Human caspase-4 mediates noncanonical inflammasome activation against gram-negative bacterial pathogens

Area of Science:

• Immunology
• Cellular Biology
• Microbiology

Background:

• Inflammasomes are crucial for host defense against bacterial infections.
• Canonical inflammasomes activate caspase-1, leading to pyroptosis and cytokine release.
• Noncanonical inflammasomes, involving caspase-11 in mice, also induce cell death and cytokine release.

Purpose of the Study:

• To define the roles of human inflammatory caspases (caspase-4 and caspase-5) in inflammasome responses to gram-negative bacteria.
• To investigate the specific inflammasome pathways regulating IL-1 family cytokine release and cell death in human macrophages.

Main Methods:

• Primary human macrophages were infected with diverse gram-negative bacterial pathogens.
• Analysis of inflammasome activation, IL-1β and IL-1α secretion, and cell death.
• Investigation of the roles of caspase-1 and caspase-4 in these responses.

Main Results:

• Human macrophages activate inflammasomes in response to gram-negative bacteria delivering products into the cytosol.
• IL-1β secretion relies on the caspase-1 inflammasome.
• IL-1α release and cell death are mediated by caspase-4, independent of caspase-1.

Conclusions:

• Human caspase-4 is a critical regulator of noncanonical inflammasome activation against gram-negative bacteria.
• Caspase-4 initiates inflammatory responses, including cell death and IL-1α release, in primary human macrophages.
• Findings elucidate distinct inflammasome pathway functions in human innate immunity.