Annexins are well-known Ca 2+ phospholipid-binding proteins, which have a wide variety of cellular functions. The role of annexin A1 (AnxA1) in the innate immune system has focused mainly on the anti-inflammatory and proresolving properties through its binding to the formyl-peptide receptor 2 (FPR2)/ALX receptor. However, studies suggesting an intracellular role of AnxA1 are emerging. In this study, we aimed to understand the role of AnxA1 for interleukin (IL)-1b release in response to activators of the nucleotide-binding domain leucine-rich repeat (NLR) and pyrin domain containing receptor 3 (NLRP3) inflammasome. Using AnxA1 knockout mice, we observed that AnxA1 is required for IL-1b release in vivo and in vitro. These effects were due to reduction of transcriptional levels of IL-1b, NLRP3 and caspase-1, a step called NLRP3 priming. Moreover, we demonstrate that AnxA1 co-localize and directly bind to NLRP3, suggesting the role of AnxA1 in inflammasome activation is independent of its anti-inflammatory role via FPR2. Therefore, AnxA1 regulates NLRP3 inflammasome priming and activation in a FPR2-independent manner.Bone marrow-derived macrophages (BMDMs) were obtained as previously described. 31 Briefly, bone marrow cells were collected from femurs of wild-type (WT), AnxA1 À/À and FPR2/3 À/À mice and differentiated for 7 days in RPMI 1640 supplemented with 20% of fetal bovine serum (FBS) and 30% L929 conditioned medium.