Evidence for osteoclast production in mixed bone cell culture.

Osteoclastlike cells (OLCs) were recognized by their morphological, histochemical, and behavioral characteristics. These characteristics were initially observed in freshly isolated osteoclasts when neonatal rat bone cells were introduced into culture. Epithelioid cells proliferated during the first week to form a confluent layer. The cells' alkaline phosphatase content and ability to produce elevated levels of cyclic adenosine monophosphate in response to parathyroid hormone (PTH) led us to tentatively describe them as osteoblastlike cells. When a second addition of neonatal bone cells was made onto this confluent layer, OLCs were produced, their numbers increasing to a maximum 7 days later and dying out 3 weeks later. Mononuclear cells with similar characteristics to these multinuclear OLCs were observed and their production and disappearance closely paralleled that of the OLCs. Fusion of OLCs was observed. The conditions under which OLCs were produced are described.