Cellular and molecular basis of the increased splenic hemopoiesis in mice treated with bacterial cell wall components.

An analysis was made of the mechanisms responsible for the increased splenic hemopoiesis occurring in mice after the injection of the bacterial cell wall components lipid A and outer membrane lipoprotein. No evidence was obtained for the presence of functional lipid A receptors on hemopoietic precursor cells. Serum from lipid A-injected mice, on injection into normal mice, induced in the spleen an increased content of all hemopoietic progenitor cells. The magnitude of the response was dependent on the dose of lipid A used and the volume of serum transferred to the recipients. C3H/HeJ mice unresponsive to lipid A exhibited similar spleen changes when injected with active post-lipid A sera. Progenitor cells of all hemopoietic lineages, including multipotential hemopoietic stem cells, were involved in the response. The results suggest that a humoral factor mediates the lipid A-induced increase of splenic hemopoiesis.