OSTEOCLASTS ARE CAPABLE OF PARTICLE PHAGOCYTOSIS AND BONE-RESORPTION

Osteoclasts are multinucleated cells specialized for the function of l acunar bone resorption. Although they are known to be capable of phago cytosis of inert particles, it is not known whether this abolishes the ir ability to respond to hormones or to form resorption lacunae, Human and rat osteoclasts were isolated from giant cell tumours of bone and rat long bones, respectively, and cultured on coverslips and cortical bone slices, both in the presence and in tile absence of particles of lates (1 mu m diameter) and polymethylmethacrylate (PMMA) (<50 mu m). By light microscopy, it was evident that osteoclasts which had phagoc ytosed both latex and PMMA particles remained responsive to calcitonin . Osteoclast phagocytosis of particles was also evident on scanning el ectron microscopy, where it could also be seen that these cells were a ssociated with the formation of resorption lacunae, These findings und erline the fact that the osteoclast is a true member of the mononuclea r phagocyte system and that phagocytosis does not abrogate either its hormonal response to calcitonin or its highly specialized function of bone resorption, That osteoclasts which have phagocytosed biomaterial particles such as PMMA are still able to carry out lacunar bone resorp tion is of interest in clinical conditions such as aseptic loosening, where a heavy foreign body particle load is often associated with exte nsive bone resorption. (C) 1997 by John Wiley & Sons, Ltd.