Fractionation of connective-tissue-activating factors from the culture medium of silica-treated macrophages.

The medium of cultured, SiO2-treated peritoneal macrophages contained a factor which enhances the incorporation of labelled proline to collagen and other proteins in granulation tissue slices, cells and polysomes. Simultaneously, the activity of alkaline RNase in the whole medium was decreased in comparison with the corresponding control. Polyvinylpyridine-N-oxide, PVNO, protected the macrophages against SiO2. Latex-particles and E. coli lipopolysaccharide decreased the RNase activity in the macrophage medium, but unlike SiO2 did not cause liberation of the collagen synthesis-stimulating factor. Fractionation of the medium by gel filtration chromatography showed the SiO2-pretreatment to have caused a very significant decrease in the aggregation state of RNase. The fraction from gel filtration chromatography that contained the SiO2-liberated factor stimulating collagen synthesis also contained the disaggregated RNase. There was no RNase-activity in the control sample. A homogenous protein (mol. wt. 14,300) was isolated with repeated gel filtrations from the medium of silica-treated macrophages. It increased the incorporation of 3H proline and 3H thymidine into cultured granuloma cells.