Humoral regulation of splenic hemopoiesis in mice.

The effects on splenic hemopoiesis were investigated of injecting the bacterial cell wall component, lipid A, or post-lipid A serum (PLAS) into mice. Both lipid A and syngeneic PLAS caused an increase in splenic numbers of multipotential hematopoietic stem cells (CFUS), committed hemopoietic progenitor cells (CFC) of different hemopoietic lineages and morphologically recognizable hemopoietic cells of various lineages. C57BL/6 Sld/Sld PLAS had a lower stimulating effect on hemopoiesis than C57BL/6 +/+ PLAS. PLAS from pre-irradiated mice was as active as normal PLAS in elevating splenic CFC levels. Serum from mice which received irradiation only, had no stimulating effect on splenic hemopoiesis. Medium conditioned by the myelomonocytic leukemia cell line WEHI-3B elevated splenic CFC numbers of similarly to PLAS, but supernatants from long-term marrow cultures or serum of mice treated with latex or phenylhydrazine did not have such an effect. Despite its marked effect on splenic numbers of nucleated erythroid cell precursors, PLAS did not contain elevated levels of erythropoietin.