Related Experiment Videos
Chronic granulomatous disease--pieces of a cellular and molecular puzzle
1Department of Basic and Clinical Research, Scripps Clinic and Research Foundation, La Jolla, California 92037.
Insights
Chronic granulomatous disease (CGD) is an inherited immune disorder. Phagocytes in CGD patients cannot produce microbicidal oxidants due to a defective respiratory burst oxidase enzyme, leading to recurrent infections.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Chronic granulomatous disease (CGD) is an inherited disorder affecting phagocytes' ability to produce microbicidal oxidants.
- Patients experience recurrent, severe bacterial infections and tissue damage due to impaired immune response.
- Current treatments include prophylactic antibiotics, which slow but do not halt disease progression.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying the respiratory burst oxidase defect in CGD.
- To understand the components of the respiratory burst oxidase and their roles in superoxide production.
- To investigate the genetic basis of CGD subtypes, including X-linked and autosomal recessive forms.
Main Methods:
- Analysis of the respiratory burst oxidase enzyme, responsible for superoxide (O2-) production.
- Identification of key components: cytochrome b558, a flavoprotein, a cytosolic factor, and 48K phosphoproteins.
- Investigation of the genetic defects in genes encoding oxidase components, particularly for the common X-linked form.
Main Results:
- CGD is characterized by a defect in the respiratory burst oxidase, preventing the generation of superoxide (O2-).
- This enzyme defect impairs the production of essential microbicidal oxidants required for pathogen killing.
- A specific gene defect in cytochrome b558 is identified as the cause of the most common form of CGD.
Conclusions:
- The failure of microbicidal oxidant production in CGD stems from a defective respiratory burst oxidase.
- Understanding the interplay of oxidase components is crucial for developing targeted therapies for CGD.
- Further research is needed to fully delineate the relationships between CGD components and oxidase activity.
Abstract:
Chronic granulomatous disease (CGD) is an inherited disorder in which phagocytes are unable to manufacture microbicidal oxidants. The disorder may be classified into subtypes depending upon the mode of transmission (X-linked or autosomal recessive) and the presence or absence of a heme protein designated 'cytochrome b558' (see below). Patients with CGD suffer recurrent deep-seated bacterial infections that respond poorly to therapy, slowly destroy affected tissues and eventually claim the patients' lives. Clinical deterioration is slowed, though not stopped, by the current practice of placing CGD patients on prophylactic antibiotics. Microbicidal oxidant production fails in CGD because of a defect in the enzyme responsible for the production of superoxide (O2-), the single precursor from which all the microbicidal oxidants ultimately arise. This enzyme, the respiratory burst oxidase, is a membrane-bound oxidase that catalyses the one-electron reduction of oxygen to O2- at the expense of NADPH. The oxidase is dormant in resting phagocytes, but comes to life when the phagocytes are exposed to bacteria or other appropriate stimuli. Components related to the respiratory burst oxidase include cytochrome b558 (one of those subunits has recently been shown to be encoded by a gene that is defective in the most common form of CGD), a flavoprotein that participates directly in O2- production, a cytosolic factor needed for the activation of the oxidase, and a group of 48K phosphoproteins. How these components relate to each other and to the O2- -forming activity of the oxidase is currently under active investigation.