The role of circulating fibrocytes in inflammation and autoimmunity.
The placenta is a highly vascularized organ thus angiogenesis is a key process in placental development. The contribution that different cells in the villous stroma play in placental angiogenesis is largely unknown. In this study we identified a novel stromal cell type in sections of term placenta which is morphologically fibroblastic and expressing the fibroblast marker TE-7 but also positive for the monocytic markers CD115 and CD14 and designated these cells as fibrocyte-like cells. Populations of fibrocyte-like cells from the placenta were isolated by two methods: culture of adherence-selected placental cells and, for higher purity, by CD45 fluorescence activated cell sorting (FACS). Fibrocyte-like cell conditioned medium increased endothelial tubule-like structure formation 2-fold versus control medium. Both pro-angiogenic growth factors vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (b-FGF) and the anti-angiogenic factor soluble-Flt were found in the conditioned medium. Neutralizing antibodies against VEGF and b-FGF reduced endothelial cell tubule-like structures to control levels. These data suggests that fibrocyte-like cells, a previously unidentified cell of the villous stroma, may play an important role in the regulation of placental angiogenesis.