NLRP3 inflammasome activity and pyroptosis are involved in CD206<sup>+</sup> macrophage activation by MPO anti-neutrophil cytoplasmic antibodies

Macrophages are key players in the pathology of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Existing studies and our previous studies have documented the role of CD206-positive M2 macrophages in the inflammatory process of AAV. Inflammasome activation is a critical pathway through which macrophages release inflammatory factors. In this study, we investigate the role of the inflammasome in macrophages in AAV and explore the role of CD206 in this process. We recruit newly diagnosed AAV patients and disease controls from our department. The expression and localization of the NOD-like receptor family, pyrin domain containing 3 (NLRP3) and CD206 in the kidney are determined via immunofluorescence experiments. Myeloperoxidase (MPO)-ANCA immunoglobulin G (MPO-ANCA IgG) is purified from new-onset AAV patients with MPO-ANCA and used to treat lipopolysaccharide (LPS)-primed macrophages in vitro. Our findings reveal that NLRP3 expression is significantly elevated in the kidneys of active AAV patients, accompanied by increased cleaved caspase-1 and N-terminal gasdermin-D (GSDMD) levels in peripheral blood mononuclear cells (PBMCs). In vitro, MPO-ANCA IgG induces NLRP3 inflammasome activation and interleukin (IL)-1β production in macrophages, which is associated with increased MPO expression and JNK signaling pathway activation. Immunofluorescence analysis demonstrates partial colocalization of CD206 and NLRP3 in AAV kidneys. Furthermore, silencing of MRC1 gene, which encodes CD206, reduces inflammasome activation induced by MPO-ANCA IgG. In conclusion, our study provides evidence that MPO-ANCA IgG contributes to NLRP3 inflammasome activation and macrophage pyroptosis, with CD206 playing a critical role in this process. These findings elucidate the mechanisms underlying inflammation in AAV and suggest potential therapeutic targets.