Intracellular growth of Mycobacterium tuberculosis after macrophage cell death leads to serial killing of host cells
- KwaZulu-Natal Research Institute for TB-HIV, South Africa
Abstract
A hallmark of pulmonary tuberculosis is formation of macrophage-rich granulomas. These may restrict Mycobacterium tuberculosis (Mtb) growth, or progress to central necrosis and cavitation, facilitating pathogen growth. To determine factors leading to Mtb proliferation and host cell death, we used live cell imaging to track Mtb infection outcomes in individual primary human macrophages. Internalization of Mtb aggregates caused macrophage death, and phagocytosis of large aggregates was more cytotoxic than multiple small aggregates containing similar numbers of bacilli. Macrophage death did not result in clearance of Mtb. Rather, it led to accelerated intracellular Mtb growth regardless of prior activation or macrophage type. In contrast, bacillary replication was controlled in live phagocytes. Mtb grew as a clump in dead cells, and macrophages which internalized dead infected cells were very likely to die themselves, leading to a cell death cascade. This demonstrates how pathogen virulence can be achieved through numbers and aggregation states.
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Author details
Funding
Bill and Melinda Gates Foundation (OPP1116944)
- Alex Sigal
Human Frontier Science Program (CDA00050/2013-C)
- Alex Sigal
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Human subjects: Blood was obtained from adult healthy volunteers after written informed consent (University of KwaZulu-Natal Institutional Review Board approval BE022/13). Alveolar macrophages were obtained from bronchoalveolar lavage as part of an indicated diagnostic procedure after written informed consent (University of KwaZulu-Natal Institutional Review Board approval BE037/12).
Copyright
© 2017, Mahamed et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Intracellular growth of Mycobacterium tuberculosis after macrophage cell death leads to serial killing of host cells
eLife 6:e22028.
https://doi.org/10.7554/eLife.22028
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