Accumulation of alveolar macrophages induced by inhalation exposure of coal fly ash in golden hamster lungs

Pathological and immunological effects of respirable coal fly ash in male Wistar rats

In this study the effects of inhalatory exposure to coal fly ash on lung pathology and the immune system in rats were examined. Rats were exposed to 0, 10, 30, or 100 mg/m(3) coal fly ash (6 h/day, 5 days/wk) for 4 wk, or to 0 and 100 mg/m(3) for 1 wk, and for 1 wk followed by a recovery in clean air of 3 wk. A concentration-related increase in lung weight was found starting from 30 mg/m(3) coal fly ash. After exposure to 100 mg/m(3), a time-related deposition of free particles in the lungs was observed as well as a time-related number of coal fly ash particles phagocytized in alveolar macrophages. Histological examination revealed increased cellularity in alveolar septa, consisting mainly of mononuclear cell infiltrate, proliferated type II cells, and a slight fibrotic reaction. After a recovery period of 3 wk the histological picture was identical to that after 1 wk of exposure, indicating no significant recovery. No toxicological significant changes were found in the hematological, clinical chemistry, or urine parameters. Effects both on nonspecific defense mechanisms and on specific immune responses were noted. With regard to the immune function in the draining lymph nodes of the lung, a significantly increased number of both T and B lymphocytes was observed. The ratio of both cell types was not changed in either of the groups. In serum of exposed rats a significant increase of up to 150% of the immunoglobulin A (IgA) content was found. The number and phagocytic capacity of macrophages were significantly increased, while the killing of Listeria bacteria per cell ex vivo/in vitro remained unchanged. Natural killer (NK) activity in pulmonary cell suspensions was slightly stimulated in rats exposed for 4 wk to 10 and 30 mg/m(3), whereas an exposure to 100 mg/m(3) resulted in a slight decrease; however, both changes were not significant. In conclusion, the alterations in lung histopathology and immunity, observed in a dose and exposure time relation at concentrations up to and including 100 mg/m(3) coal fly ash, may be considered an adverse response of the host to inhalation of particulate matter. Whether these observed alterations may effect the host resistance must be learned from infection studies.

Lung clearance of particles following excessive deposition of fly ash in golden hamsters

Male golden hamsters were exposed to coal fly ash (FA) at the concentration of 0 (control), 1, 2, or 20 mg/m3 for 3 or 6 months (20 hr/day, 7 days/week). They were sacrificed at 0, 1, 3 and 6 months after exposure to undergo morphological investigation of the lung clearance of particles ingested by alveolar macrophages (AMs) following excessive deposition of FA particles. Particle-laden AMs in a cluster decreased in inverse proportion to the dust burden after the cessation of exposure. AMs with well-spread lamellipodia frequently appeared on the degenerated AMs in a cluster. In addition, neutrophils also agglomerated mainly in the alveoli proximal to the terminal bronchioles and ingested a small amount of particles. These results suggest that AMs and neutrophils might recruit into alveoli enclosing AMs in necrosis and reingest released particles. Macrophages in bronchioles generally ingested fewer particles than those clustered in alveoli. This finding suggests that AMs ingesting a small amount of released particles could move on the mucociliary escalator of the terminal bronchioles. On the other hand, AMs ingesting a large amount of particles would agglomerate in alveoli due to the loss of their migrating ability. The latter agglomeration of particle-laden AMs might be responsible for the retardation of lung clearance in proportion to the lung burden of particles.