Studies on the nature of silicosis: a suggested mechanism of fibrogenesis.

One theory which seeks to explain the production of fibrous tissue in silicosis postulates the interaction of collagen precursors with polysilicic acid. This stage has been questioned because it is doubtful whether polymerized silicic acid is normally formed when quartz dissolves in aqueous media. A mechanism by which silicic acid may be polymerized in vivo has been demonstrated by studying the properties of polyamide monolayers, which behave like collagen monolayers when spread on silicic acid substrates. The silicic acid which is adsorbed beneath the monolayer polymerizes when the polyamide films are subjected to pressure. In fibrogenesis, the polysaccharides which are produced in large amounts may serve to prevent the premature agglomeration of the collagen units. Later, when the concentration of the polysaccharide is largely reduced, the polysaccharide may assist in aligning and cementing the units together to form fibres. The physiological process is probably reversible but, if silicic acid takes the role of the polysaccharide in this second stage, the building up of fibres is likely to be an irreversible process.