Long-lived polyclonal B-cell lines derived from midgestation mouse embryo lymphohematopoietic progenitors reconstitute adult immunodeficient mice.

Lymphohematopoietic progenitors derived from midgestation mouse embryos were established in long-term cultures with stromal cell monolayers and interleukin 7 (IL-7), giving rise to B-lineage cell lines. The initial emergence and in vitro establishment of these early embryo cell lines were highly sensitive to IL-7-mediated signals, in comparison to cell lines similarly obtained using precursors from late fetal liver (> 13 days postcoitum) and adult bone marrow. The early embryo-derived progenitors spontaneously differentiated in vitro to CD19(+)IgM(+) immature B cells in the presence of optimal concentrations of IL-7, in contrast to those progenitors obtained from late gestation and adult mice, whose differentiation only occurred in the absence of IL-7. The newly in vitro-generated B cells of the early embryo cell lines repopulated adult immunodeficient severe combined immunodeficient mice on their adoptive transfer in vivo and generated specific humoral immune responses after immunization.

Differential involvement of the transcription factor Blimp-1 in T cell-independent and -dependent B cell differentiation to plasma cells.

Along humoral immune responses, different stimuli drive the differentiation of B lymphocytes to Ig-secreting plasma cells in discrete microenvironments. The Blimp-1 transcription factor is up-regulated early during the transition of mature B cells to IgM-secreting plasma cells. In the present study, we have examined the requirement of Blimp-1 in plasma cell formation after both T cell-independent (LPS) and -dependent (CD40 + IL-4, Th cell lines) stimulation of spleen B cells. B lymphocyte-induced maturation protein (Blimp-1) was expressed early after in vitro LPS stimulation, mainly in a population of IgM+Syndecan+CD43+ preplasma cells. In contrast, the BSAP transcription factor expressed in mature B cells was down-regulated during the differentiation to plasma cells. Treatment of these cultures with Blimp-1-specific antisense phosphorothioate oligonucleotides suppressed both Blimp-1 protein levels and the emergence of IgM+Syndecan+ cells and plasma cells. However, T-B cell cocultures of spleen B cells from C3H/HeJ (H-2k) mice and syngeneic autoreactive SR.10 Th2 cells submitted to the anti-Blimp-1 therapy did not show any significant reduction in IgM- and IgG1-secreting plasma cell formation. Spleen B cells treated with anti-CD40 mAb + IL-4 differentiated to IgG1-secreting cells without significant transcription of the Blimp-1 gene; anti-Blimp-1 treatment subsequently did not have any effect in the later cultures. Altogether, these results suggest that Blimp-1 transcription factor specifically promotes T cell-independent B cell differentiation to plasma cells, probably at preplasma cell stages. In contrast, T cell-dependent plasma cell formation likely evolves through Blimp-1-independent pathways.