The interaction of presumptive osteoclastic precursors with mineralized bone matrix in vitro

In order to investigate the possibility that macrophagic- monocytic cells may be progenitors of osteoclasts, peritoneal macrophages from young rats were harvested and cultured for 2, 8, 24, 48 and 72 hours with treated calvaria. Glass coverslips served as the control substrate. Cultures were examined using phase contrast and bright-field light microscopy and scanning and transmission electron microscopy. The morphology of peritoneal macrophages cultured on glass has been described by numerous investigators. With phase contrast microscopy and scanning electron microscopy, these cells demonstrated a variety of shapes and sizes at all incubation periods. Their surfaces were covered with microvilli and ruffles. Lamellapodia were observed at the edges of cells. In cultures containing bone the morphology of peritoneal macrophages did not differ significantly from those observed on glass cover slips. With light and transmission electron microscopy the cells appeared macrophagiclike. These cells attached to the mineralized bone matrix. These results indicate that peritoneal macrophages interact with mineralized matrix in culture. However, under these culture conditions after 72 hours, cells lacked morphological evidence of differentiation into osteoclasts.