Antibody markers of incident tuberculosis among HIV-infected adults in the USA: a historical prospective study

OBJECTIVE

To assess whether serum levels of antibodies against Mycobacterium tuberculosis antigens increase before diagnosis of active tuberculosis (TB).

DESIGN

Serial serum samples were obtained from 30 human immunodeficiency virus (HIV) co-infected individuals who developed active TB during a multicenter prospective study on pulmonary complications of HIV/AIDS conducted among >1300 subjects in the USA in the 1980s. Multiple serum samples from 47 matched control individuals who did not develop TB in the same study were also tested. Immunoglobulin G (IgG) antibodies to 10 M. tuberculosis proteins were detected by enzyme-linked immunosorbent assay (ELISA), and data were analyzed by descriptive and inferential statistical techniques to assess patterns, trends and differences in antibody levels relative to time from TB diagnosis.

RESULTS

Antibodies to five antigens (ESAT-6, 38 kDa Ag, 16 kDa Ag, malate synthase and MTSA-10/CFP-10), but not to five other antigens (Rv2626c, ferredoxin A, glutamine synthetase, alanine dehydrogenase and Ag85) increased before diagnosis of TB relative to control levels. The earliest increase in the TB group was detected for MTSA-10/CFP-10 (24-30 months pre-diagnosis).

CONCLUSIONS

Levels of serum antibodies to particular proteins of M. tuberculosis increase before microbiological and clinical symptoms of active TB. The use of antibody biomarkers for prognostic purposes should therefore be feasible.

Serological markers of pulmonary tuberculosis and of response to anti-tuberculosis treatment in a patient population in Guinea

The aim of the study was to evaluate serological correlates of active tuberculosis and of response to antituberculosis treatment in a cohort of HIV-negative patients with pulmonary tuberculosis studied at diagnosis and during treatment at the Service de Pneumo-Phtisiologie, Centre Hospitalier-Universitaire Ignace Deen, Conakry, Republic of Guinea. Two similar cohorts of HIV-negative healthy households of patients and healthy community controls were included in the study. Plasma samples were obtained from 168 untreated tuberculosis patients, 167 healthy household controls, and 168 healthy community controls. Serial plasma samples were also obtained from the tuberculosis patients at 2 and 8 months after initiation of chemotherapy. IgG antibody levels were measured by an enzyme-linked immunosorbent assay (ELISA) using ten purified M. tuberculosis antigens. ELISA results were analysed by comparing geometric means of data. Of the ten antigens tested, five (14kDa Ag, 19kDa Ag, AlaDH, MS, and MPT83) elicited similar antibody responses in untreated TB patients and controls. In contrast, levels of three antibodies (ESAT-6, LAM, and 38kDa Ag) were higher in untreated TB patients than in household or community controls (p<0.0001). Levels were higher in untreated patients than in community controls also for the anti-Rv2626c antibody (p = 0.0001) and, at a lower significance level, for the anti-FdxA antibody (p<0.025). Antibody levels against ESAT-6 and Rv2626c decreased during therapy, while antibody levels to the 38 kDa antigen and LAM increased during therapy; FdxA antibody levels did not vary with treatment. Neither severity of presentation nor chest X-ray patterns affected levels of these antibodies before treatment. In contrast, after the 8-month therapeutic course, patients who presented with moderate/severe disease had higher levels of anti-ESAT-6, anti-FdxA, and anti-38kDa antibodies than those of patients with mild disease onset. Patients with bilateral lung lesions had significantly higher anti-38kDa and anti-LAM levels, both at diagnosis and after 8-month treatment, than patients with lesions involving only one lung. Antibodies to alanine dehydrogenase and malate synthetase measured at initiation of treatment were higher in tuberculosis patients who subsequently failed therapy than in those who were cured. The main conclusions of the study are: a) plasma levels of antibodies to a number of M. tuberculosis represent serological correlates of active disease; b) these correlates are affected in an antigen-specific fashion by anti-tuberculosis treatment; c) particular serological markers may be predictive of treatment outcome.

Integration of microscopy and serodiagnostic tests to screen for active tuberculosis

SETTING

University of California San Diego Medical Center, USA.

