Dynamics and phenotypes of aged and nonaged neutrophils during acute systemic inflammation. In response to lipopolysaccharide (LPS), aged neutrophils (1) arrive first to the inflamed organs/tissues and are followed by nonaged neutrophils (2). Simultaneously, the homing of aged neutrophils to bone marrow is altered and limiting their clearance. At the inflammatory site, aged neutrophils phagocytosize more intensively than the nonaged cells but reactive oxygen species (ROS) production and cytokine release are the same as in nonaged neutrophils. Recruitment of aged neutrophils is TLR-4 and macrophage-1 antigen (Mac-1)-dependent, however, the chemokine receptor CXCR4 is not involved in this process. 5-Bromo-2′-deoxyuridine (BrdU) is not incorporated into postmitotic cells, thus aged neutrophils are BrdU⁻ giving them an overall phenotype of BrdU⁻CXCR4^hiCD62L^low whereas nonaged neutrophils are BrdU⁺CXCR4^lowCD62L^hi under steady-state conditions. ?, Not studied yet in this model. Professional illustration by Patrick Lane, ScEYEnce Studios.