Immunobiology and species distribution of Mycobacterium tuberculosis antigen 5

Advances in the molecular diagnosis of tuberculosis: From probes to genomes

Tuberculosis, disease caused by Mycobacterium tuberculosis, is currently the leading cause of death by a single infectious agent worldwide. Early, rapid and accurate identification of M. tuberculosis and the determination of drug susceptibility is essential for the treatment and management of this disease. Tuberculosis diagnosis is mainly based on chest radiography, smear microscopy and bacteriological culture. Smear microscopy has variable sensitivity, mainly in patients co-infected with the human immunodeficiency virus (HIV). Conventional culture for M. tuberculosis isolation, identification and drug susceptibility testing requires several weeks owning to the slow growth of M. tuberculosis. The delay in the time to results drives the prolongation of potentially inappropriate antituberculosis therapy contributing to the emergence of drug resistance, reducing treatment options and increasing treatment duration and associated costs, resulting in increased mortality and morbidity. For these reasons, novel diagnostic methods are need for timely identification of M. tuberculosis and determination of the antibiotic susceptibility profile of the infecting strain. Molecular methods offer enhanced sensitivity and specificity, early detection and the capacity to detect mixed infections. These technologies have improved turnaround time, cost effectiveness and are amenable for point-of-care testing. However, although these methods produce results within hours from sample collection, the phenotypic susceptibility testing is still needed for the determination of drug susceptibility and quantify the susceptibility levels of a given strain towards individual antibiotics. This review presents the history, advances and forthcoming promises in the molecular diagnosis of tuberculosis. An overview on the general principles, diagnostic value and the main advantages and disadvantages of the molecular methods used for the detection and identification of M. tuberculosis and its associated disease, is provided. It will be also discussed how the current phenotypic methods should be used in combination with the genotypic methods for rapid antituberculosis susceptibility testing.

A proteomic view of mycobacteria

Tuberculosis, the disease caused by Mycobacterium tuberculosis, remains a relevant public health issue. This is due mostly to the coepidemiology with HIV/AIDS, the appearance of multidrug-resistant strains globally, and failure of BCG (bacillus Calmette-Guerin) vaccination to confer complete protection. This bacterium was one of the first to have its genome sequenced, yet over a decade after the release of the genomic information, the characterization of its phylogenetic tree and of different strain variants inside this species revealed that much is still needed to be done for a full understanding of the M. tuberculosis genome and proteome. Current methods using LC-MS/MS and hybrid high-resolution mass spectrometers can identify 2400-2800 proteins of the 4000 predicted genes in M. tuberculosis. In this article, we review relevant details of this bacterium's pathology and immunology, describing articles where proteomics helped the community to tackle some of the organism biology, from understanding strain diversity, cellular structure composition, immunogenicity, and host-pathogen interactions. Finally, we will discuss the challenges yet to be fulfilled in order to better characterize M. tuberculosis by proteomics.

An analysis of the epitope knowledge related to Mycobacteria

BACKGROUND

Tuberculosis, caused by the bacterium Mycobacterium tuberculosis, remains a leading cause of infectious disease morbidity and mortality, and is responsible for more than 2 million deaths a year. Reports about extremely drug resistant (XDR) strains have further heightened the sense of urgency for the development of novel strategies to prevent and treat TB. Detailed knowledge of the epitopes recognized by immune responses can aid in vaccine and diagnostics development, and provides important tools for basic research. The analysis of epitope data corresponding to M. tuberculosis can also identify gaps in our knowledge, and suggest potential areas for further research and discovery. The Immune Epitope Database (IEDB) is compiled mainly from literature sources, and describes a broad array of source organisms, including M. tuberculosis and other Mycobacterial species.

