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.

The influence of B-lymphocytes from various sources on splenic colony formation was studied in the syngeneic system. B-lymphocytes were obtained by panning with IgG-fraction of rabbit anti-mouse Ig, absorbed on Petri dishes. In addition, adherent cells, Thy-1+ and SC-1+ were eliminated from the fraction of Ig(+)-cells. SC-1- and SC-1+ fractions, containing, respectively, stem cells and T-lymphocyte precursors, were obtained by panning with IgG-fraction of rabbit anti-SC-1 serum. SC-1- cells transferred to irradiated syngeneic mice did not induce colony formation in the spleen. Introduction of SC-1- and SC-1+ cells induced formation of colonies. A similar helper effect occurred when SC-1(-)-cells were introduced with bone marrow or lymph node B-cells, but not with splenic B-cells. Splenic, but not bone marrow and lymph node B-cells inhibited colony formation by combination of SC-1- and SC-1+ cells. All effects of Ig+ cells were abolished by treatment of cells with rabbit anti-MBLA serum. Thus, B-cells of various origin can either enhance or inhibit colony formation. The enhancing of inhibitory effect after B (MBLA+)-cells elimination from suspension of bone marrow and lymph node (but not spleen) Ig(+)-cells resulted from the activity of B-contrasuppressors.