| Background At precent, pneumoconiosis is still one of the most seriousoccupational diseases，silicosis and coal workers’ pneumoconiosis accounted for morethan90%of the cases of pneumoconiosis. The interaction between marcrophages andSiO2dust is generally believed to play an important role in silicosis formation. Theexact pathogenesis of silicosis is still unknown. When silica dust particles (diameter0.5~5μm) drop into the alveoli through the respiratory tract, macrophages in thelungs clear the dust particles by phagocytosis. Macrophages dies when havingphagocytised a large number of quartz dust. Then the dead macrophages arephagocytised by other macrophages. This turns out to be a vicious cycle. Phagocytosisof quartz dust macrophages release a variety of cytokines, together with cytokinessecreted from other types of cells promote fibroblast growth and collagen formationthrough autocrine and paracrine way, and eventually lead to silicosis nodule formation.We established an experimental silicosis rat model by SiO2instillation.Bronchoalveolar Lavage Fluid (BALF) was collected. In order to discuss thepathogenesis of silicosis, experiments in BALF and lung tissues were performed. InBALF, we have observed the smears, counted the nucleated cell number and thepercentage of macrophage, measured the contents of cytokines interleukin-6(IL-6)and interleukin-8(IL-8). The expression of nuclear factor-κB (NF-κB) in lungs of ratswas monitored.Objective To illuminate the function of pulmonary macrophages in the lung tissuesof experimental rats after one-time silica instillation. To investigate the changes and significance of macrophages, IL-6and IL-8in BALF at different stages of rat silicoticrats.Methods Fifty four male SD rats were randomly divided into the silica exposedgroup and the control group. One ml silica suspension (40g/L) was administrated viaintratracheal instillation while equal amount of saline was instilled to the rats ofcontrol group. Animals were sacrificed at the1st,7th,14th,21st,28th,35th,77th,106th,126thday after silica instillation. The samples of BALF and lung tissues werecollected. The expression of NF-κB was observed by immunohistochemistry method;the contents of IL-6and IL-8in BALF were assayed by ELISA. The nucleated cellnumber was counted and the percentage of macrophage was calculated.Results The levels of IL-6in BALF of silicotic rats were higher than those incontrol group in the early stage (1st,7th,14thday). IL-6declined on the7thday, peakedon the14thday and the statistic difference was significant (P＜0.05). IL-6deceasedafterwards. At the late stage of experiment (77th,106th,126thday), IL-6increasedagain, but the difference was not obvious. The content of IL-8has the same tendencyas that of IL-6, but there was no statistic difference. The nucleated cell count and thepercentage of macrophage of silicotic rats in BLAF were higher than those of controlgroup at various periods and the difference was obvious (P＜0.05). The nucleated cellcount raised on the14thday and straightly increased in late stage of experiment (77th,106th,126thday). There emerged two peaks of the percentage of macrophagerespectively at14thday and126thday. In the early stage of experiment (1st,7th,14thday) and late stage of experiment (77th,106th,126thday), the levels of NF-κB in lungsof silicotic rats obviously increased than those in control group (P＜0.01). In otherstage of experiment (21st,28th,35thday), there was no obvious difference but stillhigher than those of control group.Conclusion The changes of alveolar macrophages and the secretion of inflammatory cytokines in rats exposed to silica dust have a close relationship withsilicosis occurrence and development. |
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