Conversion of cultured monocytes/macrophages into endothelial-like cells through direct contact with endothelial cells.

When culturing human umbilical vein endothelial cells in a culture medium containing 4% human serum albumin, it was possible to maintain the epithelioid morphology and function for several months without subculturing. When coculturing endothelial cells and labeled monocytes/macrophages (Mo/Φ) that were collected from peripheral blood and allowed to engulf fluorescent latex beads, some Mo/Φ changed their shapes and became epithelioid cells that were indistinguishable from vascular endothelial cells. This transformation started within several hours of coculturing. At 7 days after the start of coculturing, more than half of the labeled cells were identified as endothelial-like cells morphologically. Furthermore, morphologically altered Mo/Φ did not express Mo/Φ-specific antigens, ie, the MHC Class II molecule and CD68, but expressed VE cadherin and vWF, which are specific antigens for endothelial cells, and labeled cells that changed into endothelial-like cells no longer engulfed fluorescent latex beads. This strongly suggests that peripheral blood monocytes differentiate into endothelial-like cells.