Inflammasome

An inflammasome is an intracellular signaling platform assembled from a sensor, an adaptor, and an inflammatory caspase. Sensors commonly belong to the nucleotide-binding oligomerization domain and leucine-rich repeat-containing receptor family, or NLRs, although the AIM2 sensor detects cytosolic double-stranded DNA and pyrin detects disturbances in Rho-family GTPase signaling.¹ The adaptor ASC links many sensors to caspase-1 through matching pyrin and caspase-recruitment domains.

Activated caspase-1 cleaves precursor interleukin-1β and precursor interleukin-18 into secreted cytokines and cuts gasdermin D. Gasdermin D forms membrane pores that drive pyroptosis, allowing cytokine release and removal of an infected cell.² The term therefore describes both a molecular structure and a functional switch connecting danger detection to inflammation.

Inflammasome activation generally requires danger sensing followed by assembly of the signaling complex, but the precise sequence differs among sensors. For NLRP3, a priming signal induces transcription of NLRP3 and pro-interleukin-1β, while a second signal such as potassium efflux, lysosomal damage, mitochondrial stress, or extracellular ATP promotes complex assembly.² These signals do not necessarily bind NLRP3 directly; instead, they converge on changes in cell physiology.

Other pathways are more specific. AIM2 binds cytosolic DNA, while the NAIP–NLRC4 inflammasome responds to bacterial flagellin and components of bacterial secretion systems. Pyrin responds to toxins or pathogens that inactivate RhoA. In humans, caspase-4 and caspase-5 can detect cytosolic lipopolysaccharide and initiate noncanonical inflammasome signaling, which activates gasdermin D and can secondarily engage NLRP3.³

Inflammasomes help contain infection by eliminating compromised cells and recruiting immune responses through interleukin-1β and interleukin-18. Their activity is prominent in macrophages and other innate immune cells, but epithelial cells, neurons, endothelial cells, and tissue-resident cells can also participate in inflammasome responses.¹

Mutations that cause constitutive inflammasome activity produce hereditary autoinflammatory syndromes. Somatic or inherited changes affecting NLRP3 are associated with cryopyrin-associated periodic syndromes, including familial cold autoinflammatory syndrome and Muckle–Wells syndrome. Inflammasome signaling has also been implicated in gout, atherosclerosis, type 2 diabetes, neurodegenerative disease, and infection-related tissue injury, although its contribution differs by disease and remains a therapeutic research target rather than a single uniform mechanism.⁴

Inflammasome biology includes several systems that do not fit the simple image of one sensor and one caspase. Some inflammasomes activate caspase-8 or other inflammatory caspases in addition to, or instead of, caspase-1, linking inflammasome signaling with apoptosis and necroptosis.³ Cells can also undergo “pyroptosis-independent” cytokine secretion, in which interleukin-1β leaves viable cells through unconventional secretory routes.

Inflammasome activity is shaped by cellular location, metabolic state, organelle damage, and negative regulators that limit assembly or cytokine production. Microbial strategies illustrate this evolutionary contest: pathogens may block caspase activation, alter host ion flux, or interfere with ASC speck formation. These details matter experimentally because a rise in inflammatory cytokines does not by itself prove that a particular inflammasome assembled; researchers often combine genetic, biochemical, imaging, and cell-death measurements to identify the pathway.²

ASC

An adaptor protein that connects many inflammasome sensors to inflammatory caspases through pyrin and caspase-recruitment domains.

Caspase-1

An inflammatory protease that processes interleukin-1β and interleukin-18 and cleaves gasdermin D.

Pyroptosis

An inflammatory form of programmed cell death associated with gasdermin pore formation and cellular membrane rupture.

Noncanonical inflammasome

A pathway in which human caspase-4 or caspase-5, and related murine caspases, detect cytosolic lipopolysaccharide.