In vitro formation of mesenchymal bone marrow islets.

We studied the formation of mesenchymal islets in the culture of bone marrow cells in vitro. Islet-like structures detected on day 6 of culturing contained a central epithelioid cell (differing from macrophages and fibroblasts) surrounded with round mesenchymal cells. The number of mesenchymal islets increased on days 12-14 of culturing, but decreased to zero by the 24th day. They appeared not only as individual structures, but also entered the composition of colonies and formed assemblies with surrounding cells of different maturity. Our results show that mesenchymal islets serve as structural and functional units of mesenchymopoiesis.