Inhaled hypertonic saline for cystic fibrosis: Reviewing the potential evidence for modulation of neutrophil signalling and function

Figure 4 Schematic illustration of the NADPH oxidase of resting and formyl peptides activated cells. The neutrophil NADPH oxidase generates superoxide (O₂^-) and secondary oxygen-derived toxic products in response to bacteria or a variety of soluble stimuli (fMLP). A: The enzyme is dormant in resting neutrophils. The active site of this enzyme is located in an integral membrane cytochrome, b₅₅₈, which consists of the two subunits gp91^phox and p21^phox (subunits); B: Stimulation of the neutrophil by fMLP induces activation and phosphorylation (P) of a number of kinases including Akt; C: P21^rac is converted into the active GTP-bound form and the phosphorylation of the cytosolic components (p67^phox, p47^phox and p40^phox) occurs; D: These subunits then translocate to the membrane where they interact with cytochrome b₅₅₈ to initiate reactive oxygen species production. fMLP: Formyl peptides.