THE INFLUENCE OF S17 STROMAL CELLS AND INTERLEUKIN-7 ON B-CELL DEVELOPMENT

A clonal assay was used to study different stimuli involved in the progression of fetal liver B cell precursors to mature B lymphocytes. In this report we replaced fetal liver heterogenous feeder cells by a recombinant growth factor, interleukin 7 (IL 7), and a clonal stromal cell line, S17. Under those conditions we could clone 1 in 10 B220+ B cell precursors from fetal liver and the cells could differentiate to a mitogen‐responsive, immunoglobulinsecreting stage. We found that IL 7 stimulates proliferation of B220+ precursors but is not sufficient to support maturation of those precursors to a stage of mitogen responsiveness. We show further that the cell line S17 does not produce IL 7 at functionally detectable level but provides support for B cell maturation. We conclude that this cell line supplies an exogenous stimulus required by B cell precursors to become mature lymphocytes. We describe therefore two stages in pre‐B cell development: (a) IL 7‐dependent proliferation and (b) S17‐dependent maturation to mitogen reactivity. Further studies demonstrate that S17 has a profound effect on B cells by increasing the clonal efficiency of lipopolysaccharide‐responsive cells to nearly 1:1 B cell in the spleen of adult C57BL/6 mice. Copyright © 1990 Wiley‐VCH Verlag GmbH & Co. KGaA