[Intravital bone imaging:osteoclast.]

Osteoclasts are bone-resorbing giant polykaryons that differentiate from mononuclear macrophage/monocyte-lineage hematopoietic precursors. We have originally established an advanced imaging system for visualizing the in vivo behavior of mature osteoclasts in living bone tissues with intravital multiphoton microscopy. By means of this system, we could grasp the real time-course of osteoclastic bone resorption, and identified two distinct functional states of differentiated osteoclasts, 'bone-resorptive' and 'non-resorptive'. Intravital imaging also revealed that various biologic drugs acted directly on mature osteoclasts during inflammatory bone destruction. In this review, we show the latest data of intravital imaging of osteoclast dynamics.