The major population of human peripheral blood monocytes expresses Flt-1.

Flow cytometric analysis of peripheral blood mononuclear cells obtained by Ficoll/Paque density gradient centrifugation. The M-fraction (monocyte fraction) in panel A was further analyzed by double staining with mAbs indicated in panels B, C, E, and F. (D) The L-fraction (lymphocyte fraction) in panel A was analyzed by double staining with anti-CD34 and anti–Flt-1 mAbs. FS indicates forward scatter; SSC, side scatter.