DESCRIPTION

A comprehensive analysis of IEDB data regarding the genus Mycobacteria was performed. The distribution of antibody/B cell and T cell epitopes was analyzed in terms of their associated recognition cell type effector function and chemical properties. The various species, strains and proteins which the epitope were derived, were also examined. Additional variables considered were the host in which the epitopes were defined, the specific TB disease state associated with epitope recognition, and the HLA associated with disease susceptibility and endemic regions were also scrutinized. Finally, based on these results, standardized reference datasets of mycobacterial epitopes were generated.

CONCLUSION

All current TB-related epitope data was cataloged for the first time from the published literature. The resulting inventory of more than a thousand different epitopes should prove a useful tool for the broad scientific community. Knowledge gaps specific to TB epitope data were also identified. In summary, few non-peptidic or post-translationally modified epitopes have been defined. Most importantly epitopes have apparently been defined from only 7% of all ORFs, and the top 30 most frequently studied protein antigens contain 65% of the epitopes, leaving the majority of M. tuberculosis genome unexplored. A lack of information related to the specific strains from which epitopes are derived is also evident. Finally, the generation of reference lists of mycobacterial epitopes should also facilitate future vaccine and diagnostic research.

Mycobacterium tuberculosis LprG (Rv1411c): a novel TLR-2 ligand that inhibits human macrophage class II MHC antigen processing

MHC class II (MHC-II)-restricted CD4(+) T cells are essential for control of Mycobacterium tuberculosis infection. This report describes the identification and purification of LprG (Rv1411c) as an inhibitor of primary human macrophage MHC-II Ag processing. LprG is a 24-kDa lipoprotein found in the M. tuberculosis cell wall. Prolonged exposure (>16 h) of human macrophages to LprG resulted in marked inhibition of MHC-II Ag processing. Inhibition of MHC-II Ag processing was dependent on TLR-2. Short-term exposure (<6 h) to LprG stimulated TLR-2-dependent TNF-alpha production. Thus, LprG can exploit TLR-2 signaling to inhibit MHC-II Ag processing in human macrophages. Inhibition of MHC-II Ag processing by mycobacterial lipoproteins may allow M. tuberculosis, within infected macrophages, to avoid recognition by CD4(+) T cells.

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

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

Broad clonal heterogeneity of antigen-specific CD4+ T-cells localizing at the site of disease during tuberculosis

The repertoire of CD4+ T-lymphocytes was investigated in six patients affected by tuberculosis, who had a negative PPD skin test at diagnosis. Polyclonal CD4+ T-cell lines from the peripheral blood failed to proliferate to PPD and to the 16- or 38-kDa proteins of Mycobacterium tuberculosis, while CD4+ T-cell lines from the site of disease responded to PPD, and to the 16- and 38-kDa proteins, and derived epitopes in vitro. The repertoire of CD4+ T-cells accumulating at the site of disease was found to be widely heterogeneous as demonstrated by the finding that at least seven different peptides from the 16- and 38-kDa proteins were recognized by every patient. These results indicate that CD4+ T-cells localized at the site of disease in tuberculosis recognize a vast array of M. tuberculosis epitopes.

Rapid screening test for tuberculosis using a 38-kDa antigen from Mycobacterium tuberculosis

A screening test for the diagnosis of tuberculosis by immunodot (IDt) is described, using an antigen of Mycobacterium tuberculosis, namely, a 38-kDa glycoprotein which has shown great specificity in previous serologic analyses. The test was used to examine 28 sera from patients with lung tuberculosis. Of these, 85% were positive by micro-ELISA and by the IDt test herein described. Control sera from healthy subjects (n = 20) gave negative results for ELISA and for IDt, which indicates that the screening test is highly specific. The test is easy to handle and requires no equipment and is therefore particularly useful for field studies.

