HYPOXEMIA UP-REGULATES INTERLEUKIN-8 STIMULATED PHAGOCYTOSIS OF POLYMORPHONUCLEAR LEUKOCYTES BY DIFFERENTIAL REGULATION OF CD32W AND CD35 MESSENGER-RNA EXPRESSION

Background. The purpose of these studies was to investigate the effect of hypoxemia on interleukin-8 (IL-8) regulation of phagocytosis and surface opsonic receptor expression of whole blood polymorphonuclear leukocytes (PMNs). Methods, Whole blood PMNs were rendered hypoxemic (PvO(2) less than 15 mm Hg) or normoxic (Pvo(2) equals 60 to 80 mm Hg) and incubated with IL-8 (50 ng/ml) before the sequential addition of serum-opsonized fluorescent microspheres (emission wavelength, 560 nm) and fluorescein isothiocyanate-conjugated mouse anti-human CD32w or CD35 antibodies (emission wavelength, 513 nm). Concomitant two color flow cytometric analysis was then performed to measure the mean channel fluorescence (MCF) and the percentage of positive PMNs. Steady-state messenger RNA levels for CD32w and CD35 were quantitated by means of Northern blot analysis by using total RNA extracted from purified PMNs from each study group. Results, Hypoxemia increased IL-8 stimulated PMN phag ocytosis (percentage of positive PMNs, 38 +/- 1.5 versus 27 +/- 2.0, MCF; 5491 +/- 182 versus 4060 +/- 121 for hypoxemia plus IL-8 versus normoxia plus IL-8, respectively; p < 0. 05). Hypoxemia increased IL-8 stimulated PMN expression of CD32w and CD35 (MCF CD32w, 791 +/- 105 versus 336 +/- 81; MCF CD35, 542 +/- 87 versus 254 +/- 41; p < 0. 05). Under normoxic conditions IL-8 decreased messenger RNA levels for both CD32w and CD35, but under hypoxemic conditions IL-8 increased messenger RNA levels only for CD32w. Conclusions. Hypoxemia directly regulates IL-8 control of PMNs by increasing phagocytosis, receptor expression, and messenger RNA for these receptors. Studies investigating cytokine regulation of PMN function need to take into account oxygen tension when establishing the fundamental effects of cytokines on PMN physiology.