Mycobacterial antigens: a review of their isolation, chemistry, and immunological properties

Assessing the impact of various tuberculin PPD brands on bovine tuberculosis diagnosis

Although several brands of tuberculin purified protein derivatives (PPDs) are available for diagnosing bovine tuberculosis (bTB), comparative studies to determine their diagnostic accuracy are infrequent. In Ecuador we compared two different PPD brands for bTB diagnosis using skin testing and measuring skin thickness increase. Additionally, we evaluated four PPD brands, including those used for skin testing, in the Bovine Tuberculosis Interferon Gamma Test (IFN-γ test) measuring IFN-γ induction in whole blood. The study included 17 naturally tuberculosis-infected PPD and IFN-γ test positive bovines. Both the field and laboratory results showed significant differences in classifying the 17 bovines as bTB positive or negative. We hypothesize that several factors, such as the genetic background of the cows, sensitization to environmental mycobacteria, M. bovis strains involved in the bTB infection, and the manufacturing procedures of the PPDs, could have influenced the immune reaction toward the different tuberculin PPD brands. Our study emphasizes the necessity for comparative studies aimed at determining the diagnostic accuracy of PPD brands for bTB diagnosis as well as the development of standardized methods for PPD production and potency determination.

Comparative analysis of tuberculin and defined antigen skin tests for detection of bovine tuberculosis in buffaloes (Bubalus bubalis) in Haryana state, India

BACKGROUND

Bovine tuberculosis (bTB) is a chronic disease that results from infection with any member of the Mycobacterium tuberculosis complex. Infected animals are typically diagnosed with tuberculin-based intradermal skin tests according to World Organization of Animal Health which are presently in use. However, tuberculin is not suitable for use in BCG-vaccinated animals due to a high rate of false-positive reactions. Peptide-based defined skin test (DST) antigens have been identified using antigens (ESAT-6, CFP-10 and Rv3615c) which are absent from BCG, but their performance in buffaloes remains unknown. To assess the comparative performance of DST with the tuberculin-based single intradermal test (SIT) and the single intradermal comparative cervical test (SICCT), we screened 543 female buffaloes from 49 organized dairy farms in two districts of Haryana state in India.

RESULTS

We found that 37 (7%), 4 (1%) and 18 (3%) buffaloes were reactors with the SIT, SICCT and DST tests, respectively. Of the 37 SIT reactors, four were positive with SICCT and 12 were positive with the DST. The results show that none of the animals tested positive with all three tests, and 6 DST positive animals were SIT negative. Together, a total of 43 animals were reactors with SIT, DST, or both, and the two assays showed moderate agreement (Cohen's Kappa 0.41; 95% Confidence Interval (CI): 0.23, 0.59). In contrast, only slight agreement (Cohen's Kappa 0.18; 95% CI: 0.02, 0.34) was observed between SIT and SICCT. Using a Bayesian latent class model, we estimated test specificities of 96.5% (95% CI, 92-99%), 99.7% (95% CI: 98-100%) and 99.0% (95% CI: 97-100%) for SIT, SICCT and DST, respectively, but considerably lower sensitivities of 58% (95% CI: 35-87%), 9% (95% CI: 3-21%), and 34% (95% CI: 18-55%) albeit with broad and overlapping credible intervals.

CONCLUSION

Taken together, our investigation suggests that DST has a test specificity comparable with SICCT, and sensitivity intermediate between SIT and SICCT for the identification of buffaloes suspected of tuberculosis. Our study highlights an urgent need for future well-powered trials with detailed necropsy, with immunological and microbiological profiling of reactor and non-reactor animals to better define the underlying factors for the large observed discrepancies in assay performance, particularly between SIT and SICCT.

Diagnostic Potential of IgG and IgA Responses to Mycobacterium tuberculosis Antigens for Discrimination among Active Tuberculosis, Latent Tuberculosis Infection, and Non-Infected Individuals

Tuberculosis remains a major public health problem. Conventional tests are inadequate to distinguish between active tuberculosis (ATB) and latent tuberculosis infection (LTBI). We measured antibody responses to Mycobacterium tuberculosis antigens (Mycobacterium tuberculosis chorismate mutase (TBCM), antigen 85B (Ag85B), early secreted antigen-6 (ESAT-6), and culture filtrate protein-10 (CFP-10) in ATB, LTBI, and non-infected (NI) individuals. Serum immunoglobulin G (IgG) and immunoglobulin A (IgA) levels were measured and the QuantiFERON-TB Gold In-Tube assay was used to diagnose LTBI. IgG levels against TBCM were significantly higher in LTBI than NI subjects. IgG and IgA levels against Ag85B and IgG levels against CFP-10 were significantly higher in ATB, followed by LTBI, and then NI. When the ATB group was subdivided, IgG levels against Ag85B and CFP-10 were significantly higher in each subgroup compared with those in LTBI and NI groups. Positive correlation trends between interferon-gamma and IgG levels against Ag85B, TBCM, and CFP-10 and IgA levels against Ag85B in LTBI and NI subjects were observed. Age- and sex-adjusted models showed that IgG against TBCM and CFP-10 was independently related to LTBI diagnosis, and IgG against Ag85B was independently related to the diagnosis of ATB and could distinguish between LTBI and ATB. Overall, IgG antibody responses to TBCM, Ag85B, and CFP-10 can discriminate among ATB, LTBI, and NI groups.

Detection and characterization of purified antigenic proteins from culture filtrate of Mycobacterium bovis strain AN5

BACKGROUND AND OBJECTIVES

Bovine tuberculosis diagnosis is usually performed by various tests with specific limitations. Mycobacterium bovis culture filtrate contains antigenic proteins that could be used to improve the sensitivity of bovine tuberculosis diagnosis. The objective of this study was to identify and purify antigenic proteins from culture filtrates of M. bovis strain AN5 for use in immunological assays.

MATERIALS AND METHODS

Secreted proteins were purified from the heat-treated culture filtrate of M. bovis strain AN5. Proteins were precipitated with ammonium sulfate, fractionated by Sephadex G50 chromatography. The protein concentrations and the approximate molecular weight were determined by lowry method and 12% sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), respectively. Immunological methods, including dot-blotting and western blotting, assessed the quality of the isolated proteins.

