Human marrow stromal cells in culture: changes induced by T-lymphocytes

Suspension cultures of human bone marrow mononuclear cells form colonies of fibroblastoid cells which expand to form confluent monolayers. These fibroblastoid cells are thought to represent elements of the bone marrow stroma. Fibroblastoid cells failed to proliferate when the cultures were initiated and maintained in the presence of 50% (v/v) of medium conditioned by phytohaemagglutinin (PHA)-stimulated blood mononuclear cells or supernatant media from one-way mixed lymphocyte reactions (MLR). Under these conditions, the cultures contained a pleomorphic population of macrophage-like cells. Some of the characteristics of the fibroblastoid and macrophage-like cells have been compared and a separate origin of the two cell types has been demonstrated. Further experiments indicated that T lymphocytes were the source of the factor(s) in the conditioned media which was responsible for the growth of the macrophage-like cells at the expense of the fibroblastoid cells and suggested that activation of the T cells was necessary for them to exert their effect. The results support the idea that T lymphocytes can influence the haemopoietic microenvironment of the bone marrow.