Altered cellular infiltration and cytokine levels during early Mycobacterium tuberculosis sigC mutant infection are associated with late-stage disease attenuation and milder immunopathology in mice

<p>Abstract</p> <p>Background</p> <p>Mouse virulence assessments of certain <it>Mycobacterium tuberculosis </it>mutants have revealed an immunopathology defect in which high tissue CFU counts are observed but the tissue pathology and lethality are reduced. <it>M. tuberculosis </it>mutants which grow and persist in the mouse lungs, but have attenuated disease progression, have the immunopathology (<it>imp</it>) phenotype. The antigenic properties of these strains may alter the progression of disease due to a reduction in host immune cell recruitment to the lungs resulting in disease attenuation and prolonged host survival.</p> <p>Results</p> <p>In this study we focused on the mouse immune response to one such mutant; the <it>M. tuberculosis </it>Δ<it>sigC </it>mutant. Aerosol infection of DBA/2 and SCID mice with the <it>M. tuberculosis </it>Δ<it>sigC </it>mutant, complemented mutant and wild type strain showed proliferation of mutant bacilli in mouse lungs, but with decreased inflammation and mortality in DBA/2 mice. SCID mice shared the same phenotype as the DBA/2 mice in response to the Δ<it>sigC </it>mutant, however, they succumbed to the infection faster. Bronchoalveolar lavage (BAL) fluid analysis revealed elevated numbers of infiltrating neutrophils in the lungs of mice infected with wild type and complemented Δ<it>sigC </it>mutant strains but not in mice infected with the Δ<it>sigC </it>mutant. In addition, DBA/2 mice infected with the Δ<it>sigC </it>mutant had reduced levels of TNF-α, IL-1β, IL-6 and IFN-γ in the lungs. Similarly, there was a reduction in proinflammatory cytokines in the lungs of SCID mice. In contrast to the mouse model, the Δ<it>sigC </it>mutant had reduced initial growth in guinea pig lungs. A possible mechanism of attenuation in the Δ<it>sigC </it>mutant may be a reduction in neutrophilic-influx in the alveolar spaces of the lungs, and decreased proinflammatory cytokine secretion. In contrast to mouse data, the <it>M. tuberculosis </it>Δ<it>sigC </it>mutant proliferates slowly in guinea pig lungs, a setting characterized by caseating necrosis.</p> <p>Conclusion</p> <p>Our observations suggest that the immunopathology phenotype is associated with the inability to trigger a strong early immune response, resulting in disease attenuation. While macrophages and T cells have been shown to be important in containing <it>M. tuberculosis </it>disease our study has shown that neutrophils may also play an important role in the containment of this organism.</p

The Impact of Mouse Passaging of Mycobacterium tuberculosis Strains prior to Virulence Testing in the Mouse and Guinea Pig Aerosol Models

It has been hypothesized that the virulence of lab-passaged Mycobacterium tuberculosis and recombinant M. tuberculosis mutants might be reduced due to multiple in vitro passages, and that virulence might be augmented by passage of these strains through mice before quantitative virulence testing in the mouse or guinea pig aerosol models.By testing three M. tuberculosis H37Rv samples, one deletion mutant, and one recent clinical isolate for survival by the quantitative organ CFU counting method in mouse or guinea pig aerosol or intravenous infection models, we could discern no increase in bacterial fitness as a result of passaging of M. tuberculosis strains in mice prior to quantitative virulence testing in two animal models. Surface lipid expression as assessed by neutral red staining and thin-layer chromatography for PDIM analysis also failed to identify virulence correlates.These results indicate that animal passaging of M. tuberculosis strains prior to quantitative virulence testing in mouse or guinea pig models does not enhance or restore potency to strains that may have lost virulence due to in vitro passaging. It is critical to verify virulence of parental strains before genetic manipulations are undertaken and comparisons are made

Role of Stress Response Sigma Factor SigG in Mycobacterium tuberculosis▿ †

The sigG gene of Mycobacterium tuberculosis was disrupted by homologous recombination, and the genes regulated by SigG were examined by real-time reverse-transcription PCR and microarray studies. The SigG consensus promoter recognition sequence was identified as GCGNGT-N15-18-CGANCA. A ΔsigG mutant was found to be more resistant to mitomycin C treatment than the wild-type strain, indicating that it may be involved in the SOS response in M. tuberculosis

Rv2190c, an NlpC/P60 family protein, is required for full virulence of Mycobacterium tuberculosis.

Mycobacterium tuberculosis, the etiologic agent of tuberculosis (TB) possesses at least five genes predicted to encode proteins with NlpC/P60 hydrolase domains, including the relatively uncharacterized Rv2190c. As NlpC/P60 domain-containing proteins are associated with diverse roles in bacterial physiology, our objective was to characterize Rv2190c in M. tuberculosis growth and virulence. Our data indicate that lack of Rv2190c is associated with impaired growth, both in vitro and during an in vivo mouse model of TB. These growth defects are associated with altered colony morphology and phthiocerol dimycocerosate levels, indicating that Rv2190c is involved in cell wall maintenance and composition. In addition, we have demonstrated that Rv2190c is expressed during active growth phase and that its protein product is immunogenic during infection. Our findings have significant implications, both for better understanding the role of Rv2190c in M. tuberculosis biology and also for translational developments