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Characterization of cultured stromal layers derived from fetal and adult hemopoietic tissues.

Cultured stromal layers grown from fetal and adult hemopoietic tissues reproduce, in vitro, features that typify their in vivo counterparts. Thus, fetal liver (FL) cultures consist predominantly of macrophages, and fetal bone marrow (FBM) cultures fail to form the fat cells that are characteristic of adult bone marrow (ABM) cells grown in the presence of methylprednisolone. Further investigation showed that the lack of fat cell formation in FBM cultures was not due to absence of steroid receptors because cells from the fibroblast component of FBM and ABM possess similar numbers of receptors of similar affinities. Phenotypically, the macrophages that occur in FL, FBM, and ABM stromal cultures are RFD7+, 3.9+ UCHM1, which identifies them as mature tissue macrophages. Also, they express HLA-DR, indicating an activated state and a potential for participating in hemopoietic cell regulation, at least in vitro. Functionally, stromal layers grown from adult bone marrow provide feeder layers for blast colony-forming cells (Bl-CFC). These Bl-CFC adhere to ABM stromal cells but not to FBM or stromal cells.