Evaluation of the recombinant 38-kilodalton antigen of Mycobacterium tuberculosis as a potential immunodiagnostic reagent

The diagnosis of infection caused by Mycobacterium tuberculosis is of increased public health concern following increases in the number of cases in developed countries and major increases in developing countries associated with the spread of human immunodeficiency virus (HIV) infection. The specificity of purified protein derivative skin testing for the detection of infection is compromised by exposure to environmental mycobacteria. Examination of sputum detects the most infectious patients, but not those with extrapulmonary disease. The 38-kDa antigen of M. tuberculosis contains two M. tuberculosis-specific B-cell epitopes. We overexpressed the gene for this antigen in Escherichia coli and evaluated the recombinant product in in vitro assays of T-cell function and as a target for the antibody response in humans. The sensitivity and specificity of the antigen as a skin test reagent were also assessed in outbred guinea pigs. We found that 69% of healthy sensitized humans recognize the antigen in vitro, as manifested by both cell proliferation and the production of gamma interferon. Untreated patients initially have a lower frequency of response (38%); this recovers to 72% during therapy. A total of 292 patients (20 with HIV coinfection) and 58 controls were examined for production of antibody to the 38-kDa antigen by using a commercially available kit. The sensitivity of the test in comparison with that of culture was 72.6%, and the specificity was 94.9%. The antigen was also tested for its ability to induce skin reactions in outbred guinea pigs sensitized by various mycobacterial species. The antigen provoked significant skin reactions in M. tuberculosis-, M. bovis BCG-, and M. intracellulare-sensitized animals. The significance of these findings and the usefulness of this antigen in immunodiagnosis are discussed.

Antigenic characterization of Mycobacterium bovis BCG culture filtrate

Mycobacterium bovis BCG culture filtrate, on gelfiltration chromatography revealed four prominent regions. Of these 4, region II possessed the highest antigenic reactivity by enzyme-linked immunosorbent assay (ELISA) and delayed type hypersensitivity (DTH) skin testing in guinea pigs. On anion-exchange chromatography, region II was resolved into 5 prominent fractions of which fraction II was found to have the highest antigenic reactivity. On sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE), M. bovis BCG culture filtrate revealed 11 structural polypeptides. Fraction II yielded a homogenous polypeptide of 15.3 kDa molecular weight. All fractions cross-reacted with various mycobacteria used in this study except a 15.3 kDa polypeptide which was specific to M. bovis BCG.

T cell repertoire in tuberculosis: selective anergy to an immunodominant epitope of the 38-kDa antigen in patients with active disease

It is generally accepted that both host protection and pathogenic reactions in tuberculosis are mediated by T lymphocytes. However, little is known about the structures and discreet functions of epitopes stimulating the immune response. In this study, proliferative responses of blood T lymphocytes to synthetic peptides derived from the sequence of the 38-kDa antigen from Mycobacterium tuberculosis have been investigated in 41 healthy individuals and in 36 patients with active tuberculosis. Of the healthy purified protein derivative (PPD)-positive donors, 90% responded to a permissively recognized peptide, 38.G (residues 350-359), located at the carboxy terminus of the molecule. Four other permissively recognized epitopes of this molecule (38.A, 38.I, 38.E, 38.K) were stimulatory for more than 50% of healthy PPD-positive individuals. Patients with lymphatic tuberculosis responded to these peptides in a similar manner. In contrast, we observed a selective anergy to stimulation with peptide 38.G in the majority of patients with pulmonary (11% responders) and nonlymphatic extrapulmonary tuberculosis (25% responders). The lack of responsiveness to 38.G was epitope specific since the degree of responsiveness to the other four permissively recognized peptide epitopes was similar for patients and PPD-positive controls. Using the PEPSCAN technology and truncated peptides, the core epitope of 38.G was localized to a peptide 10 amino acids long (HFQPLPPAVV). This minimal structure was capable of inducing a proliferative response in all healthy 38.G responders tested. The mechanisms influencing this epitope-specific anergy in patients could give new insights into the immunopathogenesis of tuberculosis.

