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Role of bone marrow stroma in hemopoietic stem cell regulation.

Bone marrow plugs from C57Bl mice were irradiated with 1500 rad, implanted under the kidney capsule of (CBA x C57Bl)F1 hybrid mice and reimplanted one month later in identical F1 hybrid mice. Foci of ectopic hemopoiesis formed in which all hemopoietic cells were of recipient origin, while the stroma was from the donor bone marrow. The hybrid resistance in such foci was of donor origin. Implantation of 8--10 femoral plugs under the capsule of each kidney produced large foci of ectopic hemopoiesis containing thousands of hemopoietic stem cells (CFUS). The sum total CFUS content in such mice was two- to four-fold than in normal mice in steady-state hemopoiesis. It is concluded that the regulation of stem cell proliferation and total content in the body is governed by the stroma of hemopoietic organs.