Imaging Inflammasome Activation in Microglia

Inflammasomes are multiprotein complexes that play key roles in the host's innate immune response to insult. The assembly of an inflammatory complex is initiated with the oligomerization of the upstream inflammasome‐forming sensor and then follows a well‐orchestrated multi‐step process leading to downstream effector functions that are critical in the innate immune response. The final assembly of these steps provides a detectable readout of inflammasome complex activation in the form of an apoptosis‐associated speck‐like protein containing a CARD (ASC) speck. Inflammasome activation—and the release of IL‐1β and ASC specks from the microglia, the brain resident immune cell—have been implicated in various neurological and neurodegenerative disorders. Protocols exist for the generation of fluorescent inflammasome indicator peripheral macrophages. Building upon these protocols, we describe here a protocol that details the generation of fluorescent inflammasome indicator microglia cells using recombinant retroviruses to transduce murine BV‐2 cells. In this protocol, the cells are established in a manner to allow for experimental control of the initial priming step of the inflammasome activation process. We then provide a series of steps for using these reporter cells within an inflammasome activation assay and use real‐time imaging of ASC‐speck formation as an indicator of inflammasome activation. In addition, we describe strategies for using these cells for examining the effects of a test substance on inflammasome activation. This protocol offers an effective approach conducive to screening for and examining modifications of microglia inflammasome activation due to exposure to chemicals or pharmacological agents. © Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Basic Protocol 1: Production of retroviruses to express inflammasome indicator Basic Protocol 2: Generation of inflammasome indicator BV‐2 cells Basic Protocol 3: Priming and activation of BV‐2‐ASC‐Cerulean cells for inflammasome activation assay Basic Protocol 4: Examining modifications to inflammasome activation by test substances Basic Protocol 5: Imaging and analysis of ASC speck formation