RESULTS

The quantity of antigenic proteins in the culture medium was measured at far more than 15% of the amount of proteins secreted into medium. Three main chromatographic fractions obtained and showed concentrations of proteins ranging from 14 to 60 μg/ μl with molecular weights in the 10 to 180 kDa range. The purified antigens showed positive reactions to the infected cattle serum throughout dot-blotting. Western blotting revealed a total of 15 to 70 kDa molecular weight proteins.

CONCLUSION

Immunoblotting analysis made it possible to detect and recognize novel antigens that are useful for bovine tuberculosis diagnosis improvement. This is significant since non-specific reactions were not observed when we utilized serum of cattle experimentally infected with M. bovis as a polyclonal antibody.

Tuberculin PPD Potency Assays in Naturally Infected Tuberculous Cattle as a Quality Control Measure in the Irish Bovine Tuberculosis Eradication Programme

The Irish Bovine Tuberculosis (bTB) eradication programme operates under national legislation and fulfills OIE and EU trade requirements. Tuberculin purified protein derivative (PPD), a preparation obtained from the heat-treated products of growth and lysis of Mycobacterium bovis or Mycobacterium avium (as appropriate), is critical to the diagnosis of tuberculosis (TB). Standardization of Tuberculin PPD potency, the relative activity in sensitized animals compared to a reference standard, is essential to underpin the reliability of certification for international trade and to ensure that disease eradication programmes are effective and efficient. A Bovine International Standard Tuberculin PPD (BIS) was established by the WHO in 1986 and is used to determine comparative potencies of Tuberculin PPDs. Ideally, Tuberculin PPD potency should be evaluated in the species in which the tuberculin will be used but due to practical difficulties in performing potency assays in cattle, for routine PPD production, they are usually assayed in guinea pigs. Low potency tuberculin PPD is less efficient and thus inferior for bTB diagnosis. Difficulties experienced in the Irish bTB eradication programme have included the supply of sub-standard potency, and thus inferior, bovine (M. bovis) Tuberculin PPD in the late 1970s. The purpose of this paper is to outline the critical role of Tuberculin PPD assays carried out on naturally infected tuberculous cattle, as required by the OIE and under EU legislation in the quality control for the Irish Bovine Eradication Programme. Such assays ensure that the Tuberculin PPD used meets the diagnostic sensitivity and specificity requirements to underpin a successful national eradication programme.

Production of MPT-64 recombinant protein from virulent strain of Mycobacterium bovis

Tuberculosis (TB) is a zoonotic infectious disease common to humans and animals which has been caused by a rod shaped, acid fast bacterium, called Mycobacterium bovis. The rapid and sensitive detection is a great challenge for TB diagnosis. The virulent strains of Mycobacterium tuberculosis complex (MTBC) have 16 different regions of difference (RD) in their genome which encode some important antigens. The major protein of M. bovis 64 (MPT-64) is one of the main immune-stimulating antigens which are encode by RD-2 region. The aim of the present study was cloning, expression and purification of MPT-64 as a protein antigen of M. bovis in a prokaryotic system for the usage in the future diagnostic studies. In this experimental study, the mpt-64 gene with 687 bp has been proliferated from M. bovis whole genome by polymerase chain reaction (PCR) method. The PCR product has been digested by BamHI and HindIII restriction enzymes and cloned into pQE-30 plasmid. The recombinant protein has been expressed in the Escherichia coli M15 with induction by isopropyl-β-D-thiogalactopyranoside (IPTG). The expressed protein was analyzed on SDS-PAGE, and purified with Nitrilotriacetic acid (Ni-NTA) column. Finally, its biological properties were confirmed in Western blotting method using specific antibodies. Data showed the successful cloning of mpt-64 gene (as a 687 bp segment) in expression vector. The MPT-64 recombinant protein was ideally expressed and purified as a 24 kDa protein. The result of this study indicated that MPT-64 recombinant protein (24 kDa) has been successfully expressed and purified in a prokaryotic system, so this protein could be used for differential diagnosis of pathogenic and non-pathogenic Mycobacterium, in suspected BTB cases.

The performance of quantiferon-TB gold in-tube (QFT-IT) test compared to tuberculin skin test (TST) in detecting latent tuberculosis infection (LTBI) in the presence of HIV coinfection in a high TB-burden area with BCG-vaccinated population

OBJECTIVES

To compare quantiferon-TB gold "in tube" (QFT-IT) with the conventional tuberculin skin test (TST) for the diagnosis of latent tuberculosis infection (LTBI) in HIV-infected adults in a setting highly endemic for tuberculosis with BCG vaccinated population in Bangalore, Karnataka, India.

PATIENTS AND METHODS

The study population (100 BCG-vaccinated adults) was divided into 4 groups: HIV patients with TB patient contact, HIV patients with past history of TB, TB patients (positive control), and healthy volunteers (negative control).

RESULTS

Overall agreement between TST and QFT-IT was 52.4% (κ = 0.22). Increasing the TST cutoff value from 5 mm to 10 mm among HIV-positive groups resulted in better agreement 62.5% in Group 1 and 81.2% in Group 2.

DISCUSSION

In a setting with high TB prevalence, the TST gives increased false positives in HIV-positive groups if 5 mm is used as the cutoff value. This could be minimized by increasing the cutoff to 10 mm.

CONCLUSION

The 2-step approach (initial testing of all cases with TST and confirmation of only those positive in TST by testing with QFT-IT) will be economical and help in treating LTBI cases in lower middle income countries like India.

The prevalence and predictors of tuberculin positivity in subjects screened for reasons other than contact investigation

BACKGROUND

No previous studies have estimated the rates of tuberculin positivity (TP) in noncontact populations within the same community, which is important for prioritizing and implementing preventive measures.

OBJECTIVES

To estimate the prevalence and predictors of TP in noncontact populations.

METHODS

A retrospective analysis of tuberculin results of noncontact populations screened in British Columbia from 1990 to 2002 was conducted.

