Tubercle and lung disease : the official journal of the International Union against Tuberculosis and Lung Disease最新文献

Expression of the Mycobacterium tuberculosis 19kDa lipoprotein in saprophytic mycobacteria has been found to reduce their ability to prime a protective response to subsequent virulent challenge in the mouse model. The present study was designed to test whether 19kDa expression has an analogous detrimental effect on the efficacy of BCG vaccination. In contrast to the results in saprophytes, neither overexpression of the 19kDa antigen, nor deletion of the endogenous 19kDa gene altered the ability of BCG to protect against M. tuberculosis challenge in a mouse model.

There is a tendency among tuberculosis patients to have reduced cellular responses to mycobacterial antigens and this loss has been associated with apoptosis of CD4 T cells. In order to determine the role of CD95 in mediating apoptosis of antigen-specific lymphocytes in tuberculosis, mice with a mutated CD95L molecule were infected systemically with virulent Mycobacterium tuberculosis. Both control and CD95L mutant mice exhibited the expected loss of response to mycobacterial antigens, with the only difference being a slight delay in the loss of the response in the mutant mice. The limited persistence of the response in the mutant mice suggests that, while antigen-specific cellular responses do decline in mice infected with mycobacteria, this decline is not dependent upon CD95L.

Pediatric tuberculosis (TB) differs from adult TB in many features. To date, cytokine expression has not been studied in children with TB. The relative amounts of the various cytokines released at the site of infection may be important determinants of TB disease development and pathology. We determined cytokine transcripts in bronchoalveolar cells (BACs) recovered from 9 children presenting with TB and from 9 children with pulmonary diseases other than TB. An RT-PCR-based method was developed to quantify the mRNAs encoding six cytokines (IFN- γ, IL-12, TNF- α, IL-10, IL-4, TGF-β 1) known to play key roles in mycobacterial infections. Expression of mRNA encoding TGF- β, TNF-α and IFN- γ was statistically significantly higher in BACs from children with TB than in BACs from children with other pulmonary diseases; whereas the levels of mRNA transcription for TGF- β is high, the levels of mRNA transcription for IFN- γ and TNF- α remain low. All children had low levels of mRNA for IL-12(p40). IL-4 was barely detectable in all cases. Children with miliary TB had high levels of IL-10 transcripts and low levels of mRNA encoding TGF- β. The immunosuppressive cytokines TGF- β and IL-10, are overproduced in children with non-miliary TB and miliary TB respectively and are probably involved in the progression of the disease. These data suggest that Th1 responses are reduced in children with TB.

Setting: The interaction of tubercle bacilli with macrophages is central to understanding of tuberculosis disease.

Objective: The objective was to determine whether prior passage within macrophages affects the behavior of Mycobacterium tuberculosis (Mtb) upon re-entry into other macrophages.

Design: Transmission electron microscopy was used to monitor fusion of bacterial phagosomes with late endosomal/lysosomal compartments using thoria as a fluid phase marker. Two-dimensional polyacrylamide gel electrophoresis was used to study bacterial protein expression within macrophages.

Results: H37Rv and BCG expressed novel proteins within macrophages. H37Rv also underwent less fusion after intracellular (IC) (24.2±7.7%) than extracellular (XC) (67.4±5.5%) passage when the bacteria entered new macrophages in small clusters. These effects were inhibited by serum, and were not observed with H37Ra or BCG bacteria (78.9±1.6% fused for all conditions). In addition, vacuoles which contained single bacilli were less likely to acquire markers (26.9±2.6%) than those that contained multiple bacilli (77.3±2.8%).

Conclusion: These results indicate that phagolysosomal fusion patterns can be modulated by a variety of factors and that virulent Mtb bacteria may express proteins within macrophages that alter their interaction with these host cells.

Components of the innate immune system serve to protect the host from invading pathogens prior to the generation of a directed immune response, and influence the manner in which the directed immune response develops. The pulmonary surfactant system consists of a complex array of proteins and lipids that reduce surface tension of the alveoli, and appears to play an essential role in innate immunity. Investigators have recently gained insight into the interactions between components of the surfactant system and the respiratory pathogen Mycobacterium tuberculosis. It is likely that pulmonary surfactant and other innate immune determinants play significant roles in the pathogenesis of tuberculosis.

Setting: Strains of the Mycobacterium tuberculosis complex are being rationally attenuated in order to develop better tuberculosis vaccines than BCG, and it would be helpful if new vaccines lacked an immunogenic protein which could be used as a skin test reagent for determining infection status.

