Effect of intrabronchially instilled amosite on lavagable lung and pleural cells

Rats were instilled intrabronchially with 1 mg UICC amosite suspended in 0.2 mL of filtered saline; control animals received the saline instillation only. Five animals from each group were killed on various days after instillation, up to day 128/129. Total retrieved cell counts and differential cell analysis were performed from lung and pleural lavages. In particular, the appearance of peroxidase-positive macrophages (PPM) as indicators of newly arrived macrophages was investigated. Polymorphonuclear cells (PMN) and PPMs in lung lavages increased in number 24 hr after amosite instillation and remained at increased levels until day 62. Alveolar macrophage numbers were significantly decreased after amosite instillation. There was only a very transient increase of PPMs and PMNs in the saline group. The number of PPMs in pleural lavage fluid was already increased 24 hr after amosite instillation. The pleural PPM increase was sustained throughout the study. No pleural reaction was seen in the saline instilled group. The inflammatory reactions indicated by the composition of the lavaged cells of the lung represent the in vivo toxicity of intrabronchially instilled amosite. The stimulus for recruitment of PMNs and PPMs is different, since no PMN response was detected in the pleural space. It is suggested that the response of the pleural PPMs is caused by the early arrival of fibers at the pleural sites, which results in the recruitment of PPMs to this space by an unknown mechanism.