Morphological studies on 'adherent cells' in bone marrow cultures from humans, dogs, and mice.

Comparative morphological studies were conducted on adherent cells in bone marrow cultures obtained from humans, dogs, and mice. Scanning electron micrographs demonstrated that the adherent colonies are much more homogeneous in humans and dogs and appear larger and more flattened than in mice. In mice, many more rounded cells (macrophages) were seen intermixed with the flattened cells. Transmission electron microscopy demonstrated that the flattened type of cells are characterized by a large primitive nucleus and abundant cytoplasm exhibiting an extensive network of microtubules and submembranous microfilaments and the formation of endoplasmic reticulum-associated secretory bodies. Our results would favor a fibroblastic rather than epithelial nature of the flattened cell type.