Senescence in innate immune responses: reduced neutrophil phagocytic capacity and CD16 expression in elderly humans

Elderly humans are more susceptible to bacterial infections because of decl ining immune status. We have investigated the effect of aging on neutrophil bactericidal responses, comparing neutrophil function in healthy, young (2 3-35 years) and elderly (>65 years) volunteers. Superoxide generation in re sponse to fMLP was slightly increased in neutrophils from elderly donors, a nd serum from the elderly was able to opsonize E. coli efficiently. In cont rast, phagocytic index was significantly lower in neutrophils from the elde rly, compared with young donors (P<0.005). CD11a and CDIIb expression was n ot affected by age, but CD16 was significantly reduced in neutrophils from elderly donors (P<0.0001). CD16 expression and phagocytic index were measur ed in the same neutrophils using FITC-labeled E. coli, PE-conjugated anti-C D16 antibody, and CD16 expression correlated with phagocytic index (r=0.83; P<0.05). In elderly patients with bacterial infection, CD16 expression rem ained low. We propose that reduced neutrophil CD16 expression and phagocyto sis contribute to human immunesenescence.