Caspase-11 detection of intracellular lipopolysaccharide (LPS) from invasive Gram-negative bacteria mediates noncanonical activation of the NLRP3 inflammasome. While avirulent bacteria do not invade the cytosol, their presence in tissues necessitates clearance and immune system mobilization. Despite sharing LPS, only live avirulent Gram-negative bacteria activate the NLRP3 inflammasome. Here, we found that bacterial mRNA, which signals bacterial viability, was required alongside LPS for noncanonical activation of the NLRP3 inflammasome in macrophages. Concurrent detection of bacterial RNA by NLRP3 and binding of LPS by pro-caspase-11 mediated a pro-caspase-11–NLRP3 interaction before caspase-11 activation and inflammasome assembly. LPS binding to pro-caspase-11 augmented bacterial mRNA-dependent assembly of the NLRP3 inflammasome, while bacterial viability and an assembled NLRP3 inflammasome were necessary for activation of LPS-bound pro-caspase-11. Thus, the pro-caspase-11–NLRP3 interaction nucleated a scaffold for their interdependent activation explaining their functional reciprocal exclusivity. Our findings inform new vaccine adjuvant combinations and sepsis therapy.

Caspase-11 对侵入性革兰氏阴性菌细胞内脂多糖 (LPS) 的检测介导 NLRP3 炎症小体的非典型激活。虽然无毒细菌不会侵入细胞质，但它们在组织中的存在需要清除和动员免疫系统。尽管共享 LPS，但只有活的无毒革兰氏阴性细菌才会激活 NLRP3 炎性体。在这里，我们发现，信号细菌活力的细菌 mRNA 与 LPS 一起是巨噬细胞中 NLRP3 炎症小体非典型激活所必需的。在 caspase-11 激活和炎症小体组装之前，NLRP3 对细菌 RNA 的同时检测和 caspase-11 前体对 LPS 的结合介导了 caspase-11 前体与 NLRP3 相互作用。 LPS 与 caspase-11 前体的结合增强了 NLRP3 炎症小体的细菌 mRNA 依赖性组装，而细菌活力和组装的 NLRP3 炎症小体对于激活 LPS 结合的 caspase-11 前体是必需的。因此，Caspase-11原-NLRP3相互作用形成了一个支架，用于它们相互依赖的激活，解释了它们功能上的相互排他性。我们的研究结果为新的疫苗佐剂组合和败血症治疗提供了信息。