VIRAL BEHAVIOR OF PARACRYSTALLINE INCLUSIONS IN OSTEOCLASTS OF PAGETS-DISEASE OF BONE

Fresh tissues from six patients with Paget's disease of bone were exam ined ultrastructurally to investigate whether the characteristic parac rystalline inclusions in pagetic osteoclasts revealed viral behavior. These inclusions appeared as microfilamentous aggregates in both nucle i and cytoplasm of the osteoclasts in all six cases. The filamentous e lements of the inclusions with a diameter of 11-15 nm showed tubular s tructures with a central electron-lucent zone measuring 5-7 nm in diam eter. Viral budding-like structures containing these inclusions were f ound at the peripheral cytoplasm or cell processes in the ruffled bord er of some pagetic osteoclasts in two cases. The inclusions in the bud ding-like structures were often arrayed in a parallel fashion on the c ytoplasmic side of the cell membranes of extruded cytoplasm or cell pr ocesses. Virion-like particles were also found in the extracellular sp aces of the ruffled border. Marked nuclear degeneration was often seen in pagetic osteoclasts of three cases, although other nuclei in the s ame osteoclasts appeared normal. The degenerated nuclei showed nuclear ring formation where destroyed nuclear membranes were seen and disapp earance of nuclear matrices was noted. Since the modifications were al ways associated with the accumulation of abundant inclusions, they wer e probably caused by the inclusions. These findings suggested that the inclusions showed viral behavior in pagetic osteoclasts, and that the nuclear modifications were caused by virus infection.