Hydroxyl radical generation by polymorphonuclear leukocytes measured by electron spin resonance spectroscopy

Area of Science:

• Biochemistry
• Immunology
• Spectroscopy

Background:

• Polymorphonuclear leukocytes (PMN) are key immune cells involved in pathogen clearance.
• Phagocytosis by PMN is a complex process involving the generation of reactive oxygen species.
• Understanding the specific reactive oxygen species produced by PMN is crucial for elucidating their microbicidal mechanisms.

Purpose of the Study:

• To detect and characterize hydroxyl radical (OH.) formation by phagocytosing PMN.
• To investigate the enzymatic pathways involved in OH. generation by PMN.
• To explore the role of OH. in the context of immune deficiencies.

Main Methods:

• Electron spin resonance (ESR) spectroscopy utilizing the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO).
• Incubation of normal and patient-derived PMN with opsonized zymosan to stimulate phagocytosis.
• Assessing the effect of enzyme inhibitors (superoxide dismutase, catalase) and radical scavengers (mannitol) on ESR signal formation.

Main Results:

• An ESR signal characteristic of the DMPO/OH. adduct was observed during the phagocytosis of opsonized zymosan by normal PMN.
• Adduct formation was significantly inhibited by superoxide dismutase and mannitol, indicating OH. involvement.
• Catalase showed minimal effect on adduct formation.
• PMN from patients with chronic granulomatous disease did not form the DMPO/OH. adduct.
• PMN lacking myeloperoxidase exhibited enhanced adduct formation compared to normal PMN.

Conclusions:

• PMN generate hydroxyl radicals (OH.) during phagocytosis, evidenced by DMPO spin trapping and ESR.
• The generation of OH. by PMN is likely mediated by a myeloperoxidase-independent pathway.
• These findings provide insights into the reactive oxygen species involved in PMN function and suggest a role for OH. in certain immune conditions.