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Growth of mature B cells and their precursors from mouse bone marrow was maintained in culture for greater than 1 year. Feeder layers of adherent bone marrow cells, established in medium containing fetal calf serum and no exogenous steroids, were used to provide an in vitro environment that supported continuous growth and development of these cells. In such bone marrow cultures, the number of cells bearing membrane immunoglobulin increased gradually for 4 wk and then decreased. Between 10 and 14 wk, some of the cultures gave rise to continuously dividing B-cell populations that contained pre-B cells (producing mu heavy chains only and sensitive to transformation by Abelson murine leukemia virus) as well as mature B cells (synthesizing both light and heavy chains of IgM). Immunoglobulin molecules synthesized by cells in these populations were heterogeneous in two-dimensional gel analysis. This suggests that mature B cells arose via maturation of pre-B cells in the cultures that involved rearrangement and expression of different variable region gene segments.
Whitlock et al. (1982) studied this question.