Effect of SiO₂-liberated macrophage factor on protein synthesis in connective tissue in vitro

Abstract

1. To elucidate the role of macrophages in fibrosis the effect of the SiO₂-liberated macrophage factor was assessed on protein synthesis in granulation-tissue slices. SiO₂ could be replaced by chrysotile asbestos. The active factor is found in the 45/55% sucrose interface of macrophage homogenate. 2. There is no evidence of the involvement of collagenase. 3. The SiO₂ effect is not influenced by the addition of yeast RNA to the incubation medium. 4. At a small concentration of polyvinylpyridine-N-oxide (PVNO) protein synthesis in the granulation tissue slices is stimulated, but at higher concentrations PVNO prevented the liberation of the fibrogenic factor from macrophages by SiO₂. 5. Phospholipase C and trypsin inhibited the effect of SiO₂, which was partially abolished also by heating, and by repeated freezing and thawing. 6. The macrophage RNAse, its inhibitors and fibroblast mRNA are suggested as key factors in the development of fibrosis.

Key Words:

• collagen synthesis
• fibrosis
• granulation tissue
• in vitro
• macrophages
• protein synthesis
• silicosis