RESULTS

The period prevalence of TP in 59,791 screened subjects was 12.7% (95% CI 12.4% to 13.0%), 30.4% (95% CI 28.2% to 32.7%) and 60.9% (95% CI 60.3% to 61.6%) for Canadian-born non-Aboriginals (CBNAs), Canadian-born Aboriginals (CBAs) and foreign born (FB), respectively. After controlling for age and sex, independent predictors of TP included Bacille Calmette-Guérin (BCG) vaccination (OR 19.6, 95% CI 17.9 to 21.5), country of birth (CBA: OR 2.87, 95% CI 2.44 to 3.37; FB: OR 3.67, 95% CI 3.34 to 4.03) and the following populations: correctional centre residents (OR 4.14, 95% CI 1.87 to 9.15), residents of long-term care and community care facilities (OR 1.79, 95% CI 1.44 to 2.23), immigrants (OR 1.75, 95 % CI 1.50 to 2.04), health centre employees (OR 1.71, 95 % CI 1.56 to 1.88), volunteers (OR 1.38, 95% CI 1.14 to 1.68), self-referred healthy subjects (OR 1.30, 95% CI 1.15 to 1.48) and students (OR 1.27, 95% CI 1.19 to 1.35). CBAs, FB and male subjects were less likely to react to tuberculin than CBNAs and female subjects among those vaccinated with Bacille Calmette-Guérin (P<0.05).

CONCLUSIONS

Rates of TP correlate with disease rates by sex and origin. The continuation of tuberculin screening programs is warranted in noncontact populations with high TP rates, where unknown exposure to active cases is more likely to occur. Further research is needed to determine the reasons why a higher response to tuberculin occurs in BCG-vaccinated women and CBNAs.

Risk factors for positive tuberculin skin test in Guinea-Bissau

BACKGROUND

The tuberculin skin test is used for tracing of tuberculosis transmission and identifying individuals in need of prophylactic treatment.

METHODS

Using a case-control study design, we recruited 220 smear-positive tuberculosis cases and 223 randomly selected healthy community controls in Bissau, Guinea-Bissau, during 1999-2000. Tuberculin skin tests were performed on family members of cases and controls (n = 1059 and n = 921, respectively). Induration of 10 mm or greater was considered positive. Risk factors were calculated for children (<15 years) and adults separately in multivariate logistic regression analysis.

RESULTS

The prevalence of positive tuberculin skin test was 41% in case-contacts compared with 22% in control-contacts, resulting in a prevalence ratio of 1.48 (95% confidence interval = 1.37-1.60). Positive skin tests among case-contacts increased with age for children, as well as with proximity to a case during the night, for both children and adults. A Bacille Calmette Guerin scar increased the likelihood of having a positive tuberculin skin test for adults in case households, but not in other categories of contacts. Among control-contacts the prevalence of positive skin test was associated with older age in children, history of tuberculosis in the family, and a positive tuberculin skin test of the control person.

CONCLUSIONS

Risk factors for a positive tuberculin skin test among case- and control-contacts are closely related to tuberculosis exposure. Having a BCG scar did not increase the risk of positive skin test in unexposed individuals. Tuberculin skin testing remains a useful tool for diagnosing tuberculosis infection.

Rapid identification of tissue micro-organisms in skin biopsy specimens from domestic animals using polyclonal BCG antibody

Immunostaining with polyclonal anti-Mycobacterium bovis (BCG) was evaluated as a single screening method for the histological identification of micro-organisms in skin biopsy specimens from various veterinary species. Confirmed archival cases infected with Mycobacteria, Nocardia, Actinobacillus, Actinomyces, Streptococcus/Staphylococcus, Dermatophilus, spirochetes, Blastomyces, Coccidioides, Cryptococcus, Histoplasma, dermatophytes, Malassezia, Sporothrix, Leishmania, Pythium, phaeohyphomycetes and Prototheca organisms were selected. A total of 70 skin biopsy specimens from the dog, cat, horse, ox and llama were evaluated. The anti-BCG immunostain labelled bacteria and fungi with high sensitivity and minimal background staining but did not label spirochetes and protozoa (Leishmania). Differences were not noted between veterinary species. The results indicate that immunostaining with polyclonal anti-BCG is a suitable screening technique for the rapid identification of most common bacterial and fungal organisms in paraffin-embedded specimens. Also, mycobacterial and nocardial organisms were identified more readily with the anti-BCG immunostain in comparison to the histochemical stains.

Use of Mycobacterium tuberculosis complex-specific antigen cocktails for a skin test specific for tuberculosis

The tuberculin skin test currently used to diagnose infection with Mycobacterium tuberculosis has poor diagnostic value, especially in geographic areas where the prevalence of tuberculosis is low or where the environmental burden of saprophytic, nontuberculous mycobacteria is high. Inaccuracy of the tuberculin skin test often reflects a low diagnostic specificity due to the presence in tuberculin of antigens shared by many mycobacterial species. Thus, a skin test specific for tuberculosis requires the development of new tuberculins consisting of antigens specific to M. tuberculosis. We have formulated cocktails of two to eight antigens of M. tuberculosis purified from recombinant Escherichia coli. Multiantigen cocktails were evaluated by skin testing guinea pigs sensitized with M. bovis BCG. Reactivity of multiantigen cocktails was greater than that of any single antigen. Cocktail activity increased with the number of antigens in the cocktail even when the same amount of total protein was used for cocktails and for each single antigen. A cocktail of four purified antigens specific for the M. tuberculosis complex elicited skin test responses only in BCG-immunized guinea pigs, not in control animals immunized with M. avium. These findings open the way to designing a multiantigen formulation for a skin test specific for tuberculosis.

Purification of Mycobacterium bovis BCG Tokyo antigens by chromatofocusing, lectin-affinity chromatography, and hydrophobic interaction chromatography

A combination of chromatofocusing, lectin-affinity chromatography, and hydrophobic interaction chromatography resulted in a simple purification of protein antigens of Mycobacterium bovis BCG Tokyo culture filtrate. Identification was established on the basis of chromatographic separation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis determination of molecular weights, and N-terminal amino acid determination. Chromatofocusing on PBE 94 accomplished the separation of BCG85B from other BCG85 complex antigens and partial separation of MPB64 and MPB70 antigens. Subsequently, MPB64 and MPB70 were completely separated on a high-performance liquid chromatography TSK Phenyl 5PW hydrophobic interaction chromatography column. This column also separated BCG85B from a 17-kDa protein with an N-terminal amino acid sequence of A-V-P-I-T-G-K-L-G-S-E-L-T-M-T-D-( )-V-G-Q, which is similar to the sequence of MPT63. Concanavalin A-Sepharose-affinity chromatography separated MPB64 from a 43- and 47-kDa doublet with an amino acid sequence of D-P-E-P-A-P-P-V-P-P-V-P-A-( )-A-A-S-P, which is similar to the sequence of MPT32 and which appears to be glycosylated.

