NADPH oxidase–derived oxidants can influence multiple aspects of innate and adaptive immune responses. The phagocyte NADPH oxidase (red triangle) is assembled on the plasma membrane, phagosomes, and endocytic compartments. Superoxide is released inside membrane compartments or the extracellular space and is rapidly converted into derivative ROS. This includes dismutation to H₂O₂, which is membrane permeant and, thus, can diffuse into the cytosol. Oxidase-generated ROS can have many effects, depending on the site of ROS production, and, thus, can impact multiple pathways important for innate and adaptive immunity. See text for additional details. Professional illustration by Patrick Lane, ScEYEnce Studios.