Deficiency of Id2 enhances TRANCE-mediated osteoclast formation. (A-B) BMMs derived from WT or Id2 KO mice were incubated for 3 days with M-CSF and an increased concentration of TRANCE. (A) Cultured cells were fixed and stained for TRAP (original magnification, ×100). (B) Numbers of TRAP⁺ MNCs were counted. (C) BMMs from WT or Id2 KO mice were analyzed for phagocytosis as described in Figure 3 (original magnification, ×100). (D) BMMs from WT or Id2 KO mice were stained for FACS analysis with anti-F4/80 and anti–c-fms (solid line) or control IgG (dotted line). Data represent means ± SDs from triplicate experiments. Images were acquired as described for Figure 2.