The aim of our study was to analyze polymorphonuclear neutrophil (PMN) functions in elderly individuals compared with those in healthy young participants, directly in whole blood to avoid issues with data interpretation related to cell isolation procedures. Despite the presence of increased circulating levels of proinflammatory cytokines, resting PMNs from the elderly individuals were not activated as shown by normal CD62L and CD11b expression at the PMN surface and normal constitutive reactive oxygen species (ROS) production. However, suboptimal stimulation induced modulations of CD62L and CD11b expression, which positively correlated with the interleukin-6 circulating level, suggesting a possible in vivo preactivation of old PMNs by this cytokine. In addition, PMN phagocytosis of opsonized Escherichia Coli was decreased in elderly individuals. Furthermore, upon preincubation of elderly whole-blood samples with tumor necrosis factor-α or Toll Receptor agonists, we observed a reduced PMN oxidative burst in response to formyl peptides. Elderly participants also exhibited an increased percentage of the immunosuppressive CD16bright/CD62Ldim PMN subpopulation, which was characterized by a lower phagocytic index and a reduced ROS production compared with the CD16bright/CD62Lbright subset. Thus, the reduced phagocytosis and ROS production associated with an expansion of immunosuppressive CD16bright/CD62Ldim PMN subpopulation might be involved in the increased susceptibility to bacterial and fungal infections with old age.
Keywords: Biology of aging; Human aging; Immunosenescence; Reactive oxygen species.
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