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Updated: Jun 29, 2026
Preparation of Mycobacterium tuberculosis Culture Filtrate to Understand TB Pathogenesis
Published on: March 28, 2025
LspA inactivation in Mycobacterium tuberculosis results in attenuation without affecting phagosome maturation arrest
Silvana K Rampini1, Petra Selchow1, Christine Keller2
1Institut für Medizinische Mikrobiologie, Universität Zürich, Gloriastrasse 32, CH-8006 Zurich, Switzerland.
Abstract:
The success of Mycobacterium tuberculosis depends on its ability to survive within host macrophages. Here, M. tuberculosis avoids the acidic, hydrolytically competent environment of the phagolysosome by arresting phagosome maturation. Having shown previously that a M. tuberculosis mutant deficient in lipoprotein signal peptidase (LspA) is strongly attenuated in vivo in a mouse model of infection, we now studied putative mechanisms involved in attenuation of the lspA : : aph mutant at a cellular level. In this work we investigated the ability of the mutant to interfere with two host defence mechanisms, i.e. Toll-like receptor (TLR)2-dependent immune response and phagosome maturation. While mycobacterial lipoproteins have been reported to trigger a TLR2 signalling pathway critical for innate immune responses, we found that growth control of the lspA : : aph mutant was independent of TLR2. In addition, the lspA : : aph mutant arrested phagosome maturation to an extent similar to that of the wild-type, as measured by lysosomal-associated membrane protein 1 (LAMP1) co-localization and intraphagosomal pH. These observations demonstrate severe attenuation even in the presence of arrested phagosome maturation, and point to a role for the early phagosome in growth restriction of the M. tuberculosis lspA mutant.
Insights
Mycobacterium tuberculosis lacking lipoprotein signal peptidase (LspA) is attenuated because its growth is restricted in early phagosomes, independent of Toll-like receptor 2 signaling or phagosome maturation arrest.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Mycobacterium tuberculosis (M. tuberculosis) survival relies on evading host macrophage defenses.
- Phagosome maturation arrest is a key M. tuberculosis virulence mechanism.
- Lipoprotein signal peptidase (LspA) is crucial for M. tuberculosis virulence.
Purpose of the Study:
- Investigate the cellular mechanisms behind the attenuation of an M. tuberculosis lspA mutant.
- Determine the role of Toll-like receptor 2 (TLR2) signaling in M. tuberculosis lspA mutant attenuation.
- Assess the impact of lspA mutation on phagosome maturation and host immune response.
Main Methods:
- Studied an lspA mutant of M. tuberculosis in a cellular infection model.
- Assessed TLR2-dependent immune responses.
- Measured phagosome maturation using lysosomal-associated membrane protein 1 (LAMP1) co-localization and intraphagosomal pH.
Main Results:
- The M. tuberculosis lspA mutant's growth control was independent of TLR2 signaling.
- The lspA mutant arrested phagosome maturation similarly to wild-type M. tuberculosis.
- Severe attenuation was observed despite normal phagosome maturation arrest.
Conclusions:
- The M. tuberculosis lspA mutant is severely attenuated in a manner not dependent on TLR2 or typical phagosome maturation arrest.
- Early phagosome interactions are critical for restricting the growth of the M. tuberculosis lspA mutant.
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