Flt3-Fc administration to op/op mice reduces the number or osteoclasts and the number of nuclei per osteoclast section in vivo.

Flt3-Fc (5 μg) or vehicle was injected daily. On the first day, 2 animals were given vehicle, and the other 3 were injected with Flt3-Fc. On the second day, 2 of the latter were given Flt3-Fc; and one of these was also given a third dose on the third day. Animals were killed 24 hours after the last injection. The number of TRAP-positive cells per centimeter (A) correlates inversely (r = 0.94;P = .016) with the duration of injections, as does the number of TRAP cells per section (B) (r = 0.98;P = .003) and the proportion of such cells showing more than one nucleus per cell (C) (r = 0.937;P = .019).