Comparison of two 2,3-diacyl trehalose antigens from Mycobacterium tuberculosis and Mycobacterium fortuitum for serology in tuberculosis patients

Immunoglobulin G antibodies against two 2,3-diacyl trehalose (DAT) antigens from Mycobacterium tuberculosis (DATT) and Mycobacterium fortuitum (DATF) were studied by enzyme-linked immunosorbent assay of 356 serum samples. The sera were obtained from non-tuberculosis-infected individuals (282 serum samples) and tuberculosis patients (74 serum samples). Non-tuberculosis-infected individuals were healthy people (120 serum samples; positive purified-protein-derivative skin test, 60 patients; negative purified-protein-derivative skin test, 60 patients) patients with nontuberculosis lung disease (59 serum samples), contacts of sputum-smear-positive tuberculosis patients (57 serum samples), and human immunodeficiency virus-infected patients with nontuberculosis lung disease (46 serum samples). Of the 74 patients with tuberculosis, 14 were human immunodeficiency virus infected. The sensitivity of the method using DATT was 44.5%, and that with DATF was 48.6%. The specificities with both antigens were 99.1%. There were no significant differences between the mean values for both antigens (P = 0.2815). We therefore concluded that both antigens were interchangeable. As M. fortuitum, a fast-growing mycobacterium, could be a good source of antigen DAT, these results deserve consideration in the serology of tuberculosis.

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.

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.

Serodiagnostic efficiency of phospholipid associated protein of Mycobacterium tuberculosis H37Rv

The phospholipid-associated protein (55-67 kDa) fraction of Mycobacterium tuberculosis H37Rv was purified as the DE-V protein fraction. This DE-V fraction was used for diagnosis of tuberculosis by enzyme-linked immunosorbent assay (ELISA), detecting IgG antibody in sera collected from different categories of tuberculosis patients, i.e. with acid fast bacilli (AFB) culture-positive pulmonary tuberculosis, with AFB culture-negative, but radiologically suspected, pulmonary tuberculosis, extrapulmonary tuberculosis, and control groups of patients suffering from diseases other than tuberculosis (asthma and/or rhinitis, lepromatous leprosy) as well as from healthy volunteers. Encouraging operational ELISA validity could be achieved with 93% sensitivity, 100% specificity, 97% efficiency, 100% positive predictivity and 95% negative predictability even among the extrapulmonary and suspected pulmonary tuberculosis patients. The above assay was insensitive but with 100% specificity among control group of patients suffering from diseases other than tuberculosis. The DE-V protein fraction was associated with phosphatidyl inositol and phosphatidyl inositol mannosides. The dissociation of phospholipid-protein complex decreased ELISA specificity. ELISA reactivity of the DE-V fraction appeared to be thermostable; thus, it may have serodiagnostic utility in developing countries.

Identification of a Mycobacterium bovis BCG 45/47-kilodalton antigen complex, an immunodominant target for antibody response after immunization with living bacteria

Increased protection against a virulent challenge with Mycobacterium tuberculosis is induced mainly by a previous immunization with living avirulent mycobacteria, usually Mycobacterium bovis BCG. Only a transient and marginal protection is obtained after immunization with bacterial extracts or dead bacteria. Both living and heat-killed bacteria share a number of common antigens. In order to identify mycobacterial molecules which are dominant antigens during immunization with living bacteria, a two-step selection method was used. Two groups of guinea pigs were immunized either with living or with heat-killed BCG. Sera were then collected and used to select and counterselect antigens present in BCG culture filtrates. Each major fraction eluted from a series of high-pressure liquid chromatography columns (gel filtration, DEAE, and reverse-phase chromatography) was run on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred on polyvinylidene difluoride sheets. The molecules present on twin immunoblots were stained with antibodies raised in guinea pigs immunized either with living or with heat-killed BCG. Cross-reactive antigens stained in twin immunoblots were eliminated. Major antigens interacting with antibodies raised after immunization only with living bacteria were further purified. A complex of 45- and 47-kDa major molecules (45/47-kDa complex) was thus identified and further purified. The complex was found to interact only with antibodies present in sera of guinea pigs immunized with living bacteria and not at all with antibodies raised after immunization with dead bacteria. The 45/47-kDa antigen complex molecules were resolved on two-dimensional electrophoresis in three major and seven minor proteins detected with silver staining. All the molecules interacted with the antibodies present in sera of guinea pigs immunized with living BCG. The three major proteins (two at 47 kDa and one at 45 kDa) were amino-terminal sequenced. The sequence A-P-E-P-A-P-P-V-P-P-A-A-A-A-P-P-A, which was not previously reported, was the same for these three molecules. By using a competitive enzyme-linked immunosorbent assay, the concentrations of the 45/47-kDa antigen complex were measured in BCG culture filtrates, freeze-dried BCG, and dried heat-killed BCG; they were, respectively, 2, 0.01, and 0.001% of the total mass. The low or very low values compared with the high antibody concentration emphasized the ability of the 45/47-kDa complex delivered through live BCG to trigger an antibody response.

Lymphocyte production of gamma-interferon as a test for non-tuberculous mycobacterial lymphadenitis in childhood

Infection with Mycobacterium avium, M. intracellulare and M. scrofulaceum (MAIS) organisms in normal children may result in cervical lymphadenopathy. There is a poor response to anti-tuberculous therapy and surgical excision of infected nodes is necessary. The diagnosis therefore requires consideration in children with cervical lymphadenopathy. A simple in vitro assay is described which may be useful for diagnosis prior to excision. Whole blood is cultured with M. avium purified protein derivative. After 24 h the plasma is removed and the concentration of gamma interferon (IFN-gamma) quantified by a radioimmunometric assay. In a prospective study of 38 children with neck lesions, 16 showed MAIS organisms isolated from cultures of excised tissue. The level of IFN-gamma produced by peripheral blood lymphocytes from children in the MAIS group was significantly greater when compared with children having operations for neck lesions that were not due to MAIS organisms (P < 0.001).

