An in vivo model system for the study of avian osteoclast recruitment and activity

We have developed a model system for the study of osteoclast recruitment and activity using devitalized bovine cortical bone slices implanted onto the chorioallantoic membrane (CAM) of chicken embryos. Bone slices were examined after 3, 6, and 8 days of incubation on the CAM. A marked cellular reaction to the bone was observed, characterized by a prominent angiogenic response. Upon histological examination, numerous multinucleated giant cells were associated with the undersurface of the bone slice and concentrated towards its periphery. These multinucleated cells were often associated with resorption lacunae and demonstrated ruffled borders when viewed by transmission electron microscopy. Removal of the cells and examination of the bone surface by scanning electron microscopy revealed numerous resorption pits characteristic of osteoclastic activity. These pits were evident on day 3 of incubation and appeared to be more extensive by day 8. This work demonstrates that the cells recruited to such ectopically implanted devitalized bone slices are functional osteoclasts, and that this system may provide a useful model for the study of osteoclast recruitment and activity.