A subfraction of B220+ cells in murine bone marrow and spleen does not belong to the B cell lineage but has dendritic cell characteristics

Abstract

Although CD45R/B220 is commonly used as a pan-B cell marker in the mouse, not all B220+ cells belong to the B cell lineage. Here we report the characterization of a subpopulation of B220+CD19- cells in murine bone marrow, which failed to express markers that are present in early CD19- B cell precursors. Instead, these cells expressed low levels of MHC class II and CD11c, which are typically found on dendritic cells (DC). Moreover, these B220+CD19-CD11c+ cells expressed Gr-1, indicating that they are related to the recently identified murine plasmacytoid DC or their progenitors. Therefore, we evaluated surface marker expression of the B220+CD19-CD11c+ cells in lymphoid tissues of C57BL/6 mice, recombinase activating gene-1 deficient mice, lacking mature B and T lymphocytes, and mice with a targeted disruption of the Ig H chain μ membrane exon (μMT), lacking mature B lymphocytes. When comparing bone marrow and spleen, we found that the surface profiles of B220+CD19-CD11c+ cells were remarkably similar, indicating that they are in a comparable maturation or activation stage in the two lymphoid compartments. In addition, the almost complete absence of peripheral B220+ B-lineage cells in μMT mice allowed the anatomical localization of the B220+CD19-CD11c+ cells to the red pulp and the T cell areas in the spleen. Taken together, our findings indicate that the mouse bone marrow contains a recirculating population of B220+CD19- CD11c+ plasmacytoid DC, the development of which is largely independent of the presence of mature T and B cells.