Longevity of osteoclasts in radiation chimaeras of beige and osteopetrotic microphthalmic mice.

Beige (bg/bg) mice lethally X-irradiated (900 or 1000 rad) and rescued with spleen cells from osteopetrotic (mi/mi) mice were examined periodically up to 6 months thereafter for signs of osteopetrosis, radiographic and histological. Their metaphyses were also examined electromicrographically for general characteristics of osteoclasts and for giant lysosomal granules. Measurements of lysosomal area indicated no change in the first weeks, then an exponential decline to near base line after 3 months with a half-period of or approximately 10 days. In this combination osteopetrosis was of slower progression than hitherto reported in C57BL mice. We suggest that osteoclasts have no fixed life span and that their longevity is a function of genetic background and perhaps operational needs.