Characterization of the major membrane protein of virulent Mycobacterium tuberculosis

A protein with a molecular mass of 19 kDa was isolated and purified from enriched membrane fractions of the virulent Erdman strain of Mycobacterium tuberculosis. The protein is different from another 19-kDa protein, a lipoprotein, that was recently described (D. B. Young and T. R. Garbe, Res. Microbiol. 142:55-65, 1991). The sequencing strategy applied to this major membrane protein employed four different endoproteinases and resulted in sufficient overlapping peptide sequences for assignment of the entire protein sequence. Electron spray ionization mass spectrometry demonstrated a measured mass of 16,100, deviating from the predicted mass by only 2.86 atomic mass units. The sequence of this protein is unique. However, some similarities with other low-molecular-weight heat shock proteins were observed. Immunoblotting indicated that this protein is highly expressed in the virulent strains of M. tuberculosis. Its application to sera from patients with pulmonary tuberculosis showed promise as a serodiagnostic tool.

Detection of mycobacterial antigens in sputum by an enzyme immunoassay

An enzyme immunoassay (EIA) for the detection of mycobacterial antigens in sputum was evaluated. The system utilises commercially available anti-BCG immunoglobulin. BCG protein standard was used as positive control. Thirty-nine patients with culture-proven pulmonary tuberculosis were tested. The EIA was positive in 24 of 29 patients with positive smears and cultures, giving a sensitivity of 86.2%. It was also positive in six of ten patients with smear-negative culture-positive disease, resulting in a sensitivity of 60% in this group. In another 176 patients with different nontuberculous pulmonary infections, only nine were positive by EIA, giving a specificity of 94.9%. The high sensitivity and specificity of the assay make it a useful tool for the early diagnosis of pulmonary tuberculosis.

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.

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.

Antibody to selected strains of Saccharomyces cerevisiae (baker's and brewer's yeast) and Candida albicans in Crohn's disease

IgG serum antibody was measured by ELISA in patients with Crohn's disease (15), ulcerative colitis (15), and in normal controls (15) to 12 strains of Saccharomyces cerevisiae (baker's and brewer's yeast) and to the two major serotypes of the commensal yeast Candida albicans. Antibody to 11 of the 12 strains of S cerevisiae was raised in patients with Crohn's disease but not in patients with ulcerative colitis when compared with controls (p less than 0.001). The pattern of antibody response to these 11 strains was variable, however, suggesting the likelihood of antigenic heterogeneity within the species. Antibody to C albicans was not significantly different in patient and control groups. The specificity of this unusual antibody response in Crohn's disease for S cerevisiae suggests that it is not simply the result of a generalised increase in intestinal permeability. Furthermore, because brewing and baking strains detected the response, the relevant antigen(s) are presumably common in the diet. Hypersensitivity to dietary antigens may be involved in the pathogenesis of Crohn's disease, and the role of S cerevisiae requires further investigation.

Protein G-based enzyme-linked immunosorbent assay for anti-MPB70 antibodies in bovine tuberculosis

MPB70 is a highly species specific protein which is secreted from Mycobacterium bovis during culture. To investigate whether antibodies against MPB70 can be used as an indicator of infection with M. bovis, an enzyme-linked immunosorbent assay was developed, based on the use of biotinylated protein G, to provide a common indicator for antibody formation in different species. During experimental infection with M. bovis in cattle, a characteristic pattern of anti-MPB70 antibody production was observed with an initial flat plateau followed by a marked rise 18 to 20 weeks after infection. Skin testing with bovine tuberculin purified protein derivative (PPD), which was shown to contain antibody-reactive MPB70, was a potent stimulator of antibody production in infected animals. In experimentally infected cattle, we observed an inverse relationship between antibody activity and delayed-type hypersensitivity skin test reactions. In natural M. bovis infections, skin testing with PPD was also a potent stimulator of anti-MPB70 formation. Comparison between the enzyme-linked immunosorbent assay for antibodies to MPB70 and that for antibodies to the widely cross-reacting M. bovis BCG antigen 85B in animals with M. bovis, Mycobacterium avium, Mycobacterium paratuberculosis, and Corynebacterium pseudotuberculosis infections showed that formation of antibody to MPB70 was highly specific for infection with M. bovis. The use of an MPB70-containing PPD preparation for skin testing followed by this anti-MPB70 assay is a highly specific indicator of M. bovis infection. Adjustment of the test conditions is expected to provide an increased sensitivity of the procedure for the diagnosis of natural M. bovis infections.

Enzyme-linked immunosorbent assay for distinguishing serological responses of lepromatous and tuberculoid leprosies to the 29/33-kilodalton doublet and 64-kilodalton antigens of Mycobacterium tuberculosis

Immunoblot assays for the antibodies to Mycobacterium tuberculosis sonic extracts showed that all serum specimens of 40 lepromatous and of 28 tuberculoid leprosy patients reacted in a significant manner to 29/33-kilodalton (kDa) doublet and 64-kDa antigens, respectively. By using an enzyme-linked immunosorbent assay, we observed a significantly high immunoglobulin G antibody titer to the purified M. tuberculosis 29/33-kDa doublet and 64-kDa antigens in lepromatous and tuberculoid leprosy patients, respectively, as compared with normal subjects and tuberculosis patients. This enzyme-linked immunosorbent assay serology may be useful for distinguishing two polar types of leprosy and for diagnosing leprosy in general.

Serodiagnostic tests for tuberculosis: a need for assessment of their operational predictive accuracy and acceptability

There have been numerous unsuccessful attempts to develop clinically useful serodiagnostic tests for tuberculosis. Although the large number of published reports clearly show that antibody levels are significantly higher in patients, as a group, than in a control population, little consideration is given to the value of the tests in various operational situations. In this paper we review the criteria generally used to assess the usefulness of a diagnostic test and introduce two new concepts--namely, operational predictive accuracy and operational acceptability.

