Collagen in submucous fibrosis: an electron-microscopic study.

A comparison of the electron-microscopic features of 11 examples of submucous fibrosis in its moderately advanced and advanced stages with 15 control specimens revealed no obvious abnormality of the collagen fibrils. The notable feature of the collagen in this disease is the densely packed bundles in the lamina propria, reaching close to the epithelial-connective tissue junction, to blood vessel walls, salivary glands and muscle fibers. The width and the periodicity of fibrils vary in both groups of specimens, noticeably so, next to the junction and close to blood vessels, salivary glands and muscles. This is due to the presence of the thinner Type III collagen fibrils in these sites and the natural variation of Type I fibrils. Immunofluorescent microscopy and special staining with sirius red and polarization microscopy demonstrate both types, confirming that Type I collagen forms the bulk of the collagen and that Type III is localized in the sites mentioned above. It is concluded that although there is an excessive increase of collagen, especially Type I, in submucous fibrosis, the fibrils are still morphologically normal.