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Updated: Aug 8, 2025
Fluorescence Assays for the Study of Mycobacterium tuberculosis Interaction with the Immune Receptor SLAMF1
Published on: February 28, 2025
Single cell preparations of Mycobacterium tuberculosis damage the mycobacterial envelope and disrupt macrophage
Ekansh Mittal1,2, Andrew T Roth3, Anushree Seth4
1Division of Infectious Diseases, Department of Medicine, Washington University School of Medicine, St Louis, United States.
Abstract:
For decades, investigators have studied the interaction of Mycobacterium tuberculosis (Mtb) with macrophages, which serve as a major cellular niche for the bacilli. Because Mtb are prone to aggregation, investigators rely on varied methods to disaggregate the bacteria for these studies. Here, we examined the impact of routinely used preparation methods on bacterial cell envelope integrity, macrophage inflammatory responses, and intracellular Mtb survival. We found that both gentle sonication and filtering damaged the mycobacterial cell envelope and markedly impacted the outcome of infections in mouse bone marrow-derived macrophages. Unexpectedly, sonicated bacilli were hyperinflammatory, eliciting dramatically higher TLR2-dependent gene expression and elevated secretion of IL-1β and TNF-α. Despite evoking enhanced inflammatory responses, sonicated bacilli replicated normally in macrophages. In contrast, Mtb that had been passed through a filter induced little inflammatory response, and they were attenuated in macrophages. Previous work suggests that the mycobacterial cell envelope lipid, phthiocerol dimycocerosate (PDIM), dampens macrophage inflammatory responses to Mtb. However, we found that the impact of PDIM depended on the method used to prepare Mtb. In conclusion, widely used methodologies to disaggregate Mtb may introduce experimental artifacts in Mtb-host interaction studies, including alteration of host inflammatory signaling, intracellular bacterial survival, and interpretation of bacterial mutants.
Insights
Bacterial preparation methods significantly alter Mycobacterium tuberculosis (Mtb) interactions with macrophages. Sonication increases inflammation, while filtering reduces it, impacting Mtb survival and host responses.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Macrophages are a primary host cell for Mycobacterium tuberculosis (Mtb).
- Mtb aggregation necessitates disaggregation methods for experimental studies.
- Standard preparation techniques may influence experimental outcomes.
Purpose of the Study:
- To investigate how common Mtb preparation methods affect bacterial cell envelope integrity.
- To assess the impact of these methods on macrophage inflammatory responses.
- To determine the influence on intracellular Mtb survival and host-pathogen interactions.
Main Methods:
- Examined Mtb disaggregation using sonication and filtering.
- Assessed bacterial cell envelope integrity post-preparation.
- Measured macrophage inflammatory markers (TLR2, IL-1β, TNF-α).
- Quantified intracellular Mtb replication in bone marrow-derived macrophages.
Main Results:
- Both sonication and filtering damaged the Mtb cell envelope.
- Sonicated Mtb induced hyperinflammatory responses, including elevated TLR2 expression and cytokine secretion.
- Filtered Mtb elicited minimal inflammation and showed attenuated intracellular survival.
- The effect of the lipid phthiocerol dimycocerosate (PDIM) on inflammation was method-dependent.
Conclusions:
- Common Mtb preparation methods introduce experimental artifacts.
- These artifacts can alter host inflammatory signaling and intracellular bacterial survival.
- Findings necessitate careful consideration of preparation techniques in Mtb-host interaction studies and mutant analysis.