Identification of a 35-kilodalton Mycobacterium tuberculosis protein containing B- and T-cell epitopes

Screening of a Mycobacterium tuberculosis genomic DNA library in the lambda gt11 expression vector was carried out by using, as probes, sera from tuberculous patients and murine monoclonal antibody H61.3 recognizing a mycobacterial 35-kilodalton protein present only on the M. tuberculosis complex. The recombinant beta-galactosidase-fused protein present in the crude lysate induced the proliferation of T lymphocytes from patients with tuberculous pleuritis. As the recombinant insert contains an internal EcoRI restriction site, it was possible to identify two fragments, one proximal to the lacZ gene and 1.7 kilobases (kb) in size and the other distal to the lacZ gene and 2.2 kb in size. Southern blot analysis showed that both of them hybridized with the genomic DNA from M. tuberculosis and M. bovis but not with the DNA from other mycobacterial species. To perform extensive immunological studies, the amount of beta-galactosidase-fused protein being very low, we fused the 1.7-kb fragment to the N-terminal part of the gene coding for the DNA polymerase of bacteriophage MS2 in the expression vector pEx34. The fusion protein was partially purified, and subsequent Western blotting (immunoblotting) and T-cell proliferation experiments confirmed the presence of B- and T-cell mycobacterial epitopes. Furthermore, to isolate the chromosomal region containing the 35-kilodalton gene, we constructed another mycobacterial genomic library in the lambda 2001 vector by cloning 15 to 20 kb of foreign DNA. Screening of this library was carried out by using 1.7- and 2.2-kb recombinant fragments as probes. Restriction maps of some clones isolated were determined.

Rapid identification of serotypes of Mycobacterium avium-M. intracellulare complex by using infected swine sera and reference antigenic glycolipids

The species of 136 strains of acid-fast bacteria isolated from swine with mycobacteriosis were identified by numerical taxonomy and chemotaxonomy on the basis of mycolic acid subclass composition as members of the Mycobacterium avium-M. intracellulare (MAI) complex. The isolates were further classified by using both thin-layer chromatography of the antigenic glycopeptidolipids (GPL) obtained from the bacteria by the method of Tsang et al. (A. Y. Tsang, I. Drupa, M. Goldberg, J. K. McClatchy, and P. J. Brennan, Int. J. Syst. Bacteriol. 33:285-292, 1983) and the seroagglutination test devised by W. B. Schaefer (Am. Rev. Respir. Dis. 92[Suppl.]:85-93, 1965). For the reference standard, purified antigenic GPL of serotypes 4, 8, and 9 were isolated and their structures were analyzed by negative fast-atom bombardment-mass spectrometry. The fast-atom bombardment-mass spectrometric spectra of the intact GPL antigens of serotypes 4, 8, and 9 agreed with the structures reported earlier by Brennan et al. (P. J. Brennan and M. B. Goren, J. Biol. Chem. 254:4205-4211, 1979; P. J. Brennan, G. O. Aspinall, and J. E. Nam Shin, J. Biol. Chem. 256:6817-6822, 1981). With these antigenic GPL, the thin-layer chromatographic behaviors of the alkali-stable lipids of the above-described isolates were examined. These MAI complex isolates fell into the serotype 8 (85 strains), 4 (33 strains), and 9 (7 strains) and untypeable (11 strains) categories. Furthermore, an enzyme-linked immunosorbent assay (ELISA) based on type-specific glycolipid antigens and infected swine sera was used to diagnose the serological types of the MAI complex isolates. Of 14 cases typed by both the seroagglutination reaction and thin-layer chromatography, 13 showed clear agreement with the ELISA results. The results demonstrated that ELISA using infected sera was especially useful, and it can be recommended on the basis of simplicity, sensitivity, and specificity as an adjunct to the seroaggulutination test and thin-layer chromatography for identification of mycobacteria belonging to the MAI complex.

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

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

Detection of mycobacterial antigens in cerebrospinal fluid by enzyme-linked immunosorbent assay

By use of commonly available antibodies against Mycobacterium bovis BCG, Mycobacterium tuberculosis antigens can be detected by a rapid and sensitive double-antibody sandwich enzyme-linked immunosorbent assay (ELISA). The ELISA was dose-dependent and capable of detecting as little as 4 ng of antigens. Absorbance for 5 patients with confirmed tuberculous meningitis ranged from 0.150 to 0.600 with a mean value of 0.271 +/- 0.190. For 134 non-meningitis control patients and 6 treated tuberculous meningitis patients, optical densities were 0.032 +/- 0.009 and 0.029 +/- 0.010, respectively. Specificity was demonstrated by the negative results (0.028 +/- 0.006) with bacterial and cryptococcal antigens. Maximum cross-reactivity with non-tuberculous mycobacterial antigens was less than 7%.

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).

Crohn's disease and the mycobacterioses: a review and comparison of two disease entities

Crohn's disease is a chronic granulomatous ileocolitis, of unknown etiology, which generally affects the patient during the prime of life. Medical treatment is supportive at best, and patients afflicted with this disorder generally live with chronic pain, in and out of hospitals, throughout their lives. The disease bears the name of the investigator who convincingly distinguished this disease from intestinal tuberculosis in 1932. This distinction was not universally accepted, and the notion of a mycobacterial etiology has never been fully dismissed. Nevertheless, it was 46 years after the distinction of Crohn's disease and intestinal tuberculosis before research attempting to reassociate mycobacteria and Crohn's disease was published. Recently, there has been a surge of interest in the possible association of mycobacteria and Crohn's disease due largely to the isolation of genetically identical pathogenic Mycobacterium paratuberculosis from several patients with Crohn's disease in the United States, the Netherlands, Australia, and France. These pathogenic organisms have been isolated from only a few patients, and direct evidence for their involvement in the disease process is not clear; however, M. paratuberculosis is an obligate intracellular organism and strict pathogen, which strongly suggests some etiologic role. Immunologic evidence of a mycobacterial etiology, as assessed by humoral immune determinations, has been conflicting, but evaluation of the more relevant cellular immunity has not been performed. Data from histochemical searches for mycobacteria in Crohn's disease tissues have been equally conflicting, with acid-fast bacilli detected in 0 to 35% of patients. Animal model studies have demonstrated the pathogenic potential of isolates as well as elucidated the complexity of mycobacterial-intestinal interactions. Treatment of Crohn's disease patients with antimycobacterial agent has not been fully assessed, although case reports suggest efficacy. The similarities in the pathology, epidemiology, and chemotherapy of Crohn's disease and the mycobacterioses are discussed. The issue is fraught with controversy, and the data generated on the association of mycobacteria and Crohn's disease are in their infantile stages so that a general conclusion on the legitimacy of this association cannot be made. While no firm evidence clearly implicates mycobacteria as an etiologic agent of Crohn's disease, the notion is supported by suggestive and circumstantial evidence and a remarkable similarity of Crohn's disease to known mycobacterial diseases.

