Related Experiment Video
Updated: Jul 2, 2025
Visualization of Inflammatory Caspases Induced Proximity in Human Monocyte-Derived Macrophages
Published on: April 6, 2022
Role for Caspase-8 in the Release of IL-1β and Active Caspase-1 from Viable Human Monocytes during Toxoplasma gondii
William J Pandori1, Stephanie Y Matsuno1, Ji-Hun Shin1
1Department of Molecular Biology & Biochemistry and the Institute for Immunology, University of California, Irvine, CA.
Abstract:
Monocytes are actively recruited to sites of infection and produce the potent proinflammatory cytokine IL-1β. We previously showed that IL-1β release during Toxoplasma gondii infection of primary human monocytes requires the NLRP3 inflammasome and caspase-1 but is independent of gasdermin D and pyroptosis. To investigate mechanisms of IL-1β release, we generated caspase-1, -4, -5, or -8 knockout (KO) THP-1 monocytic cells. Genetic ablation of caspase-1 or -8, but not caspase-4 or -5, decreased IL-1β release during T. gondii infection without affecting cell death. In contrast, TNF-α and IL-6 secretion were unperturbed in caspase-8 KO cells during T. gondii infection. Dual pharmacological inhibition of caspase-8 and RIPK1 in primary monocytes also decreased IL-1β release without affecting cell viability or parasite infection. Caspase-8 was also required for the release of active caspase-1 from T. gondii-infected cells and for IL-1β release during infection with the related apicomplexan parasite Neospora caninum. Surprisingly, caspase-8 deficiency did not impair synthesis or cleavage of pro-IL-1β, but resulted in the retention of mature IL-1β within cells. Generation of gasdermin E KO and ATG7 KO THP-1 cells revealed that the release of IL-1β was not dependent on gasdermin E or ATG7. Collectively, our data indicate that during T. gondii Infection of human monocytes, caspase-8 functions in a novel gasdermin-independent mechanism controlling IL-1β release from viable cells. This study expands on the molecular pathways that promote IL-1β in human immune cells and provides evidence of a role for caspase-8 in the mechanism of IL-1β release during infection.
Insights
Caspase-8 controls interleukin-1 beta (IL-1β) release from viable human monocytes during Toxoplasma gondii infection via a novel gasdermin-independent pathway, expanding understanding of immune cell signaling.
Area of Science:
- Immunology
- Cell Biology
- Infectious Disease
Background:
- Monocytes are crucial for host defense, producing pro-inflammatory cytokines like IL-1β.
- Previous work established NLRP3 inflammasome and caspase-1 involvement in IL-1β release during Toxoplasma gondii infection.
- The precise mechanisms governing IL-1β release, particularly gasdermin-independent pathways, remain incompletely understood.
Purpose of the Study:
- To elucidate the specific roles of various caspases in IL-1β release during T. gondii infection.
- To investigate novel mechanisms of IL-1β secretion independent of pyroptosis.
- To identify the molecular players controlling IL-1β release from viable infected monocytes.
Main Methods:
- Generation and analysis of knockout THP-1 monocytic cell lines (caspase-1, -4, -5, -8, gasdermin E, ATG7).
- T. gondii infection assays with primary human monocytes and THP-1 cells.
- Pharmacological inhibition of caspase-8 and RIPK1.
- Measurement of IL-1β, TNF-α, and IL-6 secretion.
- Assessment of cell viability and parasite infection levels.
Main Results:
- Genetic ablation of caspase-8, but not caspase-4 or -5, significantly reduced IL-1β release during T. gondii infection without inducing cell death.
- Caspase-8 deficiency did not affect pro-IL-1β synthesis or cleavage but led to retention of mature IL-1β within cells.
- IL-1β release was independent of gasdermin E and ATG7, indicating a non-pyroptotic pathway.
- Caspase-8 was essential for active caspase-1 release and IL-1β secretion during infection with T. gondii and Neospora caninum.
Conclusions:
- Caspase-8 plays a critical, gasdermin-independent role in regulating IL-1β release from viable human monocytes during T. gondii infection.
- This study reveals a novel mechanism for IL-1β secretion, distinct from pyroptosis.
- Findings expand the understanding of molecular pathways governing IL-1β release in innate immune cells during infection.
More Related Videos
Related Concept Videos
01:24Caspases
01:17The Extrinsic Apoptotic Pathway