Comparative effects of inhaled silica or synthetic graphite dusts on rat alveolar cells

Alterations in population profiles, morphology, and phagocytic activity of lung cells followingin vivo exposure of Fischer 344 rats to a single dose of silica, were compared to similar changes following exposure to synthetic graphite. The effect of silica exposure on alveolar macro-phage mycocidal activity was also measured. Acute exposure by inhalation to 100 mg/m3 silica dust produced persistent pulmonary inflammation, as well as long-term changes in pulmonary alveolar macrophages (AM) typical of macrophage activation. Both particles were steadily cleared from the lungs; AM from the silica study, as well as from the 100 and 500 mg/m3 graphite studies, contained ingested particles throughout the entire 3 month experimental period. Lavaged pulmonary cells showed no reduction in viability as a result of exposure to either of the dusts. After silica inhalation, the following changes were observed constantly in bronchopulmonary lavage cell samples: increased numbers of polymorphonuclear leukocytes (PMN), hypersegmented PMN, binucleated AM, increased AM phagocytic indices and capacities, and increased mycocidal activity. Following inhalation of 1–100 mg/m3 synthetic graphite the above-mentioned effects were not seen. Exposure to 500 mg/m3 graphite produced transient inflammation and AM activation for about 24–48 hr.