Radiographic and histologic sections of the femurs of WT and

opg^−/− hosts engrafted with WT oropg^−/− TPO-overexpressing BM cells.Representative photographs from a WT control (A-C) and a 3-month-oldopg^−/− control (D-F) are shown for comparison. The middle column shows longitudinal sections of femurs stained according to Gordon-Sweet (original magnification × 25). Details of the femoral cortical area are illustrated in the right column (original magnification × 60). Histologic sections are stained according to Gordon-Sweet. Note decreased bone mineral radiodensity (D) and severe cortical bone porosity in theopg^−/− control (E-F). (G) Radiograph of the femur of a WT host engrafted with WT donor cells. Note significant radiodensification of the bone. (H-I) Representative histologic section of the femur shows the presence of numerous bone trabeculae (arrow) occluding the femoral cavity. (J) Radiograph of the femur of anopg^−/− host engrafted withopg^−/− donor cells shows poorly defined cortical region and significant loss of radiodensity. (K-L) Severe osteoporosis is confirmed histologically. (M) Radiograph of the femur of a WT host engrafted with opg^−/− donor cells. Increased bone density is seen. (N-O) Representative histologic section of the femur shows osteosclerosis with accumulation of bone trabeculae in the shaft (arrow). (P) Radiograph of the femur of anopg^−/− host engrafted with WT donor cells. Note thinning of the cortical region and decreased bone density. (Q-R) Histologically, the femur is profoundly osteoporotic with a porous cortical region. Radiography and histology were from the same animals examined 3 months after transplantation. Similar results were observed in 3 mice per experimental groups.