cFLIP_L protects macrophages from LPS-induced pyroptosis via inhibition of complex II formation

Cell death and inflammation are interdependent host responses to infection. During pyroptotic cell death, interleukin-1β (IL-1β) release occurs through caspase-1 and caspase-11-mediated gasdermin D pore formation. In vivo, responses to lipopolysaccharide (LPS) result in IL-1β secretion. In vitro, however, murine macrophages require a second "danger signal" for the inflammasome-driven maturation of IL-1β. Recent reports have shown caspase-8-mediated pyroptosis in LPS-activated macrophages but have provided conflicting evidence regarding the release of IL-1β under these conditions. Here, to further characterize the mechanism of LPS-induced secretion in vitro, we reveal an important role for cellular FLICE-like inhibitory protein (cFLIP) in the regulation of the inflammatory response. Specifically, we show that deficiency of the long isoform cFLIP_L promotes complex II formation, driving pyroptosis, and the secretion of IL-1β in response to LPS alone.