Neutrophil kinetics and tissue localization quantified by in vivo cell labeling 3917

Abstract Description Neutrophils are a key component of the innate immune system. While historically considered a circulating cell, recent mouse models indicate that a small proportion of neutrophils could be tissue-localized in homeostasis. Important questions remain: How are neutrophils distributed in the body? What are their circulating and tissue half-lives? What percentage are extravascular? Where in tissues are they localized? To address these, we combined PET/CT, in vivo flow cytometry (serial intravascular staining, SIVS), mathematical modeling, and tissue imaging, in a rhesus macaque model. Live-tracking of ex vivo Zr-89 labeled cells by PET/CT revealed that neutrophils quickly pass through the lungs before migrating to the spleen, liver, and bone marrow, where they remain in a steady state. Using SIVS for direct labeling and tracking of circulating cells, we established that the circulating half-life of rhesus neutrophils is significantly shorter (0.4–8.8 h) than previous human studies have estimated (17 h). Previously circulating neutrophils are detectable in tissues for at least 24 hours. Tissue flow cytometry of in vivo labeled cells revealed that approximately 1% of neutrophils are extravascular in homeostasis. Multiplexed confocal imaging of tissue-localized neutrophils indicates their localization in the spleen is not random but parafollicular, in proximity to migrating B and T cells. Ongoing work is aimed at establishing the spatial localization of neutrophils in other tissues. Topic Categories Cellular Adhesion, Migration, and Inflammation (CAM)