103 Role of neutrophil subpopulations during the innate immune response in sterile pulmonary inflammation

Abstract Inhalation of nanoparticles (NPs) such as quantum dots or carbon black has been shown to elicit a rapid proinflammatory response in the lungs, characterized by neutrophil recruitment into the airspace (Liu et al., 2025, Sci. Adv.). Recent evidence indicates that non-proliferative immature neutrophils act as a readily mobilizable reservoir in the bone marrow, whereas mature neutrophils exert key effector functions during inflammation. Here, we investigated the specific roles of immature and mature neutrophil subpopulations in nanoparticle-induced pulmonary inflammation. Using advanced intravital microscopy, we visualized neutrophil dynamics in alveolar microvessels of mice in real time for up to 90 min following NP inhalation. Fluorescently labelled antibodies (anti–Ly-6G and anti–CD101) were administered intravenously to distinguish immature (CD101⁻) and mature (CD101⁺) neutrophils. Consistent with our previous observations, total neutrophil numbers increased exclusively in NP-exposed mice. While the number of mature neutrophils remained constant, the proportion of immature neutrophils rose significantly over time after NP exposure. Flow cytometric analysis revealed no corresponding increase in circulating immature or mature neutrophils, suggesting a selective recruitment mechanism to the alveolar microvasculature. In conclusion, NP-induced sterile inflammation selectively recruits CD101⁻ immature neutrophils to the lungs, indicating that this subpopulation plays a pivotal role in the rapid innate immune response to nanoparticle exposure.