OBJECTIVE

To create a simple screening strategy for tuberculosis (TB) that includes antibody detection assays to improve the accuracy of microscopic examination of sputum for acid-fast bacilli (AFB smear).

METHODS

Serum samples were obtained from 190 patients suspected of having active TB. TB diagnosis was established by Mycobacterium tuberculosis culture. HIV status was determined by commercial serologic tests. IgG antibody levels were measured by ELISA using purified M. tuberculosis antigens. Data from 130 randomly selected patients were used to develop a screening strategy; data from the remaining 60 patients were used for validation.

RESULTS

AFB smear had 70% sensitivity and 88% specificity. In algorithms integrating single or multi-antigen ELISA with AFB smear and HIV results, the sensitivity improved over each test alone. The algorithm that included a four-antigen ELISA (38 kDa antigen, lipoarabinomannan, MPT-64 and glutamine synthase) had a sensitivity of 93% and a specificity of 76%. Compared to AFB smear, the sensitivity of the algorithm was significantly higher, while the specificity was not statistically different.

CONCLUSION

This study demonstrates that a screening strategy can be created by integrating multi-antigen ELISA with AFB smear and HIV testing.

Recognition of ESAT-6 sequences by antibodies in sera of tuberculous nonhuman primates

Previous work in our laboratory showed that the ESAT-6 protein of Mycobacterium tuberculosis and Mycobacterium bovis induces strong antibody responses in a large proportion ( approximately 90%) of experimentally or naturally infected nonhuman primates. Here, the antibody response to ESAT-6 in tuberculous monkeys was characterized at the epitope level by measuring antibodies to overlapping, synthetic peptides spanning the ESAT-6 sequence. The antibody response against the COOH-terminal portion of the protein was the strongest in both experimentally and naturally infected animals. Moreover, these antibodies became detectable the earliest during experimental infection, suggesting an ordered expansion of ESAT-6-specific B-cell clones in the course of infection. The data support use of synthetic peptides in lieu of the full-length ESAT-6 protein in diagnostic antibody detection assays.

Correlation between inhibitory effect of quinolones and mycolic acid metabolism in mycobacteria

Mycolic acids are important components having a significant role in maintaining the rigidity of mycobacterial cell wall. They could also be the barrier for penetration of certain drugs into the bacterial cell. A novel in vitro model system was established for assessing the effect of Ciproflaxacin on mycolic acid metabolism in pathogenic mycobacteria M. Kansasii (which has similar mycolic acid pattern to that from M. leprae) and the effect of norfloxacin in M. intracellulare. These test mycobacteria were exposed in their midlogarithmic phase of growth to 0.5, 1, 2, 3, 4, 5 and 6 micrograms ml of ciprofloxacin and norfloxacin respectively for 1, 2 and 24 hours. Ciprofloxacin completely inhibited the synthesis of mycolates in M. kansasii at 3, 4 and 5 micrograms/ml; whereas norfloxacin exhibited its maximum inhibitory action on mycolic acids in M. intracellulare at 6 micrograms/ml for all the durations of exposure. Inhibition of mycolates directly correlated with bacterial viability which was estimated by colony forming units. The effect of quinolones on mycolic acid metabolism appears to be direct and not secondary to DNA gyrase. The results obtained from this study and our previous findings show that mycolic acid metabolism is affected by various groups of drugs, whose primary sites of activity may be different. The findings of the present study may have significant therapeutic implications in leprosy and other mycobacterial diseases.

Rapid characterization of Mycobacterium fortuitum-chelonei complex by restriction fragment length polymorphism of ribosomal RNA genes

Using labelled, gamma-32P rRNA of mycobacteria as a probe restriction fragment length polymorphism (RFLP) of rRNA genes of strains belonging to the Mycobacterium fortuitum-chelonei complex was analysed. Each DNA sample was cleaved with EcoRI restriction endonuclease, the fragments were separated by agarose gel electrophoresis and transferred to nitrocellulose membrane. Fragments of DNA containing rRNA genes were identified by hybridization with gamma-32P-labelled rRNA. Patterns were found to be species specific and both the species were distinguishable from each other. Results indicate that this approach can be used for rapid genomic characterization of the Mycobacterium fortuitum-chelonei complex.