A clinical evaluation of the diagnostic usefulness of an early dermal reaction to tuberculin: a failure to distinguish between tuberculosis and other respiratory disease

Design and optimization of a recombinant system for large-scale production of the MPT64 antigen from Mycobacterium tuberculosis

Early clinical trials of a potential new tuberculosis (TB) diagnostic, the Patch Test for Active TB (PTAT), used MPB64 protein that was purified from the spent medium of Bacillus Calmette-Guérin (BCG) Tokyo 172 vaccine production. The yield was poor, 0.05 mg/L, and the process for purification of the protein was complex, requiring four chromatographic steps. The combination of yield and purification complexity compromised the ability to produce the PTAT diagnostic in quantities sufficient for larger clinical trials and commercialization. We report here a highly efficient method for the overexpression and purification of recombinant MPT64 from Escherichia coli (rMPT64) based upon a mild insolubility of rMPT64 following induction, and scalable anion-exchange and gel filtration chromatographies. Yields of protein were improved substantially to approximately 250 mg/L, and resulted in a preparation greater than 98% pure. Quantitative release assays were developed and used with MALDI-TOF mass spectrometry to confirm the identity of rMPT64. Using a guinea pig model of active TB, we found that rMPT64 elicited a specific immune response indistinguishable from that of MPB64 purified from BCG Tokyo culture filtrates. These results describe the first efficient and scalable protocol for production of rMPT64, demonstrate its activity in an animal model of active TB, and lay the foundation of ongoing and future use of the PTAT in clinical settings.

Radiographic spectrum of adult pulmonary tuberculosis in a developed country

SETTING

Bispebjerg Hospital, Department of Pulmonary Medicine P. The referral centre of adult tuberculosis in the municipality of Copenhagen, Denmark.

OBJECTIVE

To evaluate the radiographic spectrum of pulmonary tuberculosis (TB) in adults in a low-prevalence country and to correlate radiographic appearances with bacteriological results, clinical and demographic data.

DESIGN

Retrospective review of medical files on 548 cases with pulmonary TB according to the criteria of WHO.

RESULTS

Usual radiographic pattern of reactivating TB, with upper lobe involvement, was found in 92% (n = 504), eight percent (n = 44) showed unusual X-ray patterns for adults, such as isolated lower lobe infiltrations (n = 19), hilar adenopathy (n = 10), miliary TB (n = 7), tuberculoma (n = 2), pleural effusion (n = 1) and normal chest X-ray (n = 3). Eight-nine percent of cases with cavitary lesions were positive by microscopy.

CONCLUSION

The risk of missing a diagnosis of pulmonary TB may be high if patients present with an X-ray unusual for TB, but this is fortunately seen only in 8% of cases of pulmonary tuberculosis. Unusual X-ray is more commonly found in patients with concomitant disease, such as diabetes and cancer. If chest X-ray shows cavities, but the smear is negative for Mycobacterium, TB is unlikely and further diagnostic procedures should be performed without waiting for culture results.

Clinical evaluation of MPT-64 and MPT-59, two proteins secreted from Mycobacterium tuberculosis, for skin test reagents

SETTING

Department of Pulmonary Medicine P, Bispebjerg Hospital, Copenhagen, Denmark.

OBJECTIVE

To study the ability of two proteins secreted from Mycobacterium tuberculosis, MPT-64 and MPT-59 to induce delayed type hypersensitivity (DTH) reactions following intradermal administration.

DESIGN

In a small scale clinical investigation, skin reactions to these antigens were compared to reactions to tuberculin PPD RT23 in 1) patients with active tuberculosis, 2) BCG vaccinated healthy subjects with close contact with tuberculous patients, and 3) BCG vaccinated healthy subjects without contact with tuberculous patients. Tests for in vitro reactivity to these antigens were carried out in similar groups.

RESULTS

All subjects gave positive reaction to tuberculin PPD RT23, whereas approximately half of the subjects in each of the three groups reacted to MPT-59. Two subjects (one patient with tuberculosis and one healthy bacille Calmette-Guérin vaccinated subject without patient contact) reacted to MPT-64. The studies of cell proliferation and induction of interferon-gamma (IFN-gamma) following stimulation with tuberculin PPD and MPT-64 supported this profile of reactivity.

CONCLUSION

None of the experimental skin test antigens had properties superior to tuberculin PPD RT23 in humans. The failure of MPT-64 to induce delayed type hypersensitivity reactions in the majority of tuberculosis patients is discussed, in view of the potent reactivity to MPT-64 in tuberculous guinea pigs.

Early delayed hypersensitivity responses in tuberculin skin tests after heavy occupational exposure to tuberculosis

The early (six hours) reaction to tuberculin skin testing was studied in 33 Indonesian hospital workers with frequent occupational exposure to M tuberculosis and compared with responses maximal at the usual time (48 hours) in factory workers, from the same locality but with only occasional occupational exposure, to determine the nature of the early reaction. The early reaction had the same general histopathological appearance as that seen in the conventional (48 hour) reaction, and both had an infiltrate consisting largely of T lymphocytes and macrophages. The cell densities were lower in the six hour reactions, but the relative concentration of macrophages was greater in the earlier response. These histometric measurements suggested that the six hour reaction was an accelerated delayed hypersensitivity reaction. Moreover, the absence of a specific IgE response or of particulate masses of Ig or complement, made it unlikely an anaphylactoid or Arthus-type reaction could have been responsible. It is concluded that those with frequent occupational exposure to M tuberculosis have larger numbers of circulating T cells reactive with mycobacterial antigens, so that the development of the skin test response to tuberculin is less dependent on "by-stander" cell infiltration to mediate the delayed hypersensitivity reaction than the reactions in those with less intense and less frequent natural exposure. The skin test response maximal at six hours is probably a hyperimmune reaction to an antigen recognised by T cells.

Abacillary pulmonary tuberculosis

In Copenhagen, a city with a low incidence of tuberculosis, 72 patients with discrete pulmonary infiltrates on the chest X-ray had a tentative diagnosis of tuberculosis. All were sputum smear negative for acid-fast bacilli. A prospective randomised study was carried out to determine whether these patients would benefit from chemotherapy. Out of the 72 patients, 22 (30.6%) had positive cultures initially and were treated. Of the remaining 50 patients, 22 received chemotherapy and 28 were untreated controls. Among the untreated patients 8 (29%) later became culture positive for M. tuberculosis, whereas none of the treated patients developed culture positive tuberculosis during the follow-up period of 5 years.

The effect of exposure of hospital employees to patients with tuberculosis on dermal reactivity to four new tuberculins

An early (6-8 h) erythematous response to Purified Protein Derivative and to sonicate antigens (new tuberculins) prepared from Mycobacterium tuberculosis, M. vaccae, M. scrofulaceum, and M. leprae occurred much more frequently amongst hospital employees exposed to patients with tuberculosis than amongst factory workers. Biopsies taken from the skin test sites at 48 h revealed a more intense inflammatory cell infiltrate in response to PPD and the sonicate of M. tuberculosis, but not to the antigens of the other mycobacteria, amongst the hospital employees thus indicating a degree of specificity. The early response appears to be directed towards species specific antigens, but not, apparently, to the same as those that elicit the 48 h reactions. The hospital employees also had higher peripheral blood B-cell counts and total IgG levels, suggestive of an adjuvant effect. It is postulated that the early reaction results from repeated exposure to tubercle bacilli and the possible nature of the reaction is discussed.