Localization of cathepsin D in human odontoclasts. A light and electron microscopical immunocytochemical study

Odontoclasts are dentine and cementum resorbing cells whose relationship to bent: resorbing osteoclasts is not clear. Like osteoclasts, they possess d ifferent cathepsins which are involved in mineralized tissue degradation du ring the tooth root resorption process in deciduous teeth. Whether cathepsi n D, which in osteoclasts probably functions as an activator of other cathe psins, can be found in odontoclasts, has, however, not been investigated be fore. In order to determine its occurrence and localization, cathepsin D im munocytochemistry was applied to paraffin-embedded sections from 30 human d eciduous tooth roots undergoing resorption. Using immunogold postembedding immunocytochemsitry on LR-Gold embedded specimens, the distribution of cath epsin D was investigated at the ultrastructural level. We identified tartra te-resistent acid phosphatase-positive mono- and multinuclear odontoclasts near and on the periodontal surfaces of tooth roots. Nearly all of these ce lls showed cytoplasmic granular cathepsin D immunoreactivity. At the electr on microscopical level, gold labelling was seen on vacuoles and vesicles of the odontoclasts, which were identified as secondary lysosomes and phagoso mes. Extracellularly it was seen along the ruffled border and in neighboure d resorption areas of dentine and cementum. These findings indicate that ca thepsin D is secreted into the resorbing area of human odontoclasts in orde r to participate in degradation of mineralized tooth matrix, but may also f unction as an activator of other proteases in lysosomal organelles.