| Abstract: | Transplantation of a granulocytosis-inducing murine CE mammary carcinoma into mice suppresses primary B lymphopoiesis in the marrow. The mechanisms of this tumor-induced B-cell suppression were investigated using Whitlock-Witte-type lymphoid cultures. When seeded with normal marrow progenitors, stromal cells of tumor-bearing mice supported the production of B220+ cells as well as did either stomal cells derived from control mice or the stromal cell line S17. Cultured over normal stroma, marrow cells of tumor-bearing mice depleted of adherent cells and B220+ cells generated B220+ cells as effectively as a similar cell population from control mice. However, interleukin-7- responsive progenitors, were completely depleted from the marrow of tumor-bearing mice. When conditioned medium (CM) of cloned CE tumor cells known to produce granulocyte colony-stimulating factor (G-CSF) and macrophage-CSF, or recombinant murine G-CSF was added to the cultures established with S17 cells, B220+ cell production was significantly diminished. Antiserum to murine G-CSF blocked these effects. These in vitro observations were corroborated by the elimination of marrow B220+ cells in mice injected with G-CSF. These in vitro and in vivo studies suggest that G-CSF plays an inhibitory role in primary B lymphopoiesis by blocking stromal cell-mediated differentiation of early B-cell progenitors into phenotypically recognizable B220+ pre-B cells. |
