AbstractInjection of 5 μg endotoxin to adult C57BL mice caused a marked increase in the sedimentation velocity of granulocytic and macrophage progenitor (colony‐forming) cells in the bone marrow. This change was maximal two days after injection and was not accompanied by corresponding changes in total marrow nucleated cell populations. The endotoxin‐induced shift was not dependent on the presence of the thymus but did not occur in mice challenged after preinjection with endotoxin. No changes in buoyant density, cell cycle status, pattern of differentiation and responsiveness of granulocytic and macrophage progenitor cells were observed after the injection of endotoxin. The increased sedimentation velocity of progenitor cells appears to indicate an increase in cell volume but the mechanisms involved have not been identi
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