Preferential proliferation of immature B lineage cells in long-term stromal cell-dependent cultures with IL-4

IL-4 influences the cellular composition of stromal cell dependent long term cultures. In bone marrow-derived long term lymphoid cultures initiated in presence of IL-4, the majority of cells exhibited a more immmature phenotype than is usually seen in lymphoid cells grown in Whitlock-Witte type cultures. This immature cell population, lacking the B220 Ag, was purified by cell sorting. When transferred to mixed stromal layers used in conventional lymphoid long term cultures, these cells differentiated into B lineage cells that could be identified by expression of the B220 Ag and surface IgM. Abelson murine leukemia virus-transformed cell lines resulting from this immature cell population express a DJ(H) rearrangement and contained RNA that hybridized with a V(J558) probe, suggesting transcription of germ-line V genes. A culture modification allowed selective proliferation of a non-transformed cell population with characteristics of very immature B lineage cells. The proliferation of these cells was supported by a homogeneous stromal cell line that was propagated with horse serum in presence of IL-4. The lymphoid cells proliferating under those culture conditions expressed the Ag detected by the BP-1 and 6C3 mAb and were FcγRII and Ia-positive. However, more mature B cell markers were lacking. DNA analysis of these cell lines revealed J(H) rearrangement without evidence for deletion of any member of the DSP-2 family. These cell lines retained their immature phenotype after transfer to mixed stromal layers of Whitlock-Witte type. The mechanisms providing these unique culture conditions initiated by IL-4 in bone marrow stromal cells are discussed.