Bidirectional effect of interleukin-10 on early murine B-cell development: stimulation of flt3-ligand plus interleukin-7-dependent generation of CD19(-) ProB cells from uncommitted bone marrow progenitor cells and growth inhibition of CD19(+) ProB cells.

B-cell commitment and early development from multipotent hematopoietic progenitor cells has until recently been considered to be dependent on direct interaction with stromal cells. We recently showed that the flt3 ligand (FL) has a unique ability to interact with interleukin-7 (IL-7) to directly and selectively promote B-cell development from murine bone marrow progenitor cells with a combined myeloid and lymphoid potential. Here we report that whereas IL-10 alone has no ability to stimulate growth of primitive (Lin-Sca-1(+)c-kit+) bone marrow progenitor cells, it potently enhances FL + IL-7-induced proliferation (sevenfold). This enhanced proliferation results from recruitment of progenitors unresponsive to FL + IL-7 alone, as well as from increased growth of individual clones, resulting in a 7,000-fold cellular expansion over 12 days. Single cell cultures and delayed addition studies suggested that the stimulatory effect of IL-10 was directly mediated on the progenitor cells. The cells generated in response to FL + IL-7 + IL-10 appeared to be almost exclusively proB cells, as shown by their expression of B220, CD24, CD43, and lack of expression of c mu, myeloid, erythroid, and T-cell surface antigens. Although IL-10 also enhanced kit ligand (KL) + IL-7-induced proliferation of Lin-Sca-1(+)c-kit+ progenitor cells, the resulting cells were predominantly myeloid progeny. Accordingly, FL + IL-7 + IL-10 was 100-fold more efficient in stimulating production of proB cells than KL + IL-7 + IL-10. In contrast to its ability to stimulate the earliest phase of proB cell formation and proliferation, IL-10 inhibited growth of proB cells generated in response to FL + IL-7. Analysis of CD19 expression on cells generated in FL + IL-7 + IL-10 showed that almost all cells generated under these conditions lacked expression of CD19, in contrast to cells generated in the absence of IL-10, which were predominantly CD19(+). Replating of sorted CD19(+) and CD19(-) proB cells in FL + IL-7 or FL + IL-7 + IL-10 showed that IL-10 efficiently blocked growth of CD19(+), but not CD19(-) cells. Both CD19(-) and CD19(+) cells expressed lambda5 and VpreB , shown to be specific for B-cell progenitors. In addition, sorted CD19(-) cells generated CD19(+) cells in response to FL + IL-7. Thus, IL-10 has a dual regulatory effect on early B-cell development from primitive murine bone marrow progenitor cells in that it enhances FL + IL-7-induced proB-cell formation and growth before acquisition of CD19 expression, whereas growth of CD19(+) proB cells is inhibited.