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Peroxidatic activity distinct from myeloperoxidase in human monocytes cultured in vitro and in alveolar macrophages
Abstract:
Human monocytes develop a peroxidatic activity (PA) in rough endoplasmic reticulum (RER) after adherence or after culture in semi-solid medium. This enzyme activity disappears after three days of culture in the majority of macrophages derived from adult monocytes but persists for one week in macrophages derived from neonatal monocytes. The PA is due to an enzyme distinct from myeloperoxidase (MPO), since monocytes from a patient with MPO deficiency develop the same PA as that of normal monocytes after adherence. By its localization and other characteristics, PA of adherent monocytes resembles that of rodent macrophages. We therefore investigated whether human alveolar macrophages exhibit PA, using a sensitive cytochemical method which prevents inhibition by aldehyde in adherent monocytes. In various pathological cases, four types of macrophages could be identified: the majority were peroxidase-negative, a small percentage was of exudate type exhibiting a PA in granules as blood monocytes, while few macrophages were intermediate, possessing only PA in RER i.e. of type resident and a smaller proportion had PA in RER and in granules i.e. exudate-resident macrophages. These findings demonstrate that human macrophages and adherent monocytes may exhibit PA in RER as has been reported for rodent macrophages. The true nature and function of the enzyme responsible for this PA, which is distinct from MPO, remains unknown, but some arguments seem to suggest its role in prostaglandin synthesis.
Insights
Human monocytes exhibit peroxidatic activity (PA) in the rough endoplasmic reticulum (RER). This enzyme activity, distinct from myeloperoxidase (MPO), is found in various human macrophage types.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Human monocytes acquire peroxidatic activity (PA) in the rough endoplasmic reticulum (RER) upon adherence or culture.
- This enzyme activity differs from myeloperoxidase (MPO) and is present in neonatal monocyte-derived macrophages for a longer duration than in adult-derived macrophages.
Purpose of the Study:
- To investigate the presence and characteristics of PA in human alveolar macrophages.
- To compare PA in human macrophages with that observed in rodent macrophages.
- To identify different macrophage populations based on PA localization.
Main Methods:
- Utilized a sensitive cytochemical method to detect PA in human alveolar macrophages, preventing aldehyde inhibition.
- Examined monocytes from MPO-deficient patients to distinguish PA from MPO.
- Classified macrophage types based on PA presence in RER and/or granules.
Main Results:
- Identified four types of macrophages in pathological samples based on PA: peroxidase-negative, exudate type (PA in granules), resident type (PA in RER), and exudate-resident type (PA in RER and granules).
- Demonstrated that human macrophages and adherent monocytes can exhibit PA in RER, similar to rodent macrophages.
- Confirmed that the enzyme responsible for PA is distinct from MPO.
Conclusions:
- Human macrophages and adherent monocytes exhibit RER-associated PA, mirroring findings in rodent macrophages.
- The specific enzyme and function of this MPO-distinct PA remain to be elucidated, though a role in prostaglandin synthesis is suggested.