NADPH oxidase of the phagocytic cells (Nox2) transfers electrons from cytosolic NADPH to molecular oxygen in the extracellular or intraphagosomal space. The produced superoxide anion (O*2) provides the source for formation of all toxic oxygen derivatives, but continuous O*2 generation depends on adequate charge compensation. The vital role of Nox2 in efficient elimination of microorganisms is clearly indicated by human pathology as insufficient activity of the enzyme results in severe, recurrent bacterial infections, the typical symptoms of chronic granulomatous disease. The goals of this contribution are to provide critical review of the Nox2-dependent cellular processes that potentially contribute to bacterial killing and degradation and to indicate possible targets of pharmacological interventions.

β2-integrins of neutrophils play a critical role in innate immune defense but they also participate in tissue destruction during autoimmune inflammation. p190RhoGAP, a regulator of Rho-family small GTPases, is required for integrin signal transduction in fibroblasts. Prior studies have also suggested a role for p190RhoGAP in β2 integrin signaling in neutrophils. To directly test that possibility, we have generated a novel targeted mutation completely disrupting the p190RhoGAP-encoding gene in mice. p190RhoGAP deficiency led to perinatal lethality and defective neural development, precluding the analysis of neutrophil functions in adult p190RhoGAP−/− animals. This was overcome by transplantation of fetal liver cells from p190RhoGAP−/− fetuses into lethally irradiated wild type recipients. Neutrophils from such p190RhoGAP−/− bone marrow chimeras developed normally and expressed normal levels of various cell surface receptors. Though p190RhoGAP−/− neutrophils showed moderate reduction of β2 integrin-mediated adherent activation, they showed mostly normal migration in β2-integrin-dependent in vitro and in vivo assays and normal β2 integrin-mediated killing of serum-opsonized S. aureus and E. coli. A neutrophil- and β2 integrin-dependent transgenic model of the effector phase of autoimmune arthritis also proceeded normally in p190RhoGAP−/− bone marrow chimeras. In contrast, all the above responses were completely blocked in CD18−/− neutrophils or CD18−/− bone marrow chimeras. These results suggest that p190RhoGAP likely does not play a major indispensable role in β2 integrin-mediated in vitro and in vivo neutrophil functions or the effector phase of experimental autoimmune arthritis.

NADPH oxidase of phagocytic cells transfers a single electron from intracellular NADPH to extracellular O 2 , producing superoxide , the precursor to several other reactive oxygen species. The finding that a genetic defect of the enzyme causes chronic granulomatous disease (CGD), characterized by recurrent severe bacterial infections, linked generation to destruction of potentially pathogenic micro-organisms. In this review, we focus on the consequences of the electrogenic functioning of NADPH oxidase. We show that enzyme activity depends on the possibilities for compensating charge movements. In resting neutrophils K + conductance dominates, but upon activation the plasma membrane rapidly depolarizes beyond the opening threshold of voltage-gated H + channels and H + efflux becomes the major charge compensating factor. K + release is likely to contribute to the killing of certain bacteria but complete elimination only occurs if production can proceed at full capacity. Finally, the reversed membrane potential of activated neutrophils inhibits Ca 2+ entry, thereby preventing overloading the cells with Ca 2+ . Absence of this limiting mechanism in CGD cells may contribute to the pathogenesis of the disease.

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The effects of nitric oxide synthase (NOS) inhibition (effected using L-NAME, 14 mg (kg body mass (BM))(-1), administered intravenously) on systemic and renal circulation and renal excretory function has been investigated in anaesthetized Wistar rats subjected to one of two different degrees of isotonic extracellular (EC) volume expansion (40 and 60 ml x kg(-1) (240 min)(-1)). The administration of L-NAME resulted in an increase in mean arterial blood pressure and total peripheral vascular resistance (TPR), and a significant reduction in cardiac output (CO) and the kidney fraction of CO in both experimental groups. The total renal blood flow (RBF) dropped from 557 + 43.4 to 149 +/- 13.1 ml x min(-1) (100 g BM)(-1) and from 592 +/- 45.9 to 191 +/- 16.3 ml x min(-1) (100 g BM)(-1) in the 40 and 60 ml x kg(-1) (240 min)(-1) experimental volume expansion groups, respectively. A redistribution of the intrarenal circulation from the medulla of the kidney toward the cortex may have occurred. The NOS inhibition induced a significant decrease in the glomerular filtration rate (GFR; from 1.18 +/- 0.10 to 0.53 +/- 0.08 ml x min(-1) (100 g BM)(-1) and from 1.26 +/- 0.07 to 0.73 +/- 0.08 ml x min(-1) (100 g BM)(-1) in the 40 and 60 ml x kg(-1) (240 min)(-1) experimental volume expansion groups, respectively), and the filtration fraction increased. The urine excretion dropped in parallel with the GFR, while the reduction in sodium and potassium excretion was more marked than that of the GFR, raising the possibility of a direct effect on the kidney tubules. The difference in EC volume expansion (the calculated increases in the EC volume in the last 90 min were 1.30 and 5.44% in the two time control groups and 3.66 and 7.45% in the two L-NAME-treated groups) did not induce any significant modification of the L-NAME effect.