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The NADPH-dependent oxidase of phagocytes
1Department of Medicine, University of Iowa, Iowa City, USA.
Abstract:
Polymorphonuclear leukocytes (PMNs) represent a prominent cellular element in the innate immune system, serving to ingest exogenous particles and microbes and to kill phagocytosed microorganisms. The microbicidal activity of PMNs depends on the interactions of a broad array of potent systems, including relatively stable degradative proteins as well as labile reactive radicals. These systems can be categorized as oxygen-dependent and nonoxidative mechanisms, although the physiologically relative activity depends on the precisely orchestrated interplay between both systems. The enzyme complex responsible for the activity of the oxygen-dependent system is the respiratory burst oxidase and its important contribution to host defense is best illustrated by the frequent and severe infections seen in individuals whose PMNs lack oxidase activity, namely patients with chronic granulomatous disease (CGD). Multiple elements comprise the oxygen-dependent system, and significant advances have been made in the past decade in understanding the protein components of the respiratory burst oxidase, their subcellular distribution in resting PMNs, and their agonist-dependent assembly into a functional system at phagosomal and plasma membranes. In parallel, substantial insights into the molecular bases of CGD have likewise been made. Nonetheless there remain significant gaps in our understanding of the precise functional contributions of particular components of the system, the molecular mechanisms that regulate their coordinated assembly, and the role of related proteins in nonphagocytic cells.
Insights
Polymorphonuclear leukocytes (PMNs) are key to innate immunity, using oxygen-dependent and nonoxidative systems to kill microbes. Understanding the respiratory burst oxidase in PMNs is crucial for host defense and treating chronic granulomatous disease (CGD).
Area of Science:
- Immunology
- Cell Biology
Background:
- Polymorphonuclear leukocytes (PMNs) are vital innate immune cells that phagocytose and kill microbes.
- PMN microbicidal activity relies on oxygen-dependent and nonoxidative mechanisms, with the respiratory burst oxidase central to the former.
- Chronic granulomatous disease (CGD) highlights the importance of the oxygen-dependent system, as patients with oxidase deficiency experience severe infections.
Purpose of the Study:
- To review recent advances in understanding the protein components and assembly of the respiratory burst oxidase in PMNs.
- To discuss the molecular basis of chronic granulomatous disease (CGD).
- To identify remaining gaps in knowledge regarding the regulation and function of the oxygen-dependent system and related proteins.
Main Methods:
- Review of recent literature on respiratory burst oxidase components, subcellular localization, and assembly.
- Analysis of molecular insights into chronic granulomatous disease (CGD).
- Identification of knowledge gaps in the functional contributions and regulatory mechanisms of the system.
Main Results:
- Significant progress has been made in identifying protein components of the respiratory burst oxidase and their distribution in resting and activated PMNs.
- Advances in understanding the agonist-dependent assembly of the oxidase complex at cellular membranes have been achieved.
- Substantial insights into the molecular genetics and pathophysiology of chronic granulomatous disease (CGD) have been gained.
Conclusions:
- The respiratory burst oxidase is a critical component of PMN-mediated host defense, and its function is intrinsically linked to preventing severe infections seen in CGD.
- While knowledge of the oxidase system has advanced, gaps persist concerning the precise roles of individual components and regulatory mechanisms.
- Further research is needed to elucidate the coordinated assembly of the oxidase complex and the function of related proteins in nonphagocytic cells.