Regulation of Bone-Marrow Macrophage Proliferation
Macrophages are derived from pluripotent bone marrow stem cells (1). Their proliferation and differentiation can be induced in vitro by the addition of “conditioned media” that contain colony-stimulating factors (2–6). Colony-stimulating factors (CSF) are normally assayed by their ability to promote colony formation from stem cells in semi-solid (soft agar or methylcellulose) medium. Two types of colony-stimulating factors that influence macrophage growth have been identified. CSF-1 (isolated from mouse L-cell conditioned medium or human urine) gives rise to colonies entirely composed of macrophages while CSF-II (e.g. from WEHI-3 conditioned medium or endotoxinlung conditioned medium) yields mixed colonies of granulocytes and macrophages (2–6).
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