Abstract

Long-term bone marrow cultures of human fetuses ranging from 20 weeks to 28 weeks were established. The following methods were used to study the adherent layer: 1) Giemsa stain, Sudan IV stain, and Gomori silver impregnation. 2) immunocytochemical staining. 3) phagocytosis experiment with C. albicans. 4) transmission and scanning electrón microscopy. 5) ultrastructural cytidine monophosphatase (CMPase) and myeloperoxidase (MPO) reaction.  The results indicated that fibroblasts and macrophages (M0s) were principal cell components of the adherent layer. The existence of adipocytes and endothelial cells could not be proved. Fibroblasts were characterized by a large amount of rough endoplasmic reticulum and formation of reticular fibers and fibronectin (FN). Most M0s were capable of engulfing C. albicans. The salient morphologic features of fetal M0s was the presence of large numbers oí clear vacuole with positive CMPase reactivity. Extracellular matrix (ECM) was composed of FN, proteoglycan, and reticular fibers. Together with the fibroblasts and M0s, they composed the hematopoietic inductive microenvironment in vitro, in which the proliferation and maturation of myelomonocytic cells were sustained.