The distribution of types I and III collagen in mouse oral mucosa and the age-related changes over 3 days to 2 years of age were examined by immuno-fluorescence and -electron microscopy, with use of affinity-purified polyclonal antibodies. Immunofluorescence microscopy revealed that types I and III collagen existed in all tissues and at all ages examined. The staining intensity for type I collagen was stronger and increased more markedly in the lamina propria of the hard palate (HPlp) and gingiva (G), compared with that in the submucosa of the hard palate (HPsm) and the buccal mucosa (BM). The staining intensity for type III collagen was strong and increased markedly with age in all connective tissues examined. Examination of immunogold-labeled tissues demonstrated that most of the collagen fibrils were labeled for both type I and type III collagen, which suggests that they were hybrid fibrils containing both types of collagen. The quantitative evaluation of the labeling densities of gold particles revealed that the labeling density of type III collagen in BM and HPsm was higher and increased more rapidly during growth than in HPIp and G, while the labeling density of type I collagen was higher in HPIp and G. The fibril diameters in HPIp were larger and increased more rapidly during growth than in BM and HPsm. These studies are the first to demonstrate the distribution of types I and III collagen and their age-related changes in mouse oral mucosa. The results support previous suggestions that type I collagen may contribute to the stability of the connective tissue organization and that type III collagen may play an important role in the flexibility of the connective tissue of oral mucosa as well as in the regulation of the collagen fibril diameters in the tissue.
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