Transplantation of bone marrow cells (BMC) from hPLAP-tg rats into wild-type F344 recipients. Transgenic, hPLAP-labeled donor BMC were intravenously injected daily over 1 week into wild-type rats. Lung (A), spleen (C), and lymph nodes (E) from transgenic animals show strong and ubiquitous hPLAP staining. Similarly, osteocytes (arrowheads), osteoblasts (arrows), and all hematopoietic BMC show hPLAP staining in undecalcified MMA sections of ethanol-fixed tibias from hPLAP-tg rats (G). However, staining is completely absent in lung (B), spleen (D), lymph nodes (F), bone (H), and bone marrow (H) of wild-type rats intravenously injected with transgenic BMC over 1 week, 1 week after the last injection, indicating that syngeneic transplantation of transgenic BMC into wild-type recipients failed. The 5-μm-thick paraffin and MMA sections shown in A-H were stained for hPLAP enzyme activity overnight at room temperature after heat pretreatment, and were counterstained with nuclear fast red. Bar = 50 μm.