Protein-A activates membrane bound multicomponent enzyme complex, NADPH oxidase in human neutrophils

Protein-A, 42KD cell wall glycoprotein of S. aureus Cowan I enhance mononuc lear and polymorphonuclear cell counts in vivo and possesses, antitoxic, an titumor, properties. In order to explain the mechanism of its function, the respiratory burst phenomenon in cell and cell free system was studied usin g lucigenin-dependent chemiluminescence technique. A dose dependent increas e in protein A-mediated generation of superoxide radical was observed in re sting and PMA stimulated neutrophils. Superoxide dismutase (SOD) was used t o confirm the production of superoxide radicals (O-2(-)). To understand the mechanism of protein-A induced O-2(-) generation; NADPH oxidase activity w as measured in cell free system using NADPH as a substrate. A significant i ncrease in NADPH oxidase activity was observed in the membrane and post-nuc lear supernatant fraction of activated human neutrophils. Cytosolic fractio n showed slight enzyme activation. Protein A (SpA)-induced NADPH oxidase ac tivation in the membrane fraction was observed even in the absence of the s ubstrate NADPH. These data indicate that protein A attenuate the NADPH oxid ase system to produce O-2(-) radicals.