Bone marrow stromal cells — fibroblasts and macrophages

Abstract

In bone marrow, an intact system of vascular sinuses and fibroblastic stroma has been shown to be the structural basis necessary for hemopoietic activity under physiologic (1, 2) and pathologic (3) conditions. The predominant cells of this hemopoietic microenvironment are believed to be reticulum cells which expand a three-dimensional network (reticulum) of cytoplasmic extensions throughout the marrow parenchyma (4). It is generally agreed, however, that the term reticulum (reticular) cell might include several cell types that have not yet been precisely characterized (5). So far, two main types of reticulum cells have been distinguished in the rodent bone marrow by electron microscopy: a nonphagocytic reticulum cell (4, 6–8) which is believed to be mainly fibroblastic (Fig. 1) and a phagocytic reticulum cell (9) or macrophage, which is known to be the center of erythropoietic islets (Fig. 2).