B Lymphocyte Regulation of Proliferation and Differentiation of Hematopoietic Stem Cells

The fraction of bone marrow hematopoietic stem cells was isolated. To induce in vivo proliferation and differentiation of the hematopoietic fraction the helper action of B cells or T cell precursors was necessary. In presence of bone marrow T cell precursors, B cells suppressed spleen colony formation. The intensity of B cell helper or suppressive action depended on their organ localization. Bone marrow B cells were characterized with maximum helper and minimum suppressive activity. On the contrary, spleen B cells exhibited maximum suppressive action on hematopoietic stem cells without helper one. Lymph node B cells possessed intermediate activity compared to those from bone marrow and spleen. The induction of the colony formation was observed in the presence of either naive or activated B lymphocytes. In case of activated B lymphocytes the regulation of hematopoietic stem cells depended on the admixtured cells as Thy-1(+) and SC-1(+) cells, on the presence of precursors of T cells in transplant and on the organ localization of B cells, as well as on the type of the agent for B cell activation. The activation of B cells might resulted in their helper action changed into suppressive or vice-versa. The B cell regulation of hematopoietic stem cell was mediated by their soluble products of non-immunoglobulin nature. It was found, that helper and suppressive factors from B cell hybridoma supernatants regulated hematopoietic stem cells similar to B cells, of which the hybridomas were created. Thus, we attempted to work out the biotechnological basis for obtaining and researching the regulatory products secreted by B cells.