Characterization of bone marrow stromal cells in suspension and monolayer cultures

Aspirated marrow fragments from healthy adult baboons were cultured in a simple liquid suspension tissue culture system. During the incubation period, haemopoietic cells were discharged from the fragments and settled to the floor of the culture vessels, thus allowing a separation of marrow stromal elements, retained within the fragments. Cells associated with the marrow stroma in vitro were of four main types: adipocytes, macrophages, plasma cells and unidentified lipid-laden cells related to fibroblasts. These last cells were capable of DNA synthesis in vitro, and were morphologically and functionally distinguishable from typical marrow macrophages. Macrophages were characterized by their phagocytic properties. Plasma cells were capable of prolonged survival and immunoglobulin output in vitrol. In monolayer cultures of disaggregated fragment cell suspensions, the lipid-laden stromal cells rapidly assumed fibroblast-like morphology. Fibroblastic proliferation to confluent monolayers was seen within a few days. Plasma cells reorientated themselves around these cells to form rosettes, and bridge communicatons between the two cell types were seen frequently. Plasma cell immunoglobulin output rate per cell appeared to be potentiated by this association.