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

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Abstract
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.