Analysis of transplanted hematopoietic cells in nonirradiated and irradiated bone marrow. (A-F) Cross-sections of nonirradiated (A-C) and irradiated (D-F) bones illustrate the markedly reduced cell density after irradiation (DAPI). Shown are transverse sections of femur shafts (A,D) and longitudinal sections of distal femoral epiphyses (B,E) or femoral heads (C,F). (G-H) Differential distribution of transplanted hematopoietic stem/progenitor cells in nonirradiated (G) and irradiated (H) hosts. Shown here are longitudinal sections of tibiae not used for counting from recipients of similar numbers of donor cells. The efficiency of homing in nonirradiated hosts is higher than in irradiated hosts, but the distribution follows a random pattern, whereas in irradiated hosts, transplanted cells preferentially home to endosteal regions within compact bone. Corresponding quantitative data, generated in transverse sections of femurs, are shown in Table 1.