Studies on polymorphonuclear leukocyte bactericidal function: II. The role of oxidative stress

We have previously detailed the effects of exogenous cytokines (IL-1 beta, TNF-alpha, and IL-8) on polymorphonuclear leukocyte (PMN) bactericidal function during normoxia. In these studies, we have investigated the effects of hypoxia +/- reoxygenation independently and with IL-1 beta, TNF-alpha, and IL-8 on PMN bactericidal activity. Hypoxia in and of itself did not significantly alter PMN bactericidal activity against Escherichia coli or Staphylcoccus aureus; however, after 2 h of reoxygenation (H/R), PMN bactericidal activity against E. coli was significantly reduced compared with levels seen after 2 h of hypoxia. Similar to what was observed during normoxia, TNF-alpha, IL-1 beta, and IL-8 increased PMN bactericidal activity during hypoxia compared with buffer control PMN for S. aureus but not E. coli after 4 h of hypoxia. Following H/R, neither TNF-alpha, IL-1 beta, nor IL-8 reversed the decline in bactericidal activity induced by reoxygenation alone. Monoclonal antibodies that blocked the functional epitope of particular cytokine receptors demonstrated that during both hypoxia and H/R IL-1 beta R type I, IL-8R type A, and TNF-alpha R p60 were the predominant receptors responsible for mediating the bactericidal effect of the cytokines. During hypoxia and H/R, the addition of exogenous cytokines did prevent the fall in bactericidal activity seen as PMN: target ratios decreased. The decline in bactericidal activity following H/R was mediated in part by reduced phagocytosis of serum-opsonized bacteria following H/R. These results demonstrated that oxidative stress in the form of hypoxia +/- reoxygenation independently modulate the effect of exogenously added cytokines on PMN bactericidal capability.