respiratory burst

Definition

Target type: biologicalprocess

A phase of elevated metabolic activity, during which oxygen consumption increases; this leads to the production, by an NADH dependent system, of hydrogen peroxide (H2O2), superoxide anions and hydroxyl radicals. [ISBN:0198506732]

Respiratory burst is a rapid production of reactive oxygen species (ROS) by phagocytes, primarily neutrophils and macrophages, upon encountering pathogens or other stimuli. This process is a critical component of the innate immune response and plays a crucial role in killing invading microorganisms.

The initiation of respiratory burst begins with the activation of phagocytes through various mechanisms, including recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), such as toll-like receptors (TLRs). Upon activation, a signaling cascade is triggered within the phagocyte, leading to the activation of NADPH oxidase, an enzyme complex located in the cell membrane.

NADPH oxidase catalyzes the transfer of electrons from NADPH (nicotinamide adenine dinucleotide phosphate) to molecular oxygen, generating superoxide anion (O2-). This reaction requires the assembly of multiple protein subunits, including gp91phox (also known as NOX2), p22phox, p47phox, p67phox, and p40phox.

The superoxide anion is a highly reactive species and can readily dismutate into hydrogen peroxide (H2O2), which is another ROS. In the presence of myeloperoxidase, an enzyme found in neutrophils, hydrogen peroxide can react with chloride ions to generate hypochlorous acid (HOCl), a potent antimicrobial agent.

Respiratory burst produces a variety of ROS, including superoxide anion, hydrogen peroxide, hydroxyl radical, and singlet oxygen. These ROS have various antimicrobial effects, including:

- **Direct killing of microorganisms:** ROS can damage bacterial cell walls and membranes, leading to cell lysis and death.
- **Inactivation of microbial enzymes and toxins:** ROS can oxidize and inactivate microbial enzymes and toxins, preventing their activity.
- **Activation of other antimicrobial mechanisms:** ROS can activate other antimicrobial pathways, such as the complement system and the production of antimicrobial peptides.

While respiratory burst is essential for host defense against pathogens, it can also contribute to tissue damage and inflammation. Excessive ROS production can damage host cells and tissues, leading to conditions such as inflammatory bowel disease, rheumatoid arthritis, and atherosclerosis.

Therefore, a tightly regulated balance of ROS production and detoxification is crucial for maintaining immune homeostasis and preventing pathological consequences.'
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Proteins (2)

Compounds (34)