LOCALIZATION OF OSTEOPONTIN IN RESORPTION LACUNAE FORMED BY OSTEOCLAST-LIKE CELLS - A STUDY BY A NOVEL MONOCLONAL-ANTIBODY WHICH RECOGNIZESRAT OSTEOPONTIN

The characteristics of a monoclonal antibody produced against osteocla st-like multinucleated cells (MNCs) formed in rat bone marrow cultures were examined immunohistochemically and biochemically. The in vitro i mmunization was performed using as immunogen the MNCs from rat bone ma rrow cell culture, which revealed many characteristics of osteoclasts. After screening and cloning of hybridomas, the monoclonal antibody HO K 1 was obtained. This antibody reacted weakly with stromal cells and intensely with both MNCs and their putative migratory traces on cultur e dishes. Immunofluorescent examination of paraffin sections revealed intense reactivity on the epithelium of the choroid plexus, the ileum and the proximal-convoluted tubules of the kidney, and also on bone ce lls such as osteocytes, osteoblasts, and osteoclasts. Western blotting using purified rat osteopontin verified that the antigen recognized b y HOK 1 was osteopontin. Positive HOK 1 immunoreactivity was further o bserved in the resorption lacunae formed by a culture of MNCs on human tooth slices and on the surface of osteoclasts. The present data sugg ested that osteopontin is preferentially present on the resorption lac unae in resorbing calcified matrices and that osteoclasts under a spec ific state might trap this protein on their cell surface.