Immunohistochemical localization of procollagens. II. Electron microscopic distribution of procollagen I antigenicity in the odontoblasts and predentin of rat incisor teeth by a direct method using peroxidase linked antibodies.

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Abstract
In an attempt to locate procollagen I in rats odontoblasts, antibodies raised in rabbits were purified by affinity methods and linked to peroxidase. They were then incubated with chopped slices from the growing end of rat incisor teeth. The antibodies binding to the antigens in the slices were visualized by reacting the peroxidase moiety with diaminobenzidine in the presence of hydrogen peroxide. The slices were then embedded in Epon and sectioned for ultrastructural study. Within odontoblasts, the immunostaining indicative of procollagen I antigenicity is moderate in rough endoplasmic reticulum cisternae, strong in spherical and cylindrical Golgi distensions, intense in secretory granules, and variable in lysosomal structures. In predentin, immunostaining is intense close to the odontoblast layer, but decreases gradually in a distal direction. Hence, procollagen I (and/or substances endowed with similar antigenicity such as pro alpha (I) chains and procollagen fragments) is present: 1) along the intracellular pathway of collagen precursors where its concentration gradually increases to reach a maximum in secretory granules; 2) in predentin, into which it is released from the granules for transformation into nonimmunoreactive collagen I; and 3) in lysosomal structures where some of it is hydrolyzed.