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Phagolysosomal pH and location of particles in alveolar macrophages
K Nyberg1, U Johansson, A Johansson
1Section of Lung Medicine, Karolinska Institute, Stockholm, Sweden.
Abstract:
Fluorescein-labeled silica particles (FSP) were instilled into the tracheae of rabbits. Groups of four rabbits were killed after 24 hr, 1 week, 1 month, or 3 months and their lungs were lavaged. Phagolysosomal pH in the alveolar macrophages (AM) was measured using microscope fluorometry with FSP as a probe. Due to the marked decline of the fluorescence intensities from the FSP between 1 and 3 months after instillation, it was not possible to measure pH at 3 months, but the values from 24 hr, 1 week, and 1 month were quite similar, with group means of 4.8 and 4.9, respectively. Phagolysosomal pH in AM which phagocytized the FSP in vitro showed values about half a pH unit higher. AM from rabbits lavaged at 1 week had more lysosomes in contact with the FSP-containing phagolysosomes and a higher degree of vacuolization between the FSP and the phagolysosomal membrane than AM lavaged at 1 day. The location of the FSP in the AM appeared to be similar in rabbits lavaged after 1 week and 3 months. In histologic sections from the lungs the large majority of the FSP were within cells at all time points.
Insights
Fluorescein-labeled silica particles (FSP) were instilled into rabbit lungs. Phagolysosomal pH in alveolar macrophages remained stable for up to one month, indicating consistent cellular processing of these particles.
Area of Science:
- Pulmonary toxicology
- Cellular biology
- Nanoparticle research
Background:
- Alveolar macrophages (AM) are crucial for lung defense.
- Understanding nanoparticle behavior within AM is vital for safety assessments.
- Fluorescein-labeled silica particles (FSP) are used as probes in cellular studies.
Purpose of the Study:
- To investigate the phagolysosomal pH within alveolar macrophages after instillation of fluorescein-labeled silica particles (FSP) in rabbits.
- To assess the cellular processing and localization of FSP in lung tissue over time.
- To compare in vivo phagolysosomal pH with in vitro measurements.
Main Methods:
- Instillation of FSP into rabbit tracheae.
- Lung lavage and collection of alveolar macrophages at various time points (24 hr, 1 week, 1 month, 3 months).
- Microscope fluorometry using FSP as a pH probe to measure phagolysosomal pH.
- Histological examination of lung tissue.
Main Results:
- Phagolysosomal pH in AM was measured at 24 hr, 1 week, and 1 month, with group means around 4.8-4.9.
- In vitro phagocytosis of FSP by AM resulted in phagolysosomal pH values approximately 0.5 units higher.
- AM from rabbits lavaged at 1 week showed increased lysosome-FSP contact and vacuolization compared to those lavaged at 24 hr.
- FSP were predominantly found within cells in histological sections at all time points.
Conclusions:
- The phagolysosomal pH within rabbit alveolar macrophages remains relatively stable for up to one month after FSP instillation.
- Cellular processing of FSP by AM involves increased lysosomal interaction and vacuolization over time.
- FSP are primarily retained within alveolar macrophages in the lung tissue for the duration of the study.