Each value is the median fluorescence intensity (MFI) for each group (young or older subjects; n = 20 each group) with the SD in parentheses. MFI was calculated by subtracting the MFI for neutrophils incubated with anti-human CXCR1, CXCR2, and FPR1 for each subject from the MFI for neutrophils from the same subject incubated with an isotype-matched irrelevant fluorescein isothiocyanate–labeled IgG_2A. All data sets follow normal distribution (Kolmogorov-Smirnov test). Neutrophils were incubated with CXCL8 (100 nM) or fMLP (100 nM), and an aliquot of cells had surface receptor expression semiquantified by immunostaining and flow cytometry.