Objective: To delete theesat6 gene from a virulent Mycobacterium bovis strain and determine (i) whether this mutant sensitizes guinea pigs to a skin test based on ESAT6 and (ii) what effect this has on the virulence of M. bovis.

Design: An homologous recombination technique was used to produce an esat6 knockout mutant of a virulent strain of M. bovis. Guinea pigs were inoculated with either the mutant or parent strain and their reactivity in intradermal skin tests was determined to bovine purified protein derivative (PPD) and recombinant ESAT6 protein.

Results: Production of an esat6 knockout strain was demonstrated by Southern blot hybridization and the polymerase chain reaction. Guinea pigs inoculated with either the esat6 knockout strain or its virulent parent had positive skin test reactions to PPD but only animal inoculated with the parent strain had positive skin test reactions to ESAT6. Gross pathology, histopathology and mycobacterial culture of tissues indicated that the knockout strain was less virulent than its parent.

Conclusion: If an effective live tuberculosis vaccine can be produced by inactivation of virulence genes in M. bovis, then prior or subsequent knockout of the esat6 gene could contribute to the loss of virulence and enable the development of a test to distinguish between vaccinated and infected animals.

Setting: A study of Serratia marcescens and BCG aerosols.

Objective: To evaluate the effect of relative humidity (RH) on (1) the particle size and (2) sensitivity of 254nm germicidal ultraviolet (UV) irradiation.

Methods: We built a RH controlled experimental chamber into which bacteria were aerosolized, exposed to varying amounts of UV irradiance over measured time periods, and quantitatively evaluated for viability. Aerosolized Serratia marcescens and bacille Calmette-Guérin (BCG) were subject to UV doses ranging from 57–829 μW · sec/cm², and sampled with a six-stage Andersen culture plate impactor at RHs ranging from 25–95%.

Results: Percent survival for both organisms was inversely related to UV dose. Serratia marcescens was more susceptible to UV than BCG under all conditions. More than 95% of the bacterial aerosol particles were 1.1–4.7 μm in aerodynamic diameter, and particles sizes increased from low (25–36%) to high (85–95%) RH. The count median diameter ranged from 1.9–2.6 μm for Serratia marcescens and from 2.2–2.7 μm for BCG as RH increased. For both Serratia marcescens and BCG, resistance to UV increased as RH increased. The UV resistance of both Serratia marcescens and BCG aerosols dramatically increased at RH higher than 85%.

Conclusions: Our results indicate that differences in UV dose, kinds of microorganisms, airborne particle size and RH affect UV susceptibility.

Wildlife species, such as badgers, act as maintenance hosts for Mycobacterium bovis and contribute to the spread and persistence of tuberculosis in associated cattle populations. In areas in which there is a tuberculosis problem affecting a number of herds, the involvement of infected wildlife in the introduction of M. bovis infection into herds act as a constraint to eradication of the disease. Epidemiological evidence demonstrates a high prevalence of tuberculosis in badgers, and controlled studies involving comprehensive badger removal have shown that this strategy can serve to significantly reduce cattle reactor rates in the targeted areas. However, as the badger is a protected wildlife species, alternative strategies are required to combat the disease. Targeted vaccination of wildlife species against tuberculosis is an option which, if successfully employed, could directly facilitate the advancement of bovine tuberculosis eradication in affected areas. Any proposed vaccination programme would need to be undertaken against the background of an exhaustive investigation of the cattle and herd management-related factors, and take account of environmental issues.

Setting: The cloned M. tuberculosis noxR1 gene has been shown to confer resistance to reactive nitrogen intermediates (RNI) and reactive oxygen intermediates (ROI) upon Escherichia coli and Mycobacterium smegmatis.

Objective: To investigate the role of noxR1 in resistance to RNI and virulence of M. tuberculosis.

Design: The noxR1 gene was deleted from M. bovis BCG and M. tuberculosis H37Rv by allelic exchange. The mutants were compared to wild type strains with respect to resistance to chemically generated RNI. The virulence of the M. tuberculosis mutant was investigated in a murine model of infection.

Results: The NoxR1 mutants grew normally in Sautons and 7H9 broths. The BCG mutant demonstrated decreased resistance to in vitro generated RNI compared to the wild type. Resistance to RNI could be restored to the mutant by reintroduction of the noxR1 locus on a replicating plasmid. However, deletion of noxR1 from M. tuberculosis H37Rv did not result in decreased resistance to RNI nor a difference in growth and survival of the bacterium during murine infection.

Conclusion: The noxR1 gene locus in M. bovis BCG bestows ability to resist RNI generated in vitro. In M. tuberculosis H37Rv, however, noxR1 is either not involved in RNI resistance and virulence or is better compensated for by other mechanisms.