Monoclonal antibodies produced in BALB.B10 mice define new antigenic determinants in culture filtrate preparations of Mycobacterium tuberculosis

A panel of monoclonal antibodies were derived from BALB.B10 mice immunized with a culture filtrate from Mycobacterium tuberculosis H37Rv. Of these antibodies, 10 were examined more closely for antigen specificity and interspecies reactivity. Six antibodies were used as immunosorbents for affinity purification of their corresponding antigens. Two monoclonal antibodies (HBT 2 and HBT 11) reacted with a 17-kilodalton antigen, and a competition assay showed that these antibodies are directed against the same epitope or against epitopes that are sterically very close to each other. Monoclonal antibody HBT 12 reacted with the same molecule with which a previously described 38-kilodalton reactive antibody reacted but was directed against a different epitope. Antibody HBT 10 reacted with a culture filtrate of M. tuberculosis but not of Mycobacterium bovis BCG. This latter finding was further studied by testing different preparations of M. tuberculosis H37Rv antigens and, additionally, culture filtrates of four M. tuberculosis and two BCG strains. Interspecies reactivity was assayed by immunoblotting and revealed that the majority of the monoclonal antibodies were specific to M. tuberculosis complex.

Antibodies to mycobacterial peptidoglycolipid and to crude protein antigens in sera from different categories of human subjects

Sera from patients with disease caused by the Mycobacterium avium complex (M. avium and M. intracellulare), M. kansasii, or M. tuberculosis and from subjects who did not have a mycobacterial disease were tested by enzyme-linked immunosorbent assay against peptidoglycolipid antigens representing each of the 15 most common serovars of the M. avium complex and against crude protein antigen extracts of M. avium and M. tuberculosis. The highly specific peptidoglycolipid antigens yielded positive reactions in 83% of M. avium complex patients, 57% of active-tuberculosis patients, and 14% of subjects without mycobacterial disease. Reactions to more than 1 of the 15 peptidoglycolipid antigens were found only in patients with infections caused by mycobacteria, suggesting that a mycobacterial pulmonary lesion is readily colonized by mycobacteria other than the one that initiated the lesion. The two crude mycobacterial protein antigens were highly cross-reactive, with little if any capacity to discriminate between infections caused by any of the mycobacteria studied. Moreover, they did not appear to be more sensitive than the peptidoglycolipids. The data suggest that it is unlikely that a practical and reliable serological test can be developed that will distinguish between transient subclinical infection and significant disease caused by common environmental mycobacteria, such as members of the M. avium complex. Success in developing such a test for nonenvironmental mycobacteria, such as M. tuberculosis, appears more likely.

Serodiagnosis survey of tuberculosis by a new ELISA method

In a survey study, the authors used a new Elisa test, designed by Anda Biologicals, Strasbourg, France, to detect specific IgG and IgM antibodies against A60 antigen. Blood samples from 53 subjects were tested with this serological method: 22 with no tubercular diseases and 31 affected by different tubercular lesions. The IgM titers were negative in all control group subjects, in two out of fourteen patients with progressive primary tuberculosis, in thirteen out of sixteen with secondary tuberculosis and in one patient with extrapulmonary tuberculosis. The IgG titers were positive (greater than 1.25 Elisa units) in all cases, except one, of progressive primary tuberculosis, in all cases, except two, of secondary tuberculosis and in the patient affected by extrapulmonary tuberculosis. The performance of this method and the overall results indicate its sensitivity and reliability to detect specific mycobacterial antibodies at different stages of the disease.

Serodiagnostic potentialities of enzyme-linked immunosorbent assay (ELISA) using mannophosphoinositides of Mycobacterium tuberculosis H37Rv

The serological response to mannophosphoinositides of Mycobacterium tuberculosis H37Rv and to tuberculin-purified protein derivative (PPD) was examined by enzyme-linked immunosorbent assay (ELISA) in patients suffering from tuberculosis and related diseases. In sputum positive cases 94% samples were found to be positive to mannoside antigens and 77% to PPD, while in sputum negative cases, 71% of samples gave a positive reaction to mannosides and 54% to PPD. The high specificity of mannoside ELISA was demonstrated to be 97% in healthy individuals and 100% in patients suffering from other respiratory diseases, whereas PPD ELISA was 84% and 82% in healthy and infected patients respectively. Thus, ELISA is more specific and sensitive for mannosides than for PPD for the diagnosis of tuberculosis. However, antibodies to mannosides and PPD were detected in lepromatous as well as tuberculoid leprosy patients.

Cloning of a species-specific antigen of Mycobacterium bovis

A DNA library from a virulent strain of Mycobacterium bovis was constructed in the expression vector lambda gt11, and the library was probed with antisera to M. bovis. Clones expressing M. bovis antigens were isolated and characterized by using M. bovis-specific monoclonal antibodies that recognize a 22,000-molecular-weight protein (MPB70). MPB70 is a major protein antigen of the vaccine strain of M. bovis BCG and of virulent M. bovis, the causative agent of bovine tuberculosis. Of 32 clones selected by using polyclonal affinity-purified anti-M. bovis sera, 5 were recognized by the anti-MPB-70 monoclonal antibodies, and one monoclonal antibody, SB10, recognized all 5 clones. Characterization of these clones showed that one clone containing a 253-base-pair insert expressed a polypeptide bound by all of the MPB70-specific monoclonal antibodies. Western blots (immunoblots) showed that this cloned protein was recognized by sera from M. bovis-infected cattle, although not all cattle with bovine tuberculosis produced antibodies reactive to this clone. DNA sequencing of the clone showed that it coded for 84 amino acids from positions 17 to 114 of the 161-amino-acid protein, with a 16-peptide deletion between positions 79 and 94. Apart from this deletion, there were seven other variations between the cloned sequence and that deduced from M. bovis BCG MPB70.

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.

Allergenic and blastogenic reactivity of three antigens from Mycobacterium tuberculosis in sensitized guinea pigs

Three antigens from a culture filtrate of Mycobacterium tuberculosis H37Rv were purified by affinity chromatography, using monoclonal antibodies. The molecular weights of the purified antigens are 17,000 to 19,000, 32,000 to 33,000, and 39,000, respectively, and by their migration patterns in sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing and nonreducing conditions, they all appeared to be single-chain polypeptides. Western blot and enzyme-linked immunosorbent assay analyses indicated that the antigens are non-cross-reactive. All antigens generated an intermediate to strong skin reaction when tested in guinea pigs previously immunized with a live M. bovis BCG vaccine or with an oil emulsion preparation of phenol-or heat-killed M. tuberculosis. Lymphocytes isolated from peripheral blood or lymph nodes of similarly immunized guinea pigs could be stimulated by purified protein derivative and the purified antigens. Qualitative differences in stimulatory capacity between the preparations were demonstrated. The antigens may prove useful in further studies of the immunology and pathogenesis of tuberculosis.