M. tuberculosis-complex specific T-cell stimulation and DTH reactions induced with a peptide from the 38-kDa protein

An immunodominant T-cell-stimulatory epitope located near the carboxy terminus of the 38-kDa antigen from M. tuberculosis (38.G, residues 350-369) was found to be M. tuberculosis-complex specific. This was demonstrated by the presence of proliferative and delayed type hypersensitivity (DTH) responses in mice immunized with Mycobacterium tuberculosis and Mycobacterium bovis BCG, whereas mice immunized with M. avium or other non-tuberculous species of mycobacteria showed no such responses. Peptide 38.G stimulated the proliferation of peripheral blood lymphocytes from healthy purified protein derivative (PPD)-positive individuals but not from PPD-negative individuals. It also elicited DTH responses in M. tuberculosis sensitized mice and in PPD-positive healthy human volunteers. Peptide 38.G could therefore prove to be an important component in any new molecularly defined reagent used in the immunodiagnosis of tuberculous infection.

Isolation of two antigens from the culture filtrates of Mycobacterium tuberculosis and their applications in the laboratory diagnosis of the tuberculous meningitis

Two antigens were isolated from the culture filtrates of H37Ra Mycobacterium tuberculosis by immunoabsorbent affinity chromatography, M. tuberculosis antigen 5 and immunoabsorbent affinity column-purified antigen (IAP). The potential application of these two mycobacterial antigens in the laboratory diagnosis of tuberculous meningitis was evaluated by indirect enzyme-linked immunoabsorbent assay in cerebrospinal fluid specimens. IAP antigen was more sensitive than antigen 5, although antigen 5 was more specific than IAP antigen in detecting tuberculous aetiology. Technical aspects of immunoabsorbent affinity chromatography have been highlighted in this study.

Purification and characterization of major antigens from a Mycobacterium bovis culture filtrate

Ten major antigens from Mycobacterium bovis culture filtrate of 39, 32, 30, 25, 24, 22 (a and b forms), 19, 15, and 12 kDa have been purified and characterized by classical physicochemical methods. With monoclonal antibodies and/or N-terminal amino acid sequencing data, it was found that the antigens of 32, 30, 24, 22 (a), 19, and 12 kDa are related to M. bovis or M. tuberculosis antigens P32, MPB59, MPB64, MPB70, 19 kDa, and 12 kDa, respectively. The 39-, 25-, 22 (b)-, and 19-kDa antigens showed concanavalin A-binding properties and were positive in a glycan detection test, suggesting that they are glycoproteins. The 25- and 22 (b)-kDa proteins were found to be glycosylated forms of MPB70.

Antigenic epitopes on Mycobacterium tuberculosis recognized by antibodies in tuberculosis and mouse antisera

The effect of sodium periodate and proteolytic enzyme treatments on the antibody binding capacity of Mycobacterium tuberculosis antigen (Ag) was studied by ELISA. Treatment with sodium periodate resulted in a marked decrease in the capacity of M. tuberculosis Ag to bind antibodies in human TB sera, but had no effect on the reactivity with antibodies in mouse. In contrast, treatment with proteolytic enzymes (trypsin and chymotrypsin) had no effect on the reactivity of M. tuberculosis Ag with human TB sera but reduced substantially the reactivity to antibodies in mouse antisera. These results indicate that anti-M. tuberculosis antibodies in human TB sera react predominantly with carbohydrate determinants and not with protein epitopes sensitive to trypsin and chymotrypsin. The bulk of murine antibodies on the other hand were directed against protein determinants and not the carbohydrate epitopes.

Enzyme-linked immunosorbent assay to detect Mycobacterium tuberculosis antigen 5 and antimycobacterial antibody in cerebrospinal fluid of patients with tuberculous meningitis

Inhibition ELISA and indirect ELISA was standardised to detect Mycobacterium tuberculosis antigen 5 and antimycobacterial antibody in cerebrospinal fluid (CSF) specimens of 75 patients with tuberculous meningitis, (TBM) and 75 patients with non-tuberculous neurological diseases (control group). In both ELISAs, no false-negative results were observed in 15 culture proven patients with TBM. Detection of M. tuberculosis antigen 5 is more sensitive than detection of antimycobacterial antibody. However, both ELISAs showed 100% specificity for tuberculous aetiology in culture-negative patients with TBM. ELISA should be considered as one of the approaches in the laboratory diagnosis of TBM, particularly when standard bacteriological methods are unable to demonstrate M. tuberculosis in CSF specimens of patients with TBM.

