IMMUNOHISTOCHEMICAL LOCALIZATION OF CATHEPSIN-B, CATHEPSIN-D AND CATHEPSIN-L IN THE RAT OSTEOCLAST

Immunohistochemical localization of cathepsins B, D and L in the osteo clasts of rat alveolar and femoral bones was investigated by using the avidin-biotin-peroxidase complex method for semithin, 1-mum-thick cry osections. Extracellular immunoreactivity for cathepsins B and L was c learly demonstrated along the bone resorption lacunae; the intensity o f the extracellular immunoreactivity of cathepsin L was stronger than that of cathepsin B. However, the intracellular immunoreactivity of bo th cathepsins was weak compared with that of cathepsin D. The intracel lular immunoreactivity of cathespin D in the osteoclasts was clearly o bserved in the granules and/or vacuoles, but extracellular cathepsin D immunoreactivity was either negligible or not detected along the reso rption lacunae. In the adjacent sections stained with anti-cathepsin L or D, extensive extracellular deposition of cathepsin L was found alo ng the bone resorption lacunae, with or without osteoclasts, although the intracellular reactivity of cathepsin L was weak. This is the firs t morphological study in which cathepsins B and L have been demonstrat ed to be produced in the osteoclasts and extensively secreted into res orption lacunae, and in which cathepsin D was found to be present in t he cells but scantily secreted into the lacunae. These findings sugges t that cathepsins B and L directly and effectively participate in the degradation of the bone matrix.