PI3K activation in neutrophils from young and old healthy donors. PI3K activity was assessed by western blotting using an antibody to the phosphorylated p85 regulatory subunit of PI3K. β-actin was assessed as the loading control. Cells were unstimulated or incubated with CXCL8 (100 nM) for the times shown. Blots were run in duplicate. (A-B) Representative western blots for 1 young and 1 older donor. (C) The densitometric ratio of phospho-p85:β-actin for young and old adults (n = 5 each group). There was a significant difference in PI3K:β-actin densitometric ratio between young and old neutrophils across all time points. * indicates significant difference between young and old ratios (P < .05).