Electron microscopic evidence for hemopoietic and stromal cells in murine long-term bone marrow cultures.

We have generated a cell line by continuous cultivation of murine bone marrow (BM) cells in liquid phase. After more than 18 months of in vitro propagation, these cells continued to produce a mixed cell population of flat, adherent (stromal) and loose, or loosely adherent, small, round cells. Scanning electron microscopy of these cultures revealed small, round cells adhering to flat, elongated or stellar shaped stromal cells. Transmission electron microscopy of the same cultures identified the stromal cells as nonhematopoietic and fibroblastic, and the small, round cells as "hematopoietic" with features of primitive as well as more differentiated hematopoietic cells. Our results suggest that the adherent stromal cells in long-term marrow culture may contain cells with hemopoietic potential.