Effect of age on human neutrophil function.
Neutrophil phagocytosis, reactive oxygen intermediate production (intra- and extracellular), neutrophil bactericidal activity, and chemotaxis/chemokinesis were assessed in three age groups: 21-36, 38-56, and 62-83 years. A significant age-dependent reduction in the number of phagocytized Escherichia coli per neutrophil (measured by acridine orange staining) and Staphylococcus aureus phagocytosis (measured by flow cytometry) was seen (r = 0.669 and r = 0.684, P<0.001 for both). These findings correlated with an age-dependent increase in intracellular calcium concentrations in resting neutrophils (r = 0.698, P<0.001) and a reduced hexose uptake (r = 0.591, P<0.01). In addition, a significant reduction in the intracellular reactive oxygen production was seen after stimulation with S. aureus (P<0.001) with increasing age. In contrast, no differences between the groups in reactive oxygen production was seen after stimulation with E. coli. The neutrophil bactericidal activity was impaired with increasing age (64+/-4% of the phagocytized bacteria were killed in group 1; 66+/-2 in group 2, and 59+/-6 in group 3; P<0.01). In addition, a trend toward a reduced neutrophil chemotaxis was seen with increasing age (P = 0.022). The findings suggest that increased intracellular calcium concentrations in resting neutrophils and/or a reduced hexose uptake result in reduced phagocytic ability and decreased bactericidal activity of neutrophils in the elderly.