Morphological, enzymic and antigenic data are presented regarding a human bone-marrow stromal cell line maintained for 10 months and subcultured weekly. The main characteristics are a fibroblastoid morphology, diffuse growth in collagen gels, no colony formation in soft gel media, contact inhibition of growth and conversion to adipocytes when treated with hydrocortisone. The cells are non-phagocytic and membrane Fc receptors (i.e. aggregated human immunoglobulin G receptors) are absent, but they show diffuse cytoplasmic non-specific esterase activity, a strong acid phosphatase reaction, and a negative immunofluorescence (direct and indirect) against factor VIII antigen. Other cell lines also have been isolated and maintained in culture and present similar characteristics. These cell lines are thought to be derived from the acid-phosphatase-positive marrow stroma directly associated with bone trabecular matrix and probably represent a component of the haemopoietic inductive microenvironment. As such, they may provide a useful tool for studies in vitro of cell interactions and regulatory processes in the control of human bone-marrow haemopoiesis.

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