The creation of superoxide by the phagocyte-reduced NAD phosphate (NADPH) oxidase is required for innate immunity, as evidenced by chronic granulomatous disease (CGD), an immunodeficiency illness caused by abnormalities in one of its genes. The NADPH oxidase protein complex is made up of two membrane proteins (gp91phox/NOX2 and p22phox) and four cytosolic proteins (p47phox, p67phox, p40phox, and Rac1/2). The phosphorylation of p47phox is essential for the activation of NADPH oxidase in cells. 

Researchers predicted that because p47phox and p67phox may form a tight complex in cells, p67phox might control p47phox phosphorylation. To test this idea, they employed neutrophils from healthy donors and p67phox/ CGD patients, as well as phospho-specific antibodies against 5 key p47phox-phosphorylated sites (Ser304, Ser315, Ser320, Ser328, and Ser345). 

In healthy human neutrophils, formyl-methionyl-leucyl-phenylalanine and phorbol myristate acetate promoted time- and concentration-dependent phosphorylation of p47phox on Ser304, Ser315, Ser320, and Ser328. Interestingly, phosphorylation of p47phox on serine residues was drastically decreased in neutrophils and Epstein-Barr virus-transformed B cells from p67phox/ CGD patients. The presence of p67phox elevated phosphorylation of p47phox in COSphox cells. In vitro investigations revealed that distinct PKC isoforms phosphorylated recombinant p47phox on Ser304, Ser315, Ser320, and Ser328 and that the addition of recombinant p67phox alone or in conjunction with p40phox potentiated this process. Thus, in intact cells, p67phox and p40phox are essential for efficient p47phox phosphorylation on Ser304, Ser315, Ser320, and Ser328. As a result, p67phox and p40phox were new p47phox-phosphorylation regulators.