TLR7/9—IFNα—LDHB Checkpoint Rewires NET Subtypes in Lupus 2254935

Abstract Introduction Excessive NET deposition inflames SLE pathology, yet patients remain unusually susceptible to invasive bacterial infection–a paradox implying qualitative defects in neutrophil effector programs. Building on our prior work, we asked whether nucleic-acid sensing and type I IFN signaling enforce a neutrophil state that skews NET subtype output and undermines antibacterial defense. Methods Neutrophils from MRL/lpr mice and SLE patients were profiled using flow-based NET phenotyping, mitochondrial ROS assays, LDHB protein/mRNA analysis, calcium influx/degranulation readouts, and bactericidal assays. In vivo S. aureus bacteremia models tested hydroxychloroquine (HCQ) and IFNAR blockade. Ex vivo perturbations in human SLE neutrophils assessed rescue of LDHB, mitochondrial ROS, and NET programs. Results Chronic TLR7/9 stimulation repressed mitochondrial LDHB, blocking lactate-triggered mitochondrial ROS and bactericidal suicidal NETosis. Conversely, staphylococcal α-hemolysin induced calcium influx and rapid degranulation that released preformed IFNα and drove vital (non-lytic) NETs. The programs were antagonistic: inducing vital NETs suppressed subsequent suicidal NETosis and produced NETs with reduced antibacterial protein content and poor bactericidal activity. In vivo, combined HCQ and IFNAR blockade restored LDHB, rebalanced NET-subtype composition, and reduced organ bacterial burdens; human SLE neutrophils showed parallel rescue ex vivo. Conclusion Persistent TLR7/9—IFNα signaling enforces an LDHB-low, vital-NET—biased state that fuels inflammation yet impairs host defense.Consequently, NETs are not monolithic–suicidal and vital NETs arise via distinct triggers, carry different proteomic cargo, and diverge in bactericidal capacity. These findings establish a mechanistic checkpoint controlling NET subtype allocation and provide a rationale and biomarker framework for normalizing neutrophil function in SLE using HCQ and IFNAR blockade. Funding Source 1R35GM154838 Topic Categories Basic Autoimmunity (BA)