Abstract
Innate immune detection of Gram-negative bacteria depends on sensing of cytosolic lipopolysaccharide (cLPS) by the non-canonical inflammasome, mediated in humans by NLRP11 and caspase-4 (CASP4). Activation of this pathway in human macrophages triggers gasdermin-D activation and pyroptotic cell death. Although CASP4 directly binds LPS in vitro, additional host factors are required for efficient activation in vivo. Here, we show that NLRP11, a primate-specific pattern recognition receptor, facilitates CASP4 recognition of cLPS and promotes non-canonical inflammasome activation. NLRP11 functions upstream CASP4, forming an ASC-independent complex that requires a conserved CASP4 p20 residue, binds cLPS, and enhances CASP4-dependent LPS recognition. Mutational analyses demonstrate that in human macrophages, in addition to LPS binding and CASP4 catalytic activity, CASP4 interaction with NLRP11 is essential for efficient pyroptosis. Together, these findings establish NLRP11 as a primate-specific determinant that enhances CASP4-mediated cLPS detection and non-canonical inflammasome activation, revealing a mechanism for human-specific regulation of innate immunity.
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