B-lymphocytes regulate proliferation and differentiation of hemopoietic stem cells

Regulatory effects of B-lymphocytes (BL), BL-produced mediators and interaction with T-lymphocyte precursors (TLP) were studied in experimental systems with fractionation of medullary cells as regards their influence on proliferation and differentiation of syngeneic hemopoietic stem cells of the bone marrow (HSC) which underlie hemopoiesis and immunity. In the tack of accessory cells, induction of HSC functional activity may be regulated by TLP or Bt of the bone marrow without activation of B-helpers through BL-produced soluble products. The impact may be both direct and via T-cel[ system. Depending on HSC-containing cell composition, BL may have on hemopoietic precursor cells not only helper but also suppressor effects induced through soluble BL products. BL had a contrasuppressor action on syngeneic HSC. The pattern of BL regulation was related to organ origin of BL. B-cell hybridom supernatant fluid effects on HSC were similar to those of BL products used for production of hybridom cells. The regulatory effects were dependent neither on antigen used for animal immunization in hybridom design nor on the titer of the antibodies produced, their specificity, class and subclass. These were determined by activity of mediators of non-immunoglobulin nature. No genetic restrictions in the action of regulatory B-cell factors were noted.