Hypoxemia/reoxygenation down-regulates interleukin-8-stimulated bactericidal activity of polymorphonuclear neutrophil by differential regulation of CD16 and CD35 mRNA expression.

BACKGROUND

The purpose of this study was to determine the effects of hypoxemia/reoxygenation (H/R) on the regulation of interleukin-8 (IL-8)-stimulated human polymorphonuclear neutrophil (PMN) bactericidal activity.

METHODS

Venous human whole blood was rendered normoxic (Pvo2 saturation 60% to 80%), hypoxemic (Pvo2 saturation, less than 15%), or H/R (Pvo2 saturation more than 97%) by dialyzing the blood against a gas mixture of N2/H2/CO2 +/- 30% O2. Two hundred microliter aliquots from each study group were incubated with IL-8 (50 ng/ml) for 45 minutes before fluorescein isothiocyanate-conjugated mouse antihuman CD16 or CD35 antibodies were added. Bactericidal activity was measured with the release of 51Cr from labeled bacteria at 1:1, 5:1, and 10:1 PMN-target ratios. Steady-state mRNA levels for CD16 and CD35 were quantified by Northern blot analyses.

RESULTS

H/R reduced PMN bactericidal activity compared with hypoxemic levels for staphylococcus aureus (48 +/- 5.6 versus 27 +/- 3.3) and Escherichia coli (58 +/- 7.1 versus 33 +/- 4.2). H/R reduced the surface expression of CD16 but not CD35 (mean channel fluorescence CD16, 610 +/- 70 versus 310 +/- 30 for hypoxemia versus H/R; p < 0.01). After H/R was performed, IL-8 decreased mRNA levels for CD16 but not for CD35 compared with levels seen during hypoxemia + IL-8.

CONCLUSIONS

H/R down-regulates IL-8-stimulated PMN bactericidal activity by decreasing steady-state mRNA levels and surface expression of CD16. PMN bactericidal capability after H/R + IL-8 is primarily complementary and not Fc gamma receptor dependent.