• Tuberculosis and Respiratory Diseases
• /
• v.45 no.4
• /
• pp.823-834
• /
• 1998

Background: Chronic inhalation of silica induces the lung fiborsis. The alveolar macrophages ingest the inhaled silica; they liberate the pro-inflammatory cytokines such as IL-1$\beta$, IL-6, TNF-$\alpha$ and fibrogenic cytokines, TGF-$\beta$ and PDGF. Cytokines liberated from macrophage have pivotal role in pulmonary fibrosis. There is a complex cytokine network toward fibrosis. However, the exact roles and the interaction among the proinflammatory cytokines and TGF-$\beta$, a fibrogenic cytokine, have not been defined, yet. In this study, we investigated silica induced IL-1$\beta$, IL-6, TNF-$\alpha$ and TGF-$\beta$ production and the effect of IL-1$\beta$, IL-6, TNF-$\alpha$ on the production of TGF-$\beta$ from lung macrophages of Balb/C mice. Method: We extracted the lung of Balb/C mice and purified monocytes by Percoll gradient method. Macrphages were stimulated by silica ($SiO_2$) in the various concentration for 2, 4, 8, 12, and 24 hours. The supernatants were used for the measurement of protein levels by bioassay, and cells for the levels of mRNA by in situ hybridization. Results: The production of IL-6 was not observed till 4 hours, and reached the peak levels at 8 hours after stimulation of silica. The production of TNF-$\alpha$ increased from 2 hours and reached the peak levels at 4 hours after stimulation of silica. The spontaneous TGF-$\beta$ production reached the peak levels at 24 hours. TNF-$\alpha$ upregulated the silica induced TGF-$\beta$ production. Silica induced TGF-$\beta$ production was blocked by pretreated anti-TNF-$\alpha$ antibody. In situ hybridization revealed the increased positive signals at 4 hours in IL-6, at 4 hours TNF-$\alpha$ and 12 hours in TGF-$\beta$. Conclusion: The results above suggest that silica induced the sequential production of IL-6, 1NF-$\alpha$ and TGF-$\beta$ from macrophages and TNF-$\alpha$ upregultaes the production of TGF-$\beta$ from silica-induced macrophages.