Cellular interactions in haematopoiesis.

In vitro culture of haematopoietic cells has provided some surprising insights into critical interactions of blood-forming cells. Subpopulations of lymphoid cells have been shown to produce colony-stimulating activity, to interact with macrophages, and to have important effects on the very early stages of erythropoiesis. Macrophages have multiple influences on the proliferation and differentiation of other haematopoietic cells.