Most Mycobacterium leprae carbohydrate-reactive monoclonal antibodies are directed to lipoarabinomannan

Each of more than 30 monoclonal antibodies that had been raised against Mycobacterium leprae and previously classified as reactive with carbohydrate was shown to be directed against lipoarabinomannan, a prominent, highly pervasive, myo-inositol-phosphate-containing, cross-reactive antigen within the leprosy bacillus. Some of the antibodies preferentially bound to the lipopolysaccharide of M. leprae rather than to that of Mycobacterium tuberculosis, suggesting the presence of distinguishing structural features. The presence of alkali-labile inositol 1-phosphate in the lipopolysaccharide from M. tuberculosis and its apparent absence from the M. leprae product may account for the difference.

Evidence for activation of a respiratory burst in the interaction of human neutrophils with Mycobacterium tuberculosis

We examined the capacity of human neutrophils to develop a respiratory burst, as monitored by superoxide release, in response to interaction with Mycobacterium tuberculosis. Serum-opsonized, heat-killed mycobacteria induced significant release of superoxide from neutrophils after 30 min of exposure, with a maximum release of 34 +/- 1.7 nmol/30 min per 5 X 10(6) neutrophils occurring with a mycobacterium/neutrophil ratio of 40:1. Similar levels of superoxide release were induced by live mycobacteria. Neutrophil superoxide production was reduced significantly with exposure to unopsonized organisms or by substitution of heat-inactivated serum for opsonization. Mycobacterial components including culture filtrate, purified protein derivative, and the cell wall polysaccharide arabinogalactan failed to induce significant release of superoxide from neutrophils. Transmission electron microscopy demonstrated that more than 90% of the neutrophils had ingested heat-killed mycobacteria concomitant with the development of respiratory burst activity. These data suggest that the presumed failure of neutrophil killing of mycobacteria cannot be attributed to a lack of phagocytosis or respiratory burst activation.

Purification, characterization and identification of a 32 kDa protein antigen of Mycobacterium bovis BCG

An immunogenic protein called P32 has been purified from Sauton zinc deficient culture filtrate of Mycobacterium bovis BCG using successively hydrophobic chromatography on Phenyl-Sepharose, ion exchange on DEAE-Sephacel and molecular sieving on Sephadex G-100. The final preparation was found to be homogeneous as based on several analyses. This P32 protein was a constituent of BCG cells grown in normal conditions. It represented about 3% of the soluble fraction of a cellular extract, and appeared as the major protein released in normal Sauton culture filtrate. This protein was found to have a molecular weight of 32,000 by SDS-polyacrylamide gel electrophoresis and in molecular sieving. Its amino acid composition showed an abundance of acidic amino acids (or their amides). The NH2-terminal amino acid sequence (6 amino acids) was determined. Purified P32 was tested by various crossed immunoelectrophoresis techniques, and was shown to belong to the antigen 85 complex in the reference system for BCG antigens. It was more precisely identified as antigen 85A. The protein antigen elicited a weak delayed hypersensitivity reaction in guinea pigs sensitized with heat-killed or living BCG. No delayed hypersensitivity reaction was observed in living BCG sensitized mice, however, it induced significant amounts of gamma interferon in cultured spleen cells from BCG-sensitized mice. Moreover, P32 either pure or as part of BCG soluble extract promoted substantial antibody levels when injected in rabbits.

The 65-kilodalton antigen of Mycobacterium tuberculosis

The immune response of the host to the antigens of Mycobacterium tuberculosis plays the key role in determining immunity from infection with as well as the pathogenicity of this organism. A 65-kilodalton (kDa) protein has been identified as one of the medically important antigens of M. tuberculosis. The gene encoding this antigen was isolated from a lambda gt11-M. tuberculosis recombinant DNA library using monoclonal antibodies directed against the 65-kDa antigen as the specific probes. The nucleotide sequence of this gene was determined, and a 540-amino-acid sequence was deduced. This sequence was shown to correspond to that of the 65-kDa antigen by constructing a plasmid in which this open reading frame was fused to the lacZ gene. The resulting fusion protein reacted specifically with the anti-65-kDa protein antibodies. A second long open reading frame was found downstream of the 65-kDa antigen gene which could encode a protein of 517 amino acids. This putative protein contained 29 tandemly arranged partial or complete matches to a pentapeptide sequence.

Purification, partial characterization, and identification of a skin-reactive protein antigen of Mycobacterium bovis BCG

An immunogenic and skin-reactive protein called P64 was purified from Sauton zinc-deficient culture filtrate of Mycobacterium bovis BCG by using successively hydrophobic chromatography on phenyl-Sepharose, ion exchange on DEAE-Sephacel, and molecular sieving on Sephadex G-200. The final P64 preparation was found to be homogeneous based on several analyses. Protein P64 was a constituent of BCG cells since it was present in soluble cellular extract from normally grown BCG cells. It represented 8 to 9% of the soluble proteins of the extract and appeared as the major soluble protein antigen of BCG. This protein was found to have a molecular weight of 64,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but in molecular sieving it eluted at a volume corresponding to a molecular weight of 246,000. An abnormal UV spectrum was observed for this protein. Its amino acid composition showed an abundance of acidic amino acids (or their amides). Aromatic amino acids represented only 3% of the total amino acid residues. The NH2-terminal amino acid sequence of this protein (10 amino acids) was determined. Its sugar content measured with the phenol-sulfuric acid test was lower than 0.3% (wt/wt.) Isolated P64 was tested by various crossed-immunoelectrophoresis techniques and was shown to correspond to antigen 82 in the reference system for BCG antigens. The protein antigen P64 elicited a delayed cutaneous reaction in guinea pigs sensitized with either living or heat-killed BCG. Its potency in skin reaction was, respectively, two- and threefold that of the BCG purified protein derivative. The two types of sensitization used for skin test reactions promoted significant immunoglobulin G antibody production against the protein antigen P64 in guinea pigs 7 weeks after sensitization.