Transmigration of proliferating hematopoietic cells. (A) Wright-Giemsa stained proliferating cells in the upper chamber at day 15. The majority of the cells consisted of granulocytic precursors such as promyelocytes and some mature monocytes/macrophages (original magnification × 400). (B) Transmigrated cells in the lower chamber at day 15. The transmigrated cells recovered comprised almost exclusively mature monocytes/macrophages (original magnification × 400). (C) Proliferating cells in the upper chamber at day 30. In addition to myeloid precursors and monocytes, also mature granulocytes and bands were found (original magnification × 400). (D) Transmigrated cells from the lower chamber at day 30. Both mature granulocytes and monocytes transmigrated into the lower chamber. Precursors earlier than metamyelocytes were virtually not found among the transmigrated cells (original magnification × 400).