Polystyrene, poly-L-lysine and nylon as adsorptive surfaces for the binding of whole cells of Mycobacterium tuberculosis H37 RV to ELISA plates

Several methods of coating whole cells of Mycobacterium tuberculosis H37 RV to ELISA microtitre plates were compared with the aim of developing an ELISA screening assay for murine monoclonal antibodies in culture supernatants and human antibodies in patient sera. Undercoats of nylon or poly-L-lysine were compared to polystyrene as adsorptive surfaces for the bacteria, the effect of increased ionic strength and iclusion of SDS in the coating buffer measured, and methanol (70%) and glutaraldehyde (5%) investigated for their efficiency as fixatives of the bacterial monolayers. The results suggest PBS as a satisfactory coating buffer for the bacterial cells on polystyrene, and 70% methanol the preferred fixative for the dried antigen-coated plates.

Correlation between culture of Mycobacterium tuberculosis and IgG antibody to Mycobacterium tuberculosis antigen-5 in the cerebrospinal fluid of patients with tuberculous meningitis

A retrospective study was made of the correlation between culture of Mycobacterium tuberculosis and detection of IgG antibody to M. tuberculosis antigen-5 in cerebrospinal fluid (CSF) by means of an enzyme linked immunosorbent assay (ELISA). Mycobacterium tuberculosis was cultured from the CSF in 14 of 70 patients with a clinical diagnosis of tuberculous meningitis (TBM). IgG antibody to M. tuberculosis antigen-5 was demonstrated in significant titres (80-640) in all 14 culture-positive patients. Thus, positive correlation was observed between culture of M. tuberculosis and detection of IgG antibody in the CSF. As a result of this observation, the CSF from 56 culture-negative patients with a clinical diagnosis TBM was specifically investigated for the detection of IgG antibody to M. tuberculosis antigen-5 and the findings were correlated with those of culture-positive patients. The assay was positive in 34 of 56 patients, the antibody titre ranging between 80 and 640. In the CSF of 70 patients with non-tuberculous neurological diseases, the assay was negative at a dilution of 1 in 80. Thus, detection of IgG antibody to M. tuberculosis antigen-5 by indirect ELISA carried 100% specificity and 60.7% sensitivity for a tuberculous aetiology in culture-negative patients with TBM. The results of this study suggest that indirect ELISA for IgG antibody to M. tuberculosis antigen-5 in CSF holds definite promise in diagnosis of TBM, particularly when repeated cultures of CSF are negative for M. tuberculosis.

The 45 kilodalton molecule of Mycobacterium tuberculosis identified by immunoblotting and monoclonal antibodies as antigenic in patients with tuberculosis

The object of this study was to discover new M. tuberculosis antigens which are recognized by patients with tuberculosis, because effective serodiagnostic tests are likely to require combinations of different antigens. In our early experiments using immunoblotting, the findings suggested that human sera from smear-negative tuberculosis patients bound to an antigen in the 45 kDa region. Subsequently, estimates of molecular weight in the immunoblots confirmed that the murine monoclonal antibody (MAB) HGT-6 and sera from patients both recognized the same 45 kDa molecule. An antibody-antibody competition assay between MAB HGT-6 and sera from smear-positive tuberculosis patients yielded a positive result in 23 out of 43 sera from patients, but in only four out of 23 from controls. This is further evidence that the 45 kDa antigen is recognized by tuberculous patients. We analysed whether a combination of the 45 kDa antigen results and those of known antigens might better discriminate between minimal smear-negative disease and healthy controls than could test with single antigens. There is no clinically useful laboratory test for smear-negative tuberculosis. In immunoblotting, combining the results with the 65, 45, 38 and 10 kDa antigens gave the best discrimination. This suggests that future serodiagnostic tests for minimal disease, such as the antibody-antibody competition assay, should contain a MAB against the 45 kDa antigen and possibly also against the 10 kDa antigen.

