RESUMEN
The hemopoietic stem cells (HSC), obtained from the mouse bone marrow and transferred into lethally irradiated syngeneic mice, do not form colonies of hemopoietic cells in the spleen of recipients. The colony formation has been observed after transplantation of HSC together with bone marrow B-lymphocytes or precursors of T-lymphocytes (PTL), and has been mediated through soluble products of nonimmunoglobulin nature produced by B-cells. In distinction from bone marrow B-cells, the interaction of splenic B-lymphocytes with the HSC fraction does not initiate this process, but suppresses it in the presence of bone marrow PTL. The interaction of B-lymphocytes activated by LPS (in vitro) or sheep erythrocytes (in vivo) with HSC or with a mixture of HSC and PTL resulted in the formation of splenic colonies. However, the induction of colony formation has been observed only in the presence of mature T-lymphocytes (phenotype Thy-1, Sc-1), revealed as an admixture to HSC, and has been abolished after their removing in the process of fractionation of bone marrow and receiving the purified HSC fraction. It requires some membranous interaction of regulatory cells.