Human macrophages infected with virulent Mycobacterium tuberculosis undergo ESAT-6-dependent necrosis, but not pyroptosis or pyronecrosis
(English)Manuscript (preprint) (Other academic)
Mycobacterium tuberculosis (Mtb) infects lung macrophages, which instead of killing the pathogen can be manipulated by the bacilli, creating an environment suitable for intracellular replication and spread to adjacent cells. The role of host cell death during Mtb infection is debated because the bacilli have been shown to be both anti-apoptotic, keeping the host cell alive to avoid the antimicrobial effects of apoptosis, and pro-necrotic, killing the host macrophage to allow infection of neighboring cells. Since mycobacteria are able to activate the NLRP3 inflammasome, we investigated whether Mtb could induce one of the recently described inflammasome-linked cell death modes pyroptosis and pyronecrosis, in human monocyte-derived macrophages. Cells were infected with virulent (H37Rv) Mtb at a multiplicity of infection (MOI) of 1 or 10. The higher MOI resulted in strongly enhanced release of IL-1β, while a low MOI gave no IL-1β response. The infected macrophages were collected and cell viability in terms of the integrity of DNA, mitochondria and the plasma membrane was determined. We found that infection with H37Rv at MOI 10, but not MOI 1, over two days led to extensive DNA fragmentation, loss of mitochondrial membrane potential and loss of plasma membrane integrity. Although we observed plasma membrane permeabilization and IL-1 β release from infected cells, the cell death induced by Mtb was not pyroptosis or pyronecrosis, as it was independent of caspase-1 and cathepsin B. Instead, we conclude that as virulent Mtb reaches a threshold number of bacilli inside the macrophage, ESAT-6-dependent necrosis occurs, activating caspase-1 in the process.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:liu:diva-65451OAI: oai:DiVA.org:liu-65451DiVA: diva2:395799
Submitted manuscript2011-02-082011-02-082011-02-22Bibliographically approved