ASC specks are micrometer-sized structures formed by the inflammasome adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD). ASC specks are characteristic of inflammasome activation.
The inflammasome adapter ASC is localized mainly in the nucleus of macrophages and monocytes. In case of pathogen infection, it rapidly re-localizes to the mitochondria, cytoplasm, endoplasmic reticulum, and perinuclear space and links activated inflammasome sensors to the effector molecule pro-caspase-1. On triggering of inflammasome sensors, the ASC protein assembles into large helical fibrils that interact with each other serving as a supramolecular signaling platform termed the ASC speck.
In several inflammatory diseases, the presence of ASC specks in the extracellular space often correlates with poor prognosis.