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A 3-year-old girl has a history of recurrent ...

NADPH oxidase

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submitted by m-ice(126),

This girl has chronic granulomatous disease, in which the immune system cannot properly form reactive oxygen species needed to kill phagocytosed organisms. This is especially bad when dealing with catalase positive organisms (like Staph), because these organisms already use catalase to break down reactive oxygen species. The most common cause of this condition is a mutation in NADPH oxidase, responsible for the generation of the superoxide radical.

et-tu-bromocriptine  To add on: If neutrophils don't have access to NADPH oxidase, they can still use the bacteria's own hydrogen peroxidase to create ROS and kill the bacteria; however, catalase + organisms will not have this hydrogen peroxidase available (because catalase converts hydrogen peroxidase to O2 and water). So then the neutrophils are screwed and have no way of creating ROS. +1