Requirement for macrophages or for macrophage- or T cell-derived factors in the mitogenic stimulation of murine B lymphocytes by lipopolysaccharides

Splenic B cells from a variety of mouse strains could be depleted of accessory cells by removal of large cells through velocity sedimentation, followed by adherence to plastic and by passage over Sephadex G-10. Such accessory cell removal abolished the reactivity of the splenic B cells to the mitogen lipopolysaccharide (LPS), as measured by their capacity to polyclonally proliferate and mature to IgM-secreting cells. Accessory cells from different sources, such as peritoneal exudate cells, irradiated spleen cells, cells of the macrophage line P388 D1 and macrophages from a single colony grown from bone marrow precursors in semi-solid media in the presence of colony-stimulating factor all reconstituted LPS reactivity of the accessory cell-depleted B cells. Limiting dilutions of the cells of a single macrophage colony indicated that as little as 30 to 1000 macrophages can reconstitute the polyclonal response of 3 × 10⁴ B cells to LPS. Not only activated macrophages, but also activated long-term helper T cell lines and T cell hybridomas, produced supernatant factors which could also restore responsiveness of depleted B cells to LPS.