RESUMEN
Human long-term bone marrow cultures (HLTBMCs) are a valuable in vitro model for studying the role of the haemopoietic microenvironment. Here we report the spontaneous appearance of EBV-positive B cells in 6/40 HLTBMCs from patients with various haematological diseases after 3-5 months of culture. After subcultivation of these cells, a novel type of cell line could be characterized, which displayed surface markers and morphological features typical for EBV transformed B-cell lines. As the deproteinized and ultrafiltrated culture supernatants of these cell lines were found to contain an agent with stroma toxic properties, they were termed SSB lines (stroma-toxic-agent-secreting B-cell lines). This agent also exhibited a colony-inhibitory activity on in vitro myelopoiesis and erythropoiesis. These properties are typical for the two polyamines spermine and spermidine which were detected at elevated levels in the culture supernatants of SSB lines. The hypothesis that latent presence of EBV in bone marrow may induce an increased synthesis of spermine and spermidine, which are known to be associated with malignant haematological diseases and bone marrow aplasia, is discussed.