Cytokine control of PMN phagocytosis: regulatory effects of hypoxemia and hypoxemia-reoxygenation

Abstract

We investigated the effects of hypoxemia and hypoxemia-reoxygenation (H/R) on interleukin-8 (IL-8), tumor necrosis factor-alpha (TNF-alpha), or IL-1beta stimulation of whole blood polymorphonuclear leukocyte (PMN) phagocytosis and bactericidal activity. Whole blood PMN were rendered hypoxemic (venous PO2 < 15 mmHg), normoxic (venous PO2 60-80 mmHg), or reoxygenated after hypoxemia (H/ R = venous PO2 150-200 mmHg) and were incubated with IL-8, TNF-alpha, or IL-1beta before sequential addition of serum-opsonized fluorescent microspheres and fluorescein isothiocyanate-conjugated mouse anti-human CD64, CD32w, CD16, CD35, or CD11b/CD18. Concomitant two-color flow cytometric analyses were then performed measuring mean channel fluorescence and the percentage of PMN positive for phagocytosis, with simultaneous subset receptor analysis on populations of PMN that exceeded control levels of phagocytosis. During hypoxemia, whole blood PMN phagocytosis in the presence of IL-8, TNF-alpha, or IL-1beta was increased compared with normoxia. Northern blot analyses revealed an increase in steady-state mRNA levels for CD32w during hypoxemia + IL-8 and CD64 during hypoxemia + IL-1beta. During reoxygenation, both whole blood PMN phagocytosis and bactericidal activity were reduced in the presence of IL-8, TNF-alpha, or IL-1beta, and in subsets of PMN with reduced phagocytosis H/R reduced CD64, CD32w, CD16, CD35, and CD11b/CD18 expression in the presence of each cytokine. Northern blot analyses revealed that H/R reduced mRNA levels for opsonic receptors primarily for IL-1beta-stimulated PMN. These results demonstrate a direct regulatory effect of hypoxemia and H/R on whole blood PMN phagocytosis, receptor expression, and steady-state mRNA levels of both Fc(gamma) and complement receptors.