Modern approach to the diagnosis and treatment of tuberculosis in children

Tuberculosis in children remains an important infectious disease in the United States, with 1261 cases reported in 1985. The percentage of extrapulmonary manifestations is increasing. Advances in the diagnosis and treatment of tuberculosis in children have lagged behind those in adults owing to diminished familiarity with the disease and difficulty in performing clinical studies in children. Tuberculosis in the United States now occurs mainly in clusters of high-risk people, such as the foreign born, Hispanics, blacks, Native Americans, and the impoverished. In general, the diagnosis of tuberculosis is epidemiologic, supported by the chest roentgenogram, skin test, and, most important, contact tracing. As the rate of drug-resistant tuberculosis increases, greater effort should be made to obtain cultures. New advances, such as DNA probes and serodiagnosis, may improve diagnostic accuracy, especially for extrapulmonary tuberculosis. Noncompliance is the major problem in treating tuberculosis, and greater effort should be directed toward novel treatment approaches in children, such as twice-weekly supervised therapy and shorter, more intense durations of therapy.

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.

Assessment of an enzyme linked immunosorbent assay for the detection of cattle infected with Mycobacterium bovis

An indirect enzyme linked immunosorbent assay (ELISA) using an unpurified antigen was assessed for its accuracy in detecting Mycobacterium bovis infected cattle. The ELISA test recorded sensitivities of 88.7% and 63%, respectively, for infected cattle tuberculin tested positive and for infected cattle never tuberculin tested. Specificity was determined at 52.6% for cattle from confirmed free herds which had never been tuberculin tested. Significant differences in the mean ELISA values were recorded between the 3 groups. No evidence was found for long term effects of tuberculin testing upon the titre of antibodies detected by the ELISA in unaffected cattle. The indirect ELISA using the unpurified antigen of this assay was considered to be unsuitable as an alternative to tuberculin testing for the detection of M. bovis infected animals.

Characterization of Mycobacterium tuberculosis antigen 5 epitopes by using a panel of 19 monoclonal antibodies

Antigen 5 is a 35,000-dalton protein which has been purified from culture filtrates of Mycobacterium tuberculosis and shown by immunoprecipitation to be restricted in distribution to M. tuberculosis and M. bovis among 14 mycobacterial species studied. We raised 19 antigen 5-reactive monoclonal antibodies and used them to characterize epitopes of this antigen by enzyme-linked immunosorbent assay and immunoabsorbent affinity chromatography. Fifteen monoclonal antibodies, all immunoglobulin M (IgM), cross-reacted in two major patterns with culture filtrates from five species of mycobacteria and with purified mycobacterial arabinomannan and arabinogalactan. All 15 monoclonal antibodies also reacted with M. tuberculosis antigen 6. Immunoabsorbent affinity columns prepared with these antibodies yielded principally arabinomannan and arabinogalactan. Four monoclonal antibodies, three IgG2a and one IgM, reacted by enzyme-linked immunosorbent assay with antigens 5 and 6 exclusively and not with mycobacterial culture filtrates or polysaccharides. All four monoclonal antibodies yielded antigen 5 and small amounts of antigen 6 when used for immunoabsorbent affinity chromatography. We conclude from these studies that antigen 5 has two nonspecific epitopes, possibly carbohydrate in nature, and one apparent species-specific epitope which is shared with antigen 6.

Demonstration of a shared epitope among mycobacterial antigens using a monoclonal antibody

An IgM monoclonal antibody designated TB-C-1 which is broadly reactive with mycobacteria has been studied to characterize the antigens with which it reacts. Enzyme linked immunosorbent assay (ELISA) demonstrated reactivity not only with culture filtrates of several mycobacterial species but with several purified antigens of Mycobacterium tuberculosis, including protein antigens 5 and 6 and polysaccharides arabinogalactan and arabinomannan. Immunoblotting demonstrated reactivity with four distinct components of M. tuberculosis. Reactions with components of similar mol. wt were demonstrated for several other mycobacterial species, although fewer components bound with TB-C-1 in these other mycobacteria than in M. tuberculosis. Immunoabsorbents were prepared from TB-C-1 and used to isolate antigens with which the antibody reacted. Multiple antigens were identified in the eluates from M. tuberculosis, including protein antigens 6 and 7, arabinomannan, and arabinogalactan. Fewer components were recovered from other species of mycobacteria. Affinity of binding of immunoabsorbents was similar for all antigens bound. These results indicate that a common epitope is widely shared among antigens of M. tuberculosis and other mycobacteria and they suggest that species specificity of mycobacterial antigens may rest with individual epitopes rather than intact antigenic molecules.

Specificity of Mycobacterium tuberculosis antigen 5 determined with mouse monoclonal antibodies

Four mouse monoclonal antibodies have been developed which react with Mycobacterium tuberculosis antigen 5. Each of these monoclonal antibodies has been used to prepare immunoabsorbents, and antigen has been isolated from unheated M. tuberculosis H37Ra culture filtrate by affinity chromatography with these absorbents. Antigen thus obtained was found to be similar in tuberculin reactivity and in enzyme-linked immunosorbent assays to antigen 5 isolated from polyclonal immunoabsorbents, and the protein yields from the monoclonal immunoabsorbents were similar to those from polyclonal absorbents. Antigen recovered from monoclonal absorbents cross-reacted with antigens of Mycobacterium kansasii in delayed skin tests. Immunoelectrophoresis demonstrated that the major component of the antigens eluted from the monoclonal immunoabsorbents was mycobacterial arabinomannan. Antigen 5 was not identified in the eluates by immunoelectrophoresis. These observations support the hypothesis that antigen 5 and M. tuberculosis arabinomannan contain a single major shared epitope.

The immunology of mycobacterial infections

Mycobacteria are endowed with substances that profoundly affect the immune system. Leprosy and tuberculosis exemplify broad spectra of useful and detrimental immune responses of mycobacterial infections that range from intense potentiation to severe specific adn nonspecific suppression of humoral and cellular immune elements. The cellular hypersensitivity induced by mycobacteria serves as a classical model for the analysis of specific and nonspecific immune mechanisms. Mycobacterial disease are prevalent worldwide and rank among the most important bacterial diseases. The kaleidoscope of immunologic events induced by injected mycobacteria and during infections will be reviewed from the standpoint of pathogenesis, pathology, in vitro and in vivo effects on cellular and humoral arms of the immune response, diagnosis, classification, potentiation and suppression.

Specific skin-reactive protein from culture filtrate of Mycobacterium bovis BCG

A highly purified protein, named MPB70, was isolated from the culture filtrate of Mycobacterium bovis BCG. This protein accounted for more than 10% of the proteins secreted into the culture medium. MPB70 was purified by precipitation with ammonium sulfate, followed by treatment with diethylaminoethyl ion exchanger, with or without 3 M urea, and by gel filtration. The final MPB70 preparation was homogenous as judged by several analyses. The molecular weight was estimated to be 18,000 by electrophoresis or molecular sieve and 15,100 by sedimentation equilibrium. The preparation did not contain sugars. The amino acid composition did not include cysteine or tryptophan. In skin reaction, MPB70 was a strictly BCG-specific antigen and, among the guinea pigs sensitized with the heat-killed cells of the various species of mycobacteria--Mycobacterium tuberculosis strains H37Rv and Aoyama B, Mycobacterium kansasii, Mycobacterium intracellulare, Mycobacterium phlei, and BCG, it elicited a delayed cutaneous reaction only in the guinea pigs sensitized with BCG. The potency of MPB70 in the skin reaction was about one-twentieth of the standard purified protein derivative.