Burkholderia pseudomallei triggers canonical inflammasome activation in a human primary macrophage-based infection model
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Updated: Dec 2, 2025
Detection of Inflammasome Activation and Pyroptotic Cell Death in Murine Bone Marrow-derived Macrophages
Published on: May 21, 2018
Sabine Lichtenegger1, Julia Stiehler1, Sabine Saiger1
1Diagnostic & Research Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Graz, Austria.
Abstract:
Most of the current knowledge on Burkholderia pseudomallei-induced inflammasome activation and cell death in macrophages is derived from murine systems. Little is known about the involved bacterial structures and mechanisms in primary human macrophages. This is of particular relevance since murine and human macrophages as well as primary cells and cell lines differ in many aspects of inflammasome activation, including the proteins involved in the recognition of bacterial patterns. In this study, we therefore aimed (i) to establish an in vitro B. pseudomallei infection model with human monocyte-derived primary macrophages from single donors as these cells more closely resemble macrophages in the human host and (ii) to analyze B. pseudomallei-triggered cell death and bacterial elimination in those cells. Our results show that B. pseudomallei-infected primary human macrophages not only release the inflammasome-independent pro-inflammatory cytokines IL-8 and TNF-α, but are also engaged in canonical inflammasome activation as evidenced by caspase-1 and gasdermin D processing. Absence of the B. pseudomallei T3SS-3 needle protein BsaL, a potent activator of the canonical inflammasome, abolished lytic cell death, reduced IL-1β release, and caspase-1 and gasdermin D processing. IFN-γ, known to promote non-canonical inflammasome activation, did not influence pyroptosis induction or IL-1β release from infected primary human macrophages. Nevertheless, it reduced intracellular B. pseudomallei loads, an effect which was partially antagonist by the inhibition of NADPH oxidase. Overall, our data implicate T3SS-3 dependent inflammasome activation and IFN-γ induced immune mechanisms as critical defense mechanisms of human macrophages against B. pseudomallei. In addition, our infection model provides a versatile tool to study human host-pathogen interactions and has the potential to elucidate the role of human individual genetic variations in B. pseudomallei infections.
Insights
This study reveals how human macrophages fight Burkholderia pseudomallei, identifying bacterial factors and immune responses crucial for controlling infection and cell death.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Current knowledge of Burkholderia pseudomallei inflammasome activation primarily uses murine models, with limited understanding in human macrophages.
- Human and murine macrophages exhibit distinct inflammasome activation pathways and pattern recognition proteins.
- Primary human macrophages offer a more relevant model for studying host-pathogen interactions than cell lines.
Purpose of the Study:
- To develop an in vitro model using primary human macrophages to study B. pseudomallei infection.
- To analyze B. pseudomallei-induced cell death and bacterial clearance mechanisms in human macrophages.
- To identify specific bacterial components and host immune pathways involved in B. pseudomallei pathogenesis.
Main Methods:
- Established an in vitro infection model using primary human monocyte-derived macrophages.
- Analyzed inflammasome activation markers, including caspase-1 and gasdermin D processing.
- Investigated the role of the B. pseudomallei T3SS-3 needle protein BsaL and IFN-γ in host defense.
Main Results:
- Primary human macrophages exhibited inflammasome-independent cytokine release (IL-8, TNF-α) and canonical inflammasome activation (caspase-1, gasdermin D processing).
- Absence of BsaL protein abrogated lytic cell death, reduced IL-1β release, and diminished caspase-1/gasdermin D processing.
- IFN-γ reduced intracellular B. pseudomallei loads, an effect partially mediated by NADPH oxidase, but did not affect pyroptosis or IL-1β release.
Conclusions:
- T3SS-3 dependent inflammasome activation is critical for human macrophage defense against B. pseudomallei.
- IFN-γ-induced immune mechanisms, involving NADPH oxidase, play a significant role in controlling intracellular bacterial burdens.
- The developed infection model is valuable for studying human host-pathogen interactions and individual genetic variations in B. pseudomallei infections.
