Erythrocyte Sialoglycoproteins Engage Siglec-9 to Maintain Neutrophil Quiescence in the Bloodstream

摘要: Neutrophils remain functionally quiescent in the bloodstream of healthy humans. Characterized by a short lifespan (for which estimates vary widely), they exit to mediate various functions such as pathogen elimination or wound healing--or undergo spontaneous apoptosis and macrophage-mediated clearance absence an inflammatory stimulus. Understanding neutrophil quiescence, activation is relevant many clinical situations infection, sepsis, reperfusion injury, granulocyte transfusions, other neutrophil-mediated pathologies. It has long been known that neutrophils purified from blood tend be short-lived show signs activation, but this technical challenge assumed reflection their natural biology vivo. We found when whole blood, indeed rapidly express markers (low L-selectin; high CD11b) progress apoptosis. However, using novel method label situ followed flow cytometry, we these events occurred at much slower rate remained blood. This finding led us hypothesize during separation components, one may removing inhibitor normally maintains quiescence bloodstream. Co-incubation studies showed erythrocytes are primary component dampens including chemotaxis, generation reactive oxygen species, release extracellular traps. The duration viability was also lengthened upon re-incubation with erythrocytes. maintenance functional mediated largely erythrocyte surface sialoglycoproteins (particularly glycophorin A, GPA), engage Siglec-9, sialic acid-binding receptor dampen innate immune cell via cytosolic inhibitory motifs. Modification acid side chains newly developed gentle eliminated Siglec-9 binding, allowed measured species production. next sought evidence interaction occurs vivoby studying freshly collected Smears made fresh degree clustering on neutrophils, evident points contact GPA markedly reduced smears were buffy coat preparations, involves initial physical centrifugation. Taken together, data indicates acids have unexpected function carriers "self-associated molecular patterns" (SAMPs), regulating immunity maintaining bloodstream, apparently tonic engagement Siglec-9. Notably, SAMP effect blunts does not completely inhibit bacterial killing yet presumably helps limit unwanted Our findings physiological, pathological involving biology, useful reevaluation prior reinfusion-based kinetics performed isolated away Disclosures No conflicts interest declare.