Abstract: Abstract： Objective To observe the dynamic change and significance of apoptosis levels in the alveolar macrophages(AM) of the bleomycin-induced pulmonary fibrosis model mice. Methods A total of 100 mice were randomly divided into control group (n=50) and model group (n=50). The model group was received with bleomycin at 2.5 mg/kg via oropharyngeal instillation to molding. The control group was conducted with same volume of normal saline. Ten mice randomly selected were executed on the day 1, 3, 7, 14, and 21 after modeling in the two groups. Hematoxylin and eosin (HE) staining was used to observe the pathological changes of lung tissue and calculate the inflammation score and pulmonary coefficients in five mice of two groups. Alkali hydrolysis method was used to detect the content of hydroxyproline, and the bronchoalveolar lavage fluid (BALF) was collected to assess the cell counts and apoptotic levels of AM in another five mice. Results Mice of model group showed inflammatory cell infiltration and alveolar wall widening on day 3, along with an aggravate inflammation and increased inflammation score on day 7. The fibroplasia and collagen sediment were increased on day 14 and day 21. The inflammation score was decreased significantly in day 21 compared with those in day 7 and day 14. The hydroxyproline contents were increased significantly on day 21 than those on day 1, day 3 and day 7 in model group, but no significant difference when compared with those of day 14. The cell count and apoptotic rates of AM, and pulmonary coefficients showed changes of increasing first and then decreasing in model group, which reached the peak at day 7.Conclusion The cell counts and apoptotic levels increase in the preliminary stage of inflammatory and decrease in pulmonary fibrosis phase in bleomycin-induced pulmonary fibrosis model mice. These changes may play different roles in the progression of pulmonary fibrosis.

Key words: pulmonary fibrosis, macrophages, alveolar, hydroxyproline, apotosis, bleomycin, flow cytometry