Phagolysosomal pH and location of particles in alveolar macrophages.

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.