Anaphylactic degranulation by mast cells requires the mobilization of inflammasome components

The inflammasome components NLRP3 and ASC are cytosolic proteins, which upon sensing endotoxins or danger cues, form multimeric complexes to process interleukin (IL)-1β for secretion. Here we found that antigen (Ag)-triggered degranulation of IgE-sensitized mast cells (MCs) was mediated by NLRP3 and ASC. IgE–Ag stimulated NEK7 and Pyk2 kinases in MCs to induce the deposition of NLRP3 and ASC on granules and form a distinct protein complex (granulosome) that chaperoned the granules to the cell surface. MCs deficient in NLRP3 or ASC did not form granulosomes, degranulated poorly in vitro and did not evoke systemic anaphylaxis in mice. IgE–Ag-triggered anaphylaxis was prevented by an NLRP3 inhibitor. In endotoxin-primed MCs, pro-IL-1β was rapidly packaged into granules after IgE–Ag stimulation and processed within granule remnants by proteases after degranulation, causing lethal anaphylaxis in mice. During IgE–Ag-mediated degranulation of endotoxin-primed MCs, granulosomes promoted degranulation, combined with exteriorization and processing of IL-1β, resulting in severe inflammation. Abraham and colleagues found that antigen-triggered degranulation in IgE-sensitized mast cells was mediated by the inflammasome components NLRP3 and ASC.