected animals, showed that this antigen is one of the most immunoreactive components of M. bovis, recognized by the majority of animals with detectable antibody response to M. bovis. The specificity of the purified antigen is far superior to that of the crude culture filtrate, with very few false positive results. The purified antigen also elicits strong in vivo and in vitro cell-mediated responses. The amino acid compositions of two variants of this antigen have been determined and found to be similar to that of MPB-70.

Metabolism of the TMA group of antigens during the growth cycle of mycobacteria

The TMA (thermostable macromolecular antigens) group includes A60 of Mycobacterium tuberculosis and A7 of M. leprae, active components of tuberculin and lepromin. We have previously described the purification and composition of A60, and its ability to elicit immune reactions of humoral and cellular type. In the present work, the intracellular and extracellular distribution and composition of A60 have been traced, as a function of the replication cycle, in static surface cultures of M. bovis. In exponentially-growing mycobacteria, most A60 was present in the cytoplasm and had a high protein/polysaccharide ratio: this ratio, as well as the level of cytoplasmic A60, decreased after cessation of cell proliferation. The A60 fraction located within the cell wall increased during the stationary phase, but its protein/polysaccharide ratio underwent minor changes. A release of cellular polypeptides and polysaccharides into the extracellular fluid occurred during the declining and lysing phases: a fraction of it was represented by A60. This explains the practice of old tuberculin preparation by autoclaving filtrates of autolysed mycobacterial cultures. The pattern of an A60-like antigen in shaken homogeneous cultures of M. smegmatis was similar (most antigen present in cytoplasm during growth, increase of the wall fraction in stationary phase, and extracellular release during the declining phase).

The antigens of Mycobacterium tuberculosis, H37Rv, studied by crossed immunoelectrophoresis. Comparison with a reference system for Mycobacterium bovis, BCG

On the basis of a previously developed reference system for Mycobacterium bovis, BCG, in crossed immunoelectrophoresis (CIE), antigens of Mycobacterium tuberculosis were identified in an analogous system. A majority of the numbered lines in the BCG system were also present and identified in the M. tuberculosis system. The corresponding antigens in the two systems were identified by dual dilution in CIE, and using monospecific antisera and monoclonal antibodies. Some of the antigens were specifically identified by the demonstration of enzyme activity and by means of hydroxyapatite, concanavalin A (Con A), EDTA, and blue-Sepharose. Three antigens (nos 10, 78, and 81), which were found in high concentrations in M. tuberculosis culture fluid, were not identified or were present in low concentrations in BCG culture fluid. The high percentage of corresponding antigens confirms that there is a very close taxonomic relationship between BCG and M. tuberculosis. Corresponding antigens in BCG and M. tuberculosis did not differ in electrophoretic mobility in the antigenic preparations studied.

Subcellular localisation and sedimentation behaviour of antigen 60 from Mycobacterium bovis BCG

Preparation, composition and immunological properties of A60 of Mycobacterium bovis BCG were previously described (Cocito and Vanlinden 1986). The present study focused on the intracellular distribution of this antigen. Fractionation of mycobacterial homogenates by ultracentrifugation indicated that most of A60 was present within the cytoplasm. Some of the antigen was located within the cell wall, from which it was released by extraction with alkali. Submission of cytoplasm to high speed centrifugation caused A60 to cosediment with ribosomes; however, dissociation of ribosomes in low-Mg buffer did not alter the sedimentation pattern of A60. Labelled A60, after ultracentrifugation in sucrose density gradients without Mg2+, was distributed throughout the entire gradient: treatment of (125I)A60 with urea or detergents produced a peak of radioactivity located in the upper part of the gradient. It is concluded that A60 is represented by a heterogeneous family of molecules of increasing sizes: polymerization being enhanced by Mg2+ and reversibly prevented by urea. Some or all of the biological properties hitherto attributed to ribosomal particles may, in fact, be due to their contamination with cosedimented A60.

Immunological properties of antigen 60 of BCG. Induction of humoral and cellular immune reactions

Antigen 60 (A60), a member of the thermostable macromolecular antigen family (TMA) and main component of old tuberculin and purified protein derivative (PPD), has been purified from the cytoplasm of Mycobacterium bovis BCG; its structure and metabolism have already been described. In the present paper, the action of A60 on humoral immunity has been analysed by an ELISA type immunoassay, and that on cellular immunity by the mouse footpad swelling test. Injection of very low A60 doses into unprimed mice produced an undetectable level of anti-A60 antibodies; the effect of a booster inoculation was not appreciable in the absence of incomplete Freund's adjuvant, but was evident when the latter was added. Higher doses of the antigen produced an appreciable primary response, and a sharp and long-lasting secondary response, which had a 10-fold higher intensity in the presence of incomplete adjuvant. No detectable delayed hypersensitivity reactions were observed in unprimed mice after footpad injection of A60, whereas clear responses were elicited in primed mice. This effect was more pronounced when the footpad was injected after a secondary response than after a primary response, and it was invariably magnified by incomplete adjuvant. It is concluded that A60 is a powerful immunogen, which is able to induce primary and secondary responses and delayed hypersensitivity reactions, effects that are adjuvant-modulated and develop concurrently.

Analysis of monoclonal antibodies to Mycobacterium leprae by crossed immunoelectrophoresis

Monoclonal antibodies to Mycobacterium leprae were characterized in crossed immunoelectrophoresis and showed markedly different patterns of reactivity with M. leprae lines 2, 7 and 11 respectively. Line 7 corresponds to a cell wall-associated macromolecular complex containing lipid, polysaccharide, and two distinct 36 K and 65 K proteins.