Mode of C-type virus production by bone cells of C3H/Fg mice.

Electron microscopy of bone from the distal ends of femurs of six 3-month-old male C3H/Fg mice revealed varying modes and quantities of C-type virus production by cells in the preosteoblast to osteocyte developmental gradient. Production occurred by budding from the cell surface, either from very short pedicles or from longer microvillous-like processes. Although apparently absent in preosteoblasts, limited numbers of budding viruses (90-110 nM) were seen in 6 of 53 osteoblasts examined. Examination of 200 osteocytes revealed evidence of virus production in all but eight. In these cells, budding occurred from the cell body and its processes with release of viruses into the pericellular lacunar space. Budding from the longer microvillous-like processes sometimes resulted in binding together of viruses in bead-like fashion by thin strands of limiting membrane. In a few cases budding was also seen on the cell processes within the canaliculi. The quantities of viruses present within the lacunae usually increased with increasing age of the osteocytes, indicating continual virus production. Most of the viruses observed, however, were pre C-types along with lesser numbers of mature C particles. Thus, factors contributing to the production of mature C particles may be diminished in